College graduates marry other college graduates, or at least that’s the way it usually goes in the United States. A 2014 Facebook Survey found that nearly a third of Americans attended the same college as their spouses. Despite past research identifying specific genes associated with completing higher education, a new study shows nearly a century of education-driven mating has done nothing to change the country’s genetic makeup. This is a clear example of how genetics do not always mirror changes in lifestyle.

For the study, now published online in the journal Proceedings of the National Academy of Sciences, researchers from universities across the country investigated whether shifts in the marriage landscape over the past 100 years changed the American genome. Over the period from 1920 to 1955, the team evaluated more than 2,000 white, non-Hispanic married couples for differences in educational attainment, height, body mass index, and depression, along with genes associated with these traits.

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Results showed that, despite more individuals marrying others with their same level of education, there were no changes in the presence of genes linked to educational attainment. There also was no association between the educational level a couple had achieved and genes influencing their offspring's height, BMI, or depression. According to lead researcher Dr. Dalton Conley in a recent statement, these interesting results show how sexual selection and human behavior do not always have such a strong influence over genetic changes.

“Undoubtedly, spouses are increasingly sorting themselves with an eye toward the education they've received--among other traits," said Conley in the statement. "But while the existence of education-associated genes has been well-documented, choosing partners with education levels similar to our own has not resulted in children who have meaningfully altered the genetic makeup of the U.S. population."

While the tendency to marry someone with the same level of education as you has not really affected our genome, other lifestyle choices may have. One study from 2014 suggested that as humans switched from hunter gatherers to a more sedentary lifestyle with the introduction of agriculture, somewhere around 12,000 years ago, our bones became lighter and weaker.

“It started when we adopted agriculture. Our diets changed. Our levels of activity changed,” the study’s coauthor Habiba Chirchir, an anthropologist in the Smithsonian’s Human Origins Program, told Smithsonian.

A cultural switch to farming may not have only affected our bone density. Another study suggests it also caused humans to become more genetically diverse. In the hunting-gathering culture, strength was the most important trait in males. However, a switch to farming meant that other traits, such as the ability to accumulate wealth and power, also increased the reproductive success of males. As a result, there was more reproductive competition, and this helped to diversify our genome.

As for the future of human evolution, one paper written by evolutionary anthropologist Cadell Last hypothesized that advances in science and technology combined with increased desire to pursue happiness may allow humans to reproduce much later in life and even increase the average human lifespan to around 120 years.

Source: Conley D, Laidley T, Belsky DW, et al. Assortative mating and differential fertility by phenotype and genotype across the 20th century. National Academy of Sciences. 2016