Re: AAH update (was: Bipedalism and other factors and AAT)
Pat Dooley (email@example.com)
10 Jul 1995 00:01:17 -0400
Re: AAH update (was: Bipedalism and other factors and AAT)
Alex Duncan <firstname.lastname@example.org> writes:
>>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".
>By the same logic, chimps can be called disadvantageous intermediates.
I don't follow your logic. Chimps evolved. Disadvantageous intermediates
Up until the introduction of the gibbon like precursor, the debate had
on a quadrupedal ape evolving into a bipedal ape. In that context, one has
ask about the intermediate forms between the quadrupedal knuckle walker
and our bipedal ancestor.
Now we are being told that bipedalism resulted from the movement of
an arboreal ape directly to a terrestrial environment. That may well be
But the scenario painted so far has a gibbon like ape of about gibbon
size making the transition. That seems to me to be a very vulnerable
creature to go prancing about between clumps of forest. The predators
of 7.5 mybp were not notably less ferocious nor less effective than
Perhaps it might be better to ignore human evolution for a while and
focus on chimpanzee evolution. When did knuckle walking evolve?
What does the fossil record tell us about chimpanzee evolution?
Was it gradual or were there periods of rapid evolution? Does anyone
out there know anything about chimpanzee evolution?
>After all, they are by no means the most capable or efficient quadrupeds
>in the forest. All terrestrial African carnivores that I can think of
>can outrun a chimp. Its a wonder they've survived as long as they have
>(sarcasm -- for those of you who don't notice).
They did survive, so we don't have to speculate on how that happened.
Your sarcasm does raise an interesting issue, though. Ignoring the
special case of humans, apes have been relatively less successful than
monkeys over the last 15 million years. The number of species has
declined drastically, whereas monkeys have proliferated. In the time
scale of evolution, it might prove that you spoke too soon when
claiming success for chimpanzees.
> I can imagine some day in the future a more intelligent chimp
>might evolve, that might have a more efficient mode of quadrupedalism,
>and they'll be having these same kinds of arguments. The ignorant among
>them will suggest that their ancestors couldn't possibly have functioned
>in a forest/mosaic environment as largely terrestrial quadrupeds, because
>they clearly weren't as good at it as the other animals. They will claim
>that a model of chimp evolution that suggests terrestrial quadrupedalism
>combined with arboreal skills couldn't work, because the animal would
>have been a "disadvantageous intermediate". They will invent ridiculous
>stories to explain aspects of ancestral anatomy that don't seem (to them)
>to make sense, and they will adopt dogmatic positions that aren't
>supported by comparative anatomy or by examination of living animals.
Cute. But if your future chimp is 100% bipedal she would clearly be
to ask how the ancestral chimp went from quadrupedalism to bipedalism
without disadvantageous intermediates; i.e. forms that were less efficient
quadrupeds because of their bipedal tendencies, but were not yet efficient
bipeds; what I call the tottering ape problem.
Take the example of flight. So far as I know, flying animals, be they
or mammals, evolved from arboreal ancestors. Even today, we can see
intermediate examples such as the flying squirrel, and its cousin by
convergent evolution, the marsupial sugar glider. Clearly, the
forms aren't disadvantageous. Every slight improvement in gliding ability
is better than the slight loss in arboreal mobility.
Whenever somebody proposes a scenario for the evolution of bipedalism,
I like to see if it provides an advantage to the organism at each stage,
in the proposed environment.
If it can't satisfy that test, then I don't believe it could have evolved
>They will, in fact, ignore any information that doesn't support their
>"hypothesis", and cite authorities who don't know any more than they do
>to make their points.
The AAT supporters have clearly had to modify their position as new
evidence comes to light. The orthodox position has had to make even
greater modifications, particularly since the discovery of Lucy (even if
she isn't on the direct line of descent).
In Scars, Elaine Morgan cites a wide range of respected authorities. Some,
like Pond, would rather she didn't.
> I'm reminded of a quote. I don't know the source, but Isaac
>Asimov used in one of his books. "Against stupidity, the gods themselves
>contend in vain."
Asimov has turned out to be stupid on at least one count completely
to this discussion.
The issue the AAT proponents do not ever address, except with vague
mutterings about "hitch hiker" genes and learned skills, is human aquatic
capabilities. They didn't evolve for no reason and they don't show up in
our closest relatives. Do chimps dive? No. Do gorillas swim? No. If you
put a gorilla in a water filled pressure chamber and simulate a diving
of 250 feet, does its heart rate slow down dramatically? Who knows - the
gorilla couldn't hold its breath long enough for you to find out. If a
dived head first into a river, would water be forced into its nasal
Almost certainly. etc. etc.
Admittedly humans learn some of their aquatic skills. But it turns out
learn to swim before they can learn to walk. It is also the case that the
diving reflex isn't learned. Divers don't consciously reduce their heart
and cut off blood flow to their limbs when they dive deeply. (I just saw a
program on TLC exploring human diving performance in some depth (pun); the
program was unrelated to the AAT. The reduction in heart rate and the
to which the blood supply was localised to serve the brain at the expense
of the rest of the body was quite amazing. Would you believe 12 beats
per minute? Anybody else see that program?)
Some people have claimed that these adaptations are relatively recently.
But the fossil record for the past million years or so is relatively
and doesn't show much relationship with aquatic environments.
So, before you call us stupid again, please explain these aquatic
in clear evolutionary terms. Conversely, you could cite papers showing
that chimpanzees, gorillas, bonobos, and even gibbons have aquatic
abilities within a standard deviation or two, of the present human norm.