Sewall Wright on race differences, group selection, and cultural selection among humans (1978)

[From Evolution and the Genetics of Populations, Volume 4: Variability Within and Among Natural Populations, pp. 439-457]

Racial Differentiation in Mankind

The existence of conspicuous diversity among human populations in physical appearance has been common knowledge at least since the time of ancient Egypt. The subject is discussed at length in numerous books on physical anthropology and need not be considered here in detail.

There is no question that all mankind constitutes a single species in view of the absence of any physiological bar to hybridization between the most diverse races or of any recognizable loss of vigor in the first or later generations.

There is also no question, however, that populations that have long inhabited widely separated parts of the world should, in general, be considered to be of different subspecies by the usual criterion that most individuals of such populations can be allocated correctly by inspection. It does not require a trained anthropologist to classify an array of Englishmen, West Africans, and Chinese with 100% accuracy by features, skin color, and type of hair in spite of so much variability within each of these groups that every individual can easily be distinguished from every other.

[. . .] It has been indicated earlier that such an evolutionary process as that of man is much more understandable if it occurred by the shifting balance process. Simultaneous sampling drive at thousands of sufficiently neutral loci provides different material in innumerable localities without appreciable cost, material that can give the basis for effective interdeme selection.

Was the population structure of primitive man favorable to this process? There have been a number of studies of the few remaining peoples at the hunting and gathering level of culture that bear on this matter. Birdsell (1972), in an intensive study of Australian aborigines in western Australia, has described their population structure. The primary territorial unit is the band, consisting of a group of related families. Marriage is exogamous but largely restricted to the tribe, a group of bands in which the same dialect is spoken. He estimates the average total number in a tribe to be about 500, with a breeding population of about 185 and an effective number of about 100. This is small enough for the building up of considerable differences among large areas at each nearly neutral polymorphic locus merely by sampling drift. There is thus the basis for operation of the shifting balance process. [. . .]

The actual process of interdeme selection may take different forms. At one extreme, the local appearance of a superior genetic system is followed by expansion of its territory accompanied by complete elimination of its neighbors until it occupies the entire range of the species. At the other extreme there is merely excess diffusion from the superior center. Neighboring populations are graded up until they reach the point (the crossing of a saddle in the surface of selective values) at which mass selection carries them autonomously to the new selective peak, or perhaps beyond, if they contribute something that improves on the latter. The locations of the population with the highest selective peak may shift from place to place in the course of time, as a group of neighboring populations step each other up to heights well above the general level.

Bigelow (1969) has emphasized the importance of tribal warfare in the operation of this process. A tribe that is generally successful because of superior intelligence, capacity for cooperation, and high frequency of the heroic virtues as well as physical prowess, tends to increase its territory and also to grade up what is left of the defeated group by hybridization. The process is illustrated by the incessant tribal warfare of the tribes of American Indians observed by the European settlers in America, in which some tribes such as the Iroquois expanded at the expense of their neighbors.

The heroic virtues, including willingness to sacrifice one's own life for the good of the tribe, are traits that can hardly be developed (insofar as they have a genetic basis) by purely individual selection. They may to some extent arise as a by-product of familial selection in which close relatives with heredities strongly correlated with that of an individual who gives his own life to save them. As noted earlier, the effectiveness of familial selection in general is testified to by the improvement of milk production in cattle and of egg production fowls, mainly by selection of males on the basis of the performance of close female relatives. The importance of this sort of intergroup selection in evolution has been emphasized as noted in chapter 7 by Hamilton. The increase in frequency of traits deleterious on the average to their possessors but beneficial to the deme may also, however, be increased by interdeme selection (referred to as intergroup selection in early articles) if the benefit to the deme sufficiently outweighs the damage to the individual. A more rigorous demonstration of this mode of evolution of "altruistic" characters as been given by Eshel (1972).

Not all interdeme selection in man has consisted of intertribal warfare. According to Birdsell, about 15% of marriage among Australian aborigines were intertribal; not enough as shown by the wide variability of gene frequencies to homogenize the whole population but enough to permit effective interdeme selection if exchange was asymmetrical, predominantly from the more to the less successful. That differences were not swamped was presumably due to the exchange being largely between neighboring tribes which differed little, as indicated by the semiclinal nature of the pattern of gene frequencies. The average effective immigration from the population as a whole, the m of formulas, was thus very much less than 0.15. [. . .]

Evolution Since the Origin of Agriculture [. . .]

We can form a better idea of the course of event than in any earlier period but the interpretation is confused by the exponential progress of a second evolutionary process, barely existent at all in any other animal, and little if any more rapid in the earlier history man than his biological evolution.

This is the evolution of culture with its line of transmission largely from speaker to listener, supplemented in the last three thousand years by transmission from writer to reader. It began to become of major importance with the origin of language, but during the hunting and gathering phase of human life the slow advance of culture is indicated by that in the fashioning of stone tools and weapons. It was probably accompanied by relatively rapid diffusion of knowledge of such advances as were made. The success of tribes thus probably depended to a greater extent on capabilities, determined by their genes, than on the possession of techniques not known to their neighbors.

The mode of evolution of culture is analogous to that of the genetic system. Invention is the analog of mutation. Diffusion of culture is the analog of gene flow. Cultural variation is continually subject to selection on the basis of utility. There is random cultural drift, exemplified by the breaking up of languages into dialects. Finally, the most favorable conditions for cultural advance is local isolation, providing the basis for simultaneous trial and error among many variants and the diffusion of the more successful ones in analogy with the shifting balance process in biological evolution. We think here of the multiple competing cultures in ancient Southwest Asia, the evolution of culture among the city states of ancient Greece, and in much divided Europe from the Dark Ages to modern times. The great empires of the ancient Southwest Asia of Alexander and of Rome constituted an overbalancing final phase in the process, giving widespread diffusion but less progress by trial and error.

There has undoubtedly always been a considerable but incomplete correlation between the two kinds of evolution. The state of the culture has been to a considerable extent an index of the rank of populations genetically in the distinctive human line of evolutionary advance, and reciprocally the demands of culture have been the primary selective agent in this advance in its later stages. Aspects of culture are continually being borrowed, but whether such borrowings are effectively integrated into the existent culture to form new peaks (as most conspicuously in the recent period in Japan), or are adopted only superficially and to the detriment of the previous culture, is also an index of genetic capability.

The treatment of either the genetic capabilities or the cultures of peoples as if they could be ranked on single scales is, of course, a gross simplification. If the multiple genetic aspects of mental ability could be measured more independently of culture than is the case, it would no doubt be found that each local race has its own unique combination of favorable qualities. At present only IQ seems to have a repeatability that permits evaluation of the contributions of genetic and nongenetic variabilities to its variability, discussed in the previous chapter, and this only within a particular culture.

On the other hand there have probably always been wide differences among the peoples of the world in average intellectual ability and cultural level from the standpoint of progress toward the situation in civilized man. This was presumably related to the environmental conditions. Men could not endure the northern winters without fire, the use of which is documented by hearths found in France dating back over half a million years and somewhat later in Hungary and in China but only about one-tenth as far back in Africa (Campbell 1974).

The capacity to anticipate and plan for the future is a mental attribute which would be favored under northern conditions and selected for insofar as it has a genetic basis. This would presumably have come to be more advanced in the temperate zone than in the tropics. [. . .]

Linguistic evidence indicates the establishment of an important center of diffusion in east-central Europe some 5,000 years ago from which wave after wave peoples moved in all directions. The Hittites carried an Indo-European language of the western (centum) type into Asia Minor and established an empire some 4,000 years ago. A thousand years later the Iranians, who had moved east into what is now southern Russia and Turkestan, brought an Indo-European language of the eastern (satem) type into the original cultural center and later established the Persian Empire. They also carried another Aryan dialect to India. Other tribes moving south from the east-central European center reached Greece in several waves which, after mixing with the indigenous people, produced classical Greek civilization.

Other waves moved to the southwest into Italy, giving rise to Latin and other Italic languages; to the west, giving rise to Celtic languages in what is now southern Germany, France, and the British Isles; and to the northwest into what is not northern Germany and Scandinavia, to give rise, in much altered form, to the Germanic languages. Subsequent migrations greatly expanded the areas occupied by derivatives of Latin and Germanic branches at the expense in Europe of the Celtic. All the tribal migrations were undoubtedly accompanied by much intermixture with indigenous peoples, but the diffusion of language also undoubtedly implies considerable gene flow.

[. . .] The history of Europe, especially western Europe, was thus prevailingly one of inflow of genes up to the relatively recent period in which it itself became a center of massive outflow.

Related posts:

• Sewall Wright on Coefficients of Inbreeding and Relationship (1922)
• Hamilton on inclusive fitness and social behavior in humans
• More from Hamilton on kin recognition and intergroup hostility
• R. A. Fisher on group selection in humans
• James Neel and early human population structure
• Massive migration from the steppe is a source for Indo-European languages in Europe
• More ancient DNA evidence of Indo-European mass migrations
• C. S. Coon on the endocrine system and racial differences in temperament