1. 8 of the 44 presidents have been left-handed. Almost double the incidence of left-handedness in the general population.
2. Favoring a particular hand is unique to humans. Neither chimps nor gorillas favor a hand.
3. The incidence of left-handedness seems to be constant throughout history.
Some of the oldest evidence of left-handedness comes from Kenya, where of a 500,000 year-old cache of 54 stone tools made by one of our pre-human ancestors, six (or about 11 percent) were chipped using the left hand. Similarly, Neanderthals working with meat and stone tools more than 150,000 years ago left marks on their teeth at left and right angles – indicating opposite hand use – in almost perfect proportion with today’s 9:1 ratio.
4. Whereas language is usually processed in the left-hemisphere for right-handed people and in the right-hemisphere for left-handed people, left-handed people also process some language in the left-hemisphere — providing for the possibility that some sort of evolutionary advantage exists for lefties.