Chirality in humans: Why the 1:10 left-to-right ratio?
Interesting article by Hannah Fry at the BBC. From that article:
. . . Chimpanzees tend to choose a favourite hand for different tasks.
Take termite fishing. After selecting the perfect stick, the chimp pokes it into the termite mound, their sense of touch providing a host of information about how deep, wide and full of tasty termites their house may be. Then they’ll gently pull the stick out to reveal their prey, the termites’ jaws clamping down hard on the foreign invader. Unbeknown to them, they are about to get chomped by a hungry chimp. By specialising with one hand, chimps become more dexterous, and more termites bite the dust. (And, more to the point, the chimp has a more ample snack. The chimp is trying to eat, not to exterminate termites. – LG]
But when primatologists study chimpanzees in the wild, their patterns of handedness look very different to ours. For each task around 50% are right-handed, and 50% left. So where in our evolutionary tree does this 1 in 10 ratio emerge?
An important clue comes from Neanderthals’ teeth. Neanderthals, it turns out, were clever, but clumsy. Our ancestors used their teeth to anchor slabs of meat, whilst they held a knife in their dominant hand to carve it up. Now and again, they would scratch their teeth. The distinctive pattern of grooves in their front incisors reveals which hand must have been holding the food, and which was grasping the knife. Incredibly, when you compare the number of left- and right-handed Neanderthals, this same ratio of 1 in 10 left-handers that we see today pops out. . .