This Weird Anatomical Feature Shows Humans Are Still Evolving

Scientists have detected anatomical changes in modern humans that suggest we may still be evolving.

In a study published in the Journal of Anatomy, researchers found that there has been an increase in the prevalence of the "median artery" in humans since the late 19th century.

The median artery is a blood vessel that develops in growing human fetuses but usually begins to disappear around the eighth week of gestation.

Normally, the median artery—located in the forearm—is replaced by the radial and ulnar arteries. But in some people the median artery persists into adulthood, alongside the other two—and this anatomical feature is becoming more common over time, the authors of the study said.

"A lot of people think that humans have evolved and that we've stopped evolving," lead author Teghan Lucas, from Flinders University, Australia, said in a statement. "But our study has shown that humans are still evolving and this is what we call microevolution in modern humans.

"The median artery is a perfect example of how we're still evolving because people born more recently have a higher prevalence of this artery when compared to humans from previous generations."

In their study, Lucas and her colleagues dissected 78 upper limbs taken from the cadavers of Australians aged between 51 and 101 at the time of death. They found that 26 of these limbs contained median arteries—a prevalence rate of around 33 percent.

The researchers then analyzed the relevant literature, finding that the prevalence of the median artery globally has significantly increased over time from approximately 10 percent in people born in the mid-1880s to around 30 percent by the end of the 20th century.

"That's a significant increase in a fairly short period of time, when it comes to evolution," Lucas said.

Based on current trends, the authors predict that people born in 80 years time will virtually all have median arteries that persist into adulthood. They say that when the prevalence of this feature reaches 50 percent of more, it should no longer be considered a "variant" but a "normal" human structure.

The scientists say their results provide evidence of "microevolutionary changes" in the internal anatomy of the human body. But it is not yet clear whether the trend is being caused by mutations in genes responsible for the development of the median artery and natural selection pressures or health problems experienced by mothers during pregnancy—or both.

While having a median artery is associated with some health issues—such as carpal tunnel syndrome and thrombosis—the authors also say it could be advantageous in other circumstances because it can act as an "emergency" blood vessel if the radial or ulnar arteries are damaged.

The scientists say that the prevalence of some other anatomical features have also increased or decreased over the last two or three centuries, with evidence suggesting that natural selection pressures are responsible for these microevolutionary processes in modern humans.

For example, scientists have detected an increased absence of wisdom teeth over time, while it is becoming more common for people to be born with extra joints in their feet.