I don't know if you'll find this interesting or not... but I certainly did!
When a baby is growing in the womb they have three major arteries in their forearms to help supply blood to their developing hands.
Once this is done the third vessel that runs down the middle of the forearm withers away and we are left with the two major arteries like most adults.
We say most since not all people have this artery disappear... and they have an extra blood vessel in their arms.
NOW, here's the weird part... roughly three times as many men and women have this happen now than back in the 1800's and scientists are at a loss to figure out why.
One of the main conjectures for this change might be because humans are now using their hands for more intricate reasons like writing... and even typing... instead of just throwing a spear, or swinging an axe, or shoveling a ditch!
Makes sense to me!
The way I see it anyway!
