One in six Chinese men is unlikely to ever find a wife, according to the Chinese Academy of Social Sciences in Beijing (p. 261). There are currently over 111 million more men in China than women, and 120 men to every 100 women in the 15–34 age category. India's skewed sex ratio is also rapidly approaching the 120:100 ratio. What happens to societies that explicitly select for disproportionate numbers of male offspring, through abortions of female fetuses, infanticide of girls, neglect of female infants, or other forms of direct and indirect violence against girls and women? It is to this question that Valerie M. Hudson and Andrea M. den Boer turn in their extensively researched and richly detailed book.

The authors conclude that high-sex-ratio societies in which there are “surplus men” and “missing women” (the latter term referring to the number of females who would be predicted to exist were it not for gender bias in mortality) have a propensity toward chronic violence and persistent social disorder. Though analysts from a variety of disciplines have for decades debated the origins, extent, and implications of exaggerated gender imbalances in Asia, Hudson and den Boer are among the first to argue that nations with disproportionately high numbers of single males may be more prone toward interstate conflict. This conclusion derives in part from blending two relatively new subfields of security studies: environmental security, which considers the role of scarcity and inequality in producing conflict, and human security, which examines how the security of individuals is related to the security of nations (p. 1). The authors' predictions for China's and India's development in the twenty-first century are bleak: Not only will democracy likely not take root in China and India find its current democratic system challenged, but both countries will also be unable to resolve their primary international territorial disputes given the “unstable context produced by skewed sex ratios” (p. 263). Although gender imbalances may not be sufficient or necessary to spark violence within and between societies, the authors argue that they nonetheless may “amplify, aggravate, or trigger” such violence (pp. 5, 221). Indeed, they contend, nations with high sex ratios are predisposed to “see some utility in interstate conflict” (p. 263) as a tool for sending their “bare branches” (men who will never marry due to the dearth of spouses) away from national population centers.

Hudson and den Boer begin their argument by tracing the historical origin of sex-selection practices within and outside of Asia. They discuss how religion and rigid social systems of hypergyny (marriage of women to men of higher social status) contribute to the continuation of sex-selection practices long after the conditions that originally led to their practice subside. They then focus their discussion in Chapters 3 and 4 on historical and contemporary sex-selection practices in India and China, which, they argue, account for more than 90% of Asia's 90 million missing females. In a nuanced critique of existing studies on Asia's sex ratios, the authors point out that much of the current literature fails to account for variations in sex ratios over time, region, class, caste, tribe, and age category.

Chapter 5 outlines several characteristics and behavioral tendencies of bare branches culled from theories and empirical findings in sociology, anthropology, psychology, criminology, economics, political science, and security studies. Most bare branches belong to the lowest socioeconomic class, are likely to be unemployed, are transient with few ties to the communities in which they look for work, and live and socialize with other bare branches in bachelor subcultures often ostracized by mainstream society. The authors examine “seven facts”—including that males in general are more violent than females, unmarried males commit more violence than married males, and low-status males commit more violence than high-status males—to conclude that bare branches are more likely to turn to vice and violence than other males (pp. 192–200). Using as evidence several historical examples from China and India as well as medieval Portugal of bare branches engaging in widespread intrasocietal violence, the authors conclude that the strategies bare branches use to improve their own lot often lead to significant violence in society and a further decline in the status of women. They also conclude that government efforts to promote domestic stability under these conditions often leads to intersocietal violence as governments seek to distract bare branches in foreign adventures. The final two chapters offer policy options to combat increasingly distorted sex ratios and the violence the authors argue follows from them.

Bare Branches provides a valuable compilation and analysis of historical and contemporary studies of sexratios in Asia. The authors argue that “the masculinization of Asia's sex ratios is one of the overlooked stories of the century” (p. 264), and their work raises the previously ignored question of how distorted gender balances alter nations' security calculations. The study offers an insightful hypothesis that societies with large numbers of bare branches may be more prone to armed conflict than others. Further research is needed, however, as the authors themselves acknowledge, to confirm their hypotheses. A larger sample of historical cases from societies with not only high sex ratios but also low and normal sex ratios is necessary to strengthen their argument. Though the authors show an impressive command of the histories and politics of both India and China, by underestimating the degree of ethnic tensions in parts of China (p. 257), some of their policy proposals (pp. 244–45) could well lead to increased social unrest, rather than its cessation.