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Biological races in humans - PubMed

Biological races in humans

Alan R Templeton. Stud Hist Philos Biol Biomed Sci. 2013 Sep.

Abstract

Races may exist in humans in a cultural sense, but biological concepts of race are needed to access their reality in a non-species-specific manner and to see if cultural categories correspond to biological categories within humans. Modern biological concepts of race can be implemented objectively with molecular genetic data through hypothesis-testing. Genetic data sets are used to see if biological races exist in humans and in our closest evolutionary relative, the chimpanzee. Using the two most commonly used biological concepts of race, chimpanzees are indeed subdivided into races but humans are not. Adaptive traits, such as skin color, have frequently been used to define races in humans, but such adaptive traits reflect the underlying environmental factor to which they are adaptive and not overall genetic differentiation, and different adaptive traits define discordant groups. There are no objective criteria for choosing one adaptive trait over another to define race. As a consequence, adaptive traits do not define races in humans. Much of the recent scientific literature on human evolution portrays human populations as separate branches on an evolutionary tree. A tree-like structure among humans has been falsified whenever tested, so this practice is scientifically indefensible. It is also socially irresponsible as these pictorial representations of human evolution have more impact on the general public than nuanced phrases in the text of a scientific paper. Humans have much genetic diversity, but the vast majority of this diversity reflects individual uniqueness and not race.

Keywords: Admixture; Evolutionary lineage; Gene flow; Genetic differentiation; Human evolution; Race.

Copyright © 2013 Elsevier Ltd. All rights reserved.

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Figures

Figure 1
Figure 1

Distinguishing between population trees arising from splits and isolation versus recurrent gene flow with isolation by distance. In all cases, the symbol “ fst(X–Y)” indicates the genetic distance between populations X and Y. Part A graphs the expected relationship between a genetic distance from a reference population (population “A”) to other populations (“B” and “C”) as a function of their geographical distance. Part B indicates the genetic distance between two populations as the sum of the branch lengths that interconnect them in an evolutionary tree. Parts C and D show how finer geographical sampling affects these relationships.

Figure 2
Figure 2

Isolation-by-distance in human populations. The x-axis is the geographical distance between two populations, as measured through waypoints that minimize travel over oceans. The y-axis is the pairwise fst between two populations. Modified from Ramachandran et al. (2005). Copyright (2005) National Academy of Sciences, U.S.A.

Figure 3
Figure 3

Significant inferences about human evolution from multi-locus, nested-clade phylogeographic analysis. Geographical location is indicated on the x-axis, and time on the y-axis, with the bottom of the figure corresponding to two million years ago. Vertical lines indicate genetic descent over time, and diagonal lines indicate gene flow across space and time. Thick arrows indicate statistically significant population range expansions, with the base of the arrow indicating the geographical origin of the expanding population. Lines of descent are not broken because the population range expansion events were accompanied by statistically significant admixture when they involved expansion into previously inhabited areas. Modified from Templeton (2005).

Figure 4
Figure 4

A population tree of humans with arrows indicating admixture from archaic human populations in the past. Modified from Reich et al. (2010).

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