Monday, October 28, 2013

Scars of human evolution, part deux

Physical anthropologist Wilton Krogman wrote a classic article in 1951 for Scientific American called “The Scars of Human Evolution,” back when you could actually make sense of the stuff in Scientific American.  It addressed half of human evolution: bipedalism.

Hard as it may be to believe, the evolution of our other most basic adaptation is under-theorized.  I refer to our symbolic mode of communication, language.   Language, which is coterminous with symbolic thought – if you can think it, you can say it – was an unusual and apparently very good evolutionary innovation.  It was so good, indeed, that it created physical problems that the human body had to solve secondarily in order to make it work, and to some extent never did solve fully.

First, it expanded our heads.  Symbolic communication requires a big brain, as well as an extended period of immaturity in order to learn how to do it properly.  It is so difficult that we hardly even appreciate how difficult it is.  From the bottom up, we learn what sounds make sense.  Are “s” and “sh” variants of the same sound, or different sounds?  What about “l” and r”? Or “r” and “rr”?  Or the “Ch” in “Chanukah” or the “Zs” in “Zsa-Zsa”?  Are they their own sounds, or some weird variants of “Hanukah” and “Cha-Cha”?  We also learn how to combine those sounds, and use them to refer to objects, or acts, or states.  We could call those combinations of sounds “lexemes,” but for the sake of simplicity, let’s just call them “words”.  We also learn how to combine those words in meaningful ways – to state, inquire, praise, predict, recall, using any of the myriad grammatical forms at our disposal.  And on top of all that, we learn intonation, sarcasm, and bodily gestures to go along with the rules of sounds, their correspondences, and combinations.  The price for all of this was a brain inside a baby’s skull that hardly fits through the birth canal.  And the solution to that problem was to make birthing social.  Where an ape squats and delivers, a human almost always needs to have someone else around.

Second, language reorganized our throats.  To make all of those sounds, our larynx is positioned lower down in the throat than it is in apes and babies, who cannot make those sounds.  The price we pay is that the passage of air into our lungs and of food into our bellies now criss-cross, which they do not in apes, which means that we can choke on our food far more readily than a chimpanzee can.  The solution is: Don’t eat so fast, and try not to breathe while you are swallowing.

Third, language not only worked over our throats and brains, but our teeth as well.  Catarrhine primates often have large, sexually dimorphic canine teeth, which they use as social threats and in the occasional actual fight.  Classic sexual selection theory holds that in species in which males actively compete for mates, they do so using their canine teeth.   In species where there is less competition for mates, because males and females pair off, the males and females have equal-sized canine teeth, as in the monogamous gibbons.  This is often invoked as evidence that sexual selection has been reduced in the human species, which may well be true.  The problem is that those gibbon canines, which are non-dimorphic, are also actually quite large.  Ours are non-dimorphic, but small.  Why?  Because it is really hard to speak intelligibly through large, interlocking canine teeth.  Ask any vampire (and see if you can understand their response).  The price for the reduction of the canine teeth was that our canine teeth are not going to intimidate other members of our own species, nor defend us against member of other species.  Good thing we started using tools.

And fourth, in addition to reshaping our brains, throats, and teeth, language also reshaped our tongue.   To make the sounds we do, our tongue became more muscular, rounded,  and enervated than an ape’s tongue.   For this the cost was quite severe.  An ape dissipates heat, as most mammals do, by panting.  But to use your tongue primarily for talking, it will require that your body produce another way of dissipating heat.  Our ancestors did that by loading up our skin with sweat glands, for evaporative cooling.   But evaporative cooling only works efficiently with bare skin; so our body hair had to get shorter and wispier than that of an ape. 

Walking and talking are what are most fundamentally human, and it is quite extraordinary that they rhyme. So the next time you choke, sweat, scream for an epidural, or reach for a weapon to protect yourself because you lack confidence in your teeth to protect you, reflect on the fact that our body parts are interconnected, and that language was such a good way to communicate that it screwed you up in so many other ways.   I didn’t mention it, but there is a fifth price as well for language:  having to listen to people who don’t know when to shut the fuck up.