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

Zhao, Zhongwei; Zhu, Yuan; Reimondos, Anna

doi:10.4054/demres.2013.29.33

Cited by 7 publications

(5 citation statements)

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“…Understanding this variation has been labeled one of the most elusive concepts in the life sciences today 1 . Over the last several decades a variety of ecological, demographic, economic, and social variables have been evaluated to address this controversy, yet their association with the SRB has been equivocal 2–6 . Here, in an attempt to offer resolution to this conflicted literature, we examine sources of variation in SRB using detailed longitudinal and individual-level data from humans in an early 20 th century US population.…”

Section: Introductionmentioning

confidence: 99%

“…For example, from the ‘frail male’ literature, during the Dutch Hunger Winter (‘Hongerwinter’ in Dutch; 1944–45), where mothers experienced severe resource deprivation over a period of seven months during WWII, SRBs were not significantly different from those in less stressful times 5 . However, other work analyzing data from over three years in China during the Great Leap Forward, known as the Great Chinese Famine (三年大饥荒 in simplified Chinese; 1959–61), finds a precipitous drop in male births during the period of mass starvation 4 (although alternative findings have been reported 6 ). While these results seemingly conflict, one interpretation of differing findings is that shorter periods of deprivation are not enough to trigger male-biased fetal wastage, and instead these events need to be protracted, as in the case of the famine in China.…”

Section: Introductionmentioning

confidence: 99%

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Sex ratios at birth vary with environmental harshness but not maternal condition

Schacht

Tharp

Smith

2019

Sci Rep

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The sex ratio at birth (SRB) may be patterned by maternal condition and/or environmental stressors. However, despite decades of research, empirical results from across the social and biological sciences are equivocal on this topic. Using longitudinal individual-level data from a US population during the interwar period (1918–1939), inclusive of three distinct eras (Spanish Flu, Roaring ‘20 s, and the Great Depression), we evaluate predictions from two theoretical frameworks used to study patterning in SRB – (1) ‘frail males’ and (2) adaptive sex-biased investment theory (Trivers-Willard). The first approach centers on greater male susceptibility to exogenous stressors and argues that offspring survival should be expected to differ between ‘good’ and ‘bad’ times. The second approach contends that mothers themselves play a direct role in manipulating offspring SRB, and that those in better condition should invest more in sons. In-line with ‘frail male’ predictions, we find that boys are less likely to be born during the environmentally challenging times of the Spanish Flu and Great Depression. However, we find no evidence that maternal condition is associated with sex ratios at birth, a result inconsistent with the Trivers-Willard hypothesis.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Sex ratios at birth vary with environmental harshness but not maternal condition

Schacht

Tharp

Smith

2019

Sci Rep

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“…Not all existing research, however, provides supporting evidence for the hypothesis. A number of studies have questioned the previous findings of SRB declines during times of wars ( Graffelman and Hoekstra, 2000 ; Polasek et al , 2005 ; Polasek, 2006 ), political upheavals ( Schnettler and Klüsener, 2014 ) and famines ( Zhao et al , 2013 ). These equivocal results indicate that the relationship between SRB changes and idiosyncratic shocks is sensitive to data and the context under study ( James, 2009 ).…”

Section: Introductionmentioning

confidence: 97%

Maternal stress and sex ratio at birth in Sweden over two and a half centuries: a retest of the Trivers–Willard hypothesis

2021

Human Reproduction

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STUDY QUESTION Is there a negative relationship, as predicted in the Trivers–Willard hypothesis (TWH), between the intensity of maternal stress and sex ratio at birth (SRB)? SUMMARY ANSWER Using a comprehensive data set with multiple indicators of maternal stress, most measures of stress show no statistically significant association with SRB over a period spanning 243 years, indicating no support for the TWH. WHAT IS KNOWN ALREADY Evolutionary biologists have proposed a widely discussed hypothesis that women in poor and stressful conditions during pregnancy are more likely to give birth to girls, and exposure to stressful events may therefore lead to a reduction in sex (male-to-female) ratio at birth. The empirical evidence so far is mixed. STUDY DESIGN, SIZE, DURATION Annual time series data, spanning 243 years between 1749 and 1991 for Sweden at the national level, were drawn from multiple sources. The outcome is defined as the percentage of male births relative to all births in Sweden in a given year. The covariates include a set of economic and climatic variables as proxies for maternal stress. PARTICIPANTS/MATERIALS, SETTING, METHODS We conduct a series of ARIMA (autoregressive integrated moving average) models to examine the relationship between maternal stress and SRB during three periods: 1749–1991, 1749–1861 and 1862–1991. MAIN RESULTS AND THE ROLE OF CHANCE In 1749–1991, economic proxies for maternal stress showed no statistically significant association with SRB. In 1749–1861, two indicators were significantly associated with SRB, but the coefficients were opposite in direction to the TWH. In 1862–1991, five out of six covariates showed no significant association with SRB. An additional analysis found no significant correlation between sex ratio of stillbirths and all covariates in 1862–1991. Our results are incompatible with the TWH and suggest that previous findings in support of the TWH are not robust. LIMITATIONS, REASONS FOR CAUTION This study provides population-level evidence that may not necessarily reflect the nature of all individuals due to the ecological fallacy. The time series analysed in this study are annual data, and we cannot examine the potential seasonality due to the lack of disaggregated monthly data. Our findings may not be generalised to the contexts of extreme maternal stress conditions such as famine and war. WIDER IMPLICATIONS OF THE FINDINGS The results from existing studies in this topic may be speculative, and additional research with more comprehensive design, data and covariates is needed to reconsider the robustness of previous findings. STUDY FUNDING/COMPETING INTEREST(S) The author receives no external funding and has no conflict of interest to declare. TRIAL REGISTRATION NUMBER N/A.

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“…One well-developed line of inquiry targets ambient stressors as drivers of SRB outcomes given that prenatal stress is expected to negatively affect developing males more so than females (Schacht et al 2019). However, from across social science disciplines, a variety of demographic, economic, and ecological variables have been evaluated, producing mixed findings (Lydersen 2007;Ruckstuhl et al 2010;Song 2012;Stein et al 2004;Zhao et al 2013). A key consideration for this ambiguity is that living conditions in industrial societies (e.g., infrastructure development) may blunt possible adverse consequences associated with exogenous shocks (e.g., drought) due to connectivity between populations facilitating the flow of resources (Scalone and Rettaroli 2015).…”

Section: Introductionmentioning

confidence: 99%

Frail Males on the American Frontier: The Role of Environmental Harshness on Sex Ratios at Birth across a Period of Rapid Industrialization

et al. 2021

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While sex ratios at birth (SRB) have been shown to vary within and across populations, after over a century of research, explanations have remained elusive. A variety of ecological, demographic, economic, and social variables have been evaluated, yet their association with SRB has been equivocal. Here, in an attempt to shed light on this unresolved topic within the literature, we approach the question of what drives variation in SRB using detailed longitudinal data spanning the frontier-era to the early 20th century in a population from the US state of Utah. Using several measures of environmental harshness, we find that fewer boys are born during challenging times. However, these results hold only for the frontier-era and not into a period of rapid economic and infrastructure development. We argue that the mixed state of the literature may result from the impact and frequency of exogenous stressors being dampened due to industrialization.

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

Cited by 7 publications

References 34 publications

Sex ratios at birth vary with environmental harshness but not maternal condition

Sex ratios at birth vary with environmental harshness but not maternal condition

Maternal stress and sex ratio at birth in Sweden over two and a half centuries: a retest of the Trivers–Willard hypothesis

Frail Males on the American Frontier: The Role of Environmental Harshness on Sex Ratios at Birth across a Period of Rapid Industrialization

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