Re: Specification for theories on human evolution

Paul Crowley (
Fri, 17 Nov 95 20:32:24 GMT

In article <48fg8e$> "Alex Duncan" writes:

> writes:
> >It is my thesis that the adoption of bipedalism would have had
> >enormous disadvantages (helpless infants, impeded mothers, no
> >safe refuge in the trees at night, etc.) if adopted for any of
> >the standard reasons.
> 1) helpless infants. Why helpless? Why are altriciality and bipedalism
> connected? (They're not, and the fossil record speaks very strongly on
> this issue.)

When in danger, a recently born chimp can (a) hold onto mother
(b) hold onto and clamber around trees (c) rapidly scoot under a bush.
Chimp infants which are bad at these things don't survive. These
capabilities are maintained by very strong selective pressures.
A bipedal hominid infant would not have been able to do any of these.
Also it's a fair assumption that it would not be able to achieve
its normal method of locomotion until about 18 months. A chimp
infant of 1-5 years old has escape capabilities far in excess of a
hominid of the same age.

> 2) impeded mothers. This is very problematic for me to grasp. As far as
> I can see, bipedalism would be an advantage for any female burdened with
> a neonate. If the arms aren't required for terrestrial locomotion, that
> makes it easier to use them to tend to the infant, should the infant
> loose its grasp.

A chimp mother_with_infant can (a) scoot up a tree (b) throw stones at
a predator (c) use a club, and most importantly (d) run or brachiate
quickly away from any danger (which often comes from other chimps).
Chimp mothers which are bad at these things don't survive or leave
offspring. These capabilities are maintained by very strong selective
pressures. A hominid mother with infant could do none of them.

> 3) safe refuge in the trees. Again, this isn't what the fossil record
> tells us. Hypothetically speaking -- if you were left out in the African
> equatorial savanna w/ no tools or weapons (and alone), where would you
> spend the night? I would sure as hell spend it in a tree (and there's
> nothing about my -- or any non-pathological human's -- anatomy that would
> prevent me from doing so). I might be uncomfortable at first, but I
> suspect that over a period of a week or so, I would become pretty adept
> at building nests.

You have to do it for 12 hours every night, often in the bitter cold.
And if you're a mother, you have to do it holding, say, a 1 year-old,
while looking after a five year-old. You have to sleep soundly to be
fit for a hard day. You have to be far enough out on the branches to
avoid the leopards. You have to do it with an injured arm and when
you are starving and fever-ridden and when the kids are starving and
sick with diarrhea. If either you or a child turns and slips while
asleep, it's death or serious injury - which means death anyway.

Chimp and gorilla mothers have quite specific adaptions and
behaviours to deal with these problems; those which are bad at
them don't survive or leave offspring. They are maintained by
very strong selective pressures.

Sleeping in trees is not a human behaviour. No tribe anywhere
is reputed to do it. There's a complete absence of any relevant
instinctive behaviour. It's safe to conclude that homo erectus
- with a very similar morphology was the same. How did it spend
the night? If there was a major shift in night behaviour at any
time, it should be very obvious from the fossil record. It isn't.

Or to put it another way: When did man's ancestors come down from
the trees? Can you give a range? After 3.5mya? Before 1.5mya?
What fossil evidence would clarify the date more exactly?

All this is perfectly obvious and reasonable. If you were to say
"OK Paul, I can see your point and I accept that sleeping in trees
is problematical at 3.5mya, but . . . . ." whatever.

But you don't say this. I have to say that you appear to have a
fixed dogmatic belief - not unlike the creationists.