An extra artery is part of that exercise of imagining what our species might look like in the distant future, which often invites wild speculation about distinctive features such as height, brain size, and skin complexion. Yet the subtle changes in our anatomy today demonstrate just how unpredictable evolution can be.
Take something as mundane as an extra blood vessel in our arms, which according to current trends might be commonplace within a few generations. According to researchers from Flinders University and the University of Adelaide in Australia, an artery that runs temporarily down the center of our forearms while still in the womb doesn’t disappear as often as it once did.
This means there are more adults than ever before, with what amounts to being an extra channel of vascular tissue running under the wrist. “Since the 18th century, anatomists have studied the prevalence of this artery in adults and our study shows that it is clearly increasing”, Flinders University anatomist Teghan Lucas said in 2020.
“The prevalence was about 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”.
The median artery forms quite early in development in all humans, carrying blood to the center of our arms to feed our growing hands. At about eight weeks, it usually regresses, leaving the task to two other vessels: the radial (which we can feel when we take a person’s pulse) and the ulnar arteries.
Anatomists have long known that this wilting of the extra median artery is no guarantee. In some cases, it freezes for another month or so. Sometimes we are born still pumping, feeding only the forearm or, in some cases, even the hand.
To compare the prevalence of this extra persistent artery, Lucas and colleagues Maciej Henneberg and Jaliya Kumaratilake of the University of Adelaide they examined 80 cadaver limbs, all donated by Australians of European descent.
Donors went from 51 to 101 as they passed, which means that almost all of them were born in the first half of the 20th century. Noting how often they found a large median artery capable of carrying a good supply of blood, the research team compared the figures with records from a literature search, taking into account the counts that could over-represent the picture of the situation to date. Their results were published in 2020 in the Journal of Anatomy.