The more distantly related a person's parents are, the more likely they are to be taller, smarter, and better educated, researchers in the UK have found.
The results of one of the largest studies to date into genetic diversity, encompassing data from 110 genetic studies of 350,000 individuals living across Africa, Asia, Europe and North America, suggest that the increasing average in height and cognitive ability around the world could be the result of more frequent pairings of people from diverse genetic backgrounds.
Whether we're talking about flies, whales, dogs, or humans, the survival of any species on Earth relies on a healthy pool of genetic diversity. For centuries now, we've known that the more closely related a child's parents, the more at risk they'll be of developing genetic defects, such as deafness, muteness, blood diseases, and physical deformities. But it's been unclear if this scenario could be reversed: if the more distantly related a child's parents are, the more likely they'll be to possess advantageous genetic traits.
So researchers from several institutions around Britain examined the genetic information of 354,224 individuals from 102 cohorts spanning four continents, and identified every case of homozygosity - where a child inherits exact copies of genes from both parents, allowing adverse, recessive traits to be more easily expressed. A common result of inbreeding, homozygosity can be used to determine how closely related a child's parents are.
Once the team had figured this value out for their study population, they compared this to 16 traits of public health importance, including height, lung capacity, blood pressure, and cholesterol level. They found that of these traits, just four could be correlated to genetic diversity - height, lung capacity, cognitive ability, and level of eduction. For example, children that resulted from first cousin pairings ended up being on average 1.2 cm shorter and having 10 months' less education than those from more genetically diverse parents.
"Most people would believe a diverse gene-pool is a good thing, but the discovery that height is associated with diversity wouldn't have been foreseen," one of the team, Nathan Richardson from the UK Medical Research Council, told Philip Oldfield at The Guardian.
While it's still up to the researchers to prove causation through some kind of biological function, plus figure out how much of a trait is down to factors other than genetics - for example, cognition depends on a lot of environmental factors too - the results could explain why with every generation, humans are getting smarter and taller.
"These results could also go some way to explaining the 'Flynn Effect' - the increase in intelligence from one generation to the next first documented in the 20th century.
While socio-economic factors such as increased schooling and better nutrition are generally seen as primary drivers, increased genetic diversity could also play a small role. 'The increases in intelligence [from the Flynn Effect] are too big to be explained by our results alone, but they might be a contributor,' he said."
Interestingly, the team was looking specifically at traits that could seriously effect public health, and found no link between low genetic diversity and high cholesterol or blood pressure levels. "Inbreeding does not affect the cardio-metabolic factors that lead to the diseases that many of us die from," one of the team, Jim Wilson from the University of Edinburgh, told Michael Le Page at New Scientist. Which I guess is good news for the tiny, remote communities around the world that are cut off from fertile jetsetters and forced to make do with a less-than-steller gene pool.
Publishing the results in Nature, the researchers say the next step will be to identify specific parts of the genome that most benefit from increased diversity.