Re: AAT Questions...

Alex Duncan (
19 Jul 1995 19:11:15 GMT

In article <> Elaine Morgan, writes:
>Reply to Alex Duncan.
>You say there is plenty of evidence in the current literature of
>savannah-mosaic adaptation but I have ignored it
>Quite untrue. What there is in the current literature is a great deal
> of speculation about why a savanna/mosaic habitat might have led
>to bipedalism. I have not ignored it. I have a paper in press listing
>the front-running theories and saying why I disagree with them. They
>also of course disagree with one another.

Ms. Morgan,

When I talk about evidence, I am not refering to people's hypotheses
about the importance of the savanna/mosaic environment in human
evolution. I am refering to evidence that we can place in two different
categories: 1) reconstruction of the environments in which early hominids
lived, and 2) reconstruction of the locomotor habits of early hominids.
In category 1 are a series of papers that reconstruct environments at
Laetoli and Hadar as savanna/mosaic (with emphasis on mosaic) (later
habitats like Sterkfontein were probably drier), and in category 2 are
papers that reconstruct the locomotor behavior of early hominids as being
primarily terrestrial bipeds, with retained capacities for tree climbing.
Here is a list of such references:


-- Andrews PJ (1989) Paleoecology of Laetoli. J. Hum. Evol., 18: 173 -

-- Boaz NT & Burkle LH (1984) Paleoclimatic framework for African hominid
evolution. In (JC Vogel, ed.) Late Cainozoic Palaeoclimates of the
Southern Hemisphere, pp. 483-490. Rotterdam: Balkema.

-- Bonnefille R, Vincens A & Buchet G (1987) Palynology, stratigraphy and
palaeoenvironment of a Pliocene hominid site (2.9 - 3.3 M.Y.) at Hadar,
Ethiopia. Palaeogeography, Palaeoclimatology, Palaeoecology, 60: 249 -

-- Bonnefille R & Riollet G (1987) Palynological spectra from the Upper
Laetolil Beds. In (MD Leakey & JM Harris, eds.) Laetoli: A Pliocene Site
in Northern Tanzania, pp. 52-61. Oxford: Clarendon Press.

-- Gentry AW (1987) Pliocene Bovidae from Laetoli. In (MD Leakey & JM
Harris, eds.) Laetoli: A Pliocene Site in Northern Tanzania, pp. 378-408.
Oxford: Clarendon Press.

-- Grey BT (date & title unknown) Grey's PhD dissertation reconstructs
paleoenvironment at Hadar as being similar to modern Omo River region.

-- Harris JM (1985) Age and paleoecology of the Upper Laetolil Beds,
Laetoli, Tanzania. In (E Delson, ed.) Ancestors: The Hard Evidence, pp.
76 - 81. New York: Alan R. Liss, Inc.

-- Johanson DC, Taieb M & Coppens Y (1982) Pliocene hominids from the
Hadar Formation, Ethiopia (1973-1977): Stratigraphic, chronologic and
paleoenvironmental contexts, with notes on hominid morphology and
systematics. Am. J. Phys. Anthrop., 57:373-402.

These are, of course, just a few of many references which reconstruct
paleoenvironments at early hominid localities. For the most part they
all tell the same story: savanna/mosaic.

Early hominid positional behavior:

-- Day MH & Wickens EH (1980) Laetoli Pliocene hominid footprints and
bipedalism. Nature, 286: 385-387.

-- Duncan AS, Kappelman J & Shapiro LJ (1994) Metatarsophalangeal joint
function and positional behavior in Australopithecus afarensis. Am. J.
Phys. Anthrop., 67-81.

-- Gomberg DN (1985) Functional differences of three ligaments of the
transverse tarsal joint in hominoids. J. Hum. Evol., 14: 553-562.

-- Jungers WL (1982) Lucy's limbs: skeletal allometry and locomotion in
Australopithecus afarensis. Nature, 297: 676-678.

-- (1988) Relative joint size and hominoid locomotor adaptations with
implications for the evolution of hominid bipedalism. J. Hum. Evol., 17:

-- Lamy P (1986) The settlement of the longitudinal plantar arch of some
African Plio-Pleistocene hominids: a morphological study. J. Hum. Evol.,
15: 31-46.

-- McHenry HM (1986) The first bipeds: a comparison of the A. afarensis
and A. africanus postcranium and implications for the evolution of
bipedalism. J. Hum. Evol., 15: 177-191.

-- Stern JT & Susman RL (1983) The locomotor anatomy of Australopithecus
afarensis. Am. J. Phys. Anthrop., 60:279-317.

-- Susman RL, Stern JT & Jungers WL (1984) Arboreality and terrestriality
in the Hadar hominids. Folia Primat., 43: 113-156.

In combination, these articles do two things. They establish that early
hominids were living in a savanna/mosaic environment, and they
demonstrate that they had the proper locomotor anatomy to take advantage
of such an environment. What more could you ask for? (BTW -- I've only
just dented my list of references. You might try actually reading some
of this.)

>You mention credibility. Suppose you establish your credibility by
>telling us which of these mutually contradictory theories you believe;
>then I can defend mine by giving my opinion of it. This request is
>usually met with with "Oh but there are so many of them.." You are
>doing this again. It is a blatant cop-out. Stand up and be counted.
>Then we have a meaningful discussion.

Its not clear to me what you're asking for here. The question of WHY
hominids got up on their hindlimbs and began walking bipedally is one
that we'll probably never be able to answer to everyone's satisfaction.
What we can do is point out some of the potential advantages to the
behavior, and some of the adaptations to the behavior that we see in
living and extinct hominids. Many of the features (sweating,
hairlessness) that you try to steal away as support for the AAT have been
demonstrated to be advantageous to diurnal bipedal hominoids living in
largely open environments.

I don't favor any particular model of WHY hominids are bipedal. I
honestly don't think we'll ever be able to answer the question (although
we can suggest answers -- keep in mind, in science we never PROVE
anything, we can only test our models). As you can tell from some of my
earlier posts, I lean toward a gibbon-like ancestor for hominids, but I
don't have any particular stake in the matter, and wouldn't be too
surprised to see something else turn up.

By the way, you have a perfect opportunity to establish the AAT as a
serious model for the origin of hominid bipedalism. Supposedly, there is
a nearly intact postcranial skeleton of A. ramidus that will be described
soon. If A. ramidus is really about 4 Myr old, then it lived right at
the end of the time period when your proponents say we had aquatic
ancestors. As such, we should expect it to show some skeletal
adaptations to living in an aquatic environment. Does your hypothesis
permit you to make predictions about this? Please, predict for us. What
will the postcranial skeleton of A. ramidus look like?

Alex Duncan
Dept. of Anthropology
University of Texas at Austin
Austin, TX 78712-1086