A study out of Australia suggests that textbooks on human anatomy will have to reflect a fundamental change by the end of this century: Most of us will have three blood vessels running down our arm, instead of two. Researchers studying adult cadavers report a sharp increase in this third artery, reports Science Alert. The extra one runs down the middle of the arm, between the better-known radial and ulnar arteries. We actually all have this artery in the womb, the better to supply blood to growing hands, per the BBC. But as the researchers explain in the Journal of Anatomy, it usually vanishes during gestation and is long gone by the time of birth. At least, that's the way things used to be.
"Since the 18th century, anatomists have been studying the prevalence of this artery in adults and our study shows it's clearly increasing," says Teghan Lucas of Flinders University. The researchers say the artery stuck around in about 10% of adults in the mid-1880s, but that figure has since increased to 30%. "That's a significant increase in a fairly short period of time, when it comes to evolution," says Lucas. At this rate, most people will have the third artery by 2100, notes a post at SlashGear. The good news is that the extra blood supply would theoretically lead to stronger forearms and more nimble fingers, notes Science Alert. But there's a notable downside as well: Those with the extra artery appear to be more at risk for carpal tunnel syndrome. (An extra knee bone is showing up in humans, too.)