Hum. Reprod. Advance Access originally published online on September 20, 2007
Human Reproduction 2007 22(11):3002-3008; doi:10.1093/humrep/dem239
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Big and tall soldiers are more likely to survive battle: a possible explanation for the ‘returning soldier effect’ on the secondary sex ratio
1 Interdisciplinary Institute of Management, London School of Economics and Political Science, Houghton Street, London WC2A 2AE, UK 2 Department of Psychology, University College London, London, UK 3 Department of Psychology, Birkbeck College, University of London, London, UK
4 Correspondence address. Interdisciplinary Institute of Management, London School of Economics and Political Science, Houghton Street, London WC2A 2AE, UK. Tel: +44-20-7955-7297; Fax: +44-20-7955-7005; E-mail: s.kanazawa{at}lse.ac.uk
BACKGROUND: It is widely known that more boys are born during and immediately after wars, but there has not been any ultimate (evolutionary) explanation for this ‘returning soldier effect’. Here, I suggest that the higher sex ratios during and immediately after wars might be a byproduct of the fact that taller soldiers are more likely to survive battle and that taller parents are more likely to have sons.
METHODS: I analyze a large sample of British Army service records during World War I.
RESULTS: Surviving soldiers were on average more than one inch (3.33 cm) taller than fallen soldiers.
CONCLUSIONS: Conservative estimates suggest that the one-inch height advantage alone is more than twice as sufficient to account for all the excess boys born in the UK during and after World War I. While it remains unclear why taller soldiers are more likely to survive battle, I predict that the returning soldier effect will not happen in more recent and future wars.
Key words: generalized Trivers–Willard hypothesis/offspring sex ratio
Submitted on April 6, 2007; resubmitted on June 22, 2007; accepted on June 26, 2007.