Evolutionary ecology of human birth sex ratio under the compound influence of climate change, famine, economic crises and wars
Article first published online: 28 AUG 2009
© 2009 The Authors. Journal compilation © 2009 British Ecological Society
Journal of Animal Ecology
Volume 78, Issue 6, pages 1226–1233, November 2009
How to Cite
Helle, S., Helama, S. and Lertola, K. (2009), Evolutionary ecology of human birth sex ratio under the compound influence of climate change, famine, economic crises and wars. Journal of Animal Ecology, 78: 1226–1233. doi: 10.1111/j.1365-2656.2009.01598.x
- Issue published online: 13 OCT 2009
- Article first published online: 28 AUG 2009
- Received 16 October 2008; accepted 25 June 2009 Handling Editor: Alex Roulin
- infant mortality;
- natural selection;
- time-series analysis;
1. Human sex ratio at birth at the population level has been suggested to vary according to exogenous stressors such as wars, ambient temperature, ecological disasters and economic crises, but their relative effects on birth sex ratio have not been investigated. It also remains unclear whether such associations represent environmental forcing or adaptive parental response, as parents may produce the sex that has better survival prospects and fitness in a given environmental challenge.
2. We examined the simultaneous role of wars, famine, ambient temperature, economic development and total mortality rate on the annual variation of offspring birth sex ratio and whether this variation, in turn, was related to sex-specific infant mortality rate in Finland during 1865–2003.
3. Our findings show an increased excess of male births during the World War II and during warm years. Instead, economic development, famine, short-lasting Finnish civil war and total mortality rate were not related to birth sex ratio. Moreover, we found no association between annual birth sex ratio and sex-biased infant mortality rate among the concurrent cohort.
4. Our results propose that some exogenous challenges like ambient temperature and war can skew human birth sex ratio and that these deviations likely represent environmental forcing rather than adaptive parental response to such challenges.