Mate Choice and the Persistence of Maternal Mortality

Cost of mate choice: Changing patterns of global age disparity in marriage and their consequences to women's health including maternal mortality and menopause

BACKGROUND

Consistent across cultures and throughout time is the male preference for younger females. Given its prevalence, the mate choice theory proposes that age-disparate relationships may have contributed to the evolution of maternal mortality and menopause.

OBJECTIVES

The objective is to document evidence for age disparity in marriage from past and present populations and evaluate their relevance to maternal mortality and menopause.

DESIGN

Cross-sectional data were collected from various regions and time points, ranging from the Roman era to the current decade.

METHODS

To analyze both the age disparity in marriage and age at marriage, data were collected from Ancestry.ca for Quebec, Massachusetts, India, South Africa, and England and Wales. Additional data were taken from the United Nations as a more recent and comprehensive source. To analyze the relationships between age disparity in marriage and different social factors, data on gross domestic product, maternal mortality rates, fertility, primary school enrollment, child marriage rates, and percentage of women in the total labor force were collected from the World Health Organization, World Bank, and United Nations International Children's Emergency Fund.

RESULTS

The results showed that males were significantly older than females at first marriage in all populations and time frames sampled, supporting the assumption underlying the mate choice theory. Maternal mortality rates were strongly associated with age-disparate relationships, increasing by 275 per 100,000 live births for each additional year in the age disparity.

CONCLUSION

The results from this study provide support for the assumption underlying the mate choice theory of maternal mortality and menopause.

Origin of Sex-Biased Mental Disorders: Do Males and Females Experience Different Selective Regimes?

The origins of sex-biased differences in disease and health are of growing interest to both medical researchers and health professionals. Several major factors have been identified that affect sex differences in incidence of diseases and mental disorders. These are: sex chromosomes, sex hormones and female immunity, sexual selection and antagonistic evolution, and differential susceptibility of sexes to environmental factors. These factors work on different time scales and are not exclusive of each other. Recently, a combined Sexual Selection-Sex Hormones (SS-SH) Theory was presented as an evolutionary mechanism to explain sex-biased differences in diseases and mental disorders (Singh in J Mol Evol 89:195-213, 2021). In that paper disease prevalence trends were investigated, and non-sex-specific diseases were hypothesized to be more common in males than in females in general. They showed signs of exceptions to this trend with inflammatory diseases and stress-related mental disorders that were more common in females. We believe that the SS-SH theory requires the consideration of psycho-social stress (PSS) to explain the predominance of female-biased mental disorders and some other exceptions in their findings. Here we present a theory of sex-differential experience of PSS and provide quantitative support for the combined SS-SH-PSS Theory using age-standardized incidence rates (ASIRs) recording the levels of male- and female-bias in data obtained from different countries. The grand theory provides an evolutionary framework for explaining patterns of sex-biased trends in the prevalence of disease and health. Further exploration of women's vulnerability to social factors may help to facilitate new treatments for female-biased diseases.

Origin of Sex-Biased Mental Disorders: An Evolutionary Perspective

Sexual dimorphism or sex bias in diseases and mental disorders have two biological causes: sexual selection and sex hormones. We review the role of sexual selection theory and bring together decades of molecular studies on the variation and evolution of sex-biased genes and provide a theoretical basis for the causes of sex bias in disease and health. We present a Sexual Selection-Sex Hormone theory and show that male-driven evolution, including sexual selection, leads to: (1) increased male vulnerability due to negative pleiotropic effects associated with male-driven sexual selection and evolution; (2) increased rates of male-driven mutations and epimutations in response to early fitness gains and at the cost of late fitness; and (3) enhanced female immunity due to antagonistic responses to mutations that are beneficial to males but harmful to females, reducing female vulnerability to diseases and increasing the thresholds for disorders such as autism. Female-driven evolution, such as reproduction-related fluctuation in female sex hormones in association with stress and social condition, has been shown to be associated with increased risk of certain mental disorders such as major depression disorder in women. Bodies have history, cells have memories. An evolutionary framework, such as the Sexual Selection–Sex Hormone theory, provides a historical perspective for understanding how the differences in the sex-biased diseases and mental disorders have evolved over time. It has the potential to direct the development of novel preventive and treatment strategies.