30. Old World Faces in New World Places
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30 Old World Faces in New World Places A man finds room in the few square inches of his face for the traits of all his ancestors. —Ralph Waldo Emerson, 1860 Genes carry the chemical codes that control an organism’s basic nature, development , and functioning. Human beings, as bio­ logi­ cal entities, carry their genes with them as they migrate, and they introduce those genes when they mate with humans of the groups they encounter (studies of genetics have shown that males have done much more migrating than have females). Therefore, human bio­ logi­ cal comparisons among populations are particularly germane to considerations of transoceanic movements. Deoxyribonucleic acid (DNA) is genetic material in the cells of all forms of nonmicrobial life, in­ clud­ ing humans, and has spawned the vigorous and growing field of DNA research. Since about 1985, DNA has increasingly been used to trace his­ tori­ cal relationships among human populations. Although such inquiry is still in its early stages, it is evolving rapidly, and whole-­ genome studies are revealing a great deal beyond the results of the initially emphasized mitochondrial and Y chromosome DNA studies (see chapter 31). When assessing the matter of human differences, it is important to keep in mind a key finding of molecular genetics. What may strike the eye as major physical differences among vari­ ous groups of human beings is put into perspective by the overwhelming percentage of their genetic material that is shared by all of them (99.9 percent). The Australian anthropologist Matthew Spriggs has summarized the situation: When objective criteria for assessing bio­ logi­ cal differences became available with the discovery of DNA, the vast majority of genetic variation was found to occur between individuals within local populations (some 85.4 per cent). Only small amounts (8.3 per cent) occur between related local populations such as nations or tribes . . . and even less between conventionally defined “racial” groups such as Asians and Af­ ri­ cans. Con- 330 / Chapter 30 spicuous variants such as skin colour may be controlled by as few as four genetic loci. These minor differences are useful, however, in disentangling the effects of population movements . . . as possible agents of cultural change from those generated from forces internal to the region, be they social or environmental. Cultures are carried about by populations. If these popu­ lations are sufficiently different from each other as defined by rare marker genes or subtle difference in head shape then the effects of migration as opposed to [expansion] diffusion or independent invention in culture change can be assessed.1 Understanding genetically controlled variable aspects of human biology can be highly helpful, then, in gaining insights regarding possible past human movements . This chapter looks at visible, measurable phenotypic (manifest) physical human characteristics. In the following chapter, what the genes themselves tell us is examined. Body of Evidence: Traditional Physical-­ Anthropological Criteria In contemporary times, “race” among humans has been defined by constellations of physical characteristics: skin color, head form, nose form, lip form, hair form and color, and so forth. Sometimes, one or more such trait(s) is (are) especially diagnostic of one of the “races.” An example is the inner epicanthic eyefold , which is a hallmark of East and North­ east Asians and which lends their eyes that “Oriental” look. Although the epicanthic fold is far from universal among Ameri­ can Indians, it occurs among Itzá Mayan women, and outsiders have sometimes, at least briefly, mistaken them for Chinese. Does this suggest a past East Asian demographic input to the Yucatán? Perhaps, but while phenotypic physical characteristics reflect genetic makeup, they do so in interaction with environmental factors, and their usefulness for showing his­ tori­ cal contacts between separated populations is in many ways problematic. As the paleontologist Stephen Jay Gould put it, “Homology can of­ ten be recovered from morphology, but the forms of organisms of­ ten include an inextricable mixture of similarities retained by history (homology) and independently evolved in the light of common function (analogy). Morphology is not the best source of data for unraveling history.”2 For example, one’s stature is responsive not only to one’s genes but also reflects one’s nutrition during development; head form, although basically genetically controlled, is nevertheless also susceptible to alteration via intentional or incidental cradleboard or other cranial deformation; jawbone development might reflect, in part, what one chewed upon while growing up; skin color might evolve divergently fairly rapidly under different conditions of exposure to solar radiation...