Re: Missing Link (was Human Chimp Gorilla)

David Woodcock (
4 Aug 1996 19:00:55 GMT

Stanley Friesen ( wrote:
: >> I suspect that African H. erectus came *from* Asia. ...
: >> How can this be? Simple - new species tend to arise in small
: >> peripheral populations ... In fossil contexts this
: >> is called "Punctuated Equilibrium".

On this I agree.
: >thermoluminescence dating is providing dates to much less than 100,000
: And, as I said, speciation takes less than one quarter of that span.

: Stanley Friesen

I agree with you that erectus probably is a product of
Homo's adaptation to Asian conditions -- a similar
view is held by several paleoanthropologists -- B.Wood,
A.Turner, R.Ciochon, etc.

However, since I'm minimally acquainted with their work
whatever errors appear in the following are entirely my

I seriously doubt that the transition from protoHomo
to erectus took only 25,000 years. There are examples
of mammalian bone proportions changing this fast [1000 generations]
, e.g. Canus, but I doubt the selection was quite that
severe and consistent in this case. However we may differ on our
conception of protoHomo.

The starting point,i.e. what did the African hominid that
spread to Asia look like ?

The body plan was probably much closer to Lucy`s [3.1 Mya, A.afarensis],
a newly reported S.African find [A.africanus], and
OH 62's [1.8 Mya, H.habilis] than to the Turkana boy's. [1.75 Mya,H.erectus].

That is, it probably had the semi-arboreal plan which is beginning to seem
universal in australopithecines and "Homo" habilis.
Long arms, short legs, grasping feet [at 3.5 Mya], curved fingers [at 3.1]
--in short better adapted for climbing than we.

Given the presence of stone tools at 2.5 Mya at Hadar and straight
fingers at 2 Mya in S.Africa, protoHomo may have left Africa
between 2.5 and 2.1 Mya with a precision grip. However orangs can
make Hadar type flakes, and Tobias' 2 Mya phalanges might be from early

The erectus body plan [essentially the same plan as ours]
was selected for by the niche protoHomo created in Asia.
Thus the problem of distinguishing Homo from Australopithecus
is straightforward --find the postcrania.
Thus femurs dated at 1.8-1.9 Mya and associated with "H.rudolfensis".
[tho found 2 km. from the "rudolfensis" skull]
are early erectus femurs. Foot bones dated to 1.8 Mya at Oldavai
are also early erectus. Of course, a la mosaic evolution
the post crania may have changed first -- giving an erectus body
with a primitive skull. What a primitive skull in this context
might look like is unclear. The earliest known erectus cranium - 1.8 Mya
--but from Java-- has the typical H.erectus traits: robust,prominent
supraorbital torus.

"H.habilis" --all of whose definite examples postdate 2 Mya --is not a human
ancestor. However, the hominid that made the Hadar tools [2.5 Mya] is a good
candidate and may be the ancestor of both habilis and erectus.

In perhaps as little as 200 kya a small isolated
population exposed to very different selective pressure on the periphery
of its [former] specie's range changed profoundly. How and why can
be understood by comparing the australopithecine to the hominine

By 2.5 Mya at least some populations of A.s did a significant amount
of hunting and primary scavenging [taking other predator's kills].
They made sharp stone flakes to facilitate butchering --cutting thru
the hide, dismembering joints -- so they could move meat before
they had to argue with lions about ownership. They probably retured
to trees to eat, and tuck away left overs --as leopards do today.
This led to food sharing with nonhunting females and young.

Estimating the proportion of the diet so obtained is not simple.
At Gombe male chimp diet is 10% meat. Human diets range from 100%
to virtually none, tho the latter have protein sources not
available to A.s. Given the usual preference for meat in chimps
and humans over most plant alternatives, meat consumption's limit
was set by hunting/scavenging success. So the
proportion of the diet obtained this way probably varied widely
based on season, local conditions, history of the group.
In the tropical savanna mosaic something else edible is usually
available if the hunt fails. The exception is the short dry season
when the something else might be limited to roots.
Generally however, much of the diet must have been fruit,
nuts, inner bark, tubers, termites, ostrich eggs, grubs, young
shoots, etc. Climbing was important for getting food, and for refuge.
`Nests' were probably made in trees as do all other great apes.

The population that crossed the proto-Sahara during the at most 5 millenia
long pluvial when it was savanna must have been more ready than most
to follow the herds during their seasonal migration.
There was self selection for groups that put particular emphasis
on hunting. As desert returned to Sahara and across south Asia northern
groups were forced to follow the herds into another world --
a world where many trees --conifers --had no food, were often
tougher to clinb, extruded annoying sticky resin. Other more
familiar trees either never had edible food [eg oaks] or had
it for but a short time. Worse, unlike the tropical pattern of
different kinds of fruit ripening at different times of the year,
most of the best vegetable food was available all at once, but
absent most of the time. In the terribly cold season when shelter
was most needed the better leafy trees had no leaves. Night refuge
up a tree in winter often meant freezing on clear nights. At the end of the
interglacial [about 5000 years later] conditions only got worse.
By that point populations that would survive were denning or
using caves. Climbing was no longer as useful. Hunting, however,
was much more useful. During the short summers there was
a variety of food --less familiar fruit,termites and edible nuts --but
more than enough. During the winter there was nothing edible but meat.
And the best source of that was the huge herds on the steppe.
So we have little pressure to retain climbing ability, much
pressure to become a more efficient walker. More pressure
on tool use. On cooperative hunting. On obtaining famine
food [inner bark, roots from under the snow ] On adapting to the boom
and bust eating pattern of the large specialist carnivore.
On setting snares and traps. On staying warm enough to survive.
This very likely was when a number of human traits and behaviors
appeared -- use of fire, clothing, putting on fat.
Increased brain size facilitated more flexible behavior; more
powerful chewing musculature than in A.habilis reflects importance
of raw meat, fibrous famine food, and masticatory hide
processing. Reduction in sex size difference suggests females
had access to more food than previously during shortages.

By the time of the next pluvial [abt 100ky later]
protoHomo was well on its way to being Homo. It was a significantly
better hunter. When the Sahara became savanna it outcompeted the
A? from the south. At this point there may have been some
interbreeding, most of the gene flow was south contributing to
'the mess in the middle.'

After the next glacial cycle or 3 H.erectus was established in Africa,
[c. 2.0-1.9 Mya] beginning to displace both species of A. There was
too much niche overlap; better climbing was not enough, so
first A.habilis then A.robustus/boisei disappeared -- at about 1.5 and 1 Mya,

--David M.Woodcock