Ever wonder why smarter people tend to live longer? Well, science is beginning to uncover the answer, and it has all to do with your genetics.

Researchers from the London School of Economics analyzed data from both fraternal and identical twins, finding that 95 percent of the link between intelligence and a longer life is found within genes. Publishing their findings in the International Journal of Epidemiology, researchers were able to share this first-of-a-kind study and its novel insight into intelligence and longevity.

For their study, researchers compared genetics of fraternal twins with identical twins, knowing that within fraternal twins only half of DNA is shared. Because of this, researchers were better able to understand the impact of genetics separate from environmental factors like home life, school, and childhood nutrition.

Overall, what they found was that within these twin pairs, the twin who was more intelligent tended to live longer than the twin who was not as bright. This especially proved to be the case within fraternal twins.

“We know that children who score higher in IQ-type tests are prone to living longer,” said Rosalind Arden, research associate at the London School of Economics and Political Science (LSE), in a press release. “Also, people at the top of an employment hierarchy, such as senior civil servants, tend to be long-lived. But, in both cases, we have not understood why.”

She adds that thanks to their research, an explanation can finally be offered for the connection between intellect and lifespan. “Our research shows that the link between intelligence and longer life is mostly genetic,” she said. “So, to the extent that being smarter plays a role in doing a top job, the association between top jobs and longer lifespans is more a result of genes than having a big desk.”

Arden also cautions that this connection should be taken with a grain of salt, and not affect how parents treat children who display average, or lower intelligence levels. “It’s important to emphasize that the association between intelligence and lifespan is small. So you can’t, for example, deduce your child’s likely lifespan from how he or she does in their exams this summer,” Arden said.

In order to conduct their research, Arden’s team collected data from three different twin studies in Sweden, the United States and Denmark. Within these three studies, age of death and overall intelligence was recorded, and at least one twin from each pair had passed away. All twin pairs were also same-sex within this analysis. When gathering this information, researchers found that intelligence and longevity has most of its basis in genetics, independent of environmental factors that often affect development.

As far as why researchers found this genetic foundation in intelligence and longevity, Arden has a theory. “It could be that people whose genes make them brighter also have genes for a healthy body. Or intelligence and lifespan may both be sensitive to overall mutations, with people with fewer genetic mutations being more intelligent and living longer,” she said. “We need to continue to test these ideas to understand what processes are in play.”

Source: Arden R, Luciano M, Deary I, et al. The association between intelligence and lifespan is mostly genetic. International Journal of Epidemiology. 2015.