Median Artery Is Becoming More Common in Adults

Imagining what humans could look like in the distant future often leads to bold predictions about obvious traits, including stature, brain volume and skin tone. But small anatomical changes already occurring in our bodies show just how difficult evolution is to predict.

Consider an unremarkable additional blood vessel in the arm. If present trends continue, it could become common in only a few generations.

The median artery in the forearm

A 2020 study by researchers at Flinders University and the University of Adelaide in Australia found that an artery which briefly runs through the centre of the forearm in the womb is now less likely to disappear than it was previously.

As a result, more adults than ever appear to have an extra route of vascular tissue running beneath the wrist.

"Since the 18th century, anatomists have been studying the prevalence of this artery in adults and our study shows it's clearly increasing," Flinders University anatomist Teghan Lucas explained in 2020.

"The prevalence was around 10 percent in people born in the mid-1880s compared to 30 percent 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."

In every human, the median artery develops relatively early, carrying blood through the middle of the arm to nourish the developing hands.

Three major arteries in the forearm – median in the centre. (ilbusca/Digital Vision Vectors/Getty Images)

At roughly eight weeks, it normally regresses. Two other blood vessels then take over: the radial artery, which is felt when checking somebody's pulse, and the ulnar artery.

Anatomists have long understood that the median artery does not always fade away. In certain cases, it remains for another month or so.

Occasionally, people are born with the artery still active, supplying blood either to the forearm alone or, in some instances, to the hand too.

Research into persistent median arteries

To assess how widespread this enduring blood channel is, Lucas and her University of Adelaide colleagues, Maciej Henneberg and Jaliya Kumaratilake, studied 80 limbs from cadavers donated by Australians of European ancestry.

The donors were between 51 and 101 years old when they died, meaning almost all had been born during the first half of the 20th century.

After recording how frequently they identified a substantial median artery capable of transporting a strong blood supply, the researchers compared their findings with data uncovered in a literature review. They allowed for counts that may have overstated how often the vessel occurred.

Their findings appeared in the Journal of Anatomy.

The artery's apparent presence in three times as many adults today as over a century ago is a striking result. It indicates that natural selection may be favouring people who retain this extra supply of blood.

"This increase could have resulted from mutations of genes involved in median artery development or health problems in mothers during pregnancy, or both actually," said Lucas.

A persistent median artery might be expected to provide long-lasting additional blood flow to nimble fingers or powerful forearms after birth. However, carrying one also raises the risk of carpal tunnel syndrome, an uncomfortable disorder that reduces the ability to use the hands.

Determining which factors are most important in selecting for a persistent median artery will need considerably more investigation.

What the rise in median arteries could mean

Whatever those influences prove to be, the research indicates that these vessels will probably continue becoming more frequent.

"If this trend continues, a majority of people will have median artery of the forearm by 2100," said Lucas.

This sharp increase in median arteries among adults resembles the return of the fabella, a bone in the knee that is likewise three times more common today than it was 100 years ago.

Though such differences may seem minor, small microevolutionary shifts can accumulate into the large-scale variations that eventually define a species.

Collectively, they also produce fresh pressures, potentially taking humans along new routes of health and disease that are currently difficult to envisage.

This research was published in the Journal of Anatomy.

An earlier version of this article was published in October 2020.