More humans are keeping an extra artery in the forearm

Researchers at the University of Adelaide and the University of New South Wales dissected the forearms of Australian cadavers and compared how often a vessel called the median artery appeared against records going back more than a century.

The median artery normally shrinks away before birth, leaving the radial and ulnar arteries to supply the hand. It persisted in about 10 percent of adults born in the mid-1880s. In cadavers who died in 2015 and 2016, the team found it in 33.3 percent of forearms, and their model put the current population rate near 35 percent.

At that pace, the researchers projected most people could be born with the extra artery within about eighty years, fast enough to count as measurable human microevolution rather than ancient history. Why the trait is spreading is not settled; the team suggested shifts in maternal health or related genes as possible drivers, an idea not yet tested directly.

An extra artery, spreading through the population in decades.