Recent Science on Race

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DNA picture from Wikipedia

In an earlier post, I described the European practice of exhibiting people of other races in museums and zoos in the 19th century up to the present. In this post I want to discuss how science can help us approach racism.

The science on race has changed since the 19th century. Obviously people thought that race was a heritable trait. But apart from Gregor Mendel, nobody knew much about the material basis of inheritance before 1903. The analysis of DNA sequences offers evidence unavailable then. Today we know that  DNA has sequences of bases (the famous A,T,G, and C). The base sequences called genes specify the structure of enzymes. The enzymes in turn control all the processes in our bodies. Only about 1.5% of the DNA is devoted to coding for enzymes. Because of the vital importance of correct enzyme function, natural selection minimizes changes in the genes that code for enzymes, although changes (called mutations) do occur, often causing diseases such as hemophilia or cystic fibrosis. There are thousands of comparable genetic conditions in humans.

The vast regions of DNA that do not code for enzymes are subject to changes (mutations) without natural selection operating against them. These are single changes in bases, or deletions or additions of short sequences, almost all with no known biological function. This enables us to examine human history at the DNA level. How is this possible? Although the details are complicated, the basic principle is simple: Mutations accumulate freely and at random in the non-coding regions of DNA, and they will be different in different populations that do not intermingle and mate with one another. Therefore one expects that different populations will have different sets of DNA sequences. The longer the populations have been isolated from one another, the greater the differences. It turns out that these differences, while detectable and useful for tracking lineages, are very small in humans.

Many biologists today think that human races have no biological basis. This opinion is based on the marked genetic uniformity of humans all over the world. It is often the case that the DNA molecules of two people in the same population differ more from each other than either of them differs from those of a person from the other side of the world. On this view, the superficial differences between Africans and southeast Asians, for example, are just that – rather trivial matters of appearance that do not by themselves signify profound differences in ability, temperament, or any meaningful quality. However, with the advent of advanced computing techniques it has become possible to analyze very large collections of DNA sequences from different humans to identify clusters of DNA sequence variants that correspond roughly to continents of origin. If you program the computer to assume that there are 7 such clusters, the comparative analysis of the DNA sorts the sequence variants into that many clusters, and they correspond roughly to the continents where the people who provided the DNA samples came from.

225px-Rosenberg2007In the graph at the left the horizontal colored lines represent sets of sequences found in people of various origins, provided the number of sets is set in advance to 7. For the Bantu, and other African tribes, the sequence coded by yellow predominates, with some other sequences present. Among Russians, the set of sequences found in the Bantu are largely absent. The Kalash of Pakistan seem to have roughly equal mixtures of three different clusters. Many populations have contributions from several sets, but most of those in the chart are dominated by a particular set of sequences.

If you tell the computer there are two such clusters, it sorts them into two groups, one anchored by the Americas and the other by Africa. This classification does not correspond to any known races. For analyses  assuming 5 to 7 groups, the result superficially appears to support the concept of race as applied to humans.  However the conclusion rests on the assumed number of groups. If you specify larger numbers of clusters the resolution goes finer than the level of continents. Thus, if the races are real at the DNA level, it seems to require a very elaborate analysis and a pre-conceived number to identify them. Many scientists, including those that conducted the cluster analysis shown on the left, do not accept that DNA clusters correspond to conventional races. On the other hand, there is evidence that similar analysis applied to Africans can reveal genetic clusters that correspond to linquistic ones. At present, DNA cluster analysis is an active field of research and the meaning of the results is open to discussion. It may provide reliable insights into human pre-history.

Other analyses of DNA sequences confirm the conclusion that all humans are very closely related, and are descended from small groups of people who left Africa about 50 to 130 thousand years ago. Some studies, for example, show that for particular DNA regions, there are many different variants in Africa, but that as the distance from Africa increases, some of the variants drop out, to a minimum among the native Americans. This is the pattern expected if a small population left Africa, carrying only a few variants with them, and then this process was repeated sequentially across the globe as humans spread from one place to the next. The Americas were the last place to be occupied. This “Out of Africa” model implies that all humans, except for some Africans, perhaps, are immigrants or descended from immigrants.

Furthermore we know today that people of all races have equivalent abilities. They can all pursue the highest (or lowest) accomplishments, given an appropriate education. Thus, to discriminate against a person on the basis of race has no basis in science and flies in the face of obvious facts about the universality of human nature. The evidence shows that the genetic differences are very small, even for people from different continents. People from all over the world are genetically less diverse than African chimpanzees. That is why the abuse of a group of people, based on where they come from, is at the very least ignorant. The moral case against such abuse has been made by many others. The lesson was a part of our education. This is a sufficient reason why we felt that the exhibit of the preserved body of an African, that we saw in Belgium, was so creepy.

Picture credit: Rosenberg NA, Mahajan S, Ramachandran S, Zhao C, Pritchard JK, Feldman MW (December 2005). “Clines, Clusters, and the Effect of Study Design on the Inference of Human Population Structure”. PLoS Genetics. 1 (6): e70. doi:10.1371/journal.pgen.0010070. PMC 1310579Freely accessible. PMID 16355252.

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