A new study in the journal Behavior Genetics finds that human evolution is not a “relic from the laboratory of Gemeinschaft (behavioral college).” The results show that although natural selection prefers some health-related traits while selecting others, such as traits related to higher educational attainment, these traits are also selected by more social factors that continue to shape human evolution, which the authors claim are complex and largely unsupported by evidence from three generations of Americans.
Variation in the prevalence of traits in populations across generations is caused by natural selection, which considers their effect on an individual’s ability to survive and reproduce. Traits that enhance reproductive success are more likely to be present over time, while traits that reduce reproductive success are less likely to be present.
The effect of natural selection on humans is important because, while genetic, environmental, and social factors play important roles, genetic and environmental factors play a different role in survival decisions than in other species.
The new study is based on the economic theory of fertility – first popularised by economist Gary Becker – which explains how economic factors influence the pattern of childbearing. The theory is divided into two main parts.
The “substitution effect” posits that individuals must choose between working and raising children because of a trade-off between the time invested in the labour market. The study found that people with more education or income placed a greater emphasis on their time in the labour market, while those with higher education or income benefitted more from the opportunity cost of having children.
The substitution effect varies across socio-economic groups, with more highly educated individuals receiving higher wages and those with higher marginalisation receiving higher incomes.
Using data from the Health and Retirement Survey, the researchers analysed 8,827 male and female genotyped white participants (born before 1965 for men) and 2,319 genotyped black participants (for comparison purposes). They calculated polygenic scores using existing genetic data repositories.
The primary factor in the study was “relative lifetime reproductive success, which refers to the restoration of the percentage of children in an individual born in the same year compared to the average of children of people born in the same year.” The researchers calculated the magnitude and direction of natural selection on various traits by analyzing polygenic scores.
They also extended their analysis across three generations and across siblings and grandchildren to study selection effects in a cumulative form. According to the researchers, polygenic scores associated with educational attainment have a smaller effect on reproductive success, indicating that these scores are being compared to those of people who have a higher genetic propensity for education.
This finding indicates that individuals with a higher genetic propensity for educational attainment tend to have fewer offspring. In all three generations examined, this trend remained relevant, and it reinforces the economic theory of fertility that individuals with high human capital must balance this balance with their work and their family obligations.
The results for the second theory were less uniform; For example, this prediction suggests that selection pressures should be greater in socioeconomically disadvantaged (low income, low education, or unmarried) groups; although the strongest selection coefficients were found for low-income and unmarried parents, the researchers found no significant differences in levels of education or age at first birth. These findings imply that economic factors are not fully responsible for the observed selection pressures.
The study examined selection on health-related traits as well as educational traits. Interestingly, some health traits, such as self-rated health and age at first birth, showed selection pressures that were similar to those for educational attainment. This indicates that natural selection is influencing other natural selection-related traits, such as overall health and reproductive timing.
The polygenic score for self-rated health was found to be associated with reproductive success, meaning that people with a greater genetic predisposition for health are more likely to have children. The polygenic score for smoking behavior, on the other hand, was being selected against.
In addition, the researchers calculated the amount of genetic change across generations, suggesting that natural selection is responsible for measurable, albeit modest, variations in polygenic scores. As a result, they estimate that the genetic predisposition for cognitive performance will decrease by about 0.055 standard deviations per generation, meaning that these estimates are completely independent of environmental changes and other factors such as genetic measurement error.