Re: An alternative to ST and AAT

Susan S. Chin (
Fri, 15 Nov 1996 07:24:17 GMT

: In article <56cvm2$>
: "Gerrit Hanenburg" writes:
: > Why would an ape change its anatomy in the direction of Lucy's design
: > when staying in its original habitat?

Paul Crowley ( wrote:
: I'm sure that the proto-hominids would have achieved a high degree
: of social co-operation. This implies terrestriality and not a
: rain-forest habitat. So its use would have been new.

How are you so sure of this social cooperation in early hominids?
Afarensis' sexual dimorphism suggests a high degree of competition among
the males for access to females.

: I agree that the habitat has to involve more than the rainforest;
: I see it (or the palm trees) providing only part of the diet; and
: its use certainly wasn't the reason for bipedalism. I'm looking at
: it primarily as the reason for the _restraint_ on the development
: of a more effective bipedalism.

Afarensis as a species existed for almost a million years. An ineffective
biped living in a terrestrial environment would not survive as a species
for that long. An arboreal (rainforest) niche for 1my would leave us
scratching our heads as to why bipedalism anyway? Besides, all the
paleoecological evidence that is known points to Ardipithecus ramidus
living in a forrested environment. And ramidus is the *first* hominid/
hominoid (depending on what you want to call it) known to live in such a

: > Lucy's climbing abilities don't need a new explanation because it's
: > what she inherited from her ape ancestors. Only what's new needs an
: > explanation,i.e. bipedalism.

: This thinking is not clear. The whole ecology and niche have to be
: explained. Why did the bipedalism retain these strange climbing
: adaptations? (If that is what they were.) If the LCA had been a
: quasi-chimp, then it would have had short legs and long arms for
: its quadrupedal gait; bipedalism should have shortened the arms
: almost immediately, and lengthened the legs, as we see with
: H.erectus. I can't see how H.erectus would be much worse than Lucy
: at climbing ordinary trees; and it would be far better at running
: and walking.

Punctuated equilibrium notwithstanding, evolution of functional
morphological anatomy such as hominid arm length would *not* occur
instantaneously. If Lucy and other afarensis are able to walk
effectively, not necessarily "optimally" but obviously not in a waddling
manner, there is no evolutionary reason to quickly reduce the arm
length. Selection over time, possibly over the course of the afarensis
lineage might favor a reduction of arm length. But if it's not detrimental
to effective bipedalism, there's no evolutionary pressure to reduce the arm
length quickly as you alluded to. They are called "primitive retentions."
If it ain't broke, don't mess with it...

: > Contrary to shellfish the meat of artic verbrates has a high fat
: > content which results in a high caloric value. Eskimos do not have to
: > rely on protein for their energy and can subsist on animal matter
: > alone during winter. Protein content does not exceed 30% of total
: > calories.

: I know little about this, but a diet high in fat does not strike
: me as being as healthy as one high in protein. Our primate
: ancestors "who's digestive system and metabolism are mainly adapted
: to frugivory/folivory" must have consumed very little animal fat.

You're projecting modern Homo sapiens' ideas of what is healthy. I
seriously doubt our earliest ancestors choice of diet necessarily takes
this into account. If anything, fatty substances such as bone marrow from
carcasses is thought to comprise the early hominid diet. Even today, most
human diets are much higher in fat than is thought "healthy." So if our
ancestors didn't eat much fat, where did this dietary pattern come from.
Without a consistent, reliable source of food, early hominids likely
weren't worrying about their waistlines or cholesterol level, IMO.

: > Apparently I have a somewhat different view on community ecology than
: > you. If I look at todays wildlife communities in Africa I see numerous
: > sympatric species of bovids,large carnivores,monkeys,birds,etc. I
: > wonder how they all manage to have a particular "edge" over the
: > others. What "edge" do you think Vervet monkeys have over Savanna
: > baboons,Ruppell's Griffon vulture over White-backed vulture,and
: > Grant's gazelle over Thomson's gazelle?

Sympatric species don't necessarily compete for the same resources within
that environment. They develop a niche within this community. The "edge"
is that each species has learned to adapt to the same environment in very
different, yet successful ways. Success is measured purely in terms of
survival and reproduction, propagation of the species.

: Bipedalism needs at least one very good hypothesis (two or three
: very good ones might be better, but one will do for a start ;)

Hypotheses about the origin of bipedalism would be useful scientifically,
but they should proceed at a very fundamental level. There may be many
differing pressures which caused that first ape to stand up and decide 2
legs are better than 4. Will one hypothesis ever adequately explain these
various selective pressures? I have my doubts there...