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How (Most) Humans Lost Their Tails - From Fish to Tetrapods to Apes to Homo Sapiens

How (Most) Humans Lost Their Tails - From Fish to Tetrapods to Apes to Homo Sapiens


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Did you know that human embryos early in development have tails that later fail to grow for a lack of signaling from the genes? We end up with the coccyx at the end of our spines that protrudes a bit from our rear ends. The tailbone is barely noticeable, but it serves as a reminder of our ancient past.

Biologists believe we and our relatives on the evolutionary tree, the great apes, lost our tails for ease of walking and other upright movements. We might add ease of sitting, too, though most species and breeds of monkeys, cats and dogs sit despite having tails. That said, it would be difficult to sit in a chair or wear concealing clothing, recent additions to the Homo species’ props, if we did have tails.

A human embryo showing a tail in the 5 th week of pregnancy ( Wikimedia Commons /Dr. Ed Uthman)

Seeker.com reports on a new article in the journal Current Biology that says human embryos’ tails go back to our evolutionary ancestors—fish.

Lauren Sallan is the author of the study. She is an assistant professor in the Earth and Environmental Science Department at the University of Pennsylvania. She examined fossils of Aetheretmon fish hatchlings, which are distant relatives of today’s land animals. These hatchlings had a flexible tailfin below and a scaly fleshy tail above.

She concluded the two types of tails on Aetheretmon were separate. She compared Aetheretmon hatchlings to modern fish and found that the tailfin and scaly tail above eventually grew separately thought they had started out one on top of the other.

“This discovery overturns at least two centuries of scientific belief that the modern adult fish tailfin was simply added to the end of an ancestral tail shared with land animals,” Seeker.com says.

The two tails then went on to develop differently in different animals. Fish kept the flexible tail that helps them swim better and allows for more precise and refined movements. The other tail, a more muscular appendage, allowed for power swimming but disrupted refined movements, Seeker.com says.

This graphic giving the evolution of tetrapods (four-legged land or hybrid land-sea animals) shows some transitional fossils. It shows Eusthenopteron at the bottom, indisputably still a fish, through several transitional animals to Pederpes at the top, indisputably a tetrapod. (Wikimedia Commons /Maija Karala)

Some fish emerged from the water, first to be semi-aquatic and then to evolve into land animals. These animals lost the swimming fin but kept the fleshier one that cows, monkeys, felines, canines and other animals have today. Tails can be used to communicate, shoo insects and other purposes, Seeker.com says.

Many tails on monkeys that move around upright are small, which lends credence to the theory that we lost our tails to facilitate upright movement.

Most apes and humans and their ancestors lost even a vestige of a visual tail. We have the remnants of a bony tail that develops early in our embryonic stage, Sallan says. But the genes that control tail growth have stopped signaling them to grow in most people, unlike legs and arms, for example, which still receive the signals to grow.

Rani's Southamerican Monkey. Mewar, ca. 1700, anonymous ( Wikimedia Commons )

We say “most humans” because some people are born with vestigial tails.

A 1984 article in the journal Human Pathology states that a true or persistent tail in humans comes from the remnant of the embryonic tail and contains fat, connective tissue, muscles, blood vessels, nerves and is covered in skin. But bones, cartilage and spinal cord are lacking.

It may be as long as 13 cm (5.1 inches), can move and contract, and occurs twice as often in males as in females. A true tail is easily removed surgically, without residual effects. It is rarely familial. Pseudotails are varied lesions having in common a lumbosacral protrusion and a superficial resemblance to persistent vestigial tails.

An example of a vestigial tail

Featured image: A graphic showing what a human would look like with a tail ( The Daily Omnivore )

By Mark Miller


Human evolution by martin

Human evolution is the evolutionary process leading up to the appearance of modern humans. It is the process by which human beings developed on Earth from now-extinct primates. It involves the lengthy process of change by which people originated from apelike ancestors. The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, ethology, evolutionary psychology, embryology and genetics. Scientific evidence shows that the physical and behavioural traits shared by all people originated from apelike ancestors and evolved over a period of approximately six million years.
TABLE OF CONTENT
1.0 Introduction
2.0 Evolutionary Theory
3.0 Process of Evolution
4.0 History of Human Evolution
5.0 Paleoanthropology
6.0 Evidence of Evolution
6.1 Evidence from comparative physiology
6.2 Evidence from comparative anatomy
6.3 Evidence from comparative embryology
6.4 Evidence from comparative morphology
6.5 Evidence from vestigial organs
6.6 Genetics
6.7 Evidence from Molecular Biology
6.8 Evidence from the Fossil Record
7.0 Divergence of the Human Clade from other Great Apes
8.0 Anatomical changes
8.1 Anatomy of bipedalism
8.2 Encephalization
8.3 Sexual dimorphism
8.4 Other changes
9.0 Genus Homo
10.0 Homo Sapiens Taxonomy


Contents

Some disagreement exists about the scientific definition of human. Some scientists date the Homo genus back only 100,000 years while others go back 11 million years and include Neanderthals, chimps and gorillas. Most say early humans first appeared between 2–3 million years ago. [2] In common usage the word human generally just refers to Homo sapiens, the only extant species. [3]

Human is a Middle English loanword from Old French humain, ultimately from Latin hūmānus, the adjectival form of homō ("man" — in the sense of humankind). [4] The native English term man can refer to the species generally (a synonym for humanity) as well as to human males. It may also refer to individuals of either sex, though this latter form is less common in contemporary English. [5]

The species binomial "Homo sapiens" was coined by Carl Linnaeus in his 18th-century work Systema Naturae. [6] The generic name "Homo" is a learned 18th-century derivation from Latin homō, which refers to humans of either sex. [7] The species name "sapiens" means "wise", "sapient", "knowledgeable" (Latin sapiens is the singular form, plural is sapientes). [8]

Humans are primates and part of the superfamily Hominoidea. [9] The gibbons (family Hylobatidae) and orangutans (genus Pongo) were the first living groups to split from this lineage, then gorillas, and finally, chimpanzees (genus Pan). The splitting date between human and chimpanzee lineages is placed 4–8 million years ago, during the late Miocene epoch. [10] [11] [12] During this split, chromosome 2 was formed from the joining of two other chromosomes, leaving humans with only 23 pairs of chromosomes, compared to 24 for the other apes. [13]

Homo sapiens (humans)

The earliest documented representative of the genus Homo is Homo habilis, which evolved around 2.8 million years ago from Australopithicus. [14] H. erectus were the first of the hominina to leave Africa, between 1.3 and 1.8 million years ago. Homo sapiens emerged around 300,000 years ago from H. erectus (sometimes called Homo ergaster) that remained in Africa. H. sapiens migrated out of the continent gradually replacing local populations of H. erectus and other archaic humans. [15] [16] [17]

The "out of Africa" migration took place in at least two waves, the first around 130,000 to 100,000 years ago, the second (Southern Dispersal) around 70,000 to 50,000 years ago. [18] [19] H. sapiens proceeded to colonize all the continents and larger islands, arriving in Eurasia 125,000–60,000 years ago, [20] [21] Australia around 65,000 years ago, [22] the Americas around 15,000 years ago, and remote islands such as Hawaii, Easter Island, Madagascar, and New Zealand between the years 300 and 1280. [23] [24]

Human evolution was not a simple linear or branched progression, but involved interbreeding between related species. [25] [26] [27] Genomic research has shown that hybridization between substantially diverged lineages was common in human evolution. [28] DNA evidence suggests that several genes of Neanderthal origin are present among all non-African populations, and Neanderthals and other hominins, such as Denisovans, may have contributed up to 6% of their genome to present-day humans. [25] [29] [30]

Anatomical adaptations

Human evolution is characterized by a number of morphological, developmental, physiological, and behavioral changes that have taken place since the split between the last common ancestor of humans and chimpanzees. The most significant of these adaptations are bipedalism, increased brain size and decreased sexual dimorphism (neoteny). The relationship between all these changes is the subject of ongoing debate. [31] Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus. [32]

Bipedalism is the basic adaption of the hominin line, and it is considered the main cause behind a suite of skeletal changes shared by all bipedal hominins. The earliest bipedal hominin has been considered to be either Sahelanthropus [33] or Orrorin, with Ardipithecus (a full bipedal) [34] coming somewhat later. [n 1] The knuckle walkers, the gorilla and chimpanzee, diverged around the same time, and either Sahelanthropus or Orrorin may be humans' last shared ancestor with those animals. [36] There are several theories for the adaptational value of bipedalism. It is possible that bipedalism was favored because it freed up the hands for reaching and carrying food, because it saved energy during locomotion, because it enabled long-distance running and hunting, or as a strategy for avoiding hyperthermia by reducing the surface exposed to direct sun. [37] [38]

The human species developed a much larger brain than that of other primates, typically 1,330 cm 3 (81 cu in) in modern humans, over twice the size of chimpanzee or gorilla brains. [39] The pattern of encephalization started with H. habilis which at approximately 600 cm 3 (37 cu in) had a brain slightly larger than chimpanzees, and continued with H. erectus (800–1,100 cm 3 (49–67 cu in)). [40] The pattern of human postnatal brain growth differs from that of other apes, and allows for extended periods of social learning and language acquisition. The differences between the structure of human brains and those of other apes may be more significant than differences in size. [41] [42] [43] [44] The increase in volume over time has affected different areas within the brain unequally. The temporal lobes, involved in language processing, and the prefrontal cortex, related to complex decision making and moderating social behavior, have increased disproportionately. [39] Encephalization has been tied to an increasing emphasis on meat in the diet, [45] [46] or with the development of cooking, [47] and it has been proposed that intelligence increased as a response to an increased necessity for solving social problems as human society became more complex. [48]

The reduced degree of sexual dimorphism is primarily visible in the reduction of the male canine tooth relative to other ape species (except gibbons). Another important physiological change related to sexuality in humans was the evolution of hidden estrus. Humans are the only ape in which the female is intermittently fertile year round, and in which no special signals of fertility are produced by the body (such as genital swelling during estrus). Nonetheless, humans retain a degree of sexual dimorphism in the distribution of body hair and subcutaneous fat, and in the overall size, as males are around 15% heavier than females. [49]

Until about 12,000 years ago, all humans lived as hunter-gatherers. [50] The Neolithic Revolution (the invention of agriculture) first took place in Southwest Asia and spread through large parts of the Old World over the following millennia. [51] It also occurred independently in Mesoamerica (about 6,000 years ago), [52] China, [53] [54] Papua New Guinea, [55] and the Sahel and West Savanna regions of Africa. [56] [57] [58] Access to food surplus led to the formation of permanent human settlements, the domestication of animals and the use of metal tools for the first time in history. Agriculture and sedentary lifestyle led to the emergence of early civilizations. [59] [60] [61]

An urban revolution took place in the 4th millennium BCE with the development of city-states, particularly Sumerian cities located in Mesopotamia. [62] It was in these cities that the earliest known form of writing, cuneiform script, appeared around 3000 BCE. [63] Other major civilizations to develop around this time were Ancient Egypt and the Indus Valley Civilization. [64] They eventually traded with each other and invented technology such as wheels, plows and sails. [65] [66] [67] [68] Astronomy and mathematics were also developed and the Great Pyramid of Giza was built. [69] [70] [71] There is evidence of a severe drought lasting about a hundred years that may have caused the decline of these civilizations, [72] with new ones appearing in the aftermath. Babylonians came to dominate Mesopotamia while others, [73] such as Poverty Point cultures, Minoans and the Shang dynasty, rose to prominence in new areas. [74] [75] [76] The bronze age suddenly collapsed about 1200 BCE resulting in the disappearance of a number of civilizations and the beginning of the Greek Dark Ages. [77] [78] During this period iron started replacing bronze leading to the Iron Age. [79]

In the 5th century BCE history started being recorded as a discipline, so providing a much clearer picture of life at the time. [80] Between the 8th and 6th century BCE Europe entered the classical antiquity age, a period when ancient Greece and ancient Rome flourished. [81] [82] Around this time other civilizations also came to prominence. The Maya civilization started to build cities and create complex calendars. [83] [84] In Africa the Kingdom of Aksum overtook the declining Kingdom of Kush and facilitated trade between India and the Mediterranean. [85] In West Asia the Achaemenid Empire's system of centralized governance become the precursor to many later empires, [86] while the Gupta Empire in India and the Han dynasty in China have been described as golden ages in their respective regions. [87] [88]

Following the fall of the Western Roman Empire in 476 Europe entered the Middle Ages. [89] In the middle east Islam became the prominent religion and expanded into North Africa. [90] Christianity was likewise expanding in Europe, leading the Kingdom of England, the Kingdom of France and the Holy Roman Empire to declare a series of holy wars to regain control of the Holy Land from Muslims. [91] Elsewhere the Aztecs and Incas would become the dominant powers in the Americas and the Mongol Empire would conquer much of Eurasia in the 13th and 14th centuries. [92] [93] Over this same time period the Mali Empire in Africa grew to the largest empire in Africa, stretching from Senegambia to Ivory Coast. [94]

Throughout the early modern period (1500–1800) the Ottomans controlled the lands around the Mediterranean Basin, [95] Japan entered the Edo period, [96] the Qing dynasty rose in China [97] and the Mughal Empire ruled much of India. [98] Europe underwent the Renaissance, starting in the 15th century, [99] and the Age of Discovery began with the exploring and colonizing of new regions. [100] This includes the Scramble for Africa (where European control of Africa went from 10% to almost 90 in less than 50 years), [101] the British Empire expanding to become the world's largest empire [102] and the colonization of the Americas. [103] This expansion led to the Atlantic slave trade [104] and the genocide of Native American peoples. [105] This period also marked the Scientific Revolution, with great advances in mathematics, mechanics, astronomy and physiology. [106]

The late modern period (1800–present) saw the Technological and Industrial Revolution bring such discoveries as imaging technology, major innovations in transport and energy development. [107] The United States of America underwent great change, going from a small group of colonies to one of the global super powers. [108] The Napoleonic Wars raged through Europe in the early 1800's, [109] Spain lost most of its New World colonies [110] and Europeans continued expansion into the islands of Oceania. [111] A tenuous balance of power among European nations collapsed in 1914 following the Assassination of Archduke Franz Ferdinand, resulting in World War I. [112] The Great Depression of 1929 caused mass unemployment and facilitated Adolf Hitler's rise to power in Germany. [113] A Second World War, involving almost all the world's countries, broke out in 1939 when Hitler invaded Poland. [114] Following its conclusion in 1945, the Cold War between the USSR and the United States saw a struggle for global influence, including a nuclear arms race and a space race. [115] [116] The current Information Age sees the world becoming increasingly globalized and interconnected. [117]

Early human settlements were dependent on proximity to water and—depending on the lifestyle—other natural resources used for subsistence, such as populations of animal prey for hunting and arable land for growing crops and grazing livestock. [121] Modern humans, however, have a great capacity for altering their habitats by means of technology, irrigation, urban planning, construction, deforestation and desertification. [122] Human settlements continue to be vulnerable to natural disasters, especially those placed in hazardous locations and with low quality of construction. [123] Grouping and deliberate habitat alteration is often done with the goals of providing protection, accumulating comforts or material wealth, expanding the available food, improving aesthetics, increasing knowledge or enhancing exchange of resources. [124]

Humans are one of the most adaptable species, despite having a narrow tolerance to many of the earth's extreme environments. [125] Through invention humans have been able to extend their tolerance to a wide variety of temperatures, humidity, and altitudes. [125] As a result, humans are a cosmopolitan species found in almost all regions of the world, including tropical rainforest, arid desert, extremely cold arctic regions, and heavily polluted cities. Most other species are confined to a few geographical areas by their limited adaptability. [126] The human population is not, however, uniformly distributed on the Earth's surface, because the population density varies from one region to another and there are large areas almost completely uninhabited, like Antarctica and the vast swathes of ocean. [125] [127] Most humans (61%) live in Asia the remainder live in the Americas (14%), Africa (14%), Europe (11%), and Oceania (0.5%). [128]

Within the last century, humans have explored challenging environments such as Antarctica, the deep sea, and outer space. [129] Human habitation within these hostile environments is restrictive and expensive, typically limited in duration, and restricted to scientific, military, or industrial expeditions. [129] Humans have briefly visited the Moon and made their presence felt on other celestial bodies through human-made robotic spacecraft. [130] [131] [132] Since 2000 there has been continuous human presence in space through the manning of the International Space Station. [133]

Estimates of the population at the time agriculture emerged in around 10,000 BC have ranged between 1 million and 15 million. [134] [135] Around 50–60 million people lived in the combined eastern and western Roman Empire in the 4th century AD. [136] Bubonic plagues, first recorded in the 6th century AD, reduced the population by 50%, with the Black Death killing 75–200 million people in Eurasia and North Africa alone. [137] Human population was believed to have reached one billion in 1800. It has then increased exponentially, reaching two billion in 1930 and three billion in 1960, four in 1975, five in 1987 and six billion in 1999. [138] It passed seven billion in 2011 and in 2020 there were 7.8 billion humans. [139] The combined biomass of the carbon of all the humans on Earth in 2018 was estimated at 60 million tons, about 10 times larger than that of all non-domesticated mammals. [140]

In 2018, 4.2 billion humans (55%) lived in urban areas, up from 751 million in 1950. [141] The most urbanized regions are Northern America (82%), Latin America (81%), Europe (74%) and Oceania (68%), with Africa and Asia having nearly 90% of the world's 3.4 billion rural population. [141] Problems for humans living in cities include various forms of pollution and crime, [142] especially in inner city and suburban slums. Both overall population numbers and the proportion residing in cities are expected to increase significantly in the coming decades. [143] Humans have had a dramatic effect on the environment. They are apex predators, being rarely preyed upon by other species. [144] Human population growth, industrialization, land development, overconsumption and combustion of fossil fuels has led to environmental destruction and pollution that significantly contributes to the ongoing mass extinction of other forms of life. [145] [146] They are the main contributor to global climate change, [147] which may accelerate the Holocene extinction. [148] [145]

Anatomy and physiology

Most aspects of human physiology are closely homologous to corresponding aspects of animal physiology. The human body consists of the legs, the torso, the arms, the neck, and the head. An adult human body consists of about 100 trillion (10 14 ) cells. The most commonly defined body systems in humans are the nervous, the cardiovascular, the digestive, the endocrine, the immune, the integumentary, the lymphatic, the musculoskeletal, the reproductive, the respiratory, and the urinary system. [149] [150] The dental formula of humans is: 2.1.2.3 2.1.2.3 . Humans have proportionately shorter palates and much smaller teeth than other primates. They are the only primates to have short, relatively flush canine teeth. Humans have characteristically crowded teeth, with gaps from lost teeth usually closing up quickly in young individuals. Humans are gradually losing their third molars, with some individuals having them congenitally absent. [151]

Humans share with chimpanzees a vestigial tail, appendix, flexible shoulder joints, grasping fingers and opposable thumbs. [152] Apart from bipedalism and brain size, humans differ from chimpanzees mostly in smelling, hearing and digesting proteins. [153] While humans have a density of hair follicles comparable to other apes, it is predominately vellus hair, most of which is so short and wispy as to be practically invisible. [154] [155] Humans have about 2 million sweat glands spread over their entire bodies, many more than chimpanzees, whose sweat glands are scarce and are mainly located on the palm of the hand and on the soles of the feet. [156]

It is estimated that the worldwide average height for an adult human male is about 171 cm (5 ft 7 in), while the worldwide average height for adult human females is about 159 cm (5 ft 3 in). [157] Shrinkage of stature may begin in middle age in some individuals, but tends to be typical in the extremely aged. [158] Through history human populations have universally become taller, probably as a consequence of better nutrition, healthcare, and living conditions. [159] The average mass of an adult human is 59 kg (130 lb) for females and 77 kg (170 lb) for males. [160] [161] Like many other conditions, body weight and body type is influenced by both genetic susceptibility and environment and varies greatly among individuals. [162] [163]

Humans have a far faster and more accurate throw than other animals. [164] Humans are also among the best long-distance runners in the animal kingdom, but slower over short distances. [165] [153] Humans' thinner body hair and more productive sweat glands help avoid heat exhaustion while running for long distances. [166]

Genetics

Like most animals, humans are a diploid eukaryotic species. Each somatic cell has two sets of 23 chromosomes, each set received from one parent gametes have only one set of chromosomes, which is a mixture of the two parental sets. Among the 23 pairs of chromosomes there are 22 pairs of autosomes and one pair of sex chromosomes. Like other mammals, humans have an XY sex-determination system, so that females have the sex chromosomes XX and males have XY. [167] Genes and environment influence human biological variation in visible characteristics, physiology, disease susceptibility and mental abilities. The exact influence of genes and environment on certain traits is not well understood. [168] [169]

While no humans—not even monozygotic twins—are genetically identical, [170] two humans on average will have a genetic similarity of 99.5%-99.9%. [171] [172] This makes them more homogeneous than other great apes, including chimpanzees. [173] [174] This small variation in human DNA compared to other species suggests a population bottleneck during the Late Pleistocene (around 100,000 years ago), in which the human population was reduced to a small number of breeding pairs. [175] [176] The forces of natural selection have continued to operate on human populations, with evidence that certain regions of the genome display directional selection in the past 15,000 years. [177]

The human genome was first sequenced in 2001 [178] and by 2020 hundreds of thousand of genomes had been sequenced. [179] In 2012 the International HapMap Project had compared the genomes of 1,184 individuals from 11 populations and identified 1.6 million single nucleotide polymorphisms. [180] African populations also harbour the highest number of private genetic variants, or those not found in other places of the world. While many of the common variants found in populations outside of Africa are also found on the African continent, there are still large numbers which are private to these regions, especially Oceania and the Americas. [181] By 2010 estimates, humans have approximately 22,000 genes. [182] By comparing mitochondrial DNA, which is inherited only from the mother, geneticists have concluded that the last female common ancestor whose genetic marker is found in all modern humans, the so-called mitochondrial Eve, must have lived around 90,000 to 200,000 years ago. [183] [184] [185]

Life cycle

Most human reproduction takes place by internal fertilization via sexual intercourse, but can also occur through assisted reproductive technology procedures. [186] The average gestation period is 38 weeks, but a normal pregnancy can vary by up to 37 days. [187] Embryonic development in the human, covers the first eight weeks of development at the beginning of the ninth week the embryo is termed a fetus. [188] Humans are able to induce early labour or perform a caesarean section if the child needs to be born earlier for medical reasons. [189] In developed countries, infants are typically 3–4 kg (7–9 lb) in weight and 47–53 cm (19–21 in) in height at birth. [190] [191] However, low birth weight is common in developing countries, and contributes to the high levels of infant mortality in these regions. [192]

Compared with other species, human childbirth is dangerous, with a much higher risk of complications and death. [193] The size of the fetus's head is more closely matched to the pelvis than other primates. [194] The reason for this is not completely understood, [n 4] but it contributes to a painful labor that can last 24 hours or more. [196] The chances of a successful labor increased significantly during the 20th century in wealthier countries with the advent of new medical technologies. In contrast, pregnancy and natural childbirth remain hazardous ordeals in developing regions of the world, with maternal death rates approximately 100 times greater than in developed countries. [197]

Both the mother and the father provide care for human offspring, in contrast to other primates, where parental care is mostly restricted to mothers. [198] Helpless at birth, humans continue to grow for some years, typically reaching sexual maturity at 15 to 17 years of age. [199] [200] [201] The human life span has been split into various stages ranging from three to twelve. Common stages include infancy, childhood, adolescence, adulthood and old age. [202] The lengths of these stages have varied across cultures and time periods, but is typified by an unusually rapid growth spurt during adolescence. [203] Human females undergo menopause and become infertile decades before the end of their lives. [204] It has been proposed that menopause increases a woman's overall reproductive success by allowing her to invest more time and resources in her existing offspring, and in turn their children (the grandmother hypothesis), rather than by continuing to bear children into old age. [205] [206]

The life span of an individual depends on two major factors, genetics and lifestyle choices. [207] For various reasons, including biological/genetic causes, women live on average about four years longer than men. [208] As of 2018 [update] , the global average life expectancy at birth of a girl is estimated to be 74.9 years compared to 70.4 for a boy. [209] [210] There are significant geographical variations in human life expectancy, mostly correlated with economic development—for example life expectancy at birth in Hong Kong is 87.6 years for girls and 81.8 for boys, while in Central African Republic, it is 55.0 years for girls and 50.6 for boys. [211] [212] The developed world is generally aging, with the median age around 40 years. In the developing world the median age is between 15 and 20 years. While one in five Europeans is 60 years of age or older, only one in twenty Africans is 60 years of age or older. [213] The number of centenarians (humans of age 100 years or older) in the world was estimated by the United Nations at 210,000 in 2002. [214]

Humans are omnivorous, capable of consuming a wide variety of plant and animal material. [215] [216] Human groups have adopted a range of diets from purely vegan to primarily carnivorous. In some cases, dietary restrictions in humans can lead to deficiency diseases however, stable human groups have adapted to many dietary patterns through both genetic specialization and cultural conventions to use nutritionally balanced food sources. [217] The human diet is prominently reflected in human culture, and has led to the development of food science. [218]

Until the development of agriculture approximately 10,000 years ago, Homo sapiens employed a hunter-gatherer method as their sole means of food collection. [218] This involved combining stationary food sources (such as fruits, grains, tubers, and mushrooms, insect larvae and aquatic mollusks) with wild game, which must be hunted and killed in order to be consumed. [219] It has been proposed that humans have used fire to prepare and cook food since the time of Homo erectus. [220] Around ten thousand years ago, humans developed agriculture, [221] [222] [223] which substantially altered their diet. This change in diet may also have altered human biology with the spread of dairy farming providing a new and rich source of food, leading to the evolution of the ability to digest lactose in some adults. [224] [225] The types of food consumed, and the way in which they are prepared, have varied widely by time, location, and culture. [226] [227]

In general, humans can survive for up to eight weeks without food, depending on stored body fat. [228] Survival without water is usually limited to three or four days, with a maximum of one week. [229] In 2020 it is estimated 9 million humans die every year from causes directly or indirectly related to starvation. [230] [231] Childhood malnutrition is also common and contributes to the global burden of disease. [232] However global food distribution is not even, and obesity among some human populations has increased rapidly, leading to health complications and increased mortality in some developed, and a few developing countries. Worldwide over one billion people are obese, [233] while in the United States 35% of people are obese, leading to this being described as an "obesity epidemic." [234] Obesity is caused by consuming more calories than are expended, so excessive weight gain is usually caused by an energy-dense diet. [233]

Biological variation

There is biological variation in the human species—with traits such as blood type, genetic diseases, cranial features, facial features, organ systems, eye color, hair color and texture, height and build, and skin color varying across the globe. The typical height of an adult human is between 1.4 and 1.9 m (4 ft 7 in and 6 ft 3 in), although this varies significantly depending on sex, ethnic origin, and family bloodlines. [236] [237] Body size is partly determined by genes and is also significantly influenced by environmental factors such as diet, exercise, and sleep patterns. [238]

There is evidence that populations have adapted genetically to various external factors. The genes that allow adult humans to digest lactose are present in high frequencies in populations that have long histories of cattle domestication and are more dependent on cow milk. [239] Sickle cell anemia, which may provide increased resistance to malaria, is frequent in populations where malaria is endemic. [240] [241] Populations that have for a long time inhabited specific climates tend to have developed specific phenotypes that are beneficial for those environments—short stature and stocky build in cold regions, tall and lanky in hot regions, and with high lung capacities at high altitudes. [242] [243] Some populations have evolved highly unique adaptations to very specific environmental conditions, such as those advantageous to ocean-dwelling lifestyles and freediving in the Bajau. [244]

Human hair ranges in color from red to blond to brown to black, which is the most frequent. [245] Hair color depends on the amount of melanin, with concentrations fading with increased age, leading to grey or even white hair. Skin color can range from darkest brown to lightest peach, or even nearly white or colorless in cases of albinism. [246] It tends to vary clinally and generally correlates with the level of ultraviolet radiation in a particular geographic area, with darker skin mostly around the equator. [247] Skin darkening may have evolved as protection against ultraviolet solar radiation. [248] Light skin pigmentation protects against depletion of vitamin D, which requires sunlight to make. [249] Human skin also has a capacity to darken (tan) in response to exposure to ultraviolet radiation. [250] [251]

There is relatively little variation between human geographical populations, and most of the variation that occurs is at the individual level. [246] [252] [253] Much of human variation is continuous, often with no clear points of demarcation. [254] [255] [256] [257] Genetic data shows that no matter how population groups are defined, two people from the same population group are almost as different from each other as two people from any two different population groups. [258] [259] [260] Dark-skinned populations that are found in Africa, Australia, and South Asia are not closely related to each other. [261] [262]

Genetic research has demonstrated that human populations native to the African continent are the most genetically diverse [263] and genetic diversity decreases with migratory distance from Africa, possibly the result of bottlenecks during human migration. [264] [265] These populations acquired new genetic inputs from local admixture with archaic populations and have much greater variation from Neanderthals and Denisovans than is found in Africa. [181]

Humans are a gonochoric species, meaning they are divided into male and female sexes. [266] [267] The greatest degree of genetic variation exists between males and females. While the nucleotide genetic variation of individuals of the same sex across global populations is no greater than 0.1%–0.5%, the genetic difference between males and females is between 1% and 2%. Males on average are 15% heavier and 15 cm (6 in) taller than females. [268] [269] On average, men have about 40–50% more upper body strength and 20–30% more lower body strength than women. [270] Women generally have a higher body fat percentage than men. [271] Women have lighter skin than men of the same population this has been explained by a higher need for vitamin D in females during pregnancy and lactation. [272] As there are chromosomal differences between females and males, some X and Y chromosome related conditions and disorders only affect either men or women. [273] After allowing for body weight and volume, the male voice is usually an octave deeper than the female voice. [274] Women have a longer life span in almost every population around the world. [275]

The human brain, the focal point of the central nervous system in humans, controls the peripheral nervous system. In addition to controlling "lower," involuntary, or primarily autonomic activities such as respiration and digestion, it is also the locus of "higher" order functioning such as thought, reasoning, and abstraction. [276] These cognitive processes constitute the mind, and, along with their behavioral consequences, are studied in the field of psychology.

Humans have a larger and more developed prefrontal cortex than other primates, the region of the brain associated with higher cognition. [277] This has led humans to proclaim themselves to be more intelligent than any other known species. [278] Objectively defining intelligence is difficult, with other animals adapting senses and excelling in areas that humans are unable to. [279]

There are some traits that, although not strictly unique, do set humans apart from other animals. [280] Humans may be the only animals who have episodic memory and who can engage in "mental time travel". [281] Even compared with other social animals, humans have an unusually high degree of flexibility in their facial expressions. [282] Humans are the only animals known to cry emotional tears. [283] Humans are one of the few animals able to self-recognize in mirror tests [284] and there is also debate over what extent humans are the only animals with a theory of mind. [285]

Sleep and dreaming

Humans are generally diurnal. The average sleep requirement is between seven and nine hours per day for an adult and nine to ten hours per day for a child elderly people usually sleep for six to seven hours. Having less sleep than this is common among humans, even though sleep deprivation can have negative health effects. A sustained restriction of adult sleep to four hours per day has been shown to correlate with changes in physiology and mental state, including reduced memory, fatigue, aggression, and bodily discomfort. [286]

During sleep humans dream, where they experience sensory images and sounds. Dreaming is stimulated by the pons and mostly occurs during the REM phase of sleep. [287] The length of a dream can vary, from a few seconds up to 30 minutes. [288] Humans have three to five dreams per night, and some may have up to seven [289] however most dreams are immediately or quickly forgotten. [290] They are more likely to remember the dream if awakened during the REM phase. The events in dreams are generally outside the control of the dreamer, with the exception of lucid dreaming, where the dreamer is self-aware. [291] Dreams can at times make a creative thought occur or give a sense of inspiration. [292]

Consciousness and thought

Human consciousness, at its simplest, is "sentience or awareness of internal or external existence". [293] Despite centuries of analyses, definitions, explanations and debates by philosophers and scientists, consciousness remains puzzling and controversial, [294] being "at once the most familiar and most mysterious aspect of our lives". [295] The only widely agreed notion about the topic is the intuition that it exists. [296] Opinions differ about what exactly needs to be studied and explained as consciousness. Some philosophers divide consciousness into phenomenal consciousness, which is experience itself, and access consciousness, which is the processing of the things in experience. [297] It is sometimes synonymous with 'the mind', and at other times, an aspect of it. Historically it is associated with introspection, private thought, imagination and volition. [298] It now often includes some kind of experience, cognition, feeling or perception. It may be 'awareness', or 'awareness of awareness', or self-awareness. [299] There might be different levels or orders of consciousness, [300] or different kinds of consciousness, or just one kind with different features. [301]

The process of acquiring knowledge and understanding through thought, experience, and the senses is known as cognition. [302] The human brain perceives the external world through the senses, and each individual human is influenced greatly by his or her experiences, leading to subjective views of existence and the passage of time. [303] The nature of thought is central to psychology and related fields. Cognitive psychology studies cognition, the mental processes' underlying behavior. [304] Largely focusing on the development of the human mind through the life span, developmental psychology seeks to understand how people come to perceive, understand, and act within the world and how these processes change as they age. [305] [306] This may focus on intellectual, cognitive, neural, social, or moral development. Psychologists have developed intelligence tests and the concept of intelligence quotient in order to assess the relative intelligence of human beings and study its distribution among population. [307]

Motivation and emotion

Human motivation is not yet wholly understood. From a psychological perspective, Maslow's hierarchy of needs is a well-established theory which can be defined as the process of satisfying certain needs in ascending order of complexity. [308] From a more general, philosophical perspective, human motivation can be defined as a commitment to, or withdrawal from, various goals requiring the application of human ability. Furthermore, incentive and preference are both factors, as are any perceived links between incentives and preferences. Volition may also be involved, in which case willpower is also a factor. Ideally, both motivation and volition ensure the selection, striving for, and realization of goals in an optimal manner, a function beginning in childhood and continuing throughout a lifetime in a process known as socialization. [309]

Emotions are biological states associated with the nervous system [310] [311] brought on by neurophysiological changes variously associated with thoughts, feelings, behavioural responses, and a degree of pleasure or displeasure. [312] [313] They are often intertwined with mood, temperament, personality, disposition, creativity, [314] and motivation. Emotion has a significant influence on human behavior and their ability to learn. [315] Acting on extreme or uncontrolled emotions can lead to social disorder and crime, [316] with studies showing criminals may have a lower emotional intelligence than normal. [317]

Emotional experiences perceived as pleasant, such as joy, interest or contentment, contrast with those perceived as unpleasant, like anxiety, sadness, anger, and despair. [318] Happiness, or the state of being happy, is a human emotional condition. The definition of happiness is a common philosophical topic. Some define it as experiencing the feeling of positive emotional affects, while avoiding the negative ones. [319] [320] Others see it as an appraisal of life satisfaction, such as of quality of life. [321] Recent research suggests that being happy might involve experiencing some negative emotions when humans feel they are warranted. [322]

Sexuality and love

For humans, sexuality involves biological, erotic, physical, emotional, social, or spiritual feelings and behaviors. [323] [324] Because it is a broad term, which has varied with historical contexts over time, it lacks a precise definition. [324] The biological and physical aspects of sexuality largely concern the human reproductive functions, including the human sexual response cycle. [323] [324] Sexuality also affects and is affected by cultural, political, legal, philosophical, moral, ethical, and religious aspects of life. [323] [324] Sexual desire, or libido, is a basic mental state present at the beginning of sexual behavior. Studies show that men desire sex more than women and masturbate more often. [325]

Humans can fall anywhere along a continuous scale of sexual orientation, [326] although most humans are heterosexual. [327] [328] While homosexual behavior occurs in many other animals, only humans and domestic sheep have so far been found to exhibit exclusive preference for same-sex relationships. [327] Most evidence supports nonsocial, biological causes of sexual orientation, [327] as cultures that are very tolerant of homosexuality do not have significantly higher rates of it. [328] [329] Research in neuroscience and genetics suggests that other aspects of human sexuality are biologically influenced as well. [330]

Love most commonly refers to a feeling of strong attraction or emotional attachment. It can be impersonal (the love of an object, ideal, or strong political or spiritual connection) or interpersonal (love between two humans). [331] Different forms of love have been described, including familial love (love for family), platonic love (love for friends), romantic love (sexual passion) and guest love (hospitality). [332] Romantic love has been shown to elicit brain responses similar to an addiction. [333] When in love dopamine, norepinephrine, serotonin and other chemicals stimulate the brain's pleasure center, leading to side effects such as increased heart rate, loss of appetite and sleep, and an intense feeling of excitement. [334]

Human society statistics
Most widely spoken native languages [335] Chinese, Spanish, English, Hindi, Arabic, Portuguese, Bengali, Russian, Japanese, Javanese, German, Lahnda, Telugu, Marathi, Tamil, French, Vietnamese, Korean, Urdu, Italian, Indonesian, Persian, Turkish, Polish, Oriya, Burmese, Thai
Most practised religions [336] Christianity, Islam, Hinduism, Buddhism, Sikhism, Judaism

Humanity's unprecedented set of intellectual skills were a key factor in the species' eventual technological advancement and concomitant domination of the biosphere. [337] Disregarding extinct hominids, humans are the only animals known to teach generalizable information, [338] innately deploy recursive embedding to generate and communicate complex concepts, [339] engage in the "folk physics" required for competent tool design, [340] [341] or cook food in the wild. [342] Teaching and learning preserves the cultural and ethnographic identity of all the diverse human societies. [343] Other traits and behaviors that are mostly unique to humans, include starting fires, [344] phoneme structuring [345] and vocal learning. [346]

The division of humans into male and female gender roles has been marked culturally by a corresponding division of norms, practices, dress, behavior, rights, duties, privileges, status, and power. Cultural differences by gender have often been believed to have arisen naturally out of a division of reproductive labor the biological fact that women give birth led to their further cultural responsibility for nurturing and caring for children. [347] Gender roles have varied historically, and challenges to predominant gender norms have recurred in many societies. [348]

Language

While many species communicate, language is unique to humans, a defining feature of humanity, and a cultural universal. [349] Unlike the limited systems of other animals, human language is open—an infinite number of meanings can be produced by combining a limited number of symbols. [350] [351] Human language also has the capacity of displacement, using words to represent things and happenings that are not presently or locally occurring, but reside in the shared imagination of interlocutors. [151]

Language differs from other forms of communication in that it is modality independent the same meanings can be conveyed through different media, auditively in speech, visually by sign language or writing, and even through tactile media such as braille. [352] Language is central to the communication between humans, and to the sense of identity that unites nations, cultures and ethnic groups. [353] There are approximately six thousand different languages currently in use, including sign languages, and many thousands more that are extinct. [354]

The arts

Human arts can take many forms including visual, literary and performing. Visual art can range from paintings and sculptures to film, interaction design and architecture. [355] Literary arts can include prose, poetry and dramas while the performing arts generally involve theatre, music and dance. [356] [357] Humans often combine the different forms, for example music videos. [358] Other entities that have been described as having artistic qualities include food preparation, video games and medicine. [359] [360] [361] As well as providing entertainment and transferring knowledge, the arts are also used for political purposes. [362]

Art is a defining characteristics of humans and there is evidence for a relationship between creativity and language. [363] The earliest evidence of art was shell engravings made by Homo erectus 300,000 years before modern humans evolved. [364] Art attributed to H. sapiens existed at least 75,000 years ago, with jewellery and drawings found in caves in South Africa. [365] [366] There are various hypotheses as to why humans have adapted to the arts. These include allowing them to better problem solve issues, providing a means to control or influence other humans, encouraging cooperation and contribution within a society or increasing the chance of attracting a potential mate. [367] The use of imagination developed through art, combined with logic may have given early humans an evolutionary advantage. [363]

Evidence of humans engaging in musical activities predates cave art and so far music has been practised by virtually all human cultures. [368] There exists a wide variety of music genres and ethnic musics with humans musical abilities being related to other abilities, including complex social human behaviours. [368] It has been shown that human brains respond to music by becoming synchronised with the rhythm and beat, a process called entrainment. [369] Dance is also a form of human expression found in all cultures [370] and may have evolved as a way to help early humans communicate. [371] Listening to music and observing dance stimulates the orbitofrontal cortex and other pleasure sensing areas of the brain. [372]

Unlike speaking, reading and writing does not come naturally to humans and must be taught. [373] Still literature has been present before the invention of words and language, with 30,000 year old paintings on walls inside some caves portraying a series of dramatic scenes. [374] One of the oldest surviving works of literature is the Epic of Gilgamesh, first engraved on ancient Babylonian tablets about 4,000 years ago. [375] Beyond simply passing down knowledge the use and sharing of imaginative fiction through stories might have helped develop humans capabilities for communication and increased the likelihood of securing a mate. [376] Storytelling may also be used as a way to provide the audience with moral lessons and encourage cooperation. [374]

Tools and technologies

Stone tools were used by proto-humans at least 2.5 million years ago. [377] The use and manufacture of tools has been put forward as the ability that defines humans more than anything else [378] and has historically been seen as an important evolutionary step. [379] The technology became much more sophisticated about 1.8 million years ago, [378] with the controlled use of fire beginning around 1 million years ago. [380] [381] The wheel and wheeled vehicles appeared simultaneously in several regions sometime in the fourth millennium BC. [66] The development of more complex tools and technologies allowed land to be cultivated and animals to be domesticated, thus proving essential in the development of agriculture—what is known as the Neolithic Revolution. [382]

China developed paper, the printing press, gunpowder, the compass and other important inventions. [383] The continued improvements in smelting allowed forging of copper, bronze, iron and eventually steel, which is used in railways, skyscrapers and many other products. [384] This coincided with the Industrial Revolution, where the invention of automated machines brought major changes to humans lifestyles. [385] Modern technology could be seen as progressing exponentially, [386] with major innovations in the 20th century including electricity, penicillin, semiconductors, internal combustion engines, the internet, nitrogen fixing fetilisers, airplanes, computers, automobiles, the pill, nuclear fission, the green revolution, radio, scientific plant breeding, rockets, air conditioning, television and the assembly line. [387]

Religion and spirituality

Religion is generally defined as a belief system concerning the supernatural, sacred or divine, and practices, values, institutions and rituals associated with such belief. Some religions also have a moral code. The evolution and the history of the first religions have recently become areas of active scientific investigation. [388] [389] [390] [391] While the exact time when humans first became religious remains unknown, research shows credible evidence of religious behaviour from around the Middle Paleolithic era (45-200 thousand years ago). [392] It may have evolved to play a role in helping enforce and encourage cooperation between humans. [393]

There is no accepted academic definition of what constitutes religion. [394] Religion has taken on many forms that vary by culture and individual perspective in alignment with the geographic, social, and linguistic diversity of the planet. [394] Religion can include a belief in life after death (commonly involving belief in an afterlife), [395] the origin of life, [396] the nature of the universe (religious cosmology) and its ultimate fate (eschatology), and what is moral or immoral. [397] A common source for answers to these questions are beliefs in transcendent divine beings such as deities or a singular God, although not all religions are theistic. [398] [399]

Although the exact level of religiosity can be hard to measure, [400] a majority of humans professes some variety of religious or spiritual belief. [401] In 2015 the majority were Christian followed by Muslims, Hindus and Buddhists. [402] As of 2015, about 16%, or slightly under 1.2 billion humans, were irreligious, including those with no religious beliefs or no identity with any religion. [403]

Science and philosophy

An aspect unique to humans is their ability to transmit knowledge from one generation to the next and to continually build on this information to develop tools, scientific laws and other advances to pass on further. [404] This accumulated knowledge can be tested to answer questions or make predictions about how the universe functions and has been very successful in advancing human ascendancy. [405] Aristotle has been described as the first scientist, [406] and preceded the rise of scientific thought through the Hellenistic period. [407] Other early advances in science came from the Han Dynasty in China and during the Islamic Golden Age. [408] [90] The scientific revolution, near the end of the Renaissance, led to the emergence of modern science. [409]

A chain of events and influences led to the development of the scientific method, a process of observation and experimentation that is used to differentiate science from pseudoscience. [410] An understanding of mathematics is unique to humans, although other species of animal have some numerical cognition. [411] All of science can be divided into three major branches, the formal sciences (e.g., logic and mathematics), which are concerned with formal systems, the applied sciences (e.g., engineering, medicine), which are focused on practical applications, and the empirical sciences, which are based on empirical observation and are in turn divided into natural sciences (e.g., physics, chemistry, biology) and social sciences (e.g., psychology, economics, sociology). [412]

Philosophy is a field of study where humans seek to understand fundamental truths about themselves and the world in which they live. [413] Philosophical inquiry has been a major feature in the development of humans intellectual history. [414] It has been described as the "no man's land" between the definitive scientific knowledge and the dogmatic religious teachings. [415] Philosophy relies on reason and evidence unlike religion, but does not require the empirical observations and experiments provided by science. [416] Major fields of philosophy include metaphysics, epistemology, logic, and axiology (which includes ethics and aesthetics). [417]

Society is the system of organizations and institutions arising from interaction between humans. Humans are highly social beings and tend to live in large complex social groups. They can be divided into different groups according to their income, wealth, power, reputation and other factors. [418] The structure of social stratification and the degree of social mobility differs, especially between modern and traditional societies. [418] Human groups range from the size of families to nations. The first forms of human social organization were families living in band societies as hunter-gatherers. [419]

Kinship

All human societies organize, recognize and classify types of social relationships based on relations between parents, children and other descendants (consanguinity), and relations through marriage (affinity). There is also a third type applied to godparents or adoptive children (fictive). These culturally defined relationships are referred to as kinship. In many societies it is one of the most important social organizing principle and plays a role in transmitting status and inheritance. [420] All societies have rules of incest taboo, according to which marriage between certain kinds of kin relations are prohibited and some also have rules of preferential marriage with certain kin relations. [421]

Ethnicity

Human ethnic groups are a social category who identify together as a group based on shared attributes that distinguish them from other groups. These can be a common set of traditions, ancestry, language, history, society, culture, nation, religion, or social treatment within their residing area. [422] [423] Ethnicity is separate from the concept of race, which is based on physical characteristics, although both are socially constructed. [424] Assigning ethnicity to certain population is complicated as even within common ethnic designations there can be a diverse range of subgroups and the makeup of these ethnic groups can change over time at both the collective and individual level. [173] Also there is no generally accepted definition on what constitutes an ethnic group. [425] Ethnic groupings can play a powerful role in the social identity and solidarity of ethno-political units. This has been closely tied to the rise of the nation state as the predominant form of political organization in the 19th and 20th centuries. [426] [427] [428]

Government and politics

The early distribution of political power was determined by the availability of fresh water, fertile soil, and temperate climate of different locations. [429] As farming populations gathered in larger and denser communities, interactions between these different groups increased. This led to the development of governance within and between the communities. [430] As communities got bigger the need for some form of governance increased, as all large societies without a government have struggled to function. [431] Humans have evolved the ability to change affiliation with various social groups relatively easily, including previously strong political alliances, if doing so is seen as providing personal advantages. [432] This cognitive flexibility allows individual humans to change their political ideologies, with those with higher flexibility less likely to support authoritarian and nationalistic stances. [433]

Governments create laws and policies that affect the citizens that they govern. There have been multiple forms of government throughout human history, each having various means of obtaining power and ability to exert diverse controls on the population. [434] As of 2017, more than half of all national governments are democracies, with 13% being autocracies and 28% containing elements of both. [435] Many countries have formed international political alliances, the largest being the United Nations with 193 member states. [436]

Trade and economics

Trade, the voluntary exchange of goods and services, is seen as a characteristic that differentiates humans from other animals and has been cited as a practice that gave Homo sapiens a major advantage over other hominids. [437] [438] Evidence suggests early H. sapiens made use of long-distance trade routes to exchange goods and ideas, leading to cultural explosions and providing additional food sources when hunting was sparse, while such trade networks did not exist for the now extinct Neanderthals. [439] [440] Early trade likely involved materials for creating tools like obsidian. [441] The first truly international trade routes were around the spice trade through the Roman and medieval periods. [442] Other important trade routes to develop around this time include the Silk Road, Incense Route, Amber road, Tea Horse Road, Salt Route, Trans-Saharan Trade Route and the Tin Route. [443]

Early human economies were more likely to be based around gift giving instead of a bartering system. [444] Early money consisted of commodities the oldest being in the form of cattle and the most widely used being cowrie shells. [445] Money has since evolved into governmental issued coins, paper and electronic money. [445] Human study of economics is a social science that looks at how societies distribute scarce resources among different people. [446] There are massive inequalities in the division of wealth among humans the eight richest humans are worth the same monetary value as the poorest half of all the human population. [447]

Conflict

Humans commit violence on other humans at a rate comparable to other primates, but at a higher rate then most other mammals. [448] It is predicted that 2% of early H. sapiens would be murdered, rising to 12% during the medieval period, before dropping to below 2% in modern times. [449] Unlike most animals, which generally kill infants, humans kill other adult humans at a very high rate. [450] There is great variation in violence between human populations with rates of homicide in societies that have legal systems and strong cultural attitudes against violence at about 0.01%. [451]

The willingness of humans to kill other members of their species en masse through organized conflict has long been the subject of debate. One school of thought is that war evolved as a means to eliminate competitors, and has always been an innate human characteristic. The other suggests that war is a relatively recent phenomenon and appeared due to changing social conditions. [452] While not settled, the current evidence suggests warlike predispositions only became common about 10,000 years ago, and in many places much more recently than that. [452] War has had a high cost on human life it is estimated that during the 20th century, between 167 million and 188 million people died as a result of war. [453]


All these theories are interesting, but my Gran who was born to British parents, with Dutch back to the 1500’s, and nothing else that stands out as being Asian, North American Indian or other , was completely hairless from her head down. Her eyebrows were thin and her complexion leathery but she was old. My father consequently has hardly any hair on his body except his head, whilst my brother and I have hardly any leg or arm hairs, fine head hair with some areas having noticeably less follicles. My children however appear to take after my husband and have what I would consider ‘normal hair growth’. Although one child is much less hairy than the other.

So does this mean that there Must be some gene that is not working correctly, or perhaps my Gran was the milkmans and not my Great Grandads! Unfortunatley due to the death of her relatives, other than one surviving brother, I do not know if my Gran was unique in her family, or if one or both parents held this defective gene.

This is NOT alopecoa, as in gradual hairloss such as Gail Porter,, this is genetic within my family, my very European family. Although there are some gaps within my family tree where the male relatives were Sea Captains who did travel to the Carribean, so it is possible to have picked up some different nationality relatives, and my Grans condition was obviously severe whereas mine is somewhat muted.

I have found all your comments very interesting in trying to decipher why we are much more hairless than other Europeans. However, none of the answers really explain why different races have different traits, one can oly assume that evolution in the same mode as size or skin colour is to blame!

It seems as if adaptations for hairlessness could have arisen as we began living in closer proximity and in larger groups during the Neolithic. There was an increase in infectious disease during this time, so it seems as if a loss of body hair could have somewhat somewhat offset an individual’s chance of being infected during this transitional period. Of course, this would mean that the loss of body hair was a relatively recent occurrence…

Wrong. Does not explain why only white people are still hairy (even not so much as before). Native Americans, Africans, Asians, all lost the fur. Not white people. White people and their semi-white ancestors in Fertile Crescent were the first (with Egyptian) neolithic settled farmers. They lived in cities of about thousands of people quite soon after being farmers. On the other hand, even non-agricultural tribes in Australia etc. are hairless.

Veronica, Australian aboriginal people, who call themselves Koori, do HAVE body hair. I had a friend, Melinda, and she was very pround of her strong, dark hair on the legs and arms. According to the new DNA study, the Koordi are the oldest human culture on earth, reaching back ab. 75 000 years.

Since there are medical students around here, I’d like to know if the hairiness is bound with the amount of the skin pores ?

Thank you very much Bridget for your post. Yes, they are not alone, of course, also some indoeuropean haplogroups have specifically thicker hair than others. By what I wrote I do not intend to propose the straight link between hairlessness and the colour of the skin. First farmers were not white people. Some mutations of melanin related genes in their area really happened, after they had continuous recourse to the agriculture. I do not think it was due to their new type of settlement, which was in fact specific for later periods. Some dramatic changes (leading to the pouring out of Agassiz lake etc.) took places in that times and it could affect more genetic changes alltogether. But it seems to be wrong assumption hairlessness could happen due to neolithic settlements, if nations who haven’t experienced neolithic settlements at all, all around the world, Africa included, are hairless too, and even more obviously ) than many today’s white indoeuropeans who are successors of neolithic agricultural tradition. Also I think hairlessness is not due to diverse temperature in various areas. Melanin is more expected to be connected with the solar activity, with the distance from the poles and the distance some specific magnetic areas in the world as well, of course due to forests, waters (!), and many other influences, even it is not so clear too (look at the OCA2 mutation – in fact reduction of function – resulting to british blue eyes (not central african blue eyes) expecting to occur 10 000 years ago in Black sea area). But hairlessnes is due to some genetic shift, complex change preceding the others. The climate (so volcanos, waters etc. too) could function as the trigger as well of course, and probably did, but it is not the main and the single reason. The theory that people lost their hair because of the sun (and run) in tropical areas whereas in North people have been saved by fur before cold is ridiculous. No other animal does it. Also, the idea today’s white northerly population have lived in the same northern places always and for ages is bizarre and untrue. It would be similar as if people would like to explain the hairlessness in peruvian dogs as the result of climate change in Peru (here it is known today it is due to the mutation (interestingly – again lost of the part of the function) of one of FOX family genes which is responsible for development of embryonal states and it is human gene too – the dog was widespread (because considered as sacred) in Middle and South America long before Inca’s civilization and it is believed his ancestor taken to the breeding was from Asia). And also, the climate e. g. in Eem interglacial including Sun activity was different, not so much, but significantly, especially in some areas, to the possibilities of human evolution and spreading of the species. It is necessary to look for something more human-specific altogether and the suggestion of Judy Zifka below doesn’t look too sci-fi. I think Out of Africa theory impedes many truly interesting novelty suggestions, scholars tend to think within its limits, to squash their ideas in its boards because they have learn in school “it is true” and they’ve acquired the dogma. To be honest I doubt Koori population is “home” in their contemporary place as well, even it is likely their population is there much longer that some african populations on their places, but to my opinion, it beautifuly illustrates, among other examples, how the idea of losing hair due to the temperature is wrong. Or? Don’t you think? Or any other suggestions?

Veronica, thanks for the long and intense explication…

So it seems hairlessness, as a mutation, very soon became an important specie-specific, should I even say, a cultural choice. Individuals of the early Homo sapiens liked to choose the hairless partner rather than a hairy one, thus avoiding cross-breeding with different species like erectus, or later in Eurasia, with the Neanderthal).
I think that’s the closest we can get.

Personally, I don’ t agree with the “sexual choice” hypothesis at all, as well as I don’t think hairlessness is something specific for homo sapiens, even the second I regard as possible (not disproved yet). But I think homo neanderthalensis was hairless too, and even heidelbergensis and homo erectus, of course till some extent (similarly as Europeans or Arabians today, I think).

How about a totally different angel …

How much does our sex drive depent on sexual curiosity provided by clothing obscuring the genitals? What if the real adaptive value of hairlessness was that if forced us to clothe ourselves, and in so doing, generated an artifical sex drive to compensate for a weakening of the sexual instinct in the human line? We assume that humans still have a sex instinct, but do we??

) I am not aware about many animals who are able of what you call “sex instinct” 24 hours a day during the whole year ) and who use the sexual intercourse also for social hierarchy intentions (without intention of reproduction). This sex drive is similar to that of Bonobo, less to chimpanzees, so I don’t know but I would think its deviation from other animals :) (for quite a huge part of animals sex is in fact not pleasure at all and happens in allotted time) could occur much much earlier. the thing is that many people, regular homo sapiens, in most of regions of the world have been almost naked for the vast majority of their existence, long after we know they have had lost their hair. I really don’t think human species is the one who would need to be forced to sex. but I was also thinking about how the clothing could affect some physiological changes, because it is definitely for example electrostatic, it changes sweating etc. but nevertheless, to my opinion it seems more likely people started to wear clothing only after they were hairless, so they haven’t experienced these problems (otherwise they would be for example hairless only (or significantly more) in area when they wore clothing, etc.)

I disagree. I think that it might have to do with stupid people marrying each others brothers and sisters and or first cousins or something stupid like that. We get all kinds of F+cked up mutations. This interbreeding caused all kinds of defects. I know that some europeans are not very hairy at all. You are not suppose to have a uni eye brow. They should be two. I guess someone married there sister along the line and this continued.

The other thing is that these kinds of things are hidden for the most part. So that all these hairy people can hide it. If they had to walk around naked like many asians. The sexual selection process would rid us of hairy back ape people.

Arabs spend all there days waxing until death.

Though laser hair removal works. ha ha..

It’s true we went thru a bottleneck, a period when it was a necessity to inbreed. We are all children of those 20-30 men and women.

Right on Robert, yeah I think the Neolithic coulda been one of the times where hairlessness was selected for. I think you are onto something. The Neolithic transition was a critical shift, and could manifest founder-effect selection.

Again, the problem still remains to find out when did was this mutation introduced into our genome… Until we find out, this and all the other theories are very speculative.

Kambiz, any comment on this?

I’ve an OT question that relates to dinosaur feathers and hominid hair.

When hominid researchers in the field find a skull, what is their priority? To pick and brush it off right? Since we know that feather imprints can be retained if the critter was covered in fine mud (rare but not unusual), shouldn’t skull diggers be looking at the inverse of the skull for hair imprints on the dried mudstone? Of course once the skull’s soft tissues decomposed, the surrounding silts or clays moving inside would destroy some of the features, but the dead hair protein would probably leave an imprint, possibly visible through MRI or micro or nano Xray analysis or something. I for one would like to know the precise hair/beard patterns, as I’m tired of paintings, drawings, models of ancient neandertals, erectoids and apiths with short haircuts, since sapiens have hair that grows a yard long when left uncut.

But then again, some people think our ancestors were like chimpanzees on savannas, where long hair is useless. I do wish the bone & stone folks would check on hair, probably the only soft tissue recognizable after 20k years in the hardening mud.

Excellent question. I don’t know of any hominin fossils that told us something about the hair patterns and density.

It could be that people aren’t careful while excavating the remains, but from my experiences, people really slow down and take it easy when they find a precious hominin fossil. I doubt that it has to be due to their priorities because there’s nothing more important than delicately removing a fossil, taking note of the context it’s coming from.

That being said, a lot of why we don’t see fossils with evidence of hair patterns from hominins has to do with the sediment and chemistry the fossil was laid down in. Not every hominin fossil is formed because it settled in ‘soft muddy sediment.’ Fossils like famous archaeopteryx one, which show imprints of feathers, are rarities. Only a certain condition would yield such a result. Many fossils are formed in different sediments, with different chemicals, pumus, and even physical dynamics that affect the ability soft tissue is imprinted.

The process to make a fossil takes thousands, if not hundreds of thousands of years, depending on the conditions. A lot can happen during that time. And it happens in different places too.

Fossilization is the process where organic compounds in bone is replaced with inorganic minerals. Often, soft tissue, like hair and the skin it grows out of, is sloughed off and removed by natural phenomenon, scavengers, etc. Other times, hair just won’t last that long. You know how thin is, to have it degrade but still yield an imprint is rare. Even the most malleable sediment will fill in and warp.

I guess the best paleoanthropologists can do, is to sample for trace elements, like degraded hair protein since that may last. I don’t think any sort of visualization technique, can, at this time, show us what you’re looking for.

I hope that answers your question.

Neotony. I curious about that as an explanation for many of the distinctive traits we see in our fellow primates. It seems to me lately that the hairlessness that we exhibit into our adulthood is somehow allied with the suite of other expressions of neotony, traits that figure prominently in who we were and who we were to become: big heads, thin skin, cartilage growth throughout life, and covered with fat. It’s not so much that we’re hairless but that our follicles never produce hair like a normal maturing animals in the population from which we diverged. Maybe hairlessness was a genetic inevitability as a result of the way our genes work in certain relationships with other genes. So maybe big brains mean that the potential to grow a heavy pelt is proportionately reduced. At some point the lack of a hair is overcome by the emergent concept of manufactured shelter and the enhanced security of communalism. Being able to tolerate ones fellow species members becomes a requisite for success in gaining access to mates. This kind of instinct for social bonding is not uncommon in young animals but later as adults the group becomes “us” and everything else is “out there”. But in another expression of neotony, our ancestors retained their flexible/elastic social instincts into their adult lives, reinforcing the cohesiveness that provides a degree of advantage over other animals with whom they share the habitat’s resources…and as we have continued to these times.

Why are most native americans/Indians almost hairless, no arm or leg hair, yet they have a full head of hair? Is this typical? Is this a true feature of an indian or native american?

Bobbie,
I am mostly Indians actually over 3/4 and I have never had underarm hair. I have also heard that it is a characteristic of Native Americans.

my great grandfather is full blood indian , i’m white lived mostly in arizona ,i have no hair on my arms or legs or under arm , i’m the only one in my family of 6 is this way.

Bobbie Neu. East Asians generally have very little facial hair and Native Americans are presumed to have at least some East Asian ancestry. Could easily account for it. When I visited USA I met Pueblo Indians who had very sparse beards and moustaches, looked quite a bit like as Ho Chi Minh.

The naked mole rat hairlessness as a method to reduce ectoparasites and suggested to parallel the reduction of hair in humans, is not supported. Lice are warm-body-temperature dependent, living between the skin and insulative fur naked mole rats are virtually cold-blooded (very unlike the human metabolism). Their colonies are known to be very high in CO2 and low in O2, conditions not conducive to insects. Human ancestors were unlikely to have lived under those circumstances sustainably.

Since most terrestrial mammals thrive encased in their fur coats both in tropical and arctic climes despite associated ectoparasites, something else must have caused human body hair reduction concurrent with scalp hair extension and retention of three species of lice.

Here! I got another thesis!

Perhaps, with the appearance of human consciousness and therefore a specific self image/identity, our women ancestors found less hairy men more sexy, because these more resembled a physical otherness from nonhuman animals. Other animals were seen as more primitive, somehow of lower status and hence those men which more resembled nonhuman animals because of strong hairyness were also attributed with that lower status. So women at one point, because of their human sense of identity started preferring less hairy men.

Well at least that was the thing which first entered my mind 0,2 (0.2) seconds after reading the headline…

Precicely my thoughts BUT why women selecting men. In primative times men selected their female partner sometimes without consent. I see a preference of less hairy females as being wifes to fight over. And as the generations progressed the outcome was substancial less hair. Pubic hair in a lot of tribal cultures was a signal of breeding age. so it remained in the both sexes
The presence of more hair in mainly european s is largely climatic. Males having full thick beards and sometimes lots of body hair. obviously the females of european stock inherit more body hair because of this.

Yeah, why not indeed?
I have investicated the wolf / dog domestication and your argument could broaden my thought about the doggy history.
Early dogs became the first pets with full of benefits . Getting involved so closely with another species was like what Galileo Galilei felt when he looked to the skies.
That may have broaded the man’s mind and excelerated his conceptual evolution.

So somewhere there women really began to think about themselves clearly different from the other creatures – and the more their partners differed from those, the better they looked.

Obvious. Skin parasites prosper only in skin patches where there is hair. Selection favors skins that are unfriendly to parasites. Full stop.

J: Whales have skin parasites yet lack hair.
Orangutans have lots of long body hair yet lack lice, humans have very reduced hair yet have 3 species of lice.

GVF: If hair reduction was caused by females preferring less hirsute males, why do males have more hair than females? And why during puberty do males get the hairiest, if that is the time of most sexual selection? It doesn’t add up. Hair reduction in most aquatic mammals does. Seems obvious to me that human ancestors spent some time day to day in seawater at the tropics, as many people do today.

Yeah why are some better at being hairless than others? Asian/Native American/African. Could friction be part of it? Traveling through tall grass like in Africa. Native Americans are known for being able to quickly cover large ground through thick foliage. Tribes that live in thick jungles are always hairless. I’ve heard men who wear socks a lot sometimes lose hair from the sock line down….

CJONES, I’ve been thinking about your comment for sometime now. I don’t mean to offend you by saying it is rather humorous to think about your hypothesis.

To clarify to you and others, the real reason why ‘some are better’ at being hairless has to do with regional adaptations to temperature. Hair functions to regulate body heat. In colder areas, people are generally hairier. That’s not always the case, such as the Nepalese and Tibetan populations are relatively hairless. But in areas like the Caucuses,

Hair is also hormonally controlled. As you may have noticed, hair growth increases along with puberty. While all populations undergo puberty, different levels of hormones affect the amount of hair growth.

You may definitely be onto something, but I don’t think thickness of brush has a direct relation to hairiness. The reason why Africans are hairless is largely because most of Africa is hotter and losing hair may have been advantageous for thermoregulation. Asian populations, I dunno what’s going on with their hairlessness… but one of the reasons as why Native Americans are relatively hairless has to do with the fact that they were founded by Asian populations, so they were pre-dispositioned genetically with hairlessness.

You get closer to the real reason for human losing their fur. It has to do probably with temperatures, but the reason why it is important to react to temperature is completely different from all the reasons that were brought up in the article AND the comments.
I am writing an article that brings up a completly different reason for reacting to temperature with the loss of fur.

It can be shown mathematically. All what I need is the approximate times (in the past) in which there were changes in our fur coverage and the size (weight, volume, …) of the brain as a function of time. I will appreciate it very much iif someone can point or provide such data.

Ok, why i. e. arabian, persian and jewish populations are hairy? They have lived for thousands of years in the hot areas, with the very similar temperature as in Africa, South Asia, South America, and in many areas at least in few thousands of years also in the same humidity as in Africa.Why they don´t lose their hair after same thousands of years? It does not seem the temperature is the key. Also, I don´t think other mammals lose their fur in Africa ) No offence :)

Between 45ka and 30ka, the ancestors of the modern oriental people eg. Koreans, Tibetans, Vietnamese, and the Native Americans, and the Paleo-Siberians (excluding later mixtures) were geographically isolated at Lake Baikal, where they arrived during a warm inter-glacial period by following the flight path of migrating waterfowl from the African Rift and Paratethyan Black-Caspian basin.

They lived at the north end of Lake Baikal along plentiful brackish hot springs at the edge of the Amur tectonic plate, and they maintained a habit of daily bathing and foraging (fish, molluscs, seaweed, reeds, lowland millet grains as well as medium size animals that came for water and salt) in the warm-cool waters there, continuously through the ice age.
They did not have a strong stone tool culture, and probably used snares, traps, pits, weirs. Their huts were probably 1/2 dug into the ground, covered with skins and bark, insulated with reeds including tatami-like mats and furs.

35ka, tectonic shifting opened the Angara river (the only outlet of Lake Baikal) which sent much of the warm water northward into the Yenesei river and the Arctic sea, but the springs still provided warm water locally.
This caused a major diaspora.

The tribe budded off into small expanding mobile bands venturing along connected river basins (Lena, Yana, Yenesei, Angara) and Arctic-Beringia coasts, having partially adapted culturally to colder water and climate with skin boats and improved big game hunting methods and switching from hot baths (retained in Japanese) to sweatlodge/sauna cleansing which depended on firewood fuel rather than hot springs. Because these bands were mobile, running out of fuel was not an issue, unlike sedentary people. Stone tools were made, but bone and ivory were as commonly used.

At the same time in the west, people had adapted biologically by growing longer body hair, they lived along the Medit./Black/Caspian sea and marshes on fish, waterfowl and game thirsting for water and salt, including migratory herds, and quarried for stone in the Caucasus, Alps etc.

After the last glacial maimum, warming induced some Baikal people to expand eastward along the Amur and up/down coasts to Korea/China/Japan (Yayoi), and others to migrate southward inland following flocks to Tibet, Burma and then south China.

So we end up with Lapp, Manchu and Eskimo Inuit people who are relatively hairless biologically well adapted for warm seashores but culturally adapted for tundra plains and arctic coasts and blonde hairy Norwegians and swarthy Georgians biologically adapted for sub-tropical forests and deltas but culturally adapted for plains and mountain valley herding and fjord fishing in open plank boats.

A bit brief, but that’s the meat of the matter.

Truly ‘hair raising’! What is more intriguing is the evolutionary perspective of ‘intertriginous hairs’.


Endurance Running / Persistence hunting

"The endurance running hypothesis is the hypothesis that the evolution of certain human characteristics can be explained as adaptations to long distance running. The hypothesis suggests that endurance running played an important role for early hominins in obtaining food. Researchers have proposed that endurance running began as an adaptation for scavenging and later for persistence hunting [2] . a technique in which hunters use a combination of running, walking and tracking to pursue prey to the point of exhaustion. [3]

However, opponents of the theory point out that distance running animals are lightly built, with skeletons no heavier than necessary, whereas Homo erectus had thicker, heavier cranial and post-cranial bones skulls, twice as thick as a gorilla's and their bones were more dense. Furthermore, with a generally thicker cortex and narrower medullar cavity, the limb bones of Homo erectus were dense and heavy compared to Homo sapiens and other primates [4-9]. The extra weight created would have been an unnecessary burden for an endurance runner [10]. Long-distance human runners are lightly built compared to sprinters, and cursorial mammals such as dogs and horses do not have thick, heavy bones. Such heavy bones are very brittle (in other mammals & in human pathology). Most likely, if H. erectus had attempted to run long distance over open ground, he would have suffered fractures and exhaustion easily.

Endurance running as an explanation of human evolution (why we lost our fur, started running on two legs, etc.) does not make much sense. Of course, a few people today run sometimes after kudus, but that doesn't mean that our ancestors would have done the same several million years ago. Whatever conventional "wisdom" tells us, long distance running is at best a very recent (Holocene, or perhaps late-Pleistocene) adaptation of some adult males (H.sapiens) a few isolated inland populations (E.Africa, Australia), with "modern" technology such as water containers, etc.

Another problem with the endurance running theory is that humans use eccrine glands for sweating, unlike almost all other terrestrial mammals, which pant or sweat from apocrine glands. Human sweating is profligate with both water and salt, meaning that we need to replace both if we engage in any strenuous activity or if we are exposed to hot temperatures. In fact, human beings need to drink more often than any other animal that lives on the savannah as we cannot consume much in one go and we waste so much. Therefore, running for hours or days across a hot arid landscape without ready access to water would in most cases be / have been fatal.

Homo sapiens also possesses a greater distribution of subcutaneous fat, a derived characteristic that would have been an extra burden of some ten kilograms for an animal reliant on endurance running such adipose deposition is never seen in savannah predators. Compare, for example, the subcutaneous body fat levels in marathon runners vs. endurance swimmers. Furthermore, loss of sun-reflecting fur in an open, terrestrial environment would have increased the risk of overheating and sunburn since fur helps protect the skin from solar radiation [11].

Humans also have a shortened femoral neck, which could have been an adaptation to more efficient running, yet this feature first appears in Homo sapiens and is absent from earlier Homo species such as Homo erectus. This implies that erectus, with a relatively long and more horizontal femoral neck [12] was a less efficient runner than Homo sapiens. Also to be considered is that humans have a very small olfactory bulb [13] relative to apes [14], a significant flaw seeing as primary hunting predators or scavengers rely on their highly developed sense of smell. We also have a drastic and abrupt reduction of human masticatory muscles [15] unlike savannah carnivores such as dogs and hyenas that have well-developed masticatory muscles and use their excellent olfactory abilities to detect carcasses and prey.

Another important point as regards this theory: any evolutionary adaptation has to benefit all members of a species, regardless of gender. If our ancestors had evolved long legs for running after prey on the savannah, women carrying babies would have had to do it too, and in no extant persistence hunting human tribe does this happen - for obvious reasons. The only exception to this evolutionary preclusion would be epigamic (sexual selection) adaptations. If, as some endurance running proponents would have us believe, it was the males that went hunting while the females stayed at home with the babies, our species would have evolved differently as long-legged, bare-skinned, sweaty males and small, short-legged, furry females, but that is clearly not the case.

However we look at it, humans are poor runners capable of reaching speeds of only up to 20 km/hr over long distances, 36 km/hr over short distances. Some paleoanthropologists still believe that H.ergaster (Nariokotome Boy 1.6 Ma Kenya) had long legs for running over the savannah. The boy died in a swamp amid reeds, fish bones and hippo footprints, but since he had a tooth abscess, some paleoanthropologists speculated he might have had fever and gone into the swamp to cool off, where unfortunately he died. Long legs do not necessarily imply they evolved for running. Ostriches have relatively long legs, but flamingos have relatively longer legs. Our very long legs and bipedal stride are an indication for wading ancestors as with most birds and even probably dinosaurs.[16]

The walking / running theories of evolution have come about because certain features associated with human locomotion (pelvis, legs, spine etc.) are derived compared to apes, and because humans can run bipedally and apes can not, it may seem logical to assume these features must have come about as a result of humans running bipedally. However, humans can also tread water, swim and dive more efficiently than apes, and until these differences are also considered equally by researchers, any favouritism towards the above hypothesis must be considered incomplete.

"In today's hunting-gathering tribes they don 't run after game but they might have done once. But they would have had to walk on two legs before they could run on them. Wading enforces walking on two legs. There is no other activity that regularly leads to bp walking in any ape. Running after game would be a consequence of being bipedal, not a cause of it. Running on four legs is faster." [17]

From: "Was Man More Aquatic in the Past: Fifty Years after Alister Hardy. Chapter two: Littoral Man and Waterside Woman: The Crucial Role of Marine and Lacustrine Foods and Environmental Resources in the Origin, Migration and Dominance of Homo sapiens
C. Leigh Broadhurst1,*, Michael Crawford2 and Stephen Munro3

"The concept that early Homo populations may have hunted large mammals by running them to exhaustion has been criticized by Pickering and Bunn, who point to the fact that since large savannah mammals are considerably faster than humans, they would easily have been able to outrun any pursuing hominins, thus prey would soon be out of sight, meaning any successful pursuit would have required sophisticated tracking without utilizing visual contact. However, there is no evidence that early Homo populations had such tracking skills. Pickering and Bunn also note that the palaeo-ecology of early Homo sites would have been counter-conducive to successful tracking. Scavenging large mammals is another model, which has been discussed at length.

While undoubtedly a mechanism that was utilized, it is difficult to envision the entire human revolution based on this practice. African Plio-Pleistocene (5.33-2.59-0.012 Ma) savannahs were inhabited by numerous fast, efficient, well equipped predators and scavengers such as hyenas (e.g., Crocuta crocuta), felids (e.g., Panthera leo), hunting-dogs (Lycaon pictus) and vultures (e.g., Torgos tracheliotus), meaning there were no empty hunting or scavenging niches for early Homo populations. Early Homo could not have competed in terms of olfaction or running speed with hyenas, dogs and jackals nor in visual identification and speed of arrival with vultures and marabou storks. Also no primate has the physiology or immune system of a carrion consumer, so relatively fresh kills would be obligatory for this model.

It is difficult imagining pregnant women, nursing mothers or children taking part in endurance running our scouting for fresh kills, so provisioning is an essential component of these models. Yet this implies that after consuming their share of the carcass, the scavenging or hunting party would then transport sufficient meat – including the nutrient rich but highly perishable organs – back to the pregnant women, nursing mothers and children. The most important item – the DHA-rich brain – would only last a day or two in the hot African sun.

Transporting fresh meat without pack animals or vehicles is costly in terms of extra weight, and greatly increases the risks of predator attack, and meat decay. Further, the rise in metabolism associated with increased protein digestion creates extra heat, and consumption of meat by the hunters would require increased water intake." [18]

1. Morgan, Elaine. Foreword to "Was Man More Aquatic in the Past? Fifty Years After Alister Hardy". Banthom ebooks.
2. https://en.wikipedia.org/wiki/Endurance_running_hypothesis
3. https://en.wikipedia.org/wiki/Persistence_hunting
4 Klein RG. The human career. Chicago: University of Chicago Press 1999.
5. Jacob T. Solo Man and Peking Man. In: Sigmon B, Cybulski J, Eds. Homo erectus: Papers in honor of Davidson Black. Toronto: University of Toronto Press 1981 pp. 87-104.
6. Mania D, Vlcek E. Homo erectus in middle Europe: The discovery from Bilzingsleben. In: Sigmon B, Cybulski J, Eds. Papers in honor of Davidson Black. Toronto: University of Toronto Press 1981 pp. 133-51.
7. Kennedy GE. Bone thickness in Homo erectus. J Hum Evol 198514: 699-708.
8. Rightmire G. The human cranium from Bodo, Ethiopia: Evidence for speciation in the middle Pleistocene? J Hum Evol 1996 31: 21-39.
9. Wood B. The history of the genus Homo. Hum Evol 2000 15: 39-49.
10. Verhaegen M, Munro S, Vaneechoutte M, Bender-Oser N, Bender R. The original econiche of the genus Homo: Open plain or waterside? In: Muñoz S, Ed. Ecology research progress. New York: Nova Publishers 2008 pp.155-86.
11. Schmidt-Nielsen K. Desert animals. New York: Dover 1979.
12. Ruff C. Biomechanics of the hip and birth in early Homo. Am J Phys Anthropol 1995 98: 527-74.
13. Stephan H, Frahm H, Baron G. New and revised data on volumes of brain structures in insectivores and primates. Folia Primatol 1981 35: 1-29.
14. Gilad Y, Man O, Pääbo S, Lancet D. Human specific loss of olfactory receptor genes. Proc Natl Acad Sci USA 2003 100: 3324-7.
15. Stedman H, Kozyak B, Nelson A, et al. Myosin gene mutation correlates with anatomical changes in the human lineage. Nature 2004 428: 415-8.
16. Marc Verhaegen, AAT group.
17. Elaine Morgan, AAT group discussions.
18. "Was Man More Aquatic in the Past: Fifty Years after Alister Hardy. Chapter two: Littoral Man and Waterside Woman: The Crucial Role of Marine and Lacustrine Foods and Environmental Resources in the Origin, Migration and Dominance of Homo sapiens. C. Leigh Broadhurst1,*, Michael Crawford2 and Stephen Munro3

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Ancient mixers

The new research illustrates the complexity of humanity's deep history. Evidence has long been accumulating that humans and Neanderthals mated while their populations overlapped in Europe, before Neanderthals went extinct around 30,000 years ago. In 2010, researchers reported that between 1% and 4% of modern human genes in people in Asia, Europe and Oceania came from Neanderthal ancestors. When you add up all the snippets of Neanderthal DNA present in all modern humans today, some 20% of the Neanderthal genome may be preserved, according to 2014 research.

As scientists have been able to sequence more fragile fragments of DNA from fossils of ancient human ancestors, they've discovered a complex web of interbreeding stretching back millennia. Some Pacific Islanders, for example, carry pieces of the DNA of a mysterious ancient species of humans known as Denisovans.

The researchers of the new study used a computational method of comparing the genomes of two Neanderthals, a Denisovan and two modern African individuals. (Africans were chosen because modern people in Africa don't carry Neanderthal genes from the well-known human-Neanderthal interbreeding that occurred in Europe starting 50,000 years ago.) This method allowed the researchers to capture recombination events, in which segments of chromosomes — which are made up of DNA — from one individual get incorporated into the chromosomes of another.

"We are trying to build a complete model for the evolutionary history of every segment of the genome, jointly across all of the analyzed individuals," Siepel said. "The ancestral recombination graph, as it is known, includes a tree that captures the relationships among all individuals at every position along the genome, and the recombination events that cause those trees to change from one position to the next."

One advantage of the method, Siepel said, is that it allows researchers to find recombination events inside of recombination events. For example, if a bit of ancient hominin DNA from an unknown ancestor were incorporated in the Neanderthal genome, and then a later mating event between Neanderthals and humans inserted that mystery DNA into the human genome, the method allows for the identification of this "nested" DNA.


Paranthropus

This genus is also known as the robust australopithecine, and there is ongoing debate if the species should belong to the Australopithecus genus or should exist in a separate genus of Paranthropus. What is clear, however, is that they descended from Australopithecines. These species had more features similar to those of modern humans, as compared to their immediate ancestors. Mainly, they had stronger jaws and employed the use of muscles for chewing. They had flared cheekbones and bigger brains. They also had quite a thick layer of enamel on their teeth.

Paranthropus boisei (Photo Credit : Cicero Moraes/Wikimedia Commons)

Finally, we come to the genus to which we belong. This genus came about 2.4 million years ago, and Homo sapiens are currently the only living members. The first species in this genus, Homo habilis, existed about 2.4 &ndash 1.4 million years ago. They are credited with the first use of stone tools but scientists have found stone tools from before their time as well.

Another important species of this genus is Homo erectus. They are the oldest species with features and proportions that are very similar to modern humans. They had short arms and long legs, which marked the end of tree-swinging abilities and showed that these individuals were not arboreal. Studies also strongly suggest that they cared for the weaker and older beings in their groups. Homo erectus was also the first species to expand their demography outside Africa, although it is unclear as to whether they reached Europe.

Existing about 700,000 to 200,000 years ago, Homo heidelbergensis was the first species to live in colder climates. They also lived at a time where there was the definitive use of fire. They were the first species who regularly hunted larger animals and built simple shelters of wood and rocks. They had a comparatively flatter face, and possessed very prominent brow ridges.

Homo heidelbergensis (Image Credit: Flickr)

Homo neanderthalensis are the closest species to us as modern humans. They lived about 400,000 to 40,000 years ago and closely resembled us in appearance. They wore clothes, lived in shelters and had relatively sophisticated tools. They hunted regularly, and also consumed plants. Evidence suggests that they would bury their dead, often even giving offerings of flowers. They also made ornaments. All the H. neanderthalensis fossils have been discovered in Europe.

Homo neanderthalensis (Photo Credit : Matteo De Stefano/Wikimedia Commons)

There is another species in this genus, known as the Denisovans. They still haven&rsquot been classified properly, but they seem to have existed around the time of H. neanderthalensis. There is also evidence that suggests there was interbreeding within these groups, which led to variations.

According to current estimates, Homo sapiens arose about 300,000 years ago. The best way to establish a rough idea of their appearance would be to simply look in the mirror.

A number of these species existed at the same time, because the appearance of a new species did not mean the immediate extinction of the previous ones. As we have seen in the case of the Denisovans, Neanderthals and Homo sapiens, there was also interbreeding between them. According to some scientists, this is the cause behind the variations between the different races currently existing on Earth. That being said, there are still plenty of unanswered questions about our ancestors, as well as discrepancies in the timeline. Time estimates are constantly changing, so please don&rsquot hold me responsible, it depends on which source you trust! In time, however, hopefully we can get more concrete answers to the fascinating questions of our origin!


PRIMATE CLASSIFICATION

We are primates, that is, members of the order Primates (prī-mā’-tēz). The pie chart in Figure 2.2 shows the various orders of animals within the class Mammalia. We are most closely related to tree shrews (order: Scandentia) and colugos (order: Dermoptera, also known as flying lemurs). Primates are distinguished by a suite of characteristics known as evolutionary trends (see table below). However, we do not exhibit all of them to the same degree, and some are absent in certain species or lineages. For example, prosimians retain a claw on the second digit of their feet, whereas anthropoids do not (more about the two primate groups later). These trends were first proposed by Napier and Napier (1967) and Le Gros Clark (1959), and more recently primatologists have refined and added to the list.

Orders within the class Mammalia. “Mammal species pie chart” by Aranae is in the public domain.

PRIMATE EVOLUTIONARY TRENDS

  • Generalized, unspecialized skeleton:
    • No loss of limb bones from the ancestral condition.
    • Presence of a clavicle that allows greater mobility.
    • Capable of varied movement and locomotion.
    • Reduction of snout and olfactory bulb in frontal cortex.
    • Enlarged visual cortex, greater visual acuity, and color vision.
    • Forward-oriented, overlapping fields (binocular) of vision, and excellent depth perception.
    • Nails instead of claws.

    Taxonomic charts of the living primates can be found below. The primates are divided into two major taxonomic groups: strepsirrhines, which retain primitive characteristics, such as the lemurs of Madagascar and the bushbabies of Africa, and the more derived haplorrhines, that is, the tarsier, monkeys, and apes. The older terms for the suborders that are still in popular use are Prosimii (see figure 2.3) and Anthropoidea. However, tarsiers (small, nocturnal prosimian from the islands of the Southeast Asian archipelago) have characteristics of both groups. The strepsirrhine primates have more typical mammalian noses or rhinaria (see Figure 2.4) that are moist and more complex. They have a larger olfactory bulb in the frontal cortex of their brains and scent glands in various locations on their bodies. They use those glands to communicate to other members of their species. We haplorhines have simpler, dry noses and do not smell as good!

    Prosimian classification. Prosimian noses (A through D) and the nose of a New World monkey (E). “Prosimian noses” by Reginald Innes Pocock is in the public domain. New World anthropoid classification. Old World monkey classification. Ape classification.

    As we learn more about biochemical and evolutionary relationships among the various groups of primates, primate taxonomy is changing. The New World monkeys (see Figure 2.5) have changed substantially in recent years, with the creation of multiple families that were formerly grouped into two or three.

    The Old World anthropoids (monkeys and apes) and New World monkeys are also distinguished by our noses. Old World anthropoids have more ovoid, downward-facing nostrils, whereas New World monkeys’ nostrils are round and forward-facing.

    The Old World monkeys (see figure 2.6) are divided into the cercopithecines, with their cheek pouches and more generalized diet, and the leaf-eating colobines, with their complex guts. Think baboon (Africa) or snow monkey (Japan) for the former and black-and-white colobus (Africa) or Hanuman langur (primarily Indian subcontinent) for the latter. When asked, most people are more familiar with the cercopithecines, but if they see a picture of a black-and-white colobus (also known as a guereza) leaping through the air with its white mantle of fur and tail flying (or not…see Figure 2.8! I couldn’t find an action shot!) or a Hanuman langur sitting on the steps of a temple (OK, a fort . . . see Figure 2.9!) in India, they usually recognize them.

    Black-and-white colobus monkey. “Colobus guereza Mantelaffen” by Yoky is licensed under CC BY-SA 3.0. Hanuman langur. “Langur-Amber Fort” by McKay Savage is licensed under CC BY 2.0.

    The taxonomy of the apes (see Figure 2.7) has finally been updated. Until recently, humans were separated from the other great apes at the “family” level. All great apes are too closely related to be separated into different families. The lesser apes, i.e. the gibbons and siamangs of Southeast Asia, are still separated into their own family, the Hylobatidae. All of the great apes are now in the family Hominidae, formerly our exclusive domain. The orangutans come out at the subfamily level, leaving the African great apes in the subfamily Homininae. The gorillas have their own tribe, Gorillini (using the genus Gorilla to form the name) and if the chimps (genus Pan) are taken out of our tribe (Hominini), they are assigned the tribe Panini! I did not make that up! Some experts suggest that chimps and humans should be included in the same genus.


    New Study Shows Neanderthals Were Not Our Ancestors

    In the most recent and mathematically rigorous study to date determining whether Neanderthals contributed to the evolution of modern humans, a team of anthropologists examining the skulls of modern humans and Neanderthals as well as 11 existing species of non-human primates found strong evidence that Neanderthals differ so greatly from Homo sapiens as to constitute a different species.

    The findings could potentially put to rest the decades-long debate between proponents of the regional continuity model of human origins, which maintains that Neanderthals are a subspecies of Homo sapiens which contributed significantly to the evolution of modern Europeans, and the single-origin model, which views Neanderthals as a separate, distinct species. The research will be published in the Proceedings of the National Academy of Sciences.

    The scientists, led by Katerina Harvati of New York University, used a new technique known as geometric morphometrics to measure the degree of variation between and amongst living primate species, represented by over 1000 specimens. The scientists measured 15 standard craniofacial landmarks on each of the skulls and used 3-D analysis to superimpose each one in order to measure their shape differences, irrespective of size. Random samples were chosen from each species and the differences between them were calculated 10,000 times, in order to simulate the sampling effects of the fossil record. . The data used included Neanderthal fossils , Upper Paleolithic European modern human fossils, and recent human populations, as well as data from living African apes and Old World Monkeys.

    "Our motivation was to devise a quantitative method to determine what degree of difference justified classifying specimens as different species," said Harvati. "The only way we could effectively do this was to examine the skeletal morphology of living species today and come up with models. From these data, we were able to determine how much variation living primate species generally accommodate, as well as measure how different two primate species that are closely related can be."

    The study found that the differences measured between modern humans and Neanderthals were significantly greater than those found between subspecies or populations of the other species studied. The data also showed that the difference between Neanderthals and modern humans was as great or greater than that found between closely related primate species.

    Among the species of existing primates included in the study were gorillas and chimpanzees, which are known to be the closest relatives to humans, as well as mandrills, macaques and baboons, who represent a greater degree of geographic and ecological diversity. As a result, Harvati's team's study constitutes the most extensive inter- and intra-species comparison of primate evolution ever recorded.

    "What the data give us is a robust analysis of a widely representative sample of primates, and provides the most concrete evidence to date that Neanderthals are indeed a separate species within the genus Homo," Harvati added.

    The PNAS paper, entitled "Neanderthal taxonomy reconsidered: Implications of 3D primate models of intra- and interspecific differences," was co-authored by Stephen R. Frost of New York College of Osteopathic Medicine at the New York Institute of Technology and Kieran P. McNulty of Baylor University, and will be available on their website the week of January 26-30, 2004.

    Katerina Harvati is an assistant professor of anthropology at New York University, specializing in human evolution, Neanderthals and modern human origins. She conducts fieldwork in her native Greece. She earned a bachelors degree from Columbia University and a Ph.D. from the City University of New York Graduate Center. The studies were funded by grants from the National Science Foundation, L. S. B. Leakey, Wenner-Gren and Onassis Founadion, the American Museum of Natural History, the Smithsonian Institution and the New York Consortium in Evolutionary Primatology.

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    Reptiles (Reptilia)

    Reptiles arose during the Carboniferous period and quickly took over as the dominant form of land vertebrates. Reptiles freed themselves from aquatic habitats where amphibians had not. Reptiles developed hard-shelled eggs that could be laid on dry land. They had dry skin comprised of scales that served as protection and helped retain moisture.

    Reptiles developed larger and more powerful legs than those of amphibians. The placement of the reptilian legs beneath the body (instead of at the side as with amphibians) enabled them greater mobility.


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