Nostrils: a definition
Elaine Morgan (Elaine@desco.demon.co.uk)
Sun, 23 Jul 1995 11:55:24 GMT
Just on a point of information: A misunderstanding has arisen
because of a stupidly simplistic term I employed describing human
nostrils as "pointing downwards". I have been told that in
catarrhines all nostrils point downward. A lot of truth in that. If
you look at a foraging gelada, the nostrils point straight to mother
earth.
So are we all the same? No. The air coming out of the gelada's
nose when it exhales is travelling on a line parallel to the line of
its jaws. The air coming out of our nostrils when we exhale is
travelling on a line almost at right angles to our jaws. The phenomenon
I was trying to explain is the direction down towards the chin (except
that we're the only primate that possesses a chin) rather than down
towards the ground.
This trajectory also involves an awkward detour- the air has to go up,
and over the top, and down. I believe I quoted this as one of the
"scars"of evolution, an unwanted consequence of the aquatic phase.
If I were a follower
of SMT (savannah-mosaic theory) I would say boo-sucks to Elaine Morgan.
That curve is the consequence of bipedalism, and would be there whatever
the cause of bipedlaism might be. It is the same kind of development as
the course of the vagina - straight in quadrupeds, awkwardly curved in
the only biped.
EM would reply:Up to a point. But if it was due only to bipedalism the
top end of the respiratory canal would travel up from the lungs, and
turn through say 90% to face outwards - i.e. parallel to the surface of
the earth, as it is in most primates when their torsos are erect. (That
applies to
platyrrhines as well as catarrhines.) .They don't feel the need to go
further and make a positive downturn (let's call it
dorsally-directed) and cover the whole thing with a lid, buttressed
with cartilage, and flanked by fleshy and
muscular nostrils flaps. The worst that can happen to them is that in
a very severe rainstorm some rain might get in and make them
sneeze.If they dived into water from a few hundred feet up as proboscis
monkeys do they would need a bit more protection. And the proboscis has
got it.
Elaine Morgan.
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