Jump to content

Returning soldier effect

From Wikipedia, the free encyclopedia

The returning soldier effect is a phenomenon which suggests that more boys are born immediately after wars.[1][2] This effect is one of the many factors influencing human sex ratio. It was especially noticeable worldwide during and right after both of the World Wars.[3]

The phenomenon was first noticed in 1883 by Carl Düsing of the University of Jena, who suggested that it was a natural regulation of the status quo. Writing in 1899, an Australian physician, Arthur Davenport, used Düsing's findings to hypothesize that the cause was the difference between the comparative ill-health of the returning troops compared to the good health of their partners.[4]

Research published in 1954 by Brian MacMahon and Thomas F. Pugh showed that the sex ratio of white live births in the United States had shown a marked increase in favor of boys between 1945 and 1947, after World War II, with a peak in 1946.[5]

In 2007, Kanazawa Satoshi published a paper theorizing that the effect was due to "the fact that taller soldiers are more likely to survive battle and that taller parents are more likely to have sons". This was based on his research of British Army records from the First World War, which showed that "surviving soldiers were on average more than one inch (3.33 cm) taller than fallen soldiers".[1] Other genetic explanations have been proposed.[6]

Valerie Grant attributed it to changing hormone levels of women during war, as they tended to "adopt more dominant roles".[7][8]

William H. James writing in 2008 gave an increase in coital rates by returning soldiers as a possible cause. He also noted that a fall in the ratio of male births had been recorded in Iran following the Iran–Iraq War, "explained by psychological stress causing pregnant women disproportionately to abort male fetuses".[9]

The normal ratio is estimated to be some 1.03 to 1.06 males per female,[10] which appears to compensate for the fact that child mortality rate among boys is slightly bigger than among girls, and that adult men are more likely to die from an accident than women.[3]

See also[edit]


  1. ^ a b Kanazawa, S. (27 September 2007). "Big and tall soldiers are more likely to survive battle: a possible explanation for the 'returning soldier effect' on the secondary sex ratio". Human Reproduction. Vol. 22, no. 11. pp. 3002–3008. doi:10.1093/humrep/dem239. Retrieved 25 December 2020.
  2. ^ "Returning soldier effect". Jagiellonian University. Retrieved 25 December 2020.
  3. ^ a b Rutherford, Adam; Fry, Hannah (2 October 2023). "Introducing… Uncharted with Hannah Fry". The Curious Cases of Rutherford & Fry. BBC Radio 4. Retrieved 24 February 2024.
  4. ^ Davenport, Arthur Frederick (1901). "Notes on the Origin of Sex". Intercolonial Medical Congress of Australasia: Transactions of the Fifth Session, Held in Brisbane, Queensland, September 1899: 123–130. Retrieved 26 December 2020.
  5. ^ MacMahon, Brian; Pugh, Thomas F (June 1954). "Sex ratio of white births in the United States during the Second World War". American Journal of Human Genetics. 6 (2): 284–292. PMC 1716540. PMID 13158334.
  6. ^ Allen, Laura (18 December 2008). "Why Does War Breed More Boys?". Popular Science. Retrieved 12 July 2023.
  7. ^ Grant, Valerie J (2008). "Sex-of-Offspring Differences between Mothers". Evolutionary Psychology. 6 (1). doi:10.1177/147470490800600117. S2CID 146289598.
  8. ^ Ridley, Matt (6 October 1994). The Red Queen: Sex and the Evolution of Human Nature. Penguin UK. ISBN 978-0-14-196545-1.
  9. ^ James, William H (March 2009). "The variations of human sex ratio at birth during and after wars, and their potential explanations". Journal of Theoretical Biology. 257 (1): 116–23. Bibcode:2009JThBi.257..116J. doi:10.1016/j.jtbi.2008.09.028. PMID 18952111. Retrieved 26 December 2020.
  10. ^ Chao, Fengqing; Gerland, Patrick; Cook, Alex R.; Alkema, Leontine (7 May 2019). "Systematic assessment of the sex ratio at birth for all countries and estimation of national imbalances and regional reference levels". Proceedings of the National Academy of Sciences. 116 (19): 9303–9311. Bibcode:2019PNAS..116.9303C. doi:10.1073/pnas.1812593116. PMC 6511063. PMID 30988199.