American Journal of Human Biology最新文献

Compared to our closest living cousins, the great apes, humans can live longer with a distinctive postmenopausal lifespan; our development is slower, yet our babies are weaned earlier. Continued investigation since 2003 shows our grandmother hypothesis is a robust explanation for those differences and many other distinctive human features: When ecological changes in ancient Africa spread profitable foraging targets for ancestral adults that infants and small juveniles couldn't handle, reliable foraging by females near the end of their own fertility could subsidize dependent grandchildren and shorten their daughters' time to next conception. Coevolution of shorter birth intervals with slower aging expanded the pool of older still-fertile males. With more competitors, guarding a mate wins more paternities, linking pair bonds to our mid-life menopause. Mate guarding plus older males' advantage in reputation building explains many aspects of human patriarchy. In addition, final brain size in placental mammals depends on the duration of development. As increasing longevity slowed development and expanded brain size, earlier weaning of still physically helpless ancestral infants prioritized their attention and capacities to engage carers. Resulting socially precocious infancies wire us with lifelong appetites for cooperation.

The study of physical growth and development of Indigenous children from Nuñoa, Perú, in the 1960s showed that growth in body size and skeletal maturation was slow and delayed, while growth in lung volume, measured by forced vital capacity (FVC), was accelerated. Hence, I proposed that the high functional adaptation of high-altitude natives was influenced by developmental processes. To test this hypothesis, my co-investigators and I conducted two sets of major physiological studies at high altitudes. The first studies were conducted in Cusco (3400 m) and Puno (3840 m), Perú. This research showed that the FVC and aerobic capacity of low-altitude Peruvian urban natives acclimatized to high altitudes during the developmental period were similar to those of high-altitude urban natives. In contrast, Peruvian and US participants acclimatized during adulthood did not have the same FVC and aerobic capacity as the high-altitude urban natives. The second set of studies was carried out in the city of La Paz, Bolivia (3752 m), and included Europeans who were acclimatized to high altitudes at different ages. This research confirmed that acclimatization during the developmental period was a major component of the high functional adaptation among high-altitude urban natives. These conclusions have been confirmed by epigenetic studies, which demonstrated that acclimatization to high altitude leads to modifications in the activity of the DNA that facilitate adaptation during the developmental period.

Human brain imaging took off in the 1980s and has since flooded the zone in the analysis of gender differences in behavior and mental health. Couched in the aims of “precision medicine,” the vast majority of this research has taken a binary approach, dividing participants according to the M/F box at intake and asserting that the sex differences found in neuroimaging will lead to important advances for treating neuropsychiatric disorders. However, the actual findings from this 40-year project have not lived up to its promise, in part because of the over-binarization of sex and general ignorance of gender as a complex variable influencing human behavior and brain function. This paper reviews the history of failed claims about male–female brain difference in the modern era, illuminates the deep-pocketed incentives driving such research, and examines the limitations of this binary approach for understanding gender-related behavior and health disparities. It then considers more recent efforts to “break the binary” by using measures of “gender” in addition to “sex” as an independent variable in brain imaging studies. Given the multidimensional nature of gender—as identity, expression, roles and relations—this is challenging to implement, with initial efforts producing little of substance. Better approaches to addressing male–female disparities in brain health will require focusing on specific behaviors (e.g., anxiety, risk-taking, verbal memory, spatial navigation) and specific components of sex and gender (e.g., body size, hormone levels, gene expression, caregiver role, financial independence, discrimination) when seeking brain-behavior correlates in a diverse population.