Re: AAH update (was: Bipe
Alex Duncan (aduncan@mail.utexas.edu)
6 Jul 1995 20:16:25 GMT
In article <3t7fjl$8sc@newsbf02.news.aol.com> Pat Dooley,
patdooley@aol.com writes:
>Hominids and modern chimpanzees share a common ancestor from about
>7.5 mya. Gorillas branched off about 2 million years earlier. What you are
>claiming for the ancestral hominds must also be true for chimpanzees and
>gorillas; that their immediate ancestors were as arboreal as modern
>gibbons.
First off, while there are certainly data that support that we and chimps
are each other's closest relatives, the issue is by no means resolved.
Neither are the dates.
Second, why must my claim for pre-hominids also be true for pre-gorillas
and pre-chimps? You seem to be making the assumption that the divergence
event that resulted in hominids also resulted in bipedalism. While this
assumption is widely held, even among paleoanthropologists, it is not
supported by a single scrap of evidence.
<stuff deleted>
> The initial evolutionary imperative would have been to
>minimise exposure on the ground rather than maximise energy efficiency.
>Evolving a whole new mode of locomotion doesn't satisfy that imperative.
>Walking fully upright rather than staying low doesn't satisfy that
>imperative
>either (those who claim that bipedalism makes it easier to spot predators
>should realise that supposed advantage cuts both ways - it also makes it
>much easier to be seen by predators).
Who said anything about evolving a whole new mode of locomotion? I'm
suggesting a gibbon-like ancestor for hominids. Gibbons are so
specialized for arboreality that they are usually bipedal when walking on
the ground. I'm suggesting a similar anatomy for pre-australopiths.
Hominid bipedalism would have involved an elaboration of an already
existing mode of locomotion, rather than the acquisition of a new means
of locomotion.
<stuff deleted>
>It is hard to see how 100% bipedalism, reduced arboreal skills,
>and increased visibility would prove a better strategy in the short-run.
Again, who said 100% bipedalism, or reduced arboreal skills? The
australopith postcranial skeleton indicates substantial arboreal skills.
>>I can think of no oddities that wading and swimming fit in with. Please
>>enlighten me. I'm not suggesting that early hominids didn't occasionally
>>enter the water, but to postulate an aquatic existence as the precursor
>>to all that is "hominid" flies in the face of all of the evidence I'm
>>aware of.
>
>It seems odd to me that humans have aquatic capabilities far greater
>than those of any other apes or primates. Evolution doesn't fill your
>kitbag with capabilities you never use nor ever used. In particular,
>it doesn't equip you with conscious control over your breathing, if
>you don't need it. It doesn't heighten your diving reflexes if you
>don't need it. It doesn't give you a layer of subcutaneous fat if you
>don't need it. It doesn't give you the ability to dive to 250 feet if you
>never dive. It doesn't add salt to your tears and sweat if you never
>needed to exude it. Yet, evolution bestowed all those useless gifts
>on homo sapiens, and all in the last 7.5 million years. Despite having
>98% of their DNA in common with us, chimpanzees share none of those
>features with us. They also missed out on 100% bipedality,
>eccrine sweating, and loss of most of their body hair.
It seems odd to me that we play the piano so much better than the other
apes, and that we manufacture computers, etc. Clearly, there must have
been some advantage to these capabilities among our ancestors (After all,
"music hath charms..."). You are making the mistaken assumption that
every thing we are capable of must be an adaptation. This is ridiculous.
I strongly suggest reading some Gould on this subject (see the article
about the "Panglossian paradigm").
And now, a point by point refutation:
1) The best explanation I've seen for conscious control over breathing
is that it is required for language. There is evidence that human spoken
language skills HAD NOT evolved by the time of KNM-WT 15000. I hope
you're not going to suggest that this individual PRECEEDED our move into
an aquatic environment. Finally, are you quite positive that other
primates aren't capable of conscious control over breathing? Remember,
absence of evidence is not evidence of absence.
2) Diving reflex. OK, I admit, I don't even know what this is. Please
inform me.
3) I assume you think a layer of subcutaneous fat would be advantageous
to living in an aquatic environment. You're right, of course, but it
would only be really advantageous if it were evenly distributed over the
entire body, as is the case for cetaceans. Human fat distribution is far
too uneven to provide a good insulative barrier. And why is fat
distributed differently in males and females? -- and indeed, between
different modern human populations? A more plausible explanation is that
human fat distribution is sexually selected for. We would likely suffer
the greatest heat loss from our distal extremities in an aquatic
environment, and yet fat is most thickly distributed over the proximal
extremities and torso. And finally -- are you sure other primates don't
have subcutaneous fat? I've dissected other primates, and I can state
positively that they do.
4) Dive to 250 feet? Again, I don't have an explanation. But I must
restate a basic tenet of biology that you seem to have never learned: the
fact that we are capable of doing something DOES NOT mean that it is an
adaptation. Again, see Gould.
5) You probably ought to check your references for salt in the tears and
sweat. There has been, and still is, a great tendency for us to assume
that everything we humans do is unique. The more we learn about other
primates, the more we find that this is not true.
Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086
512-471-4206
aduncan@mail.utexas.edu
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