Gene mixing promotes height and intelligence – but is this an evolutionary benefit?

A new international study of the genetic make up and physical characteristics of 350,000 people indicates that greater genetic diversity leads to an increase of height and cognitive skills. But – somewhat surprisingly – lower genetic diversity did not lead to any visible increase in complex diseases. Genetic diversity was found to have no effect on blood pressure or cholesterol levels.

But I question the assumption that increased height and faster thinking are of “evolutionary advantage”. Evolutionary advantage must lead to an individual having a greater number of offspring than one without the advantage. Previous work has indicated that both child nourishment and genetics determine height.

And so I wonder what evolutionary advantage height may have in modern society? Does the ability to think faster lead to a greater number of surviving descendants? Richer and “more intelligent” groups tend to have much lower fertility rates than poorer, “less intelligent” groups.

Using the criterion of greatest surviving descendants indicating evolutionary advantage, leads to the conclusion that populations in Africa with the highest population increase rates must also have the greatest evolutionary advantages!

Peter K. Joshi et al. Directional dominance on stature and cognition in diverse human populations. Nature, 2015 DOI: 10.1038/nature14618

Abstract: Homozygosity has long been associated with rare, often devastating, Mendelian disorders, and Darwin was one of the first to recognize that inbreeding reduces evolutionary fitness. However, the effect of the more distant parental relatedness that is common in modern human populations is less well understood. Genomic data now allow us to investigate the effects of homozygosity on traits of public health importance by observing contiguous homozygous segments (runs of homozygosity), which are inferred to be homozygous along their complete length. Given the low levels of genome-wide homozygosity prevalent in most human populations, information is required on very large numbers of people to provide sufficient power. Here we use runs of homozygosity to study 16 health-related quantitative traits in 354,224 individuals from 102 cohorts, and find statistically significant associations between summed runs of homozygosity and four complex traits: height, forced expiratory lung volume in one second, general cognitive ability and educational attainment (P < 1 × 10−300, 2.1 × 10−6, 2.5 × 10−10 and 1.8 × 10−10, respectively).

University of Edinburgh Press Release:

People have evolved to be smarter and taller than their predecessors, a study of populations around the world suggests. Those who are born to parents from diverse genetic backgrounds tend to be taller and have sharper thinking skills than others, the major international study has found. Researchers analysed health and genetic information from more than 100 studies carried out around the world. These included details on more than 350,000 people from urban and rural communities.

The team found that greater genetic diversity is linked to increased height. It is also associated with better cognitive skills, as well as higher levels of education. However, genetic diversity had no effect on factors such as high blood pressure or cholesterol levels, which affect a person’s chances of developing heart disease, diabetes and other complex conditions.

Researchers from the University of Edinburgh examined individuals’ entire genetic make-up.

They pinpointed instances in which people had inherited identical copies of genes from both their mother and their father – an indicator that their ancestors were related. Where few instances of this occur in a person’s genes, it indicates greater genetic diversity in their heritage and the two sides of their family are unlikely to be distantly related. It had been thought that close family ties would raise a person’s risk of complex diseases but the researchers found this not to be the case.

The only traits they found to be affected by genetic diversity are height and the ability to think quickly.



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