Imagining what our species might look like in the distant future often invites wild speculation about distinctive features such as height, brain size, and skin complexion. Yet the subtle changes in our anatomy today demonstrate how unpredictable evolution can be.
Take something as mundane as an extra blood vessel in our arms, which following current trends could be commonplace within a few generations.
Researchers from Flinders University and the University of Adelaide in Australia have noticed that an artery that temporarily runs down the center of our forearms while still in the womb doesn’t disappear as often as it did before.
This means that there are more adults than ever running around with what amounts to being an extra channel of vascular tissue running under the wrist.
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“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 of evolution. “
The median artery forms quite early in development in all humans, carrying blood down the center of our arms to feed our growing hands.
At about 8 weeks, it usually regresses, leaving the task to two other vessels: the radial (which we can feel when we detect a person’s pulse) and the ulnar arteries.
Anatomists have long known that this wilting of the median artery is no guarantee. In some cases, it remains pending for another month or so.
Sometimes we are born with it continuing to pump away, feeding only the forearm or in some cases even the hand.
To compare the prevalence of this persistent blood channel, Lucas and colleagues Maciej Henneberg and Jaliya Kumaratilake of the University of Adelaide examined 80 corpse limbs, all donated by Australians of European descent.
Donors went from 51 to 101 as they passed, meaning they were almost all 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, they compared the figures with records from a literature search, taking into account the counts that might over-represent the vessel’s appearance.
The fact that the artery appears to be three times more common in adults today than it was more than a century ago is a surprising finding that suggests that natural selection is favoring those who cling to this extra bit of blood.
“This increase could be the result of mutations in genes involved in median artery development or health problems in mothers during pregnancy, or both actually,” says Lucas.
We might imagine that having a persistent median artery could give skillful fingers or strong forearms a reliable push of blood long after we are born. However, having one also puts us at greater risk for carpal tunnel syndrome, an uncomfortable condition that makes us less able to use our hands.
Identifying the types of factors that play an important role in the selection processes of a persistent median artery will require much more investigation.
Whatever they are, we will likely continue to see more of these ships in the coming years.
“If this trend continues, most people will have a median forearm artery by 2100,” says Lucas.
This rapid rise in the median artery in adults is no different from the reappearance of a knee bone called fabella, which is also three times more common today than it was a century ago.
However small these differences are, small micro-evolutionary changes add up to large-scale variations that come to define a species.
Together they create new pressures themselves, putting us on new pathways of health and disease that at this time we may find it difficult to imagine today.
This research was published in Journal of Anatomy.