Re: AAT
Elaine Morgan (Elaine@desco.demon.co.uk)
Thu, 13 Jul 1995 10:32:32 GMT
Alex Duncan writes:
>A feature does not have to be an adaptation in order to exist.
In that case we may as well close down this newgroup and take up
knitting. Why are we naked? There doesn't have to be a reason. Why are
we bipedal? there doesn't have to be a reason. Why the big brain? there
doesn't have to be a reason...
I entirely agree that some of the features we now have are not
adaptations to our present mode of existence (like the appendix) but I
suggest they would not be there unless they had at some point been
adaptations to a previous mode of life led by our ancestors at some
point in time.
You say :"Is there a functional or adaptive reason why gibbons are
largely bipedal when on the ground? I've never heard one suggested".
You then go on to give a perfectly good one, which I believe to be
accurate.i.e. because their arms have grown too long for them to able to
walk efficiently on two legs. Why do you say that is not an adaptation?
What do you mean by adaptation? What I mean by it is a change in either
behaviour or physical structure in response to a change in the
realtionship between an animal and its environment. The gibbon responds
to the demands of brachiation by growing longer and longer arms. That
is an adaptation. It then has to respond to the vicissitudes of
occasional groundwalking by abandoning the quadrupedal gait which its
ancestors, however distant, at one time employed. That is another
adaptation.
What would happen if gibbons found themselves in a treeless habitat is
a very good question. I suspect they are so overspecialised for
arborealism that they would become extinct. It is just conceivable that
they would instead become better at bipedalism and their arms would
become shorter and voila! a biped!
Now that is an ingenious scenario. But do you, or does anyone, really
believe that it throws any light on human bipedalism? Do you think our
ancestors bcame more over specialised for arborealism than the gorillas
and chimps so that they were driven down this path? Everything I have
read about primate evolution has stressed that the whole secret of
human evolution is that we remained the most unspecialised of the apes,
and thus were able to adapt more quickly to the vicissitues of change.
You say: "I don't recall anyone even suggesting that human running
capability was all that important, " In that case remember that you
read it here first, because I am suggesting it now, Actually Carrier
wrote a paper on it, the one I quoted from. And maybe the !Kung can
walk an armadillo to death, but I can't see Homo erectus walking a
zebra to death, nor walking away from a leopard or a lion.
Elaine Morgan
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