Wednesday, September 13, 2006

Distinctively Human

I am studying a fabulous book, Trail Guide to the Body by Andrew Biel and Robin Dorn. It will be my kinesiology text this winter. I'm busily memorizing muscles and where they attach to bones, their "origins" and "insertions," as they're called. As always a new nomenclature has its delights and its mysteries -- the selection of which end to call the "origin," supposedly the end that attaches to the bone that holds more or less still, perplexes me sometimes. Obviously both bones move, and which will hold more still depends on what you're doing. And instead of calling the attachment at the other end the "destination," they use this queer word "insertion," which makes it sound as though the muscles thread into holes in the bones. Which they don't.

The Latinate and Greekish words don't bother me; it's nice to have a standard terminology, so that, theoretically, American and Latvian and Malay and Zambian bodyworkers could all have the same names for these things. But this advantage is lessened by the outlandish English pronunciations of the terms. Stresses fall apparently randomly, c's are softened into s's according to whim, short vowels are made long and long made short. It's neither Latin nor Greek nor English, but a strange thing all its own.

But I digress. The book is wonderful, with terrific illustrations, written in lively, clear prose. And it's playful. Among the illustrations of the sternocleidomastoid (SCM) muscles of the neck, the prominent ropes that run down from the ear to the sternum, is an old engraving of Byron with his head torqued sideways, with the SCM highlighted in red. The legend beneath runs: "Lord Byron shows off his SCM."

Biel delights in pointing out what is distinctively human. He notes that the commonly-held notion that an opposable thumb is uniquely human is quite false -- many primates have an opposable thumb. Ours is just longer and more heavily muscled. But there are many distinctively human traits. One is the copious fatty tissue of our buttocks. No one really knows what it's there for. Another is that we, alone among primates, can't grasp objects with our big toes.

When I was studying science in school, long ago, we were told that our large brains and opposable thumbs were what set us apart from other animals: we were (so ran the obvious implication) uniquely gifted in thinking and manipulation. But this was a selective filtering of traits, and not even a correct one. You come away with a different picture if you pick other traits -- we're the primates with fat asses, and the ones who can't keep a grip with our feet. No wonder we're always trying to "save" labor (by making someone or something else do it). And no wonder we lose touch so easily with the ground.

Addendum, December 2006

"Make it as simple as possible," Einstein famously said, "but no simpler." After a couple months of studying with Biel & Dorn's book, I'm a little disenchanted. Every once in a while Biel tries to make things simpler than they can be. In a couple cases this leads him to say something that is clear and easy to remember, but which is unfortunately not true. Hopefully he'll fix these things in the next edition. It's still a great book for hands-on learning your way about the body, and I'd still recommend it for that: but if Netter's atlas says something different, listen to Netter. The extensor pollicis brevis does not extend the interphalangeal joint of the thumb -- it doesn't even cross that joint. And the extensor carpi radialis brevis inserts at the lateral epicondyle, not the lateral supracondylar ridge. These are inaccuracies of only an inch or two. But an anatomy text, even a friendly informal one, should not say things that aren't true.

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