The study 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 modest correlation between height and IQ has been documented in multiple studies stretching back to the 1970s. But the reasons for the relationship between the two traits has not been well understood.
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.
"Not just in humans but also in animals, you see that traits that are sexually attractive tend to be correlated," said Matthew Keller, assistant professor of psychology and neuroscience at CU-Boulder and lead author of the study appearing in the journal PLOS Genetics. "So if you have animals 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.
It has been common in the past to use information about identical twins and fraternal twins to determine whether a particular trait is inherited, caused by environmental factors or affected by some combination of both. This kind of twin study assumes that each twin grows up with the same environmental factors as his or her sibling.
If a trait that's present in one twin is just as often present in the other — regardless of whether the twins are fraternal or identical — then the trait is likely caused by environmental conditions. On the other hand, if a trait is generally found in both identical twins but only in one of a set of fraternal twins, it's likely that the trait is inherited, since identical twins have the same genetic material but fraternal twins do not.
Similar studies also can be done for linked traits, such as height and IQ. But while scientists could determine that a pair of traits is passed down genetically, they could not further resolve whether inherited traits were linked due to the same genes influencing both traits, called "pleiotropy," or because people who have those traits are more likely to mate with each other, known as "assortative mating."
The new CU-Boulder study solves this problem by including the parents of twins in its analysis. While this has occasionally been done in the past for single traits, information on parents has not previously been used to shed light on why two traits are genetically correlated. In part, that's because existing twin registries, where information for heritability studies is drawn, don't often contain information on the parents.
Additionally, creating the computer programs that are necessary to crunch the data for multiple traits from twins and their parents in order to understand environmental effects and both types of genetic effects is difficult.
"These designs have never taken off because they're very difficult to code," Keller said. "It's a challenge. They're very complicated models."
For this study, the research team used data collected from 7,905 individuals — including twins and their parents — by the Colorado Twin Registry at CU-Boulder and the Queensland Twin Registry at the Queensland Institute of Medical Research in Australia.
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.
The research team found that pleiotropy and assortative mating were about equally responsible for the genetic connection between height and IQ.
"It does look like there are genes that influence both height and IQ," Keller said. "At the same time, it also looks like people who are taller are slightly more likely to choose mates who are smarter and vice versa. Such mate choice causes 'IQ genes' and 'tall genes' to become statistically associated with one another. There are a lot of exceptions, but there's a statistical relationship that does happen more than would be expected by chance."
Now that the CU-Boulder team has built a computer model that is capable of disentangling the causes for linked traits, Keller said he hopes twin registries will begin to collect more data from parents and that other people in the field take advantage of the model.
Matthew Keller | EurekAlert!
Some brain tumors may respond to immunotherapy, new study suggests
11.12.2018 | Columbia University Irving Medical Center
Climate change and air pollution damaging health and causing millions of premature deaths
30.11.2018 | International Institute for Applied Systems Analysis (IIASA)
The more objects we make "smart," from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.
Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved...
What if, instead of turning up the thermostat, you could warm up with high-tech, flexible patches sewn into your clothes - while significantly reducing your...
A widely used diabetes medication combined with an antihypertensive drug specifically inhibits tumor growth – this was discovered by researchers from the University of Basel’s Biozentrum two years ago. In a follow-up study, recently published in “Cell Reports”, the scientists report that this drug cocktail induces cancer cell death by switching off their energy supply.
The widely used anti-diabetes drug metformin not only reduces blood sugar but also has an anti-cancer effect. However, the metformin dose commonly used in the...
A research team from the University of Zurich has developed a new drone that can retract its propeller arms in flight and make itself small to fit through narrow gaps and holes. This is particularly useful when searching for victims of natural disasters.
Inspecting a damaged building after an earthquake or during a fire is exactly the kind of job that human rescuers would like drones to do for them. A flying...
Over the last decade, there has been much excitement about the discovery, recognised by the Nobel Prize in Physics only two years ago, that there are two types...
12.12.2018 | Event News
10.12.2018 | Event News
06.12.2018 | Event News
14.12.2018 | Power and Electrical Engineering
14.12.2018 | Physics and Astronomy
14.12.2018 | Physics and Astronomy