Human Evolution: This Forearm Artery Shows Our Species Is Still Evolving

Humans are still evolving and are doing so at a faster rate than before, shows a new study. The evidence backing this "microevolution" can be found in people's forearms.

When talking about evolution, people tend to think of it as something that happened in the past and perhaps of changes that are quite drastic such as aquatic creatures developing legs to walk on land. But a study by researchers from the University of Adelaide and Flinders University, both in Australia, found that humans are still evolving in small ways that are not easily observed.

The new study, published in the Journal of Anatomy, analyzed the prevalence of the median artery, the main vessel that supplies blood to the hand and forearm, in humans. It is considered as an "embryonic structure" developed in the womb, which eventually regresses, typically around the eighth week of gestation. But several past studies have observed the presence of the vessel in newborns, infants and even adults.

To determine the prevalence of the median artery in postnatal humans in the past 250 years, the researchers performed a comprehensive literature review. They also studied a sample of 78 upper limbs from Australians who died between the ages of 51 and 101 in 2015 and 2016. The team found a total of 26 median arteries, displaying a prevalence rate of 33.3%.

The study also revealed that the prevalence of the median artery in adults has been increasing at a faster rate than at any time in the last 250 years, a news release from the Flinders University said. In fact, the researchers found that the number of people retaining their median artery tripled in the last 125 years.

"Since the 18th century, anatomists have been studying the prevalence of this artery in adults and our study shows it's clearly increasing," study co-author Dr. Teghan Lucas of Flinders University said in the news release. "The prevalence was around 10% in people born in the mid-1880's compared to 30% in those born in the late 20th century, so that's a significant increase in a fairly short period of time, when it comes to evolution."

This means, what was once a temporary feature in the womb is now present in more and more adults who retained it instead of losing it during development in the womb.

"If extrapolated using the same regression line, could predict that the median artery will be present in 100% of individuals born in the year 2100 and later," the researchers wrote. "That is approximately 250 years from the beginning of the artery's first reported incidence as a 'variant.'"

If the prevalence of the median artery reaches 50%, something that does not seem too far-fetched given the speed at which the change is happening, it will no longer be a unique trait but will be considered as normal.

Although it is not clear why more and more people are retaining their median artery, the researchers note the possibility of gene mutations or health problems in mothers during pregnancy.

Because of its small scale, the researchers call it a "microevolution" that shows how humans are still evolving even in little ways. Another example of such small-scale evolution is the increasing absence of wisdom teeth.

Although they seem like small changes, they show how humans are still changing.

"This is micro evolution in modern humans and 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 generation," study senior author Professor Maciej Henneberg, of the University of Adelaide, said in the news release.