Directional and stabilizing selection
Natural selection has made the British harder
Daria Spasskaya, N+1
Using the example of a large sample of data from white residents of the UK, presented in the UK Biobank database, the researchers showed how natural selection works in modern populations. In particular, the influence of directional selection was found for such phenotypic traits as body mass index, height and age of birth of the first child. The study is published in the Proceedings of the National Academy of Sciences (Sanjak et al., Evidence of directional and stabilizing selection in contemporary humans).
A research group led by Peter Visscher from the University of Queensland (Australia) has shown the effect of several types of selection, in particular, directed and stabilizing, on phenotypic traits in the modern British population. For the analysis, the UK Biobank database was used, which includes information on various health indicators and the genotype of 500 thousand Britons. The study included data for 217728 women and 157807 men over 45 years old. Scientists measured the level of correlation between relative reproductive success (RLRs – relative lifetime reproductive success) and three dozen different phenotypic traits using linear regression.
Among the studied signs were, for example, body mass index, hip circumference, fat percentage, bone mineral density, education level, height, heart rate and others.
Directed selection implies that there is a positive correlation between a phenotypic trait and fitness. Over time, the representation of this trait in the population increases. Examples of the action of directed selection in post-industrial human societies are an increase in the age of menopause, weight gain and a decrease in height in women. Stabilizing selection acts against extreme variants of the manifestation of some trait and fixes an average variant in the population. A well-studied feature in this case is the average weight of newborns.
The researchers found weak traces of targeted selection on 23 of the 37 studied traits for women and 21 of 33 for men. The most significant correlations were found for women's height and body mass index (BMI) for men, as well as for the age of birth of the first child in women. The analysis showed that reproductive success is accompanied by short women who started giving birth as early as possible, and men with a higher BMI.
For 12 and 14 traits, respectively, traces of stabilizing selection were found. An example of a trait that stabilizing selection acts on in modern society is growth – the tallest and lowest people have reduced fitness compared to more "average" options.
Graphs of the dependence of height on fitness for men
(right shoulder of the graph) and women (left shoulder).
There are many studies devoted to natural selection among modern humans. We told, for example, that based on data from the UK Biobank and the American GERA database (Genetic Epidemiology Research on Adult Health and Aging), genetic variants were found that negatively affect life expectancy and are rejected in older age groups.
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