How Human Races Formed on Earth and Why People Have Different Skin Colors
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Human races formed on Earth as populations of a single species, Homo sapiens, adapted to the different climates they settled in — races are groupings by outward physical traits such as skin colour, hair, and eye shape, not separate biological types ranked as superior or inferior. Where, how, and why the races arose is a question that still occupies modern science, and the short answer is that natural conditions shaped visible differences over roughly the last 200,000 years, while genetics shows every human belongs to one shared humanity (more: Article on racism).
The pages below move from the simplest picture of race to the deeper questions: what "race" actually means, when humankind emerged as a biological genus, how climate produced the familiar physical differences, what anthropology and DNA reveal, and why no division into "first-class" and "second-class" races has any scientific basis.
What race is: the biological concept and the scientific definition
Race, in its biological sense, refers to large human populations that share visible inherited features — skin colour, hair form, facial structure — that arose as adaptations to particular environments. In biology the nearest formal term is subspecies, and the criteria used in conservation biology (such as those behind the U.S. Endangered Species Act) require deep, discrete genetic divergence between groups. Human populations do not meet that threshold, which is why the concept of race as a set of clearly bounded biological types has been formally set aside by the scientific mainstream.
What unites people into a single humanity is far greater than what visibly divides them. All living people belong to Homo sapiens sapiens, share the same ancestry, and interbreed freely wherever they meet — the surest test that they form one species. National and racial features exist, but they concern appearance and local adaptation, not the capacities that would justify separating humanity into higher and lower groups.
Race as a social construct: the modern view
Most anthropologists today describe race primarily as a social construct — a system of categories invented by societies rather than dictated by biology. Scholars such as Audrey Smedley and John Hartigan Jr. trace how racial classification developed historically to organise social hierarchy, and racial formation theory and critical race theory examine how those categories continue to shape law, politics, and daily life. The point is not that racial categories are imaginary in their effects, but that their boundaries are drawn by culture, not by nature.
The category "white" itself illustrates the fluidity. Legal definitions of whiteness in the United States shifted repeatedly across the nineteenth and twentieth centuries, and the United States Census Bureau has rewritten its racial classifications many times. In Brazil, a person might be counted in a different racial category than the "same" person in the United States, and someone reclassified again in South Africa. Because the lines move across countries and eras, race functions as a social label attached to appearance rather than a fixed biological fact.
Biological and social approaches to dividing people into races
The debate between biological and social understandings of race turns on how genetic variation is distributed. Population geneticists including Alan R. Templeton and David Reich have shown that most human genetic variation lies within groups rather than between them, and that traits vary continuously across geography rather than falling into discrete blocks. Statistical measures such as pairwise FST and AMOVA (analysis of molecular variance) applied to DNA sequence data confirm that between-group differences are modest compared with the diversity found inside any single population.
A striking comparison drives the point home: by the genetic yardstick used to define subspecies in animals, chimpanzee populations are more differentiated from one another than human populations are. In other words, humanity is genetically more uniform than a single species of great ape. This is why bodies such as the U.S. National Academies of Sciences, Engineering, and Medicine — with input from researchers like Vence L. Bonham Jr. and Dr. Charmaine Royal — have urged science to move away from race as a biological variable and toward geographic ancestry and specific genetic markers instead.
When humankind emerged as a biological genus
Humankind emerged as a distinct biological genus a very long time ago, and the visible races appeared much later still. Anthropologists place the divergence of the large human races no earlier than about 200,000 years ago and no later than roughly 20,000 years ago; most likely it was a slow process spread across 180,000 to 200,000 years. Long before that, the human fossil record and paleoanthropology chart a lineage stretching back millions of years through forms such as Australopithecus — the group that includes the famous skeleton "Lucy" — and later Homo erectus, whose remains are distributed across Africa and Asia and show a marked increase in brain size over earlier ancestors.
The scientific classification of modern people places every living human in Homo sapiens, and specifically Homo sapiens sapiens. Evolution, in this framework, means shared ancestry and gradual change over time rather than a ladder of superior and inferior forms. Transitional fossils that bridge earlier primates and later humans are read against measurable criteria — cranial capacity, jaw and tooth structure, evidence of upright walking — to decide whether a given find is classified as more ape-like or more human.
Not every claimed link has survived scrutiny, and science's willingness to correct itself is part of its strength. Piltdown Man was exposed as a hoax when J.S. Weiner and colleagues showed the "fossil" combined a human skull with an orangutan jaw, and the Peking Man finds have been the subject of long-running creationist fraud claims that mainstream paleoanthropology rejects. These episodes show self-correction at work rather than a weakness in the fossil evidence as a whole.
The age of the Earth and the timeline of the appearance of humans
The age of the Earth — about 4.5 billion years — and the long timeline of life on it frame the debate between evolution and scientific creationism over the origin of races. Scientific creationism, as a movement, argues that a young Earth and a literal reading of Genesis better explain human origins, invoking Adam as the first man, Noah and Noah's Flood as the source of later peoples, and the Tower of Babel as the origin of language diversity. Flood legends do recur across many cultures, which creationist writers cite as corroboration.
Mainstream geology, however, finds no evidence for a single recent global flood, and the proposed timeline conflicts with dated rock strata and the fossil sequence. A well-known test case is the Paluxy River near Glen Rose, Texas, where alleged human footprints were said to appear alongside dinosaur tracks. Detailed study by investigators — with organisations such as the NCSE documenting the analysis — attributed the marks to dinosaur track misidentification, erosion patterns, and infilling, once stride length and weight distribution were examined; the "human" prints did not hold up. Evolutionary biology explains the diversity of peoples through natural selection acting on inherited variation, not through a recent dispersal from a single flood.
Skin colour in the first humans
The skin colour of the first humans was almost certainly neither very dark nor very light. It is likely that some individuals were somewhat paler and others somewhat darker, and the natural conditions in which different groups of people found themselves then shaped the skin tones we see today. The formation of races on Earth by skin colour was, above all, a response to climate.
How natural conditions and climate shaped the races
Climate is the driving force behind the visible differences between the races, because the traits that distinguish them are largely adaptations to sunlight, temperature, and dust. Skin pigment, hair form, skull shape, and eye structure each track the environment in which a population lived for many generations. The sections below take skin colour, then eye shape, as the clearest worked examples of environmental adaptation.
Ultraviolet light, pigmentation, and the adaptation of skin
Skin colour is an adaptation to ultraviolet radiation, controlled by the pigment melanin. Some groups of people settled in the tropical belt, where the sun's rays can easily burn exposed skin. From physics we know that black absorbs sunlight more fully, so at first glance dark skin seems disadvantageous — but it turns out that only the ultraviolet rays burn and can scorch the skin, and pigmentation acts as a shield protecting the body's skin. On the Von Luschan Scale, the range of human skin tones maps closely onto the intensity of ultraviolet light at each latitude.
Everyone knows that a light-skinned person gets sunburned faster than a dark-skinned one. In the equatorial grasslands of Africa, people with dark skin proved better suited to life, and from them the Negroid peoples descended. This is shown by the fact that dark-skinned people live not only in Africa but throughout the tropical regions of the planet.
Light-skinned and dark-skinned people
The original inhabitants of India are very dark-skinned people. In the tropical grassland regions of America the skin of the people living there proved darker than that of their neighbours who lived in the forests and sheltered from the direct rays of the sun in the shade of the trees.
And in Africa too, the native inhabitants of the tropical forests — the pygmies — have lighter skin than their neighbours who work the land and are almost always out under the sun.
The Negroid race: the native inhabitants of Africa
The Negroid race, associated with the equatorial regions of Africa, carries several adaptations to intense sun and heat beyond skin colour alone. These features formed over the course of development and were driven by the need to cope with tropical conditions of life.
Features of the Negroid race: hair and skull shape
Tightly curled black hair, for instance, protects the head well from overheating by direct sunlight, and its inheritance is one of the clearest examples of an adaptive trait passed between generations. Narrow, elongated skulls are likewise an adaptation against overheating. The same skull shape is found in the Papuans of New Guinea (more: The collections of N. N. Miklouho-Maclay), as well as in the Melanesians (more: The drawings of N. N. Miklouho-Maclay).
Features such as skull shape and skin colour helped all these peoples in the struggle for existence. In modern classifications this group, together with related tropical populations sometimes labelled Australoid, illustrates how visible traits cluster geographically without marking off a separate kind of human.
The Caucasoid race and the peoples of the northern latitudes
The Caucasoid race, whose lighter skin developed in temperate and northern regions, owes that trait to the very same ultraviolet rays — but this time to a shortage of them. Why did the skin of the white race turn out lighter than that of primitive people? The cause is those ultraviolet rays, under whose influence the human body synthesises vitamin D.
The synthesis of vitamin D and white skin
People of the temperate and northern latitudes need pale skin, transparent to sunlight, so as to capture as much ultraviolet as possible and produce enough Vitamin D for survival in cold, dim climates. Dark-skinned people living in those regions constantly suffered vitamin deficiency and proved less hardy there than light-skinned people. This is the classic account of how vitamin D production and cold-climate survival selected for reduced melanin as populations moved away from the equator.
The Mongoloid race and its distinctive features
The third great race is the Mongoloid group, whose distinctive features formed under a harsh continental climate. Its skin colour, it seems, was inherited from the most distant ancestors and is well suited both to the severe conditions of the North and to the hot sun. The eyes, however, deserve special comment.
It is thought that the Mongoloids first appeared in the parts of Asia lying far from any ocean; the continental climate there is marked by sharp temperature differences between winter and summer, day and night, and the steppes of those lands are interspersed with deserts.
Strong winds blow almost without pause, carrying enormous quantities of dust. In winter the region is a glittering expanse of endless snow. Even today, travellers through the northern areas put on goggles to guard against that glare; without them they pay with eye disease.
The Mongolian fold and the adaptation of the eyes
An important distinguishing trait of the Mongoloids is the narrow, slit-like eyes, and a second is the small fold of skin covering the inner corner of the eye — the almond-shaped eye that also helps keep dust out. This skin fold is usually called the Mongolian fold, or epicanthic fold. From here, from Asia, people with prominent cheekbones and narrow, slit-like eyes spread across Asia, Indonesia, Australia, and Africa.
Is there anywhere else on Earth with a similar climate? Yes, there is: certain regions of Southern Africa. They are peopled by the San (Bushmen) and Khoikhoi (Hottentots) — peoples belonging to the Negroid race. Yet the Bushmen there usually have dark-yellow skin, narrow eyes, and the same eye fold in place. At one time it was even thought that Mongoloids who had migrated from Asia lived in these parts of Africa; only later was the mistake understood. The example shows that similar traits can evolve independently under similar conditions — convergence, not shared descent.
The main races and their subdivisions
The classical scheme divides humanity into three or four large races — Caucasoid, Negroid, Mongoloid, and sometimes Australoid — each of which anthropologists further split into smaller races. This division is unstable: the total number of small races varies from one classification to another depending on which scientist drew it up, but there are certainly dozens of them. Races differ from one another in more than skin colour and eye shape, and modern anthropologists have catalogued a great many such differences.
These basic racial divisions and their subdivisions grew out of geographic clustering of visible traits, not out of any sharp genetic boundaries. Because the small races blend gradually into their neighbours, any line drawn between them is a matter of convention. The pattern is best understood as continuous variation across space, described in genetics through gene pools, demes (local breeding populations), gene flow, and admixture rather than through fixed racial blocks.
Anthropological perspectives on the origin of races
Anthropology asks by what criteria races might even be compared — head shape, brain size, blood group? — and finds no essential feature that marks any race as better or worse. It has been shown that brain weight differs between races, but it differs just as much between individuals of the same nationality. For example, the brain of the brilliant writer Anatole France weighed only 1,077 grams, while the brain of the no less brilliant Ivan Turgenev reached an enormous 2,012 grams. Every race on Earth falls between these two extremes.
That brain weight signals no mental superiority is confirmed by further figures: the average brain weight of an Englishman is 1,456 grams, of American Indians 1,514, of the Bantu 1,422 grams, and of the French 1,473 grams. Neanderthals had larger brains than modern people, yet they were hardly cleverer than we are. And still, racists remain on the globe — in the United States and in South Africa — though they have no scientific data to support their theories.
Anthropologists, the scientists who study humanity precisely from the standpoint of the traits of individuals and their groups, are unanimous:
All people on Earth, regardless of their national and racial affiliation, are equal. This does not mean that racial and national peculiarities do not exist — they do. But they determine neither intellectual abilities nor any other qualities that could be treated as decisive for dividing humanity into higher and lower races.
This conclusion is one of the most important in all of anthropology. It is not the only achievement of the science, however, or there would be no point in developing it further. Anthropology continues to advance, letting us peer into the most distant past of humankind and clarify moments once wrapped in mystery, reaching back to the very first days of the human being. Even the long stretch of history before writing existed grows clearer through anthropological research.
The methods have expanded beyond measure. A hundred years ago a traveller who met an unknown people could limit himself to describing them; today that is far from enough. The anthropologist now must take numerous measurements, neglecting nothing — neither the palm of the hand, nor the sole of the foot, nor, of course, the shape of the skull. Blood and saliva are collected for analysis, prints of feet and palms are taken, and X-ray images are made.
DNA analysis and genetic variation between races
DNA analysis has decisively answered the question of how much genetic variation lies between races: very little compared with the variation inside any group. All the measurements an anthropologist gathers are summed up into special indices characterising a given group of people, and even blood groups — the very groups used in transfusion — can correlate with racial background. For instance, people with blood group A are most common in Europe and absent among some populations of Southern Africa, China, and Japan; group B is nearly absent in the Americas and Australia; and fewer than ten percent of Russians have group AB.
Blood-group studies illustrate how population genetics can reconstruct history. The peopling of the Americas is a good case: archaeologists long searching for the oldest human cultures there had to conclude that people arrived comparatively late — only a few tens of thousands of years ago — and analysis of ash from ancient fires, bones, and the remains of wooden structures later confirmed a figure of roughly 20,000 to 30,000 years. The first Americans crossed near the Bering Strait and moved slowly south as far as Tierra del Fuego.
The fact that native Americans lack blood groups B and AB suggests that, by chance, the first settlers of the vast continent happened to include no one carrying those groups. For such a coincidence to show, the founding party must have been small — and it gave rise to all the Indian peoples with their endless variety of languages, customs, and beliefs. After that group set foot in Alaska, no one else could follow, or later arrivals would have brought the missing blood factor with them.
When the descendants of these first Columbuses reached the Isthmus of Panama, its tropical swamps, disease, wild beasts, and venomous creatures let only another equally small band cross. The proof is the absence of blood group A among native South Americans: once again the accident repeated itself, just as the first settlers of North America had lacked groups B and AB. Modern genomic science, and the geographic ancestry assessment that grew out of the Human Genome Project, refines these older blood-group inferences with far more precise molecular markers — while confirming their central lesson, that human diversity is patterned by migration and gene flow, not by sharp racial dividing lines.
Many readers know Thor Heyerdahl's famous book about the voyage of the Kon-Tiki, undertaken to argue that the ancestors of Polynesians might have come not from Asia but from South America, prompted by certain similarities between the two cultures. Heyerdahl himself understood that even his magnificent journey offered no decisive proof, yet most readers, carried away by the grandeur of the feat and the author's literary talent, steadfastly believe the bold Norwegian was right.
Still, Polynesians appear to descend from Asians rather than South Americans, and again the deciding argument is blood composition. South Americans lack blood group A, whereas a good many Polynesians carry it — which leans toward the conclusion that Americans took no part in peopling Polynesia. Almost everything recounted here, however, remains hypothesis.
The influence of culture and religion on the development of the races
Culture and religion have shaped the races as much as climate has, but through learned behaviour rather than inherited biology. Language, custom, religious belief, and shared background bind people into peoples and give rise to cultural markers — from African-American English in the United States to the distinct religious traditions found from Myanmar to Brazil — that are transmitted socially, not through genes. These factors form a large part of what people actually mean by "racial identity" in everyday life.
Because these cultural traits are learned, they can shift within a single lifetime and cross so-called racial lines freely, which is one more reason race behaves like a social category. The Biblical account in Genesis, with Adam, Noah's descendants, and the scattering of tongues at the Tower of Babel, offered earlier cultures a religious explanation for why peoples differ in language and appearance. Scholars in the Department of African & African American Studies and in the history and philosophy of biology now study such narratives as part of the cultural history of how humans have explained their own diversity.
What unites people into a single humanity
What unites people into a single humanity is a shared biology and ancestry that vastly outweigh every visible difference. Every living person belongs to one species, descends from common ancestors, and can have fertile children with any other — the plainest biological sign of one humanity. The differences that catch the eye, colour of skin, form of eye, texture of hair, are surface adaptations to sun, cold, and dust, not markers of separate human kinds.
The convergence of genetics and anthropology reinforces this unity. Genetic recombination reshuffles the same shared pool of variation in each generation, so that two people of the "same" race can differ more from each other than from someone of another race. Scientific literacy on this point matters for social justice, because the recognition that biological essentialism in race is false pulls the ground out from under any claim that one group is innately superior to another.
Is there any division into first-class and second-class races
There is no division of humanity into first-class and second-class races, and no scientific evidence has ever supported one. Racism arises when invented racial hierarchies are treated as natural fact, and its harm is real even though its biological basis is not. Scientific racism — the long attempt to rank races by brain size, skull form, or blood group — collapsed precisely because, as the brain-weight and blood-group figures show, no such ranking survives measurement.
The material effects of racial categorisation are nonetheless serious, working through institutionalised discrimination rather than through biology. The legacy of slavery and Jim Crow in the United States, racial profiling and inequality in the criminal justice system, and documented racial bias in healthcare and medicine all show how a social category can produce concrete inequality. Recognising race as socially constructed does not erase these effects; it locates their cause in human institutions and choices, which is exactly where they can be confronted.
Hypotheses in this field are constantly tested. Some scientists doubt that racial features are adaptive at all; others argue the Americas were settled in successive waves, with certain blood factors displaced over generations. There is still not enough evidence to settle every question. But hypotheses are either replaced by better ones or gather new confirmation until they become coherent theories — and the coherent theory that has emerged is that all races belong to one equal humanity, differentiated only at the surface by the environments in which our ancestors lived.
