The human lineage has evolved over millions of years in a variety of environments, and many traits (morphological, psychological, genetic, social, developmental, etc.) have been selected. While some traits are shared by all human populations (such as the long period of childhood dependence), others are specific to certain populations. This is the case of local adaptations, resulting from human adaptation to geographically variable environments. Understanding these local adaptations makes it possible to understand the modalities of migrations, natural selection and, sometimes, to study the interactions between genes and behaviors. When environmental changes are abrupt and very recent, this offers an opportunity to understand the adaptive lag (since a new adaptation will take many generations to become predominant in a population) and the associated costs. This can be illustrated in the West by the recent dietary change after World War II, with the massive introduction of refined carbohydrates, whose physiological and hormonal effects have well-known health effects from a medical point of view, but also certainly behavioral and social consequences that are largely underestimated.
Some traits present in the human species seem paradoxical: these traits are heritable (they can increase or decrease in frequency according to the selection that is exercised), but are associated with a decrease in reproduction and/or longevity (the selection is negative). Their persistence, at relatively high frequencies, for many generations seems therefore counter-intuitive. This is the case for menopause, observed in very few species outside the human species, but also for homosexual preference (unknown in other primates). Left-handedness, which persists in all populations, also represents a paradox of the same nature.
More generally, the study of life history traits of human populations, in their temporal and geographical diversity, allows us to understand how biology and culture (or gene and environment, including social environment) interact and co-evolve...
