Re: AAT Theory

chris brochu (
9 Oct 1995 14:10:28 GMT

In article <45b6fv$> Thomas Clarke, writes:
>I guess I did miss your point. Now I don't understand you at all,
>however. What do you mean by "scenario"?
>The facts are a few fossils and present day animals. There are
>no "scenarios" in nature. The phylogeny inferred from the fossils
>and (now) DNA evidence is an hypothesis.

I wasn't being clear. I apologize. The scenario to which I refer is the
phylogenetic hypothesis. It shows terrestrial/arboreal, functionally
bipedal primates closely related to terrestrial/arboreal, largely bipedal
primates (Australopithecines) and fully terrestrial, bipedal forms
(ourselves). Why is an aquatic phase needed?

>> For a good model, take a look at macropodids. The earliest relatives of
>> bettongs, wallabies, and kangaroos were forest animals that became
>> bipedal, probably to jump over obstacles. When the forests went away,
>> they stayed bipedal. (And no, before you flame, I'm not proposing a
>> saltatorial phase in our evolution. Only pointing out that we aren't the
>> only bipedal open-ground creatures, and that the evolution of bipedality
>> in macropodids might be a worthwhile analogy.)
>You almost make my point. Are there not several species of macropopids?
>The environment favored the development of bipedal jumping (saltation)
>and several species "answered the call" by becoming macropopids.

In all likelihood, only one lineage "answered the call." This one
lineage diverged. In effect, I made my own point - bipedalism only
evolved once in Australia.

>If the general forest/savannah paleo-environment of Africa favored
>bipedalism, then where are the other bipedal animals?

I don't know. Where are the other bipedal Australasian marsupials?

(Keep in mind - bipedality has been a fact of life for the macropodids
for much longer than it has for hominids - more available time for