Evolution never really stops, so it stands to reason that we humans are still undergoing evolutionary changes. Now some researchers have figured out how, finding evidence in the human genome that our fertility and heart function is changing.
Natural selection isn't like getting superpowers. It involves slowly wrought changes that take generations, and are often so subtle that we don't even notice.
Geneticists from the University of Queensland in Australia have figured out a way to detect what those changes are - a statistical method to find mutations in the DNA.
Jian Yang, Jian Zeng and a team of researchers from the university's Institute for Molecular Bioscience and Queensland Brain Institute studied the genomic data from 126,545 individuals in the UK Biobank, an anonymised health database in the UK.
They closely examined 28 complex traits, such as heel bone mineral density, male pattern baldness, BMI, female age at first menstruation and menopause, female age when giving live birth for the first time, grip strength, and hip-to-waist ratio.
By studying the genes associated with these traits in individuals at different ages, it's possible to see differences between generations.
"In natural selection, or 'survival of the fittest', characteristics that improve survival are more likely to be passed on to the next generation," Yang said.
"The opposite also occurs, when DNA mutations with a detrimental effect on fitness are less likely to be passed on, by a process called negative selection.
The researchers said they found evidence of negative selection - the removal of deleterious gene variants - in several traits. And the strongest evidence was in traits related to cardiovascular function and reproductive function.
For cardiovascular function, the team found changes associated with waist circumference and waist-to-hip ratio. An excess of fat around the waist had previously been found to be significantly linked to an increased risk of cardiovascular disease.
They also found evidence of changes in blood pressure.
But female age at menopause - associated with fertility - showed the strongest change. Age at first menstruation and age at first live birth also showed markers - which, the researchers said, made sense, since there's a strong correlation between fertility and genetic fitness.
This isn't the first time scientists have analysed materials from the Biobank for evolutionary changes in humans.
Last year, researchers from the University of California, Irvine studied the DNA of over 500,000 individuals, looking for both positive and negative selection. They found that evolution was favouring a higher BMI in men - probably due to muscle mass - and women that give birth younger.
Don't get too excited, though. Other scientists found in a 2011 study that evolutionary changes develop fairly frequently, but don't "stick" - it takes about a million years for an evolutionary trait to develop and last.
The point of the study isn't necessarily to determine changes we're going to see make a huge impact anytime soon, but to learn more about evolution, and how selection works.
"Negative selection prevents 'bad' mutations from spreading through the population, meaning that common DNA variants are likely to have small or no effect on traits," Zeng said.
"This study will help us better understand the genetic basis of complex traits and inform the design of future experiments in complex traits and medical genomics."
The team's research has been published in the journal Nature Genetics.