My girlfriend is an animal lover and has had a wide variety of pets. She noticed this commonality - none of them had belly-buttons, so asked me why. I am hoping LastWord can provide an answer - I can't.

JimL remarked:"This mystery leaves me scratching my head." A commonplace? But how innate is the head-scratching gesture? I had always regarded scratching one's head in puzzlement as an affectation, something one read of, or saw in a film. Then I read of a cultural gap between two businessmen, one Japanese and one American. The American had scratched his head in puzzlement. The Japanese later asked why the American had been angry. Head-scratching in Japan apparently is a gesture of anger, in particular, the gesture of raising the elbow at right angles and scratching the middle of the scalp with all four fingers. This too seemed artificial to me, until years later I repeatedly found myself spontaneously scratching my head in annoyance in just that way when frustrated by a fast computer game.

Does this match the experience of others? Does anyone know of similar gestures in other Primates? Do other primates recognise it in humans? Is it associated with any particular types of stress or frustration?

Any remarks welcome, unless they involve parasites...

I read somewhere recently that humans had all but finished evolving over the natural course of time. Whether that may be disputed or not, what I'm wondering is this: in some fifteen million years (which, according to David Attenborough's Life On Earth, is the amount of time it took us to make the transition) will primates evolve to be like us?