In many parts of Asia, the Middle East and North Africa, women and children
are so undervalued, neglected, abused, and so often killed, that sex ratios are now strongly
male biased. In recent decades, sex-biased abortion has exacerbated the problem. In this
article I highlight several important insights from evolutionary biology into both the origin
and the severe societal consequences of “Asia’s missing women”, paying particular
attention to interactions between evolution, economics and culture. Son preferences and
associated cultural practices like patrilineal inheritance, patrilocality and the Indian Hindu
dowry system arise among the wealthy and powerful elites for reasons consistent with
models of sex-biased parental investment.
Several times in Chinese history, female infanticide and neglect created large
surpluses of males. These men drifted into criminal gangs that terrorized other citizens;
sometimes, these men formed larger militias that wreaked large-scale havoc. The Nien
rebellion in 19th Century China was one such event that resulted in the death of 100 000
troops and civilians over a 15-year period; the rebellion devastated the economy and
eventually contributed to the demise of the Qing dynasty (Hudson and den Boer, 2004).
Although spectacular sex-ratio biases on the scale of Asia’s missing women are
relatively rare, polygynous traditional societies are more likely to experience betweengroup and within-group violence because poor young men have little prospect of finding a
single wife (Ember, 1974; Ember et al., 2007). Similarly, the renowned lawlessness of the
early American West is often attributed to strongly male-biased sex ratios (Courtwright,
1996). The intense jockeying by young men for status, respect and economic success that
so often spills over into violence and, occasionally, homicide (see Daly and Wilson, 1988b)
is made all the more intense by the fact that the prospect of never finding a mate is higher
in polygynous and, by extension, male-biased societies.
In a similar vein, in late medieval and early modern Europe, elite titled and landed
families proliferated beyond the number of titles and area of land available. The younger
sons of these families, jockeying for status and titles, regularly threatened the political
stability of their societies, becoming the “spearhead of feudal aggression” (Duby, 1977).Asia’s missing women
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Expansionist campaigns, from the Crusades (Duby, 1977) to colonialism (Boone III, 1986),
were driven, at least in part, by this surplus of ambitious and aggressive younger sons with
otherwise poor reproductive prospects.
Male-biased sex ratios trigger the phenotypically plastic hyper-competitive
masculine traits that allow young men - especially poor and low-status young men - to
compete furiously for status and wealth in order to win a mate. They also appear to be
triggering related behaviors: risk-taking, violence, gambling, alcohol and drug abuse,
kidnapping and trafficking of women, and the use and abuse of prostitutes. All of these
maladies are on the steep rise in India, China and elsewhere where sex ratios are malebiased (Edlund et al., 2007, 2008; Hudson, 2002; Hudson and den Boer, 2004).
Not only can we trace the causes of Asia’s missing women to interactions between
evolution, economics and culture, but the direst consequences are also evolutionary in
origin. Even if childhood sex ratio biases can be eliminated, societies with skewed sex
ratios will continue to experience high rates of violence and crime for at least one
generation. Those disaffected gangs of young men also make perfect fodder for
fundamentalism and violence of a more global nature. An important future challenge for
applied evolutionary psychology will be to recognize and ameliorate the frustrations and
challenges created by male-biased sex ratios.