The evidence of the hands.

A sphinx has the body of a lion and the face of a man. Why is this no good? Simple: Because in order to have a face, you need a pair of hands. Paws won't do. Animals with paws must have big, furry, jutting muzzles, which rule out a face. They need muzzles for biting, to defend themselves, and to attack prey, whereas possessors of hands can fashion and chuck a spear or throw a punch. Animals need muzzles to carry things and to gnaw on their food, whereas possessors of hands can make a fire to tenderize their viands. And in order to have growing scalp hair--as humans uniquely do--you need to have hands to cut it, lest it get so long that it jeopardizes your survival. So faces presuppose hands. Sphinxes and centaurs and other countenanced but handless creatures not only do not exist, they could not exist.

That exciting aperçu occurred to me in the course of reading The Face and The Hand, two books that otherwise brought me unremitting boredom. Well, almost unremitting. The Face made me cringe a lot. Its author, Daniel McNeill, won a science-writing prize a few years ago, and this seems to have gone to his head. His prose oozes a kind of rotten poetry, and no observation is too banal to be left unspoken.

Take McNeill's extended meditation on kissing--please:

A kiss can pour love from lips to lips, two receptacles filling each other. ... The lovers' tongues caress each other, dance about the teeth and inner cheeks, bathe in each other's oral fluids. ... Long, luxurious smooches can end in a sound like planes of glass rubbing, or even in a cheep. ... Family members and relatives commonly kiss. ... The kiss is often a gesture of greeting.

I didn't know all that, did you?

As for The Hand, by California neurologist Frank R. Wilson, even the epigraphs are tedious. One of them reads:

The true relevance of lateralization of function will be ascertained only by careful research that acknowledges that aspects of this function develop throughout the life span, beginning at birth, if not before.

Try as I might, I can detect no lambent flicker of humor in these pages.

There are some scattered interesting bits in both The Face and The Hand, however. Someone ought to extract and put them in a concise form, to save people the trouble of reading the books. In fact, that's what I'll do.

L et's begin with the chin. It is a singularly human facial feature, one that even the Neanderthals lacked. The chin seems to have emerged around 130,000 years ago. Why? Scientists have no idea. What they do know, however, is that men's chins have been getting larger over the last 200 generations. They have a theory for this. The male chin grows during puberty in response to testosterone. Testosterone weakens the immune system. So, paradoxically, a big chin on a healthy man is an advertisement of robustness: It means that, despite an excess of testosterone, his immune system is still powerful enough to fight off disease. Therefore women should fancy a big chin on a mate, and the trait is sexually selected. (Insert Jay Leno joke here.) I do not know whether this theory is true. I do know that in good society, chins are very important. Style largely depends on the way the chin is worn. They are worn very high at present.