Why taller people tend to be slightly smarter is due to two phenomena - the same genes affect both traits and taller people are likelier to mate with smarter people, according to a study.
The study led by the University of Colorado Boulder did not find that environmental factors contributed to the connection between being taller and being smarter, both traits that people tend to find attractive.
The technique developed by the researchers at CU-Boulder to tease out those reasons may open the door for scientists to better understand why other sexually selected traits-characteristics that individuals find desirable in mates-tend to be linked. People who are attractive because of one trait tend to have other attractive traits as well.
Lead author Matthew Keller, assistant professor of psychology and neuroscience at CU-Boulder said that not just in humans but also in animals, you see that traits that are sexually attractive tend to be correlated.
He said that if animal that are high on one sexually selected trait they are often high on other ones, too. And the question has always been, 'What's the cause of that?' And it has always been very difficult to tease apart the two potential genetic reasons that those could be related."
The key to the technique developed by Keller, also a fellow at CU-Boulder's Institute for Behavioral Genetics, and his colleagues is using data collected about fraternal twins, identical twins and, importantly, their parents.
Keller and his colleagues found that for the twins in their study, the correlation between height and IQ was not impacted by environmental conditions. Though Keller cautions that in societies where there is more nutritional variation among families, environmental factors could come into play.
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The research team found that pleiotropy and assortative mating were about equally responsible for the genetic connection between height and IQ.
The study has been published in the journal PLOS Genetics.