Johannesburg

Characteristics that distinguish us from apes may have been forced on
our ancestors by the presence of water, writes Ruben=

Mowszowski

If the proponents of a revolutionary theory of human origins are
correct, our ancestors abandoned the trees not for the savannah, but
for the water - and humans share more physical traits with dolphins
than with=

apes.

The 3,5-million-year-old Australopithecine fossil found recently in
Sterkfontein and billed as our ancestor is to be the subject of an
opening talk at the World Congress of Archaeology in Cape Town this
week.

Inevitably the question will be asked: in what kind of environment
did this 1,2m-tall ancestor of ours live?

A mural in the Sterkfontein tearoom makes it quite clear. A group of
hominids holed up in a cave is beating off another group apparently
intent on moving in, if not actually devouring them. The cave is
located in the middle of savannah grassland.

But evidence which has been accumulating since the discovery in the
1970s of the Australopithecus fossil nicknamed Lucy indicates that
the environment in which the Australopithecines and the earlier
Ardipithecus ramidus lived and died was not savannah but tropical
forest.

This means that the story of how our ancestors developed the
characteristics that distinguish us from the apes will have to change.

The version most of us know is called the savannah hypothesis and it
goes like this: a change in climate shrunk the forests and expanded
the savannah, forcing a branch of tree-living apes into the open, so
they stood up.

The recently discovered 4,5-million- year-old partly bipedal
Ardipithecus ramidus lived not in dry savannah, but in a forest. This
means that the human origins story has to be rewritten.

At the recent Dual 98 Congress on Palaeontology and Human Biology one
of the delegates was Elaine Morgan. The non-scientist author of The
Descent of Women put the female gender back into the evolutionary
story in the 1970s.=

For the past 27 years she has been promoting an alternative
hypothesis on human origins which was put forward by scientist
Alistair Hardy in 1960. Hardy noticed that humans share certain
physiological attributes with aquatic mammals. It occurred to him
that bipedalism might have been an adaptation to an environment that
had become not dry, but wet.

Hardy was advised by his academic mentors not to pursue the subject
for fear of damaging his career. In the savannah hypothesis
palaeontology already had a "good enough" story to explain bipedalism.

The image of our ancestors coming down from trees, emerging stooped
from the primeval damp forest and striding out into the open
grasslands to become erect humans is a vision of humankind
triumphant. It finds biblical expression in the story of our
expulsion from Eden.

Who wants ancestors who stood up just so that they could breathe?
Hardy let the theory lie for the sake of his career. Morgan took it
up and gave it the provocative name "aquatic ape theory" and it might
have been ignored for longer if the savannah hypothesis had not begun
to fail.

In 1995, the eminent South African palaeontologist Phillip Tobias
delivered a lecture to the University of London. Foot bones from
Sterkfontein, he said, showed there was an "arboreal element" in the
life of the hominids whose fossils were found there. His conclusion:
the relatively scrubby trees one would find in savannah would not
have been adequate for the size of australopithecines.

New findings of fossil animals, plants and pollen and recent evidence
by way of the 4,5-million-year-old Ardipithecus ramidus fossil, he
said, indicated that hominids were upright before the forest shrunk,
before they got big brained. End of hypothesis.

Not entirely. There are all sorts of theories still being offered
that seek to explain our physiological peculiarities as adaptations
to the savannah environment.

Standing on two legs, for instance, is said to reduce exposure to the
sun at noon (though critics say any sensible hominid would be lying
under a tree at that time) and to keep our overheated brain away from
the hot ground. An older theory is that our ancestors needed to free
their arms in order to reach food and carry it home, after which they
progressed to throwing stones at predatory animals or, as the
Sterkfontein mural shows, at each other.

None of these is particularly convincing. It seems like palaeontology
has reached one of those difficult moments which science must every
now and then face, when cherished beliefs that underpin established
frameworks collapse.

Tobias has recognised that moment. "All the former savannah
supporters (including myself) must swallow our earlier words in the
light of the new results from the early hominid deposits ... And the
savannah hypothesis is washed out ... if savannah is eliminated as a
primary cause or selective advantage of bipedalism, then we are back
to square one and have to try to find consensus on some other primary
cause," he said in his London lecture.=

Significant words that lead us to Hardy and Morgan's world of flooded
forests where apes who live both on the ground and in the trees have
to adapt to a wet environment or die.

Which is why Morgan, who has been out in the cold for 30 years, is
now, at Tobias's invitation, taking her place on the rostrum in front
of the brightest brains in evolutionary science.

Morgan says that the adaptations that distinguish us from the our
closest primate cousins were forced on our ancestors by the presence
of water. That, for a couple of million years, which is not very long
as these things are measured, our ancestors lived like sea otters in
a semi- aquatic environment.

The aquatic hypothesis suggests that nakedness, bipedalism and many
other distinctly human adaptations evolved long before our ancestors
moved onto the savannah. It is founded on the observation that a
number of the features that characterise our physiology, "though rare
or unique among land mammals, are common in aquatic ones".

A feature of the aquatic ape hypothesis is that it deals with a large
number of physiological and structural features, the best-known of
which is bipedalism. Morgan says perpendicular gait has many
disadvantages. It is slower, unstable, needs to be learned and
exposes vulnerable organs to=

attack.

"Only some powerful pressure could have induced our ancestors to
adopt a way of walking for which they were initially so ill-suited,"
she says.We are still suffering the consequences of this adaptation
in the form of backaches, varicose veins, haemorrhoids, hernias and
difficult childbirths.

Morgan points out that all the other primates that stand up on
occasion have a habitat that is wet rather than dry. The proboscis
monkey, which stands very readily, lives in mangrove swamps. The
habitat of the bonobo, which - like dolphins, beavers, sea otters and
humans - mates face to face, includes a seasonally flooded forest.

She says "the only animal that ever evolved a pelvis like ours,
suitable for bipedalism, was the long-extinct Oreopithecus - known as
the swamp ape".=

Then there is our nakedness. The only other mammals which are naked
are swimmers like the whale and dolphin, wallowers like the
hippopotamus and pig, and animals like the elephant and rhinoceros,
which, she says, "bear traces of a watery past".

Human hair direction (we are naked by virtue of thinner hair, rather
than fewer hair follicles) occurs in whorls corresponding to the
movement of water against a swimming body. In all the other apes it
points downward.=

Humans are the fattest primate. We have 10 times as many fat cells in
our body as any other animal of similar size. Unlike other primates,
our children are born fat with a large proportion of white fat which
is good for insulation and buoyancy but not for energy.

Morgan thinks it is an adaptation that protected babies that had
fallen out of trees. As with most aquatic animals, but unlike other
primates, our fat is present all year and is stored, not deep within
the body, but under the skin where it serves as an insular layer. The
only other mammals that store fat in this way are aquatic, like
dolphins, seals and hippos.

Humans are the only primates which have the ability to hold their
breath voluntarily. The only other mammals able to do this are
aquatic, like seals and dolphins. The descent of the larynx that
occurs in the human infant at about three months is an adaptation
that allows air to be gulped in large quantities through the mouth.
The only other mammals that have a descended larynx are the sea lion
and the dugong.

"Without voluntary breath control, it is very unlikely that we could
have learned to speak," says Morgan.

We have larger brains than any other ape. The mammal with the largest
proportionate brain size after humans is, of course, the dolphin - a
terrestrial animal that returned to the sea.

Morgan's scenario for these evolutionary adaptations is based on
known geological events. About six million years ago, the low-lying
section of land near the Red Sea known as the Afar triangle (where
Lucy was found) was flooded and became the Sea of Afar. Some
hominids, she says, would have been isolated on islands, others would
have found themselves having to survive in flooded forests, among
marshes and swamps.

Rapid speciation, such as occurred in the change from ape into
hominid, Morgan says, "is almost invariably a sign that one
population from a species has become isolated by a geographical
barrier such as a stretch of water. Survivors of such massive
flooding would have been forced into adapting."

When the sea became landlocked and evaporated their descendants would
have followed the waterways of the Great Rift Valley upstream,
towards the south, and emerged, as at Sterkfontein, erect, with no
body hair, the ability to hold their breath and with a descended
larynx, ready to speak.

Tobias's invitation to Morgan to speak at a congress of professionals
has brought her inside the walls of the citadel, and scientific
evolutionary theory, in so far as human origins are concerned, might
never be the same.