Could changes in reported sex ratios at birth during China's 1958-1961 famine support the adaptive sex ratio adjustment hypothesis?

Abstract

AbstractBACKGROUNDThe adaptive sex ratio adjustment hypothesis suggests that when mothers are in poor conditions sex ratio of their will be biased towards females. Major famines provide opportunities for testing this hypothesis they lead to widespread deterioration of living conditions in affected population.OBJECTIVEThis study examines changes in sex ratio at birth before, during, and after China's 1958-1961 famine, to see whether they provide any support for adaptive sex ratio adjustment hypothesis.METHODSWe use descriptive statistics to analyse data collected by both China's 1982 and 1988 fertility sample surveys and examine changes in sex ratio at birth in recent history. In addition, we examine effectiveness of using different methods to model changes in sex ratio at birth and compare their differences.RESULTSDuring China's 1958-1961 famine, reported sex ratio at birth remained notably higher than that observed in most countries in world. The timing of decline in sex ratio at birth did not coincide with timing of famine. After famine, although living conditions were considerably improved, sex ratio at birth was not higher but lower than that recorded during famine.CONCLUSIONThe analysis of data collected by two fertility surveys has found no evidence that changes in sex ratio at birth during China's 1958-1961 famine and post-famine period supported adaptive sex ratio adjustment hypothesis.1. IntroductionTrivers and Willard proposed a major hypothesis in study of sex ratios in 1973. The hypothesis suggests that because reproductive success of male tends to be more variable and resource-sensitive than that of female offspring (Song 2012: 1), natural selection should favour parental ability to adjust sex ratio of produced according to parental ability to invest (Trivers and Willard 1973: 90). This kind of adjustment or control can take place both before and after birth. Accordingly, when maternal condition declines, mothers tend to produce a lower ratio of males to females (Trivers and Willard 1973: 90; also Cronk 2007). This hypothesis, also referred to as adaptive sex ratio adjustment hypothesis, has been tested by several studies of human populations in recent years, although results have been mixed (Keller et al. 2001; Lazarus 2002; Gibson and Mace 2003; Stein et al. 2004; Cronk 2007).In a recent paper published by Proceedings of Royal Society B, which is entitled Does famine influence sex ratio at birth? Evidence from 1959 -1961 Great Leap Forward Famine in China?, Shige Song examined impact of this famine on changes in sex ratio at birth (SRB) through analysing data collected by China?s 1982 National One-Per-Thousand Population Sample Survey. According to author, the study identified an abrupt decline in sex ratio at birth between April 1960, over a year after Great Leap Forward Famine began, and October 1963, approximately 2 years after famine ended, followed by a compensatory rise between October 1963 and July 1965. These findings support adaptive sex ratio adjustment hypothesis that mothers in good condition are more likely to give birth to sons, whereas mothers in poor condition are more likely to give birth to daughters (Song 2012: 1). Song?s paper has been publicized widely. In commenting on Song?s results, Nature reported in its news section that Hungry mothers give birth to more daughters (Corbyn 2012). LiveScience, a major science website, also reported that Hard times mean fewer baby boys (Pappas 2012).In this paper, using data collected by both China?s 1982 National One-Per- Thousand Population Sample Survey on Fertility and 1988 National Sample Survey on Fertility and Contraception, we further examine changes in reported SRB during China?s 1958-1961 famine. …