We have examined humanity as a whole. Yet it is quite clear that over the course of history, humans have lived in different groups that have evolved different languages, cultures, and physical traits. What does genetics tell us about how individuals relate to a group and how different groups relate to one another? We begin discussion by considering orangutans and jaguars.
Orangutans live in two large islands in Southeastern Asia, Borneo and Sumatra. By visual inspection, the orangs inhabiting Sumatra are indistinguishable from their cousins on Borneo. Yet genetically, the two populations are quite different. They are two different races of orangutan.
Most jaguars have conspicuous orange, tan, and black sports. Yet occasionally a jaguar is born with a dark, black coat that makes the spots impossible to see from a distance. Despite the glaring visual differences, these two types of jaguars are not different races.
To the geneticist race need not imply visual morphological differences and visual morphological differences need not imply race. Clearly, there are important differences between how geneticists define race and societies define race. The social definition is absolute and categorical.
It is the type of box that we check when filling out a form; it is how demographic statistics are broken down; it is often how we think of someone that we have seen but never met simply on the basis of that person’s appearance; and it is based on clear, visual morphological differences.
Geneticists define race as a population with a characteristic set of allele frequencies and whose ancestors have tended to mate among themselves for an appreciable amount of time. Geographical separation prevented the orangs on Borneo from freely mating with those on Sumatra and evolutionary forces resulted in different allele frequencies on the two islands.
The orangs qualify as genetic races. Only a few genes are responsible for the differences between black and spotted jaguars. The ancestors of spotted jaguars have freely mated with those of black jaguars. They fail to meet the genetic definition of race.
The genetic definition is relative, not absolute. For this reason, some geneticists eschew the term “race” in favour of the term “genetic population.” The Irish, Scots, and Welsh could be considered three different “races” of Celts or they could be combined into a Celtic “race” if they were being compared to Greeks. The Zulus in South Africa, the Kung in the Kalahari Desert and Ibo in Nigeria could legitimately be compared as three different “races.”
The genetic definition can also be dimensional. Genetically, human populations do not fall neatly into categories. Instead, they tend to blend into one another often as a function of geographical proximity. The gradual expansion of humans throughout the Old World resulted in some geographical isolation, but many populations grew, expanded, and migrated to merge with other populations.
As a result, when one colour codes populations according to allele frequencies and then paints them onto a map of the Old World, the result resembles subtle changes in hue as one move from one area to another. It does not resemble an impressionist painting with dabs of quite different colours placed adjacent to one another. The majority of human populations—or “races” if you prefer that term—genetically resemble the people geographically closest to them.
Note how the genetic definition of race mentions nothing about those visual and morphological characteristics that highlight the social definition. Genes for skin colour; hair texture, etc. are only a small part of the tens of thousands of loci in the human genome.
Furthermore, the population geneticist, Mashitoshi Nei suspects that genes for external morphology can give misleading impression of genetic distance because they change at a different evolutionary tempo than the rest of the genome. This is an important point, so let us further explore it.
Consider the following- The proverbial Martian biological anthropologist visits earth and is asked to pick the “odd ape out” from the following collection of great apes— gibbons, orangutans, gorillas, chimps, and humans.
The phenotype of human skin colour follows the same lesson that we learned in discussing sickle-cell anemia. The primary correlate of gene frequency differences for sickle cell anemia is malarial ecology not race. Similarly, the primary correlate of skin pigmentation differences is distance from the equator.
Dark skin is an evolutionary adaptation that has something to do with exposure to the sun and is found among the majority of Old World populations living in equatorial areas. Many people in southern India and Sri Lanka are more darkly pigmented than some African populations, yet they are genetically closer to Scandinavians than they are to sub-Saharan Africans. Similarly, some populations in Papua New Guinea are visually indistinguishable from equatorial Africans, but are genetically closer to current-day Japanese and Chinese than they are to Africans.
In fact, the difference between the genetic and the social definitions of race becomes even more striking when one examines the actual types of data used by population geneticists to measure similarities and differences among populations. However, to avoid the problem that natural selection may have created these differences, scientists prefer to study neutral genes.
Neutral genes are those that have no selective advantage or disadvantage and are most often found among the “junk” part of the human genome. We can corrupt the English language—and logic—by saying that these are the most invisible of the invisible phenotypes.