by Dennis O'Neil
January 02, 2010

from ModernHumanVariation Website




With the exception of monozygotic twins, every one of us is genetically different from every other human who ever lived.


Each of us is unique in terms of the combination of tens of thousands of genetically determined characteristics that we possess. However, we clearly have some traits in common with other people. Most of us have readily identifiable male or female sexual characteristics which we share with others of our gender.

Photo of 4 chinese children age 4-6
Similar appearance of children from the same region of Asia
due to a shared gene pool


People who are closely related to each other usually have even greater similarity in appearance because much of their genetic makeup is shared. Unrelated people whose ancestors came from the same part of the world often are generally similar in terms of such body features as skin and hair color, facial characteristics, body shape, and stature.


Not surprisingly, these traits have a strong genetic component as well. However, they can be affected by environmental influences. For instance, skin color often can be darkened, or tanned, seasonally by prolonged exposure to ultraviolet radiation from the sun. Likewise, stature can be affected by nutrition.


When young children do not receive sufficient calories in their diet, especially protein, their growth is likely to be stunted - they will not reach their full genetically programmed height.

Humans like to classify and use identity labels for people and things with which we come in contact. It satisfies our apparent need for a sense of order. In addition to gender and age, most of us readily classify each other into distinct categories on the basis of what we consider to be races.


In North America, people usually think in terms of Black, White, Asian, Hispanic or Latino, and Indian or Native American. These are all archaic concepts of physical types that have little biological reality.


Academics may use more sophisticated sounding terms for these perceived biological groupings, such as Negroid, Caucasoid or Caucasian, and Mongoloid.


Nevertheless, they are still bad science. However, they are important to contemporary life in North America because they reflect culturally defined differences in our society. They are essentially labels of ethnicity that are used for categorizing and discriminating.

We now know that clearly distinct human biological races do not now exist. This does not mean that our species is lacking anatomical and physiological variation between populations. Rather, the true nature of that variation is far more complex. It does not correspond to commonly believed simple racial lines.

The physical traits that we think of as clustering together among particular peoples often have much broader distributions.


They continue well outside of the geographic areas in which a "race" is stereotypically supposed to exist. For instance, dark brown skin is usually thought of as the key trait in distinguishing sub-Saharan Africans from people elsewhere in the world.


However, dark brown skin is also found in parts of southern Asia, Australia, New Guinea and on the nearby islands of Melanesia, as well as in much of the Americas.


Map of the world showing the distribution of human skin color in about 1500 A.D.

Darker skin colors are found mostly between 20 degrees north and south of the equator

(Data for native populations collected by R. Biasutti prior to 1940.)


Young man from Papua New Guinea

in the Southwest Pacific Ocean

The non-African peoples with dark brown skin color (like the man in the photo from New Guinea) do not share a close common ancestry with Africans.


Their skin coloration is largely due to natural selection rather than recent shared descent. The environmental factors that led to dark brown skin among Africans apparently led to it elsewhere as well.

Genetically inherited traits often have a clinal distribution. That is to say there is a continuous, progressive gradation moving from one geographic region to another. The frequency of yellow-brown hair among Australian Aborigines illustrates this trend (as shown by the map on the left below). This trait generally becomes more common with distance from the coast.


Such patterns can result when selective pressures differ from one region to another and when people mate mostly with their immediate neighbors. Selective pressures favoring or discriminating against a trait may come from several sources. There may be natural selection resulting from environmental constraints.


At the same time, there also may be patterns of culturally defined discriminatory mate selection that vary from region to region.


Map of Australia showing the progressive distribution of yellow-brown hair color among Australian Aborigines

The highest frequencies of this color hair are in west central Australia

Map of most of Britain showing the frequency of people with red hair in England and Scotland

The highest frequencies of red hair are in Wales and southern Scotland

          Clinal distribution of hair color among Australian Aborigines                                   Discontinuous distribution of red hair in Britain

Sometimes, the distribution of genetically inherited traits does not follow a pattern of gradual change from one geographic region to another but has a discontinuous distribution.


The frequency of red hair in Britain illustrates this sort of pattern. Note in the map on the right above that there are several relatively isolated pockets where there is a high frequency of people with red hair.


Such a pattern can result when groups of people migrate into a new area or when there are closed breeding groups that select mates based on such a trait.

Models of Classification

How can we accurately classify people in a manner that corresponds to real biological differences rather than culturally defined stereotypes? The answer to this question is not simple.


There are three basic ways in which anthropologists have tried to do it in the past.


These models are generally referred to as,

  • typological

  • populational

  • clinal

Typological Model
During the 19th and early 20th centuries, anthropologists and biologists naively divided all people into distinct geographical groups on the basis of what they saw as the regular occurrence together of selected traits.


They were using the typological model which has the same basis as the commonly used categories of race today. This approach focuses on a small number of traits that are readily observable from a distance such as skin color, hair form, body build, and stature.


Inherent in the typological model is the notion that there have been "pure" unmixed races in the past. The roots of this model for classifying people go back at least to the 18th century Swedish naturalist, Carolus Linnaeus.


He proposed the existence of four biological varieties or races of humans corresponding to geographic regions:

  • Homo sapiens Eoropeus albescens ("white" people from Europe)

  • Homo sapiens Africanus negreus ("black" people from Africa)

  • Homo sapiens Asiaticus fucus ("dark" people from Asia)

  • Homo sapiens Americanus rubescens ("red" people from the Americas)

The typological model is based on what is now known to be a false assumption concerning the nature of human variation - that is, that we can be unambiguously assigned to a "race" on the basis of selected anatomical traits.


In fact, when we look at specific individuals, we often run into difficulty trying to categorize them. For example, on the basis of skin color, we might put them into one "race" and on the basis of nose shape, body form, or blood type, they might go into others.

Even if we base the classification on a single characteristic, the typological model fails because most biological traits are continuous variables. That is to say, there is a progressive range of variation that our preconceptions sometimes prevent us from seeing. The typological model causes us to lump people together into arbitrarily assigned categories.


For instance, we tend to classify people as being slender, medium build, or fat despite the fact that there is a continuum of body weight and size among humans. The same is true of skin color and other commonly used "racial" characteristics.

The typological model usually leads us to wrongly assume that the people within any "race" are genetically and anatomically more alike than they are like people from other "races". This all depends on the traits that are being compared. For instance, many Americans believe that people of African descent have broad noses. In fact, both the widest and the narrowest noses are found among the people of that continent.


Recent research comparing human DNA sequences from around the world has shown that 85% of human genetic variation exists within what we have previously assumed to be more or less separate "races" and only 15% between them. In other words, "racial" groups are far from being homogenous.

Another major problem with the typological model is that the number of "races" you end up with depends on the number and kinds of traits employed in the classification. The more traits used, the fewer people in the world there are who share them.


For example, light skin color is considered to be a defining characteristic of Europeans. However, when you add the criteria of narrow noses, straight hair, and tall stature, many Europeans would be excluded altogether or the European racial category would have to be further subdivided into several smaller "races."


Since the number of "races" can be so easily changed by the way they are defined, it is clear that they do not really exist as distinct biological groupings of people. Instead, they are arbitrary creations that reflect our ethnocentric click this icon to hear the preceding term pronounced views of ourselves and other people.


They are mainly cultural rather than biological groupings.

Populational Model
By the early 1940's, most biological anthropologists recognized these problems and adopted the populational model as an alternative.


This is based on the idea that the only significant groups, in evolutionary terms, consist of people whose ancestors have more or less exclusively mated with each other over long periods of time. Individuals in such distinct breeding populations would be expected to share many genetically inherited traits and to have a similar appearance.

This approach to understanding the patterns of human biological diversity differs radically from the typological model. The latter starts by defining traits that presumably characterize a "race" and then looks around the world to see who has them. In contrast, the populational model looks for breeding populations first and then considers the anatomical and physiological traits that may distinguish them.

While the populational approach makes theoretical sense, it is undermined by the fact that throughout history humans have rarely mated within a single group for long.


Cultural and geographic barriers to intergroup mating have most often broken down over time. Speeding up this process of intermixture of humanity have been the mass intercontinental migrations of the last 500 years. This process is actually accelerating today largely due to relatively inexpensive and easy intercontinental travel. Biological anthropologists have found only a few moderately distinct breeding populations still existing. As a result, the populational model is of little help in understanding most of human variation today.


However, it is of value in studying the few relatively isolated communities that have survived.

Clinal Model
By the early 1960's, sufficient data had been gathered for Biological anthropologists to understand that a clinal model reflects the true nature of human biological variation.


This model is based on the fact that genetically inherited traits most often change gradually in frequency from one geographic area to another. For instance, the allele for type B blood generally increases from west to east in Europe. We can record different frequency zones, or clines (as shown in the map below).


Unlike the typological and populational models, the clinal model does not result in the definition of distinct groups or races of people.


Map of Europe showing B blood type allele clines

The frequencies of B type progressively increase from Western to Eastern Europe

In the west they are as low as 0-5% B, while in the east they are as high as 25-30% B

Clinal distribution of the B blood allele in Europe
(the arrow shows the direction of increasing B blood allele frequency)

Gradual changes in gene frequency from one region to another are mostly due to the simple fact that the chance of our mating with someone is usually directly related to the distance they live from us.


People whose ancestors have lived close to ours for many generations are more likely to share genetically inherited traits with us than are people who live further away. However, as long distance transportation systems have become more accessible and dependable, the distance from home that we travel and potentially find mates has increased.


Despite this change, most people still usually end up marrying others who live within a few hundred miles of their home.

Unfortunately, the pattern of human variation around the world cannot be entirely understood by the clinal model alone. The distribution of some traits is partly discontinuous. The example of red hair in England (described in the first section of this tutorial) is not unique. There are other traits that have non-clinal distribution patterns.


These also can be understood as results of historical migrations or exclusive breeding within more or less closed communities.


For example, the map below shows that the frequency of people who have the B blood allele generally increases from southeast and northeast Asia to central Asia. Within this more or less continuous cline, there are isolated pockets of relatively low B allele frequency.


Therefore, the distribution of this genetically inherited trait appears to be mostly clinal but, in part, it is also discontinuous.


Map of Asia showing B blood type frequencies

They are generally higher in Central and Eastern Asia,

but there are isolated pockets of low B frequencies in southern China and Siberia

Clinal and discontinuous distribution
of the B blood allele in Asia

How Can Human Variation Be Best Described?
It is clear that all of the models fail to adequately carry out the entire job. The typological model is the most unsound because presumed racial traits are not found exclusively within defined races.


In addition, focusing on new sets of traits often results in assigning people to different races, despite the fact that they were lumped into the same race before.

  • The populational model makes sense theoretically but fails to account for most of the distribution patterns around the world because we do not limit our breeding to isolated populations.

  • The clinal model comes the closest to grasping the real nature of human variation. However, it is undermined by the occasional discontinuous distribution resulting from migrations and the few remaining small isolated communities.

The patterns of human variation around the world are not only highly complex but also are constantly shifting through time.


Furthermore, the rate of change in the patterns has been accelerating as our numbers grow and as long distance travel and migration become more routine.

In the final analysis, it is important to keep in mind that all humans around the world today are biologically quite similar despite our superficial differences. In fact, we apparently are 99.9% genetically identical. Most of the differences between us are due to our unique individual traits and being male or female. When we are compared to many other kinds of animals, it is remarkable how little variation exists within our own species.


There is 2-3 times more genetic variation among chimpanzees, 8-10 times more among orangutans, and thousands of times more in many insect species. Most biological anthropologists would agree that human variation is not now sufficient to warrant defining separate biological races, varieties, or sub-species.


However, it very likely was in our distant prehistoric past.

In order to better understand the true patterns of human variation, biological anthropologists have gathered detailed data about genetically inherited traits. Most of this work has been done with blood typing, but DNA sequence comparisons are now providing an even more detailed understanding of our human biological diversity.


The next section of this tutorial presents some of this evidence.


Two teams of geneticists at Stanford University compared the DNA of 938 people from 51 populations in order to better document human diversity and past migrations around the world.


They focused on 650,000 DNA nucleotides to discover differences. This provided what they believe to be clear evidence of human origins in Sub-Saharan Africa and its subsequent dispersion into various parts of the world.


They believe that it is also evidence of more recent migrations that resulted in genetic differences between populations today such as North and South Chinese. (Jakobosson, Mattias, Nature February 21, 2007 and Jun, Z. Li, Science February 22, 2007)

Distribution of Blood Types

Blood provides an ideal opportunity for the study of human variation without cultural prejudice.


It can be easily classified for many different genetically inherited blood typing systems. Also significant is the fact that we rarely take blood types into consideration in selecting mates. In addition, few people know their own type today and no one did a century ago. As a result, differences in blood type frequencies around the world are most likely due to other factors than social discrimination.


Contemporary Japan is somewhat of an exception since there are popular Japanese stereotypes about people with different blood types. This could affect choice in marriage partners for some Japanese.

All human populations share the same 27 known blood systems, although they differ in the frequencies of specific types. Given the evolutionary closeness of apes and monkeys to our species, it is not surprising that some of them share a number of blood typing systems with us as well.

When we donate blood or have surgery, a small sample is usually taken in advance for at least ABO and Rh systems typing. If you are O+, the O is your ABO type and the + is your Rh type. It is possible to be A, B, AB, or O as well as Rh+ or Rh-.


You inherited your blood types from your parents and the environment in which you live can not change them.

ABO Blood Type System
We have learned a good deal about how common each of the ABO blood types is around the world.


It is quite clear that the distribution patterns are complex. Both clinal and discontinuous distributions exist, suggesting a complicated evolutionary history for humanity. This can be seen with the global frequency patterns of the type B blood allele (shown in the map below).


Note that it is highest in Central Asia and lowest in the Americas and Australia. However, there are relatively high frequency pockets in Africa as well.


Overall in the world, B is the rarest ABO blood allele. Only 16% of humanity have it.

Map of the world showing the frequency of the B blood allele among indigenous populations

It was absent in Australia, New Zealand, and most of the New World except for western Alaska

It was present throughout the Old World with its highest frequencies in Central and East Asia

Distribution of the B type blood allele in native populations of the world

The A blood allele is somewhat more common around the world than B. About 21% of all people share the A allele.


The highest frequencies of A are found in small, unrelated populations, especially,

  • the Blackfoot Indians of Montana (30-35%)

  • the Australian Aborigines (many groups are 40-53%)

  • the Lapps, or Saami people, of Northern Scandinavia (50-90%)

The A allele apparently was absent among Central and South American Indians.

Map of the world showing the frequency of the A blood allele among indigenous populations

It was absent in Central and South America, but present throughout the rest of the world

It was at its highest frequency in Western Europe, Australia, and the sub-arctic regions of North America and Greenland

Distribution of the A type blood allele in native populations of the world


The O blood type (usually resulting from the absence of both A and B alleles) is very common around the world.


About 63% of humans share it. Type O is particularly high in frequency among the indigenous populations of Central and South America, where it approaches 100%. It also is relatively high among Australian Aborigines and in Western Europe (especially in populations with Celtic ancestors).


The lowest frequency of O is found in Eastern Europe and Central Asia, where B is common.

Map of the world showing the frequency of the O blood allele among indigenous populations

Most regions were 50% or higher in frequency

It was highest in the New World (90-100%) and lowest in Central Asia (50-60%)

Distribution of the O type blood in native populations of the world

Other Blood Type Systems
The majority of the people in the world have the Rh+ blood type.


However, it is more common in some regions. Native Americans and Australian Aborigines were very likely 100% Rh+ before they began interbreeding with people from other parts of the world. This does not imply that Native Americans and Australian Aborigines are historically closely related to each other. Most African populations are around 75% Rh+.


Europeans have the lowest frequency of this blood type for any continent. They are 60% Rh+. The lowest known frequency is found among the Basques of the Pyrenees Mountains between France and Spain. They are only 47% Rh+.

The distribution patterns for the Diego blood system are even more striking. Evidently, all Africans, Europeans, East Indians, Australian Aborigines, and Polynesians are Diego negative. The only populations with Diego positive people may be Native Americans (2-46%) and East Asians (3-12%).


This nonrandom distribution pattern fits well with the hypothesis of an East Asian origin for Native Americans.

These patterns of ABO, Rh, and Diego blood type distributions are not similar to those for skin color or other so-called "racial" traits.


The implication is that the specific causes responsible for the distribution of human blood types have been different than those for other traits that have been commonly employed to categorize people into "races."


Since it would be possible to divide up humanity into radically different groupings using blood typing instead of other genetically inherited traits such as skin color, we have more conclusive evidence that the commonly used typological model for understanding human variation is scientifically unsound.

The more we study the precise details of human variation, the more we understand how complex are the patterns.


They cannot be easily summarized or understood. Yet, this hard-earned scientific knowledge is generally ignored in most countries because of more demanding social and political concerns. As a result, discrimination based on presumed "racial" groups still continues. It is important to keep in mind that this "racial" classification often has more to do with cultural and historical distinctions than it does with biology.


In a very real sense, "race" is a distinction that is created by culture not biology.