"Mongoloid," a term from physical anthropology, refers to the skull shape typically found among East Asians and many American Indians. Skull shape figured prominently in racial theories of the nineteenth century, which erroneously linked skull type with behaviors or abilities deemed characteristic of certain races. Modern craniometry, or skull measurement, is almost purely descriptive and has nothing to say about behavior. It depends on examining a large number of detailed anatomical features of the skull and making statistical correlations between them. Though these assessments are not easily translated into simple physical descriptions, contemporary East Asian skulls generally have fine features, broad head shape and flattened faces. Skulls vary from gracile to robust, terms used by physical anthropologists to denote the general thickness of the bone; mongoloid skulls are the most gracile in the human family.
Mongoloid skulls are also associated with a special kind of teeth. Many human groups, such as sub-Saharan Africans and Europeans, retain the generic, undifferentiated human teeth of the ancestral population. But people in southeast Asia, Polynesia, Australia, southern China and ancient Japan have developed a different dental complex known as sundadonty, after Sunda, the former continent that included Malaysia and much of Indonesia. A third category of teeth, itself derived from sundadonty, is sinodonty. Sin odonts include the people of northern China, modern Japan, and the native peoples of
North and South America.144 Mongoloids in general have both of the two derived types of teeth, with southern mongoloids being sundadont and northern mongoloids sinodont.
The puzzle is that mongoloid skull types, although now owned by the largest of all human racial groups, do not show up indisputably in the archaeological record until about 10,000 years ago. There were of course people in China before then, but those inhabitants possessed generic early modern human skulls. The mongoloid skull type is a very recent evolutionary development. No one knows for sure what factors prompted the emergence of the mongoloid peoples from their predecessors, but two explanations have been suggested, both invoking the Last Glacial Maximum.
One is that the mongoloids emerged by genetic drift, the random fluctuation in gene frequencies that occurs between generations. Drift can lead to a single version of a gene becoming universal, or fixed, and all other versions being lost. Fixation of a gene depends on the size of the population, being faster in smaller populations, so anything that breaks a population into small, separately breeding communities will spur genetic drift and evolutionary change. The Last Glacial Maximum, by freezing the landscape in a patchy fashion, could well have fractured the habitat of the people living in the northern latitudes of East Asia into small populations subject to rapid drift. In one of these, presumably the most successful, the particular features of the mongoloid skull would have evolved by chance alone (since drift is a random process) and that group went on to dominate East Asia.
Another proposal is that the mongoloid skull type arose from natural selection. Biologists have long speculated that mongoloid features are an adaptation to cold. An extra layer of fat in the eyelid (the epicanthic fold) gives the eye more insulation. Pale skin lets in more sunlight, which the body requires for synthesis of vitamin D. A stockier body reduces heat loss. It's a plausible guess that genes favoring such features would have grown more frequent during the 5,000 or so years of the Last Glacial Maximum.
Drift and selection can of course act together. "It is possible that with the onset of glacial conditions the widespread population of eastern Asia contracted its range in its northern latitudes, resulting in a number of temporarily isolated groups," writes the physical anthropologist Marta Mirazon Lahr. "Under strong environmental pressure, morphological change could have become rapidly fixed in a population of small size."145 Or, in less technical language, new versions of genes that favored the mongoloid physical appearance could have become universal in one of these groups through the selective pressure of the cold climate. East Asians seem to have evolved light skin independently of the 358
Europeans. They also have a gene that leads to a dry form of earwax and 359
less sweating. When the glaciers retreated 15,000 years ago, the mongoloids would have expanded northward, like their counterparts did in Europe. When the glaciers started to retreat some 15,000 years ago, the mongoloids, still a small population, would have started to expand and recolonize northern territories, just as their counterparts are known to have done in Europe. The first modern humans who migrated out of Africa almost certainly had dark skin, as do their descendants in Australia and the relict populations who still survive at points in between. Given that early modern human skulls are all much the same, it's possible that for many thousands of years all modern humans outside Africa, as well as those inside, had black skin. But at some stage, populations in both the western and eastern halves of Eurasia must have evolved into, or been replaced by, people with lighter skin. When that happened is at present a matter of speculation. But one point at which replacement could have occurred is during the Late Glacial Maximum. The populations living in northern latitudes had perhaps developed lighter skin, either for reasons of vitamin D synthesis or through sexual selection, by 20,000 years ago. When the glaciers returned, the cold-adapted northerners would have moved slowly south, along with the frigid climates to which they, but not their southern neighbors, were adapted. The freezing temperatures could have given them an edge in displacing their darker-skinned cousins in southern latitudes. Later, after the glaciers' retreat, the populations that expanded from their southern refuges, both in Europe and East Asia, would have been the descendants of the light-skinned northerners.
This might explain why the regional variations in skull type that characterize caucasoid peoples (those of western Eurasia: India, Europe and the Near East) and mongoloids (peoples of East Asia) do not become evident until the Holocene, the warm period that succeeded the great Pleistocene ice age 10,000 years ago. "Most early modern skulls do not exhibit unequivocal characteristics of any present-day race," writes the paleoanthropologist Richard Klein, "and it seems increasingly likely that the modern races formed mainly in the Holocene, after 12-10 ky [thousand years] ago. This is perhaps particularly clear for eastern Asia (the present-day hearth of the 'Mongoloids'), but it also applies to
Europe (the homeland of the 'Cauca soids')."146
With the end of the Last Glacial Maximum, the dominance of the hunter-gathering way of life, the only kind of existence humans had ever known, also began at last to wane. It was in the Near East that the first sustained experiments in settled living were about to begin.
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