tree-climbing hominids
Alex Duncan (aduncan@mail.utexas.edu)
6 Oct 1995 03:43:53 GMT
PC wrote:
a) A species of ape became fully bipedal sometime between 7mya and 2mya.
To which I responded:
Your entire argument rests on this incorrect premise. If, by "fully
bipedal" you mean "bipedal in the same manner as modern humans", then you
are incorrect. Your statement is not supported by the fossil record.
The fossil record suggests that the hominid species that were extant
between ~4.5 and 2.0 Myr WERE NOT bipedal in the same manner as modern
humans, and that they retained significant tree-climbing abilities.
To which PC responded:
Please state what you mean by "significant tree-climbing ability"
If you mean that the hominid was probably able to grasp branches with
its foot, please quote references.
And here they are:
Lamy P (1986) The settlement of the longitudinal plantar arch of some
African Plio-Pleistocene hominids: a morphological study. Journal of
Human Evolution, 15:31-46.
Latimer BM, et al. (1982) Hominid tarsal, metatarsal, and phalangeal
bones recovered from the Hadar Formation: 1974-1977 collections. American
Journal of Physical Anthropology, 53:701-719.
McHenry HM (1986) The first bipeds: a comparison of the A. afarensis and
A. africanus postcranium and implications for the evolution of
bipedalism. Journal of Human Evolution, 15:177-191.
Stern JT & Susman RL (1983) The locomotor anatomy of Australopithecus
afarensis. American Journal of Physical Anthropology, 60:279-317.
Susman RL (1983) Evolution of the human foot: evidence from
Plio-Pleistocene hominids. Foot and Ankle, 3:365-376.
Susman RL, Stern JT & Jungers WL (1984) Arboreality and bipedality in the
Hadar hominids. Folia Primatologia, 43:113-156.
Tuttle RH (1981) Evolution of hominid bipedalism and prehensile
capabilities. Philosophical Transactions of the Royal Society, 292:89-94.
and last (hopefully not least):
Duncan AS, Kappelman J & Shapiro LJ (1984) Metatarsophalangeal joint
function and positional behavior in Australopithecus afarensis. American
Journal of Physical Anthropology, 93:67-81.
PC: 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.
AD: I would really have to say that this depends on a lot of other
factors that you haven't addressed. But, for the sake of this particular
argument I'll agree with it.
PC: I'd like to know the "other factors".
AD: Well, aside from the obvious question of whether or not
australopithecines were effective tree-climbers, the most important
question would be whether or not they may have built nests in the trees
as modern chimps do. Such nests would make sleeping in the trees a much
simpler business.
PC: 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.
AD: This is incorrect. "Fully bipedal" hominids are large, tool-using,
group-living primates. For a carnivore to a attack a GROUP of healthy
humans is foolhardy.
PC: At night? Lions, leopards and hyenas are nocturnal. Hominids are
diurnal and effectively blind at night. They would only injure each
other, and their females and young, if they were to use clubs and
stones whenever they heard a rustle and thought a big cat was near.
This must be one of the craziest ideas of all time. How much sleep
would any of them get each night? What's the life expectation?
Can you imagine the stress levels with the screams of the hyenas and
the lions' growls?
AD: Here I assume PC is refering to later hominids such as H. erectus,
who presumably lived in fairly large groups, had a reasonably advanced
tool kit that included the Acheulean hand ax, and might well have had
fire. I agree that spending a night on the savanna under such
circumstances would not necessarily have been easy, but not far from
impossible.
PC: g) They did not suffer devastating predation, so they must have had
some other form of safe refuge during the night.
AD: What are you suggesting -- they lived behind locked doors?
PC: I'm sure you know what I'm suggesting - they waded or swam to an
island
on the rocky foreshore, and snored contentedly in the warm breeze from
the sea to the sound of lapping water. Which way would you and your
family prefer to spend the night - and every night?
AD: Are there lots of islands available in the middle of the African
grasslands?
AD: My anatomy (and yours) is not similar to that of the earliest
hominids in
all significant aspects. In fact, it is very different in many
significant aspects. You still have not provided any support for your
basic assertion.
PC: All standard accounts of human evolution have all hominids, from the
CA to civilisation, sleeping either in trees or on the ground. As I
argued above, the ground is not sensible. It's easier to see what a bad
idea trees are, if you think about more recent hominids (say <1.6 mya)
because their post-cranial anatomy is near enough identical with yours.
Once you accept that you and your family, with infants and children,
could not possibly sleep naked in the trees, you can see that the same
would apply to hominids at
1.6 mya (e.g. KNH-WT 15000). So where was he sleeping? When you have the
answer to that, you can readily work back to the CA. Any differences in
anatomy will be seen to have no significance to the problem and its
answer.
AD: Well, we have a lot of problems here. First, prior to 1.8 Myr, we
know that hominids had an anatomy appropriate to part-time life in an
arboreal substrate. Essentially fully modern postcranial anatomy seems
to arrive with the appearance of H. erectus. If we assume, for the
moment, that H. erectus could not climb trees and wasn't safe on the
ground, then I suppose we can entertain PC's suggestion that they must
have utilized the abundant savanna islands to sleep on. At this point of
course, AAT has become a non-theory for the explanation of the origin of
bipedalism, because bipedalism would have arisen prior to any aquatic
stage. Additionally, the suggestion that 2 short distance swims daily
(to the island and back) would have been a potent selective force is
problematic.
But a real issue is whether or not an H. erectus band would have
been able to survive at night on the ground. Modern humans with tools
not much advanced over H. erectus (e.g., !Kung) manage it without
recourse to those abundant savanna islands (the islands are even more
abundant in the near-desert the !Kung inhabit).
PC: [lots of nonsense about us high-horsed academics] For the moment, you
just need a little balls.
AD: Evidence would be nice, as well. A point: if I really wanted to make
a name for myself in anthropological circles, all I would have to do is
find convincing evidence that the AAT is correct. The reason no one has
done it yet is because the evidence doesn't exist.
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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