Article: Frost 2023
Excerpt:
DNA evidence shows a rise, fall, and renewed rise in mean cognitive ability in ancient Rome... The Imperial era saw a decline, possibly due to reduced natural selection and social factors like increased slavery and lower reproductive rates among the upper classes. Late Antiquity, marked by the rise of Christianity, showed an increase in cognitive ability, possibly due to biocultural changes in marriage and reproduction.
Rome went through cognitive decline due to lower fertility rates among the upperclass, unfit spouse selection and hypergamy. This decline only ended and reversed course with the rise of Christianity with their strict social familial standards, such as having many children (high fertility rate), monogamous spouse selection (pressure to select fitter spouses, only get one) and sexual modesty.