Alex Duncan (firstname.lastname@example.org)
19 Sep 1995 00:33:05 GMT
In article <email@example.com> Elaine Morgan,
>Could you please give me a firmer idea of what has now replaced the
>late savannah theory? These are not catch questions. I genuinely want
>to get it clearer in my mind.
The savanna theory basically suggested that at some point in our past, a
chimp-like animal decided to begin living on the savanna, and >>WHAM<<
became bipedal. The idea has been abandoned for two reasons: 1) evidence
that the earliest bipeds lived in mosaic habitats, and had adaptations
that would have allowed them to use all aspects of those habitats, and 2)
a greater recognition of the limits of anthropological science. As an
aspect of this second point is the realization that we will never know
exactly why hominids became bipedal. The best we can do is suggest
models. These models all have the common feature that at some point in
hominid evolution there was an advantage to being bipedal (not
necessarily BECOMING bipedal). I suspect that modern
paleoanthropologists are about evenly split between those who hold to an
exaptive view, and those who hold an adaptive view for the acquisition of
>1. Do you think the last common ancestor was or may have been bipedal?
Personally, I doubt that the last common ancestor of humans and African
apes was bipedal. I suspect that the best way to look at this issue is
that bipedal positional behaviors occured with varying frequencies in the
LCA, and in the more direct ancestors of gorillas, chimps & humans. I
don't think it's out of line to propose that the LCA was a more frequent
bipedalist than either modern gorillas or chimps.
>2. If not, do you think the first hominids became bipedal before or
>after the open spaces began to appear? If after, do you think the
>open spaces caused the bipedalism?
I do not think that the appearance of open space caused bipedalism. My
view on this has been that if a basically quadrupedal/suspensory arboreal
animal (let's use a chimp as a model) is suddenly plopped down in open
country, it's not suddenly going to become a biped. Chimps are more
comfortable w/ knuckle-walking than bipedalism when traversing open
country. I suspect that the evolutionary response to LOTS of open country
would have been to increase the effectiveness and efficiency of the mode
of terrestrial locomotion that was already extant.
Chimps may not be the best model for the earliest hominids, however.
>3. Is it your understanding that bipedalism was the only one of the
>species-specific human features to appear by 4+mya, and that other
>changes e.g. in skin and respiratory canal emerged later or much later?
>Do you think they emerged simultaneously or serially? If you think
>they came later than bipedalism, since neither of us has been able to
>produce conclusive evidence one way or other, what is it that inclines
>you to think they came later?
My feeling is that bipedalism came first, and that other uniquely human
features came later. As Wheeler has pointed out, naked skin and heavy
sweating are adaptive under certain circumstances -- i.e., you're a
biped, you have certain body proportions, and you spend lots of time
exposed to direct sunlight. The best evidence bearing on this issue is
the H. erectus boy's skeleton at ~1.6 Myr. Except for a scrap or two
that may belong to H. rudolfensis, it appears that earlier hominids had
more ape-like body proportions, and probably didn't venture into open
country too frequently or for too long. In other words, I think naked
skin and heavy sweating appeared about the same time H. erectus did (or
perhaps w/ H. rudolfensis, but better postcranial evidence is needed).
I'm not well versed enough in laryngeal anatomy to respond to your
question on that issue, except to say that I have seen no evidence that
contradicts the supposition that human laryngeal anatomy is associated w/
human speech capabilities, and thus is relatively recent acquisition.
You are correct to point out that the association between laryngeal
anatomy and basicranial flexion is tenuous. Hopefully it'll get better
as the fossil record improves.
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086