In my last post, I argued that hunter-gatherers became less polygynous with increasing distance from the equator. Second wives became costlier because longer winters restricted food gathering and increased female dependence on male provisioning (Frost, 2006; Kelly, 1995, pp. 262-270; Hoffecker, 2002, p. 8; Martin, 1974, pp. 16-18).
How did this situation change with the advent of agriculture? In the tropics, year-round agriculture made women self-reliant in feeding themselves and their children. It thus became less costly for men to take second wives. In fact, the cost of polygyny became negative—a man stood to gain from getting as many wives as possible.
In non-tropical environments, however, women were self-reliant at best only in summer and autumn. By early spring, the larders were bare in most farming societies, as in Europe five hundred years ago:
Rates of conception fell off dramatically in late winter and early spring, when stocks of food ran low, rising sharply in early summer when food again became abundant. This was a society in which there was but a thin margin of safety most of the time. (Danborn, 2006, p. 10).
The food scarcity could be lessened in two ways: 1) by increasing food production during the growing season and storing the produce for off-season consumption; and 2) by domesticating animals as a year-round food source. Both strategies, however, tended to increase male participation in agriculture and thus decrease female self-reliance.
With respect to the first strategy, Burton and White (1984) note:
With many dry months and a shorter growing season there is more time pressure in planting and harvesting crops, and this increased time pressure may account, in part, for increased male participation in cereal crop agriculture. Maclachlan (1983) provides ethnographic data on a South Indian intensive farming system which support the seasonality hypothesis. He argues that a narrow “seasonal window” puts a premium on the labor of young men; the time pressure of soil preparation is so great that physically demanding tasks must be done very rapidly, and under these circumstance, the physical strength advantage of young men over all other members of the population makes them the best candidates for farm labor.
The second strategy also tended to decrease female self-reliance. Animal husbandry, as its very name suggests, was a male preserve, in part because of the strength needed to handle animals and in part because of a deep-seated belief, going back to hunter-gatherer times, that only men should kill animals (Cauvin, 2000, p. 133).
Only one animal—the guinea fowl—has ever been domesticated in sub-Saharan Africa, despite an abundance of large birds and mammals that would have made interesting candidates for domestication (Murdock, 1959, p. 70). It is also in this same region that women have been the most self-reliant in feeding themselves and their children and where polygyny has been the most common.
References
Burton, M.L. and D.R. White. (1984). Sexual division of labor in agriculture. American Anthropologist, 86, 568-583.
Cauvin, J. (2000). The Birth of the Gods and the Origins of Nature. Cambridge University Press: Cambridge.
Danborn, D.B. (2006). Born in the Country. A History of Rural America. 2nd edition, JHU Press.
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103
Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.
Kelly, R.L. (1995). The Foraging Spectrum. Diversity in Hunter-Gatherer Lifeways. Washington: Smithsonian Institution Press.
Maclachlan, M.D. (1983). Why They Did Not Starve: Biocultural Adaptation in a South Indian Village. Philadelphia: Institute for the Study of Human Issues Press.
Martin, M.K. (1974). The Foraging Adaptation — Uniformity or Diversity? Addison‑Wesley Module in Anthropology 56.
Murdock, G.P. (1959). Africa. Its Peoples and Their Culture History. New York: McGraw-Hill.
Sunday, February 24, 2008
Monday, February 18, 2008
Polygyny and human evolution
Many evolutionary biologists believe that men used to be largely polygamous. Ernst Mayr (1970, p. 386) writes:
Among Alaskan Eskimos, among New Guinea mountain Papuans, and among relatively untouched South American Indians, polygamy is widespread, and it is the individual with leadership qualities who has the greatest chance to have several wives.
He then goes on to quote J.V. Neel’s statement that “it may be that the single most dysgenic event in the history of mankind was departure from a pattern of polygamy based on leadership, ability, and initiative.” Mayr concludes that polygyny (i.e., male polygamy) drove the increase in human brain size and that a shift to monogamy explains why this increase came to a halt some 100 thousand to 200 thousand years ago.
This viewpoint has several weaknesses. First, if modern humans began spreading out of Africa only 50,000 or so years ago, one can hardly point to Eskimos, New Guineans, and South American Indians as examples of human behavior before 100,000-200,000 BP.
Second, polygyny does intensify selection of men, but it also relaxes selection of women. Indeed, it greatly increases the reproductive opportunities of low-status women who, otherwise, might not reproduce. Polygynous men usually recruit their additional wives from the lower ranks of society; this is, after all, where they can elbow out low-status rivals. In fact, out of all mating systems, monogamy is arguably the one most conducive to natural selection, since it curbs ‘marrying up’ and condemns most low-status individuals to eventual genetic death (their places being taken by downwardly mobile descendants of higher-status individuals). This is the argument that Gregory Clark has recently made in A Farewell to Alms.
Third, before 10,000 years ago all humans lived by hunting and gathering and among present-day hunter-gatherers the polygyny rate is low: 9.5% of all sexual unions among the Inuit in general (Kjellstrom, 1973, pp. 114-115); 6% among !Kung Bushmen (Howell, 1979, p. 235); 5% among Eastern (Ituri) Pygmies (Turnbull, 1986, p. 111); 16.6% among Western Pygmies (Cavalli-Sforzi, 1986, p. 37); and 15% among central Australian Aborigines (Birdsell, 1993). Only with the advent of agriculture, especially tropical agriculture, do these rates enter the 20%-50% range, notably in sub-Saharan Africa and Papua-New-Guinea. Year-round farming enables women to become self-reliant in feeding themselves and their children, thus making it less costly for men to take second wives.
Some have argued that present-day hunter-gatherers now live in resource-poor environments and are thus unrepresentative of ancestral hunter-gatherers. Among other things, this means that some ancestral environments may have favored high food self-sufficiency among women and correspondingly high polygyny rates among men. If true, this argument simply drives home the point that modern humans did not live in a uniform environment of evolutionary adaptedness. Some parts of the world had more polygyny than did others.
Among hunter-gatherers, generally speaking, polygyny was costlier for men with increasing distance from the equator. Longer winters restricted food gathering and made women depend more on their mates for provisioning (Frost, 2006; Kelly, 1995, pp. 262-270; Hoffecker, 2002, p. 8; Martin, 1974, pp. 16-18). In the Arctic, where women had almost no opportunities for gathering, only the ablest hunter could provide for a second wife (Kjellström, 1973, p. 118).
References
Birdsell, J.B. (1993). Microevolutionary patterns in Aboriginal Australia: A gradient analysis of clines. New York: Oxford University Press.
Cavalli-Sforza, L.L. (1986). Demographic data. In (L.L. Cavalli-Sforza ed.). African Pygmies, pp. 23-44. Academic Press.
Clark, G. (2007). A Farewell to Alms: A Brief Economic History of the World. Princeton (NJ): Princeton University Press.
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103
Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.
Howell, N. (1979). Demography of the Dobe !Kung. New York: Academic Press.
Kelly, R.L. (1995). The Foraging Spectrum. Diversity in Hunter-Gatherer Lifeways. Washington: Smithsonian Institution Press.
Kjellström, R. (1973). Eskimo Marriage. An Account of Traditional Eskimo Courtship and Marriage. Lund: Nordiska Museets Handlingar 80.
Martin, M.K. (1974). The Foraging Adaptation — Uniformity or Diversity? Addison‑Wesley Module in Anthropology 56.
Mayr, E. (1970). Populations, Species, and Evolution. Cambridge (Mass.): Harvard Press.
Turnbull, C.M. (1986). Survival factors among Mbuti and other hunters of the equatorial African rain forest. In (L.L. Cavalli-Sforza ed.). African Pygmies, pp. 103-123. Academic Press.
Among Alaskan Eskimos, among New Guinea mountain Papuans, and among relatively untouched South American Indians, polygamy is widespread, and it is the individual with leadership qualities who has the greatest chance to have several wives.
He then goes on to quote J.V. Neel’s statement that “it may be that the single most dysgenic event in the history of mankind was departure from a pattern of polygamy based on leadership, ability, and initiative.” Mayr concludes that polygyny (i.e., male polygamy) drove the increase in human brain size and that a shift to monogamy explains why this increase came to a halt some 100 thousand to 200 thousand years ago.
This viewpoint has several weaknesses. First, if modern humans began spreading out of Africa only 50,000 or so years ago, one can hardly point to Eskimos, New Guineans, and South American Indians as examples of human behavior before 100,000-200,000 BP.
Second, polygyny does intensify selection of men, but it also relaxes selection of women. Indeed, it greatly increases the reproductive opportunities of low-status women who, otherwise, might not reproduce. Polygynous men usually recruit their additional wives from the lower ranks of society; this is, after all, where they can elbow out low-status rivals. In fact, out of all mating systems, monogamy is arguably the one most conducive to natural selection, since it curbs ‘marrying up’ and condemns most low-status individuals to eventual genetic death (their places being taken by downwardly mobile descendants of higher-status individuals). This is the argument that Gregory Clark has recently made in A Farewell to Alms.
Third, before 10,000 years ago all humans lived by hunting and gathering and among present-day hunter-gatherers the polygyny rate is low: 9.5% of all sexual unions among the Inuit in general (Kjellstrom, 1973, pp. 114-115); 6% among !Kung Bushmen (Howell, 1979, p. 235); 5% among Eastern (Ituri) Pygmies (Turnbull, 1986, p. 111); 16.6% among Western Pygmies (Cavalli-Sforzi, 1986, p. 37); and 15% among central Australian Aborigines (Birdsell, 1993). Only with the advent of agriculture, especially tropical agriculture, do these rates enter the 20%-50% range, notably in sub-Saharan Africa and Papua-New-Guinea. Year-round farming enables women to become self-reliant in feeding themselves and their children, thus making it less costly for men to take second wives.
Some have argued that present-day hunter-gatherers now live in resource-poor environments and are thus unrepresentative of ancestral hunter-gatherers. Among other things, this means that some ancestral environments may have favored high food self-sufficiency among women and correspondingly high polygyny rates among men. If true, this argument simply drives home the point that modern humans did not live in a uniform environment of evolutionary adaptedness. Some parts of the world had more polygyny than did others.
Among hunter-gatherers, generally speaking, polygyny was costlier for men with increasing distance from the equator. Longer winters restricted food gathering and made women depend more on their mates for provisioning (Frost, 2006; Kelly, 1995, pp. 262-270; Hoffecker, 2002, p. 8; Martin, 1974, pp. 16-18). In the Arctic, where women had almost no opportunities for gathering, only the ablest hunter could provide for a second wife (Kjellström, 1973, p. 118).
References
Birdsell, J.B. (1993). Microevolutionary patterns in Aboriginal Australia: A gradient analysis of clines. New York: Oxford University Press.
Cavalli-Sforza, L.L. (1986). Demographic data. In (L.L. Cavalli-Sforza ed.). African Pygmies, pp. 23-44. Academic Press.
Clark, G. (2007). A Farewell to Alms: A Brief Economic History of the World. Princeton (NJ): Princeton University Press.
Frost, P. (2006). European hair and eye color - A case of frequency-dependent sexual selection? Evolution and Human Behavior, 27, 85-103
Hoffecker, J.F. (2002). Desolate Landscapes. Ice-Age Settlement in Eastern Europe. New Brunswick: Rutgers University Press.
Howell, N. (1979). Demography of the Dobe !Kung. New York: Academic Press.
Kelly, R.L. (1995). The Foraging Spectrum. Diversity in Hunter-Gatherer Lifeways. Washington: Smithsonian Institution Press.
Kjellström, R. (1973). Eskimo Marriage. An Account of Traditional Eskimo Courtship and Marriage. Lund: Nordiska Museets Handlingar 80.
Martin, M.K. (1974). The Foraging Adaptation — Uniformity or Diversity? Addison‑Wesley Module in Anthropology 56.
Mayr, E. (1970). Populations, Species, and Evolution. Cambridge (Mass.): Harvard Press.
Turnbull, C.M. (1986). Survival factors among Mbuti and other hunters of the equatorial African rain forest. In (L.L. Cavalli-Sforza ed.). African Pygmies, pp. 103-123. Academic Press.
Sunday, February 10, 2008
Origins of black Africans
It is often assumed that black Africans, out of all human populations, most closely resemble our common ancestral state. After all, is not Africa the cradle of humanity? And did not modern humans spread ‘out of Africa’ some 50,000 or so years ago?
Indeed, we are all offspring of Africa. What is less true is the assumption that evolution stood still there while continuing elsewhere. Yes, some African groups do approximate ancestral Homo sapiens in their mode of subsistence, family structure, and physical appearance. These are the Khoisan and pygmy peoples. They still live by hunting and gathering, are overwhelmingly monogamous, and have light-brown skin and gracile, almost childlike bodies.
But they now inhabit only a few marginal environments, essentially the Kalahari and patches of rain forest. As elsewhere, time has moved on. There have arisen new populations who differ as much from ancestral Homo sapiens as do Europeans and Asians. These are the ‘true’ black Africans.
On the basis of genetic and archaeological data, black Africans seem to have radiated from a relatively small West African and possibly pygmy population within the last 20,000 years (Coon, 1962, pp. 651-656; Spurdle et al., 1994; Watson et al., 1996). The time and place of origin can be further narrowed down with linguistic data. Speakers of proto-Niger-Congo broke up c. 10,000 BP and the oldest derived group appear to be proto-Mande speakers, whose descendants inhabit the Niger's headwaters near the Mali-Guinea border (Blench, 1984, pp. 128-129; Ehret, 1984; Murdock, 1959, pp. 44, 64-68).
Murdock (1959, pp. 44, 64-68) associates black Africans with the spread of agriculture in sub-Saharan Africa. He too locates their place of origin on the Niger’s headwaters because this region is the cradle of the Sudanic food complex—a wide range of native crops now found throughout the continent (sorghum, pearl millet, cow pea, etc.). Other authors, like Shaw (1980), postulate an earlier, proto-agricultural phase that initially covered much of West Africa. This transitional period may have begun among Sangoan hunter-gatherers, who probably resembled present-day pygmies in appearance and lifestyle. These people gradually moved toward agriculture by first protecting fields of wild grains and making clearings for wild yams and oil palms (Davies, 1968; Shaw 1980, pp. 111-114). They began using hoes c. 12,000 BP and tending pili nut trees c. 8,000-9,000 BP (Posnansky, 1984, p. 149; Stahl, 1995, p. 262). Some form of agriculture is furthermore indicated by certain reconstructed words of proto-Niger-Congo, probably spoken before 10,000 BP (Ehret, 1984).
At a certain point in time, some of these proto-agriculturalists—apparently the ones inhabiting the Niger’s headwaters—surpassed the others in the transition to agriculture. They formed a nucleus of farming populations that would ultimately spread throughout sub-Saharan Africa. Meanwhile, this transition had already triggered a cascade of changes that would have profound behavioral and morphological consequences.
Increase in polygyny
Agriculture, especially year-round agriculture, enables women to become more self-reliant in feeding themselves and their children, thus making it less costly for men to take second wives (van den Berghe, 1979, p. 65). As a result, the polygyny rate is 20-50% of all marriages in sub-Saharan agricultural societies (Bourguignon and Greenbaum, 1973, p. 51; Goody, 1973; Pebley and Mbugua, 1989; Welch and Glick, 1981; White, 1988).
These societies seem to have long been highly polygynous. The ratio of Y chromosome to X chromosome variability is much lower than in other populations, apparently because proportionately fewer men have contributed to the gene pool (Excoffier et al., 1996; Scozzari et al., 1997; Spurdle et al., 1994; Torroni et al., 1990). Generalized polygyny is also attested by reconstruction of proto-Bantu, which was spoken approximately 3,000 years ago and has a specific term for "taking a second wife" (Polome, 1977).
Intensified sexual selection of men
If some men have more wives, others will have to do without. In general, men will have to compete more keenly with each other for access to women. When such rivalry intensifies in non-human species, the result is an intensification of sexual selection for larger, stronger, and more muscular males. This may explain why the highly polygynous, agricultural peoples of sub-Saharan Africa are so physically robust. They and their African American descendants outclass European-descended subjects for weight, chest size, arm girth, leg girth, muscle fiber properties, and bone density (Ama et al., 1986; Ettinger et al., 1997; Himes, 1988; Hui et al., 2003; Pollitzer and Anderson, 1989; Todd and Lindala, 1928; Wolff and Steggerda, 1943; Wagner and Heyward, 2000; Wright et al., 1995).
This masculinization of body build may be hormonally mediated. When Winkler and Christiansen (1993) studied two Namibian peoples, the weakly polygynous hunter-gatherer !Kung and the highly polygynous agricultural Kavango, the latter were found to have markedly higher levels of both total testosterone and DHT. The authors suggest that lower levels of these hormones may account for the !Kung’s neotenous appearance, i.e., sparse body hair, small stature, pedomorphic morphology, and light yellowish skin.
High testosterone/DHT levels are widely attested among sub-Saharan agriculturalists and their New World descendents. Young black men have more circulating testosterone than do young white men whereas young East Asian men, though intermediate in testosterone levels, have less 5α-reductase—an enzyme that converts testosterone into the physiologically more active DHT (Pettaway, 1999; Ross et al., 1992). These three geographic groupings also exhibit analogous differences in androgen receptor receptivity (Kittles et al., 2001). Broadly speaking, lifetime exposure to testosterone/DHT correlates with the incidence of prostate cancer and the highest incidences in the world are among African American men (Brawley and Kramer, 1996). Other populations of black African descent (i.e., West Indians and sub-Saharan Africans) exhibit lower incidences, but these have been shown to reflect underreporting and are probably just as high (Glover et al., 1998; Ogunbiyi and Shittu, 1999; Osegbe, 1997).
Relaxed sexual selection of women
If male-male rivalry intensifies sexual selection of men, it also tends to relax sexual selection of women. Because fewer women remain unmated, men are less able to translate their aesthetic criteria into actual mate choice. Such relaxed selection is suggested by visible female-specific characteristics. African Americans girls have narrower hips, broader waists, and thinner deposition of subcutaneous fat than do Euro-American girls (Hrdlička, 1898; Meredith and Spurgeon, 1980; Nelson and Nelson, 1986). Even before birth, Euro-American fetuses show significantly more sexual dimorphism than do African American fetuses (Choi and Trotter, 1970).
Relaxed sexual selection of women may also explain why, among sub-Saharan Africans, skin color is visibly darker in high-polygyny agriculturalists than in low-polygyny hunter-gatherers (i.e., Khoisans, pygmies) even though both are equally indigenous (Bourguignon and Greenbaum, 1973, pp. 171-175; Cavalli-Sforza, 1986a; Cavalli-Sforza, 1986b; Manning et al., 2004; Weiner et al, 1964). Skin color does, in fact, influence mate choice in all human societies; generally speaking, men prefer women who are lighter-skinned than the population mean (van den Berghe and Frost, 1986). In sub-Saharan societies, the preference is for so-called 'red' or 'yellow' women (see earlier post). Wherever African men were less able to act on this preference, there would have been less selection for lighter-skinned women and thus less counterbalancing of selection for darker skin to protect against sunburn and skin cancer (Aoki, 2002; Frost, 2007; Frost, 1994).
This preference may also have been crowded out by other mate-choice criteria. Vilakazi (1962, pp. 59-60) states: "The traditional Zulu does not make physical beauty a first priority or even an important qualification in a wife; and the skin colour of the woman is of little importance." In a rating study, Dixson et al. (2006) examined mate-choice criteria among subsistence farmers in Bakossiland, Cameroon, including preferred skin color of a potential female partner. No consistent preference emerged. This ambivalence was noted by Ardener (1954, p. 72) among the Ibo of Nigeria:
In Kenya, McVicar (1969, p. 242) notes similar views on the merits of ‘black’ versus ‘brown’ wives: "Among these tribes black girls are usually regarded as hard workers, possibly because many consider themselves fortunate enough to be married." In traditional African societies, women had to produce enough food for the entire family, typically through hoe farming in the sun. There was thus a premium on darker women. Lighter women may have been preferred aesthetically, but this preference remained unexpressed.
Timeline of expansion out of West Africa
All of these physical and hormonal characteristics seem to have arisen within a narrow timeframe. In sub-Saharan Africa, the beginnings of proto-agriculture cannot be pushed back much further than 12,000 BP. A tall, clearly black African skeleton has been dated to 6,500 BP (Camp, 1974, p. 241; Coon, 1962, pp. 649-650). This leaves a window of barely six thousand years for the changes that differentiate black Africans from their hunter-gatherer ancestors, i.e., a shift from a gracile, almost childlike body to a much more robust one, with attendant increases in stature, weight, and muscle mass.
By 6,000 to 7,000 years ago, the transition to agriculture had been completed in West Africa and these early agriculturalists were able to support much higher population densities than they had as hunter-gatherers. Inevitably, this nucleus of farming populations began to spread outward at the expense of more sparsely distributed Khoisan and pygmy peoples. By about 4,000 BP, the expansion had reached as far east as the middle Nile, when black Africans first appear in paintings from Pharaonic Egypt and in skeletal remains from Nubia (Junker, 1921). About 3,000 BP, another wave of advance began along the Nigerian-Cameroon border and spread rapidly throughout central, eastern, and southern Africa (Cavalli-Sforza, 1986c, pp. 361-362; Diamond, 1997; Oliver, 1966). By 300 AD, pioneering groups had advanced as far south as KwaZulu-Natal (see Bantu Expansion – Wikipedia).
Thus, black Africans were still absent from most of sub-Saharan Africa even within historic times. When the Egyptians began to build their pyramids, the peoples living to the south were scarcely darker in color. They were simply seen as uncivilized Egyptians. Thus, the civilized world initially encountered a much narrower range of human phenotypes than it would later on. This context shaped the intellectual worldview in its early stages, including theorizing on universal brotherhood. To a degree not easy to assess, we are heirs to notions of human sameness that were first conceived ‘before Africa became black’.
References
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Ardener, E.W. (1954). Some Ibo attitudes to skin pigmentation, Man, 54, 71-73.
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Brawley, O.W. and Kramer B.S. (1996). Epidemiology of prostate cancer. In Volgelsang, N.J., Scardino, P.T., Shipley, W.U., and Coffey, D.S. (eds). Comprehensive textbook of genitourinary oncology. Baltimore: Williams and Wilkins.
Camps, G. (1974). Les civilisations préhistoriques de l'Afrique du Nord et du Sahara. Paris: Doin.
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Pettaway, C.A. (1999). Racial differences in the androgen/androgen receptor pathway in prostate cancer. Journal of the National Medical Association, 91, 653-660
Pollitzer, W. S. and Anderson, J. JB. (1989). Ethnic and genetic differences in bone mass: a review with a hereditary vs environmental perspective. American Journal of Clinical Nutrition, 50, 1244-1259.
Polome, E.C. (1977). The reconstruction of Proto-Bantu culture from the lexicon. In L. Bouquiaux (Ed.) L'Expansion bantoue, 2, 779-791. Centre national de la recherche scientifique.
Posnansky, M. (1984). Early agricultural societies in Ghana. In J.D. Clark & S.A. Brandt (Eds.) From Hunters to Farmers: The Causes and Consequences of Food Production in Africa (pp. 147-151). Berkeley: University of California Press.
Ross, R.K., Bernstein, L., Lobo, R.A., Shimizu, H., Stanczyk, F.Z., Pike, M.C., and Henderson, B.E. (1992). 5-apha-reductase activity and risk of prostate cancer among Japanese and US white and black males. Lancet, 339, 887-889.
Scozzari, R., Cruciani, F., Malaspina, P., Santolamazza, P., Ciminelli, B.M., Torroni, A., Modiano, D., Wallace, D.C., Kidd, K.K. et al. (1997). Differential structuring of human populations for homologous X and Y microsatellite loci. American Journal of Human Genetics, 61, 719-733.
Shaw, T. (1980). Hunters, gatherers and first farmers in West Africa. In J.V.S. Megaw (Ed.) Hunters, Gatherers and First Farmers beyond Europe (pp. 69-125). Leicester: Leicester University Press.
Spurdle, A.B., Hammer, M.F., Jenkins,T. (1994) The Y Alu polymorphism in southern African populations and its relationship to other Y-specific polymorphisms. American Journal of Human Genetics, 54, 319-330.
Stahl, A.B. (1995). Intensification in the west African Late Stone Age: a view from central Ghana. In T. Shaw, P. Sinclair, B. Andah, & A. Okpoko (Eds.) The Archaeology of Africa (pp. 261-273). London: Routledge.
Todd, T.W. & Lindala, A. (1928). Dimensions of the body: Whites and American Negroes of both sexes. American Journal of Physical Anthropology, 12, 35-101.
Torroni, A., Semino, O., Scozzari, R., Sirugo, G., Spedini, G., Abbas, N., Fellous, M. et al. (1990). Y chromosome DNA polymorphisms in human populations: differences between Caucasoids and Africans detected by 49a and 49f probes. Annals of Human Genetics, 54, 287-296.
van den Berghe, P.L. (1979). Human Family Systems. An Evolutionary View. New York: Elsevier.
van den Berghe, P.L., and Frost, P. (1986). Skin color preference, sexual dimorphism and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies, 9, 87-113.
Vilakazi, A. (1962). Zulu Transformations, Pietermaritzburg: University of Natal Press.
Wagner, D.R., and Heyward, V.H. (2000). Measures of body composition in blacks and whites: a comparative review. American Journal of Clinical Nutrition, 71, 1392-1402.
Watson, E., Bauer, K., Aman, R., Weiss, G., von Haeseler, A., & Pääbo, S. (1996). mtDNA sequence diversity in Africa. American Journal of Human Genetics, 59, 437-444.
Weiner, J.S., Harrison, G.A., Singer, R., Harris R and Jopp, W. (1964). Skin colour in southern Africa. Human Biology, 36, 294-307.
Welch, C.E., and Glick, P.C. (1981). The incidence of polygamy in contemporary Africa: A research note. Journal of Marriage and the Family, 43, 191-193.
White, D. R. (1988). Rethinking polygyny. Co-wives, codes, and cultural systems. Current Anthropology, 29, 529-572.
Winkler, E-M., and Christiansen, K. (1993). Sex hormone levels and body hair growth in !Kung San and Kavango men from Namibia. American Journal of Physical Anthropology, 92, 155-164.
Wolff, G. & Steggerda, M. (1943). Female-male index of body build in Negroes and Whites: An interpretation of anatomical sex differences. Human Biology, 15, 127-152.
Wright, N.M., Renault, J., Willi, S., Veldhuis, J.D., Pandey, J.P., Gordon, L., Key, L.L., and Bell, N.H. (1995). Greater secretion of growth hormone in black than in white men: possible factor in greater bone mineral density—a clinical research center study. Journal of Clinical Endocrinology & Metabolism, 80, 2291-2297.
Indeed, we are all offspring of Africa. What is less true is the assumption that evolution stood still there while continuing elsewhere. Yes, some African groups do approximate ancestral Homo sapiens in their mode of subsistence, family structure, and physical appearance. These are the Khoisan and pygmy peoples. They still live by hunting and gathering, are overwhelmingly monogamous, and have light-brown skin and gracile, almost childlike bodies.
But they now inhabit only a few marginal environments, essentially the Kalahari and patches of rain forest. As elsewhere, time has moved on. There have arisen new populations who differ as much from ancestral Homo sapiens as do Europeans and Asians. These are the ‘true’ black Africans.
On the basis of genetic and archaeological data, black Africans seem to have radiated from a relatively small West African and possibly pygmy population within the last 20,000 years (Coon, 1962, pp. 651-656; Spurdle et al., 1994; Watson et al., 1996). The time and place of origin can be further narrowed down with linguistic data. Speakers of proto-Niger-Congo broke up c. 10,000 BP and the oldest derived group appear to be proto-Mande speakers, whose descendants inhabit the Niger's headwaters near the Mali-Guinea border (Blench, 1984, pp. 128-129; Ehret, 1984; Murdock, 1959, pp. 44, 64-68).
Murdock (1959, pp. 44, 64-68) associates black Africans with the spread of agriculture in sub-Saharan Africa. He too locates their place of origin on the Niger’s headwaters because this region is the cradle of the Sudanic food complex—a wide range of native crops now found throughout the continent (sorghum, pearl millet, cow pea, etc.). Other authors, like Shaw (1980), postulate an earlier, proto-agricultural phase that initially covered much of West Africa. This transitional period may have begun among Sangoan hunter-gatherers, who probably resembled present-day pygmies in appearance and lifestyle. These people gradually moved toward agriculture by first protecting fields of wild grains and making clearings for wild yams and oil palms (Davies, 1968; Shaw 1980, pp. 111-114). They began using hoes c. 12,000 BP and tending pili nut trees c. 8,000-9,000 BP (Posnansky, 1984, p. 149; Stahl, 1995, p. 262). Some form of agriculture is furthermore indicated by certain reconstructed words of proto-Niger-Congo, probably spoken before 10,000 BP (Ehret, 1984).
At a certain point in time, some of these proto-agriculturalists—apparently the ones inhabiting the Niger’s headwaters—surpassed the others in the transition to agriculture. They formed a nucleus of farming populations that would ultimately spread throughout sub-Saharan Africa. Meanwhile, this transition had already triggered a cascade of changes that would have profound behavioral and morphological consequences.
Increase in polygyny
Agriculture, especially year-round agriculture, enables women to become more self-reliant in feeding themselves and their children, thus making it less costly for men to take second wives (van den Berghe, 1979, p. 65). As a result, the polygyny rate is 20-50% of all marriages in sub-Saharan agricultural societies (Bourguignon and Greenbaum, 1973, p. 51; Goody, 1973; Pebley and Mbugua, 1989; Welch and Glick, 1981; White, 1988).
These societies seem to have long been highly polygynous. The ratio of Y chromosome to X chromosome variability is much lower than in other populations, apparently because proportionately fewer men have contributed to the gene pool (Excoffier et al., 1996; Scozzari et al., 1997; Spurdle et al., 1994; Torroni et al., 1990). Generalized polygyny is also attested by reconstruction of proto-Bantu, which was spoken approximately 3,000 years ago and has a specific term for "taking a second wife" (Polome, 1977).
Intensified sexual selection of men
If some men have more wives, others will have to do without. In general, men will have to compete more keenly with each other for access to women. When such rivalry intensifies in non-human species, the result is an intensification of sexual selection for larger, stronger, and more muscular males. This may explain why the highly polygynous, agricultural peoples of sub-Saharan Africa are so physically robust. They and their African American descendants outclass European-descended subjects for weight, chest size, arm girth, leg girth, muscle fiber properties, and bone density (Ama et al., 1986; Ettinger et al., 1997; Himes, 1988; Hui et al., 2003; Pollitzer and Anderson, 1989; Todd and Lindala, 1928; Wolff and Steggerda, 1943; Wagner and Heyward, 2000; Wright et al., 1995).
This masculinization of body build may be hormonally mediated. When Winkler and Christiansen (1993) studied two Namibian peoples, the weakly polygynous hunter-gatherer !Kung and the highly polygynous agricultural Kavango, the latter were found to have markedly higher levels of both total testosterone and DHT. The authors suggest that lower levels of these hormones may account for the !Kung’s neotenous appearance, i.e., sparse body hair, small stature, pedomorphic morphology, and light yellowish skin.
High testosterone/DHT levels are widely attested among sub-Saharan agriculturalists and their New World descendents. Young black men have more circulating testosterone than do young white men whereas young East Asian men, though intermediate in testosterone levels, have less 5α-reductase—an enzyme that converts testosterone into the physiologically more active DHT (Pettaway, 1999; Ross et al., 1992). These three geographic groupings also exhibit analogous differences in androgen receptor receptivity (Kittles et al., 2001). Broadly speaking, lifetime exposure to testosterone/DHT correlates with the incidence of prostate cancer and the highest incidences in the world are among African American men (Brawley and Kramer, 1996). Other populations of black African descent (i.e., West Indians and sub-Saharan Africans) exhibit lower incidences, but these have been shown to reflect underreporting and are probably just as high (Glover et al., 1998; Ogunbiyi and Shittu, 1999; Osegbe, 1997).
Relaxed sexual selection of women
If male-male rivalry intensifies sexual selection of men, it also tends to relax sexual selection of women. Because fewer women remain unmated, men are less able to translate their aesthetic criteria into actual mate choice. Such relaxed selection is suggested by visible female-specific characteristics. African Americans girls have narrower hips, broader waists, and thinner deposition of subcutaneous fat than do Euro-American girls (Hrdlička, 1898; Meredith and Spurgeon, 1980; Nelson and Nelson, 1986). Even before birth, Euro-American fetuses show significantly more sexual dimorphism than do African American fetuses (Choi and Trotter, 1970).
Relaxed sexual selection of women may also explain why, among sub-Saharan Africans, skin color is visibly darker in high-polygyny agriculturalists than in low-polygyny hunter-gatherers (i.e., Khoisans, pygmies) even though both are equally indigenous (Bourguignon and Greenbaum, 1973, pp. 171-175; Cavalli-Sforza, 1986a; Cavalli-Sforza, 1986b; Manning et al., 2004; Weiner et al, 1964). Skin color does, in fact, influence mate choice in all human societies; generally speaking, men prefer women who are lighter-skinned than the population mean (van den Berghe and Frost, 1986). In sub-Saharan societies, the preference is for so-called 'red' or 'yellow' women (see earlier post). Wherever African men were less able to act on this preference, there would have been less selection for lighter-skinned women and thus less counterbalancing of selection for darker skin to protect against sunburn and skin cancer (Aoki, 2002; Frost, 2007; Frost, 1994).
This preference may also have been crowded out by other mate-choice criteria. Vilakazi (1962, pp. 59-60) states: "The traditional Zulu does not make physical beauty a first priority or even an important qualification in a wife; and the skin colour of the woman is of little importance." In a rating study, Dixson et al. (2006) examined mate-choice criteria among subsistence farmers in Bakossiland, Cameroon, including preferred skin color of a potential female partner. No consistent preference emerged. This ambivalence was noted by Ardener (1954, p. 72) among the Ibo of Nigeria:
In the choice of a wife, yellow-skinned girls are regarded as beauties, and, other things being equal, they command higher bride prices. On the other hand it is generally held, especially by dark-complexioned persons, that yellow-skinned people are not as strong as the dark and do not live as long. A 'black' girl is said to be a harder worker. … A Mission headmaster was of the opinion that the preference for yellow girls was greater nowadays than in his youth. He thought that the reason for this was that people formerly looked for strength rather than beauty and tended to marry black girls. He claimed that black people had greater powers of endurance, and he cited his own village where, he said, of the oldest six or seven people, only one was yellow.
In Kenya, McVicar (1969, p. 242) notes similar views on the merits of ‘black’ versus ‘brown’ wives: "Among these tribes black girls are usually regarded as hard workers, possibly because many consider themselves fortunate enough to be married." In traditional African societies, women had to produce enough food for the entire family, typically through hoe farming in the sun. There was thus a premium on darker women. Lighter women may have been preferred aesthetically, but this preference remained unexpressed.
Timeline of expansion out of West Africa
All of these physical and hormonal characteristics seem to have arisen within a narrow timeframe. In sub-Saharan Africa, the beginnings of proto-agriculture cannot be pushed back much further than 12,000 BP. A tall, clearly black African skeleton has been dated to 6,500 BP (Camp, 1974, p. 241; Coon, 1962, pp. 649-650). This leaves a window of barely six thousand years for the changes that differentiate black Africans from their hunter-gatherer ancestors, i.e., a shift from a gracile, almost childlike body to a much more robust one, with attendant increases in stature, weight, and muscle mass.
By 6,000 to 7,000 years ago, the transition to agriculture had been completed in West Africa and these early agriculturalists were able to support much higher population densities than they had as hunter-gatherers. Inevitably, this nucleus of farming populations began to spread outward at the expense of more sparsely distributed Khoisan and pygmy peoples. By about 4,000 BP, the expansion had reached as far east as the middle Nile, when black Africans first appear in paintings from Pharaonic Egypt and in skeletal remains from Nubia (Junker, 1921). About 3,000 BP, another wave of advance began along the Nigerian-Cameroon border and spread rapidly throughout central, eastern, and southern Africa (Cavalli-Sforza, 1986c, pp. 361-362; Diamond, 1997; Oliver, 1966). By 300 AD, pioneering groups had advanced as far south as KwaZulu-Natal (see Bantu Expansion – Wikipedia).
Thus, black Africans were still absent from most of sub-Saharan Africa even within historic times. When the Egyptians began to build their pyramids, the peoples living to the south were scarcely darker in color. They were simply seen as uncivilized Egyptians. Thus, the civilized world initially encountered a much narrower range of human phenotypes than it would later on. This context shaped the intellectual worldview in its early stages, including theorizing on universal brotherhood. To a degree not easy to assess, we are heirs to notions of human sameness that were first conceived ‘before Africa became black’.
References
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Diamond, J. 1997. "How Africa Became Black" in Guns, Germs and Steel: The Fates of Human Societies, New York: W.W. Norton.
Dixson B.J., Dixson, A.F., Morgan, B., and Anderson, M.J. (2006). Human Physique and Sexual Attractiveness: Sexual Preferences of Men and Women in Bakossiland, Cameroon. Archives of Sexual Behavior, 36, 369-375.
Ehret, C. (1984). Historical/linguistic evidence for early African food production. In J.D. Clark & S.A. Brandt (Eds.) From Hunters to Farmers: The Causes and Consequences of Food Production in Africa (pp. 26-35). Berkeley: University of California Press.
Ettinger, B., Sidney S., Cummings, S.R., Libanati, C., Bikle, D.D., Tekawa, I.S., Tolan, K., and Steiger, P. (1997). Racial differences in bone density between young adult black and white subjects persist after adjustment for anthropometric, lifestyle, and biochemical differences. Journal of Clinical Endocrinology & Metabolism, 82, 429-434.
Excoffier, L., Poloni, E.S., Santachiara-Benerecetti, S., Semino, O., Langaney, A. (1996). The molecular diversity of the Niokholo Mandenkalu from Eastern Senegal: an insight into West Africa genetic history. In A.J. Boyce & C.G.N. Mascie-Taylor (Eds.) Molecular Biology and Human Diversity. Cambridge University Press: Cambridge, pp. 141-155.
Frost, P. (2007). Comment on Human skin-color sexual dimorphism: A test of the sexual selection hypothesis, American Journal of Physical Anthropology, 133, 779-781.
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Hui, S.L., Dimeglio, L.A., Longcope, C., Peacock, M., Mcclintock, R., Perkins, A.J., and Johnston Jr., C.C. (2003). Difference in bone mass between Black and White American children: Attributable to body build, sex hormone levels, or bone turnover? Journal of Clinical Endocrinology & Metabolism, 88, 642–649.
Junker, H. (1921). The first appearance of the Negroes in history. Journal of Egyptian Archaeology, 7, 121-132.
Kittles, R.A., Young, D., Weinrich, S., Hudson, J., Argyropoulos, G., Ukoli, F., Adams-Campbell, L., and Dunston, G.M. (2001). Extent of linkage disequilibrium between the androgen receptor gene CAG and GGC repeats in human populations: implications for prostate cancer risk. Human Genetics, 109, 253-261.
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Manning, J.T., Bundred, P.E., and Mather, F.M. (2004). Second to fourth digit ratio, sexual selection, and skin colour. Evolution and Human Behavior, 25, 38-50.
McVicar, K.G. (1969). Twilight of an East African Slum. Ann Arbor, University Microfilms (UCLA Dissertation 1968).
Meredith, H.V., and Spurgeon, J.H. (1980). Somatic comparisons at age 9 years for South Carolina White Girls and girls of other ethnic groups. Human Biology, 52, 401‑411.
Murdock, G.P. (1959). Africa. Its Peoples and Their Culture History. New York: McGraw-Hill.
Nelson, J.K., and Nelson, K.R. (1986). Skinfold profiles of Black and White boys and girls ages 11‑13. Human Biology, 58, 379‑390.
Ogunbiyi, J. and Shittu, O. (1999). Increased incidence of prostate cancer in Nigerians. Journal of the National Medical Association, 3, 159-164.
Oliver, R. (1966). The problem of the Bantu expansion. Journal of African History, 7, 361-376.
Osegbe, D. (1997). Prostate cancer in Nigerians: facts and non-facts. Journal of Urology, 157, 1340.
Pebley, A. R., and Mbugua, W. (1989). Polygyny and Fertility in Sub-Saharan Africa. In R. J. Lesthaeghe (Ed.), Reproduction and Social Organization in Sub-Saharan Africa, Berkeley: University of California Press, pp. 338-364.
Penny, D., Steel, M., Waddell, P.J., & Hendy, M.D. (1995). Improved analyses of human mtDNA sequences support a recent African origin for Homo sapiens. Molecular Biology and Evolution, 12, 863-882.
Pettaway, C.A. (1999). Racial differences in the androgen/androgen receptor pathway in prostate cancer. Journal of the National Medical Association, 91, 653-660
Pollitzer, W. S. and Anderson, J. JB. (1989). Ethnic and genetic differences in bone mass: a review with a hereditary vs environmental perspective. American Journal of Clinical Nutrition, 50, 1244-1259.
Polome, E.C. (1977). The reconstruction of Proto-Bantu culture from the lexicon. In L. Bouquiaux (Ed.) L'Expansion bantoue, 2, 779-791. Centre national de la recherche scientifique.
Posnansky, M. (1984). Early agricultural societies in Ghana. In J.D. Clark & S.A. Brandt (Eds.) From Hunters to Farmers: The Causes and Consequences of Food Production in Africa (pp. 147-151). Berkeley: University of California Press.
Ross, R.K., Bernstein, L., Lobo, R.A., Shimizu, H., Stanczyk, F.Z., Pike, M.C., and Henderson, B.E. (1992). 5-apha-reductase activity and risk of prostate cancer among Japanese and US white and black males. Lancet, 339, 887-889.
Scozzari, R., Cruciani, F., Malaspina, P., Santolamazza, P., Ciminelli, B.M., Torroni, A., Modiano, D., Wallace, D.C., Kidd, K.K. et al. (1997). Differential structuring of human populations for homologous X and Y microsatellite loci. American Journal of Human Genetics, 61, 719-733.
Shaw, T. (1980). Hunters, gatherers and first farmers in West Africa. In J.V.S. Megaw (Ed.) Hunters, Gatherers and First Farmers beyond Europe (pp. 69-125). Leicester: Leicester University Press.
Spurdle, A.B., Hammer, M.F., Jenkins,T. (1994) The Y Alu polymorphism in southern African populations and its relationship to other Y-specific polymorphisms. American Journal of Human Genetics, 54, 319-330.
Stahl, A.B. (1995). Intensification in the west African Late Stone Age: a view from central Ghana. In T. Shaw, P. Sinclair, B. Andah, & A. Okpoko (Eds.) The Archaeology of Africa (pp. 261-273). London: Routledge.
Todd, T.W. & Lindala, A. (1928). Dimensions of the body: Whites and American Negroes of both sexes. American Journal of Physical Anthropology, 12, 35-101.
Torroni, A., Semino, O., Scozzari, R., Sirugo, G., Spedini, G., Abbas, N., Fellous, M. et al. (1990). Y chromosome DNA polymorphisms in human populations: differences between Caucasoids and Africans detected by 49a and 49f probes. Annals of Human Genetics, 54, 287-296.
van den Berghe, P.L. (1979). Human Family Systems. An Evolutionary View. New York: Elsevier.
van den Berghe, P.L., and Frost, P. (1986). Skin color preference, sexual dimorphism and sexual selection: A case of gene-culture co-evolution? Ethnic and Racial Studies, 9, 87-113.
Vilakazi, A. (1962). Zulu Transformations, Pietermaritzburg: University of Natal Press.
Wagner, D.R., and Heyward, V.H. (2000). Measures of body composition in blacks and whites: a comparative review. American Journal of Clinical Nutrition, 71, 1392-1402.
Watson, E., Bauer, K., Aman, R., Weiss, G., von Haeseler, A., & Pääbo, S. (1996). mtDNA sequence diversity in Africa. American Journal of Human Genetics, 59, 437-444.
Weiner, J.S., Harrison, G.A., Singer, R., Harris R and Jopp, W. (1964). Skin colour in southern Africa. Human Biology, 36, 294-307.
Welch, C.E., and Glick, P.C. (1981). The incidence of polygamy in contemporary Africa: A research note. Journal of Marriage and the Family, 43, 191-193.
White, D. R. (1988). Rethinking polygyny. Co-wives, codes, and cultural systems. Current Anthropology, 29, 529-572.
Winkler, E-M., and Christiansen, K. (1993). Sex hormone levels and body hair growth in !Kung San and Kavango men from Namibia. American Journal of Physical Anthropology, 92, 155-164.
Wolff, G. & Steggerda, M. (1943). Female-male index of body build in Negroes and Whites: An interpretation of anatomical sex differences. Human Biology, 15, 127-152.
Wright, N.M., Renault, J., Willi, S., Veldhuis, J.D., Pandey, J.P., Gordon, L., Key, L.L., and Bell, N.H. (1995). Greater secretion of growth hormone in black than in white men: possible factor in greater bone mineral density—a clinical research center study. Journal of Clinical Endocrinology & Metabolism, 80, 2291-2297.
Friday, February 1, 2008
Beginnings of black slavery - II
In my last post, I argued against the view that black slaves were numerically insignificant outside sub-Saharan Africa until the rise of Islam in the 7th century. It looks like black slaves began to enter the Middle East in growing numbers some time before 0 AD, the result being a slow but steady increase in the region’s black population throughout the early Christian era and into the Islamic era.
I will now discuss the origins of the black slave trade in terms of its causation. This subject has generally been approached from the demand side, i.e., the Muslim world and later the European world. Here, I will focus on the supply side. What causes, internal to sub-Saharan Africa, tended to create slaves in excess of local demand?
The question may seem incomprehensible to many. It is widely assumed that sub-Saharan Africans were enslaved because they were politically and militarily helpless in the face of European or Arab outsiders. Yet before the 19th century most black slaves were purchased peacefully at trading posts on the periphery of sub-Saharan Africa, either on the coasts or in the Sahel. They were procured from indigenous middlemen, who in turn procured them from indigenous sellers.
A more nuancé view holds that these indigenous agents enslaved their fellow Africans in response to rising demand outside Africa for black slaves, particularly on New World plantations from the 17th century onward. Nonetheless, there is evidence from earlier periods that some sub-Saharan societies were already generating slaves well in excess of their own needs. When Portuguese traders reached the Niger delta in the late 15th century they were able to purchase large quantities of slaves from indigenous sellers. This trade, at least in its initial stages, seems to have been supply-driven rather than demand-driven.
Who were these slaves? Overwhelmingly, prisoners taken in war. Although historians agree that endemic warfare was linked to the slave trade, they are less sure about the direction of cause and effect. Did the slave trade provide an incentive for warfare—as a way to get the wherewithal with which to buy foreign goods? Or did warfare provide an incentive for the slave trade—as a way to get rid of unwanted prisoners of war? The former view was propounded by abolitionists and is still popular, witness this Wikipedia article:
Enslavement became a major by-product of war in Africa as nation states expanded through military conflicts in many cases through deliberate sponsorship of benefiting Western European nations.
Yet, further on, the same article states:
The practice of enslaving enemy combatants and their villages was widespread throughout Western and West Central Africa, although wars were rarely started to procure slaves. The slave trade was largely a by-product of tribal and state warfare as a way of removing potential dissidents after victory or financing future wars.
Clearly, European traders benefited from the warfare that occurred endemically throughout sub-Saharan Africa. But they were at most an auxiliary cause. If we exclude hunter-gatherers, all sub-Saharan societies had warrior castes that predated European contact and encompassed all unmarried men. Although militarization of single males has equivalents in most cultural areas, it had a greater impact in sub-Saharan Africa because enforced bachelorhood lasted much longer and affected virtually all young men.
African men stayed single longer because so many women were siphoned off by older, high-status males. Generally 20-50% of all marriages were (and often still are) polygynous in sub-Saharan agricultural societies (Bourguignon and Greenbaum, 1973, p. 51; Goody, 1973; Pebley and Mbugua, 1989; Welch and Glick, 1981; White, 1988; see Figure 1). Year-round agriculture made women largely self-reliant in feeding themselves and their children, thus letting more men take second wives. More polygyny for some, however, meant no wives at all for others. Usually the wife shortage was resolved by raising the age of marriage for men. For instance, among the Nyakyusa:
There is no evidence of any marked difference in the survival rate of males and females, but there is a difference of ten years or more in the average marriage-age of girls and men, and it is this differential marriage-age which makes polygyny possible. (Wilson, 1950, p. 112)
Raising the marriage age, however, simply concentrated celibacy in one age group. For these young men the only way to get a woman was to abduct one through warfare. Indeed, although the decision to wage war usually lay with older, married males, the warfare itself was more easily initiated and pursued because young males saw it as the best means to become sexual, reproducing beings, i.e., ‘real men.’ The stresses created by this situation are described by Pierre van den Berghe (1979, pp. 50-51):
Typically, the more men are polygynous in a given society, the greater the age difference between husbands and wives. … The temporary celibacy of young men in polygynous societies is rarely absolute, however. While it often postpones the establishment of a stable pair-bond and the procreation of children, it often does not preclude dalliance with unmarried girls, adultery with younger wives of older men, or the rape or seduction of women conquered in warfare. Thus, what sometimes looks like temporary celibacy is, in fact, temporary promiscuity. These young men often devote themselves to warfare during their unmarried years and sometimes homosexuality is tolerated during that period.
There is a large body of literature, called Youth Bulge Theory, that relates the probability of war to the proportion of young single males in the population (Mesquida and Wiener, 1996; see also Wikipedia –War). This proportion is at its highest where the polygyny rate exceeds 20% of all marriages—mostly in the agricultural societies of sub-Saharan Africa and Papua-New Guinea.
In such regions, this internal social contradiction could be resolved by externalizing it, i.e., by abducting women from adjacent peoples through warfare and by selling off any male captives.
References
Bourguignon, E. and Greenbaum, L.S. (1973). Diversity and Homogeneity in World Societies, HRAF Press.
Goody, J. (1973). Polygyny, Economy and the Role of Women, in J. Goody (Ed.) The Character of Kinship, Cambridge: Cambridge University Press, pp. 175-190.
Mesquida, C. G. and Wiener, N.I. (1996). Human Collective Aggression: A Behavioral Ecology Perspective, Ethology and Sociobiology, 17, 247-262
Pebley, A. R., and Mbugua, W. (1989). Polygyny and Fertility in Sub-Saharan Africa. In R. J. Lesthaeghe (Ed.), Reproduction and Social Organization in Sub-Saharan Africa, Berkeley: University of California Press, pp. 338-364.
van den Berghe, P.L. (1979). Human Family Systems. An Evolutionary View. New York: Elsevier.
Welch, C.E., and Glick, P.C. (1981). The incidence of polygamy in contemporary Africa: A research note. Journal of Marriage and the Family, 43, 191-193.
White, D. R. (1988). Rethinking polygyny. Co-wives, codes, and cultural systems. Current Anthropology, 29, 529-572.
Wilson, M. (1950). Nyakyusa kinship, in Radcliffe-Brown, A.R., and Forde, D. (Eds). African Systems of Kinship and Marriage. (pp. 111-139), London: Oxford University Press.
I will now discuss the origins of the black slave trade in terms of its causation. This subject has generally been approached from the demand side, i.e., the Muslim world and later the European world. Here, I will focus on the supply side. What causes, internal to sub-Saharan Africa, tended to create slaves in excess of local demand?
The question may seem incomprehensible to many. It is widely assumed that sub-Saharan Africans were enslaved because they were politically and militarily helpless in the face of European or Arab outsiders. Yet before the 19th century most black slaves were purchased peacefully at trading posts on the periphery of sub-Saharan Africa, either on the coasts or in the Sahel. They were procured from indigenous middlemen, who in turn procured them from indigenous sellers.
A more nuancé view holds that these indigenous agents enslaved their fellow Africans in response to rising demand outside Africa for black slaves, particularly on New World plantations from the 17th century onward. Nonetheless, there is evidence from earlier periods that some sub-Saharan societies were already generating slaves well in excess of their own needs. When Portuguese traders reached the Niger delta in the late 15th century they were able to purchase large quantities of slaves from indigenous sellers. This trade, at least in its initial stages, seems to have been supply-driven rather than demand-driven.
Who were these slaves? Overwhelmingly, prisoners taken in war. Although historians agree that endemic warfare was linked to the slave trade, they are less sure about the direction of cause and effect. Did the slave trade provide an incentive for warfare—as a way to get the wherewithal with which to buy foreign goods? Or did warfare provide an incentive for the slave trade—as a way to get rid of unwanted prisoners of war? The former view was propounded by abolitionists and is still popular, witness this Wikipedia article:
Enslavement became a major by-product of war in Africa as nation states expanded through military conflicts in many cases through deliberate sponsorship of benefiting Western European nations.
Yet, further on, the same article states:
The practice of enslaving enemy combatants and their villages was widespread throughout Western and West Central Africa, although wars were rarely started to procure slaves. The slave trade was largely a by-product of tribal and state warfare as a way of removing potential dissidents after victory or financing future wars.
Clearly, European traders benefited from the warfare that occurred endemically throughout sub-Saharan Africa. But they were at most an auxiliary cause. If we exclude hunter-gatherers, all sub-Saharan societies had warrior castes that predated European contact and encompassed all unmarried men. Although militarization of single males has equivalents in most cultural areas, it had a greater impact in sub-Saharan Africa because enforced bachelorhood lasted much longer and affected virtually all young men.
African men stayed single longer because so many women were siphoned off by older, high-status males. Generally 20-50% of all marriages were (and often still are) polygynous in sub-Saharan agricultural societies (Bourguignon and Greenbaum, 1973, p. 51; Goody, 1973; Pebley and Mbugua, 1989; Welch and Glick, 1981; White, 1988; see Figure 1). Year-round agriculture made women largely self-reliant in feeding themselves and their children, thus letting more men take second wives. More polygyny for some, however, meant no wives at all for others. Usually the wife shortage was resolved by raising the age of marriage for men. For instance, among the Nyakyusa:
There is no evidence of any marked difference in the survival rate of males and females, but there is a difference of ten years or more in the average marriage-age of girls and men, and it is this differential marriage-age which makes polygyny possible. (Wilson, 1950, p. 112)
Raising the marriage age, however, simply concentrated celibacy in one age group. For these young men the only way to get a woman was to abduct one through warfare. Indeed, although the decision to wage war usually lay with older, married males, the warfare itself was more easily initiated and pursued because young males saw it as the best means to become sexual, reproducing beings, i.e., ‘real men.’ The stresses created by this situation are described by Pierre van den Berghe (1979, pp. 50-51):
Typically, the more men are polygynous in a given society, the greater the age difference between husbands and wives. … The temporary celibacy of young men in polygynous societies is rarely absolute, however. While it often postpones the establishment of a stable pair-bond and the procreation of children, it often does not preclude dalliance with unmarried girls, adultery with younger wives of older men, or the rape or seduction of women conquered in warfare. Thus, what sometimes looks like temporary celibacy is, in fact, temporary promiscuity. These young men often devote themselves to warfare during their unmarried years and sometimes homosexuality is tolerated during that period.
There is a large body of literature, called Youth Bulge Theory, that relates the probability of war to the proportion of young single males in the population (Mesquida and Wiener, 1996; see also Wikipedia –War). This proportion is at its highest where the polygyny rate exceeds 20% of all marriages—mostly in the agricultural societies of sub-Saharan Africa and Papua-New Guinea.
In such regions, this internal social contradiction could be resolved by externalizing it, i.e., by abducting women from adjacent peoples through warfare and by selling off any male captives.
References
Bourguignon, E. and Greenbaum, L.S. (1973). Diversity and Homogeneity in World Societies, HRAF Press.
Goody, J. (1973). Polygyny, Economy and the Role of Women, in J. Goody (Ed.) The Character of Kinship, Cambridge: Cambridge University Press, pp. 175-190.
Mesquida, C. G. and Wiener, N.I. (1996). Human Collective Aggression: A Behavioral Ecology Perspective, Ethology and Sociobiology, 17, 247-262
Pebley, A. R., and Mbugua, W. (1989). Polygyny and Fertility in Sub-Saharan Africa. In R. J. Lesthaeghe (Ed.), Reproduction and Social Organization in Sub-Saharan Africa, Berkeley: University of California Press, pp. 338-364.
van den Berghe, P.L. (1979). Human Family Systems. An Evolutionary View. New York: Elsevier.
Welch, C.E., and Glick, P.C. (1981). The incidence of polygamy in contemporary Africa: A research note. Journal of Marriage and the Family, 43, 191-193.
White, D. R. (1988). Rethinking polygyny. Co-wives, codes, and cultural systems. Current Anthropology, 29, 529-572.
Wilson, M. (1950). Nyakyusa kinship, in Radcliffe-Brown, A.R., and Forde, D. (Eds). African Systems of Kinship and Marriage. (pp. 111-139), London: Oxford University Press.
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