Re: Becoming altricial/bipedal

Paul Crowley (
Wed, 04 Oct 95 21:22:32 GMT

In article <44ttrj$> "Alex Duncan" writes:

> Please explain to me how YOU know that the earliest hominids didn't climb
> trees,

I thought I had. I rely on the following propositions. Please tell
me at what point you start to disagree.

a) A species of ape became fully bipedal sometime between 7mya and 2mya.
b) The adults and infants of this species became bipedal at the same
c) A fully bipedal adult foot is not capable of grasping branches.
d) A fully bipedal infant foot is not capable of clinging to either
(i) branches or (ii) the mother.
e) It is not a viable lifestyle for a bipedal maternal ape to spend
every night in the trees (which she cannot grasp with her feet)
while looking after a bipedal infant which cannot grasp her
with its feet.
f) Such creatures would suffer devasting predation if they were to
regularly spend nights on the ground in the forest, or in the
savannah, or in the mosaic/savannah.
g) They did not suffer devastating predation, so they must have had
some other form of safe refuge during the night.

> >You're a primate. Here's an experiment: Take your extended family with
> >wife, grandparents, cousins, several small children and newborn infants
> >and spend a night in a tree. You must all be naked and have nothing
> >artificial. Imagine it every night, for twelve cold, dark hours, while
> >keeping alert for leopards. Imagine trying to spend your days finding
> >food for all of them while enduring such nights.
> Whether or not I can do it is irrelevant to the discussion.

No, it's not. We're discussing your ancestry. Your anatomy is similar
to theirs in all significant respects. If you couldn't do it, then it's
a fair conclusion that they couldn't. If you disagree, you should say
what advantages they would have that you haven't. And making an
informed judgement - and using your extensive paleoanthropological
knowledge - you should say when these advantages disappeared.

> Other than your unsupported claim that the earliest hominids couldn't
> climb trees, you have provided no data to support your assertions.

I have never suggested that the earliest hominids *couldn't* climb
trees. I said that they could not have lived in close association
with them, because they established a lifestyle that did not depend
on their use. I also said that it would be very difficult for a
transitional mother to climb a tree while carrying an infant that
could not cling to her with all its limbs. I further said that it
is very hard to see how she could spend twelve hours every night,
holding such an infant, while trying to sleep in a tree.