For decades demographers and epidemiologists have observed a peculiar phenomenon during and after war. In these times, the ratio of male to female newborns shifts ever so slightly towards the former. In other words: more boys are born during and soon after wars. The change is slight, MacMahon and Pugh’s 1954 study finds one sex ratio shifted from 51.406 to 51.481 after WWII.
A number of theories explaining this ‘returning shoulder effect’ have been posited. One in particular has potential broader application in conflict research. Satoshi Kanazawa of the London School of Economics and Politics argues that the phenomenon is a “byproduct of the fact that taller soldiers are more likely to survive battle and that taller parents are more likely to have sons”.
Kanazawa tests his theory by examining the height of a non-random sample of British enlisted men serving in WWI. More specifically, Kanazawa draws his sample from only one of the 23,608 reels of microfiche at the UK National Archives. Since the reels are organized by last name, his sample contains only soldiers with the names Ababreltom to Ablett. Methodological problems of a non-random sample aside, the author finds supportive results: “The surviving soldiers in my sample have a significantly higher mean height than fallen soldiers”. Since height is positively related to the probability of having a son, war would have a positive relationship on the number of male births after intense conflict.
While Kanazawa resists providing a theory on why taller soldiers are more likely to survive warfare, he does offer some possibilities. First, taller and larger soldiers are more resilient to disease and wounding. Second, since height is related to intelligence, taller soldiers would be more likely to rise in the ranks and avoid the most dangerous duties. Third, and my personal favorite:
Dominic D. P. Johnson suggests another interesting hypothesis. If vital organs in the body do not increase in size linearly with the body size (height and weight), then it means that taller and heavier soldiers, while they may be more likely to be shot because of their larger body size, have nonetheless more room in their body where they can be ‘safely’ shot and still survive the injury.
Beyond explaining the returning soldier effect, the article is a reminder that even among similarly aged enlisted soldiers, war does not try men equally. Armies are not unitary objects, but organizations of individuals facing individualized risk. The same argument can be applied to civilian populations. Warfare’s effect and risk is unique to the person. Populations face war as individuals.
Update: Eduardo Leoni points out that a data scientist I respect very much has serious questions about Kanazawa’s statistics in this and similar papers.
Sources
Kanazawa, Satoshi. 2007. “Big and tall soldiers are more likely to survive battle: a possible explanation for the ‘returning soldier effect’ on the secondary sex ratio.” Hum. Reprod. 22(11): 3002-3008.
Christopher Albon is a Ph.D. candidate specializing in armed conflict, public health, human security, and health diplomacy.
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