Re: AAH update (was: Bipe
Pat Dooley (firstname.lastname@example.org)
5 Jul 1995 09:22:56 -0400
email@example.com (J. Moore) wrote :
Pa> The recognition that humans probably didn't evolve bipedalism on the
>Pa> savannah is relatively recent.
>No, the problem is that you equate "savannah" with "treeless, waterless
>place". "Relatively recent" that we figured that hominids didn't evolve
>in a sort of arid desert? Well, we're talking at least 20-30 years;
>I suppose that *is* recent...in geological time.
I have never claimed the savannah was a treeless, waterless desert.
My understanding is that the savannah is a relatively open environment;
that trees are in isolated clumps rather than in a continous forest; that
seasons can be divided into a wet and dry season rather than the four
seasons of temperate climates; that the days in the dry season can
be extremely hot; the nights quite chilly etc. etc.
>Pa> If bipedalism is such a great adaptation, why is it restricted to
>Pa> just one primate species. I know this comment will set off Nicholls
>Pa> in another long-winded exposition about how human bipedalism is
>Pa> just a slight exaggeration of an existing ape tendency towards
>I've never seen him make any comment which said that apes have a
>"tendency towards bipedalism", only that bipedalism is one mode
>of locomotion among many for *all* apes and monkeys. Bipedalism is
>*not* "restricted to just one primate species". This is a fact,
>and why this fact should upset you so is beyond me.
In that case, please advise which other primates have gone through the
major skeletal changes that constrain them to 100% bipedalism.
(Gibbons don't work; they are virtually 100% arboreal and so far off
the human line as to be irrelevant to the discussion).
<< deletions >>
>Thank you for clarifying your previously-incomprehensible thought; this
>shows that your problem in understanding the role of display in
>bipedalism is two-fold: (1) you're looking for a single *cause*, rather
>than a suite of advantages; and (2) you apparently don't understand that
>male humans and female humans are the same species, and that therefore
>the changes in basic structure of one are very likely to be changes to
I don't care whether we have one evolutionary factor propelling the
evolution of 100% bipedalism or a number of interacting factors. What I
would want to see is an explanation that deals with the reasons why
Australopithecenes is bipedal and all its primate relatives in similar
environments stayed quadrupedal. To put it another way, the human
skeleton is radically different to that of a gorilla or chimpanzee or
bonobo, and those differences are all a consequence of the fact that
humans are truly bipedal. The other guys show no such shift from
the original ape stock of 7 mya. What forced Australopithecenes
to go bipedal.
Anyone with the faintest knowledge of zoology can give you
examples of sexual dimorphism. Gorillas are the closest example.
<< More deletions>>
>So you're saying that we would have to be somewhat like our closest
>relatives. I am astonished that you find it so difficult to believe
>that we were undoubtedly like our closest relatives, as in fact we still
When I see a sweating,hairless chimpanzee walking exclusively on two
legs, that can, when so conditioned, dive regularly to depths of 80 feet,
for 4 or more hours per day, I might believe that our closest DNA
are as like us as the DNA evidence would suggest.
>Pa> It's obvious that the last ape to reach
>Pa> the safety of a tree would be
>Pa> the first one eaten.
>See how chimps take care of the problem in similar environments.
You miss the point. I was referring to species, and to the old joke
about the two safari hunters who, when they were out of ammunition,
were confonted by a rather hungry lion. Hunter #1 says, "Let's run".
#2 says, "Why? The lion can run faster than either of us.". #1 replies,
"Yes, but I can run faster than you." The tottering ape going through
the transition to exclusive bipedalism would always be #2 - what
I'd call a "disadvantageous intermediate".
>You could get yourself a library card and use it, or just read what's
>been available online here. David Burkhead did one or the other,
>enabling him to point out to you:
<< yet more nonense about sharks deleted>>
Shark attacks on humans are so rare they are ranked with lightening
If you are unlucky enough to get struck by one, you probably won't
see it coming and will have little time left to you to reflect on the fact
that of all the millions of people who swim and dive in the ocean, you
were the poor sucker that drew the short straw, even after surviving the
rather more hazardous drive to the beach.
The point remains; there is no evidence that sharks would have been
a major predator of semi-bipedal apes frolicking in the shallows.
>PD> >That option is not available to an ape trying to outrun a leopard.
>DB> Still clinging to that "treeless, waterless savanna"? Fleeing
>DB> the trees is comparable to fleeing for the shallows--and the race is
>DB> _much_ more even. Go look at my numbers again. The fastest human
>DB> swimmer there ever was is less than half as fast, compared to typical
>DB> swimming predators, as an average runner against the fastest land
If a semi-bipedal ape being pursued by a leopard tried to escape up a
I suspect it wouldn't have a hope in hades. If a land mammal makes it to
shore when pursued by a crocodile, it is generally safe. (Just saw nature
program showing hapless zebras stupidly trying to cross crocodile
infested waters despite ample evidence that preceding zebras were
having a little difficult with the crocs. Those that got ashore were not
pursued, although some lions were waiting to catch the injured).
>DB> The idea that an aquatic environment is, somehow, safer from
>DB> predators than a savannah environment (not the mythical "treeless,
>DB> waterless savannah" but a real one) is patently false.
>DB> David L. Burkhead
On statistical grounds alone we can dismiss the shark threat. Whether or
not apes marooned on Danakil island had anything to fear from mythical
African Salt Water crocodiles remains to be seen.
>Chimps modify their tools. Chimps re-use tools. Maybe *your* ancestors
>weren't as smart as chimps, but *mine* were. Tools "in the fossil
>record" (actually stone tools are not "fossils", of course) are, so far,
>stone tools, and our ability to recognise non-cutting stone tools, or
>wooden tools, grasses, etc., at that time-distance is at present
It might distress you to know this, but it is easily proven by simple
mathematics that every human living today has a common ancestor.
Since you claim your ancestors are not mine, I can only assume you
are claiming not to be human.
Recognizable human tools date from around 2.6 mya, about 1.4 million years
after the emergence of bipedalism. The only point I was making is that it
difficult to claim humans evolved bipedalism to free two hands to carry
tools, when there is no sign that they were significant tool users 4 mya.
You mention chimpanzees; they were evolving alonside humans, for the
same time period. They make rudimentary use of tools now. How good were
their ancestors 4 million years ago?
<< yet more deletions>>
>Pa> You might try reading Richard Dawkins "The Blind Watchmaker"
>Pa> before making such a statement. It is a simple principle of
>Pa> evolution that its progress
>Pa> is not directed by the desirability of particular outcomes, but
>Pa> by the accumulation of small changes that are not, in themselves,
>Not *critically* disadvantageous; in other words, not so horribly wrong
>that the creature couldn't survive long enough to raise a few kids to
>the age where they raise some kids of their own.
Evolution proceeds randomly and over a long time scale. The slightest
mutation that enhances survival will become the norm; the disadvantageous
mutations, no matter how slight, die out, in the long run.
Yeah, some of the disadvantageous forms will survive and breed
but, over time, they will become an increasingly smaller fraction of the
At some point, that fraction becomes zero.
The point is that the slightest disadvantage in the short term translates
extinction in the long run.
You obviously don't understand that process or you would not have used
the phrase "critically disadvantageous" and gone on about surving "long
to raise a few kids". Since your understanding of evolution is so limited,
is obviously pointless to discuss the problem of disadvantageous
>Pa> You have to demonstrate that each intermediate form between the
>Pa> gait of the human/chimpanzee common ancestor, and the bipedal
>Pa> gait of Australopithicenes, was advantageous.
>No, you don't show that it was *advantageous*, but rather that it *was
>not* horribly disadvantageous.
Oh dear. I see you believe that evolution will proceed so long as the
adaptations are not "horribly disadvantageous". That's about on a par
>You know, like standing around in crocodile-infested water
>4-8 hours a day would be.
Now, that's a great example of a strawman argument for you.