Re: Dissecting the Aquatic Ape: Bipedalism

29 Jul 1996 01:30:48 GMT

Paul Crowley ( wrote:
: In article <4tb3b9$>
: "HARRY R. ERWIN" writes:

: > The niche is large-bodied suspensory feeding in open-canopy forest. This
: > differs from large-bodied suspensory feeding in closed-canopy forest in
: > that you can't bridge from tree to tree (as can Pongo or Hylobates).
: > Instead, you have to climb down out of the tree to move to another tree.

: Do you really believe this? Or are you just repeating a formula?

Yes, I believe this. Published studies of Pan trog. and Pan paniscus show
that Pan trog. never bridges and Pan paniscus rarely bridges.

: I'm putting forward the hypothesis that predominantly ground-based
: catarrhines and hominoids are a major part of the normal fauna of
: open-canopy forests. They are now, and if you are going to maintain
: that it was different in the past then the onus is on you to say why.
: If you can't then I suggest that we should assume that our hominoid
: ancestors have been predominantly ground-based for 20 Myr or more.

There have been semi-terrestrial hominoids for about 20 MYr, but our
ancestors came down to the ground sometime between 10 and 4 MYr ago.

: The fossil evidence is so patchy and so indeterminate, that it is
: of little assistance.

In the last four years, it has improved markedly.

: > In relatively closed open-canopy forest, a bipedal stance doesn't give you
: > useful early warning of attack.

: Again: Do you really believe this? Or are you just repeating a
: formula? Have the assumptions involved here ever been tested in
: the real world?

This comes from study of human populations and the reason why they put a
lot of effort into cutting down underbrush in the areas they live
in--visibility. Also studies of infantry attack on tanks and the factors
that lead to success or failure. (I used to be an operations analyst
specializing in this area.)

: None of the accounts in Goodall where a chimp
: or other primate is attacked, or ambushed, or where a group appears
: threatened would seem to support them. Nearly all the lethal
: attacks on vulnerable chimps, baboons, or other primates appear to
: occur when a single victim is feeding or resting in a tree and the
: attacking group moves silently on the ground to cut off all avenues
: of escape.

Not very applicable to leopard attacks, then.

: Sounds, smells and other indications of presence are relied on
: heavily. There are no (or very few) accounts of an attacker or
: a victim standing tall (like a meercat) to see what's coming.

: > That set of selective pressures leads to
: > Pan and Gorilla. In more open forest, or in close forest if the understory
: > is not overgrown, the height above ground of the sensory organs in a
: > bipedal posture is useful in giving early warning of attack, and you get
: > various hominids.

: If you were in a forest with only a knife, afraid of being attacked
: by leopards, chimps or gorillas, which you couldn't see but you
: knew were there, what stance would you take? What stance do
: soldiers on patrol in the jungle take, especially when they are
: under threat? Come on, let's have a little bit of common sense
: around here.

They're a good deal more comfortable in an area with little undergrowth
so they have good visibility. One of the more interesting phenomena is
that a team leader or tank commander is great deal more effective if he
maximizes his ability to observe and ignores the risk that entails. I
studied this phenomenon professionally.

: Paul.

Harry Erwin, Internet:, Web Page:
49 year old PhD student in computational neuroscience ("how bats do it" 8)
and lecturer for CS 211 (data structures and advanced C++)