BRIAN DEER:
NATURE'S PREY Page
2
The
night before my drive across the Serengeti, I had an
amazing dream. As it happened, it was prompted more
by the side-effects of the anti-malarial mefloquine
than by anything Freud would have recognised, but the
form it took was to transport me back to the gates of
just such an Eden. Knuckles swinging like an
Australopithecus, through a dim, humid forest, I was
trying to find a tree within which to take shelter
from a driving, monsoon rain. A dense green canopy
filtered the light, and from beyond it came the
ominous dull rumble of thunder, which eventually woke
me up.
If
the drug was the trigger, then the mood had been set
by a chilling bedtime story. On Saturday afternoon, I
had descended alone into the Ngorongoro crater,
climbed from the Hyundai to photograph hippos, and
was confronted by an adult animal at 20 feet.
Figuring - ever the liberal - that I was disturbing
the wildlife, I walked slowly back to my car. But
over dinner, a celebrity American photographer, Peter
Beard, graphically explained that I was a lucky man
indeed to be alive to pass him the yams. The kiddies
favourite soft toy killed more people than crocs or
cats, he said, and had this one seen a glimmer of
water behind me, it would have run me down, shaken me
to death and pounded my car to scrap.
So I
was surging with medicine and the residue of terror
when the dream formatted this story. At the heart of
the new origins research has been a amazingly recent
acceptance among anthropologists that humans were
created by, and not merely in specific
ecological settings - most notably the great primeval
rain forest which once swathed the planet's tropics.
To fathom us, the new thinking goes, you don't just
go hunting skulls, or watching chimps, you have to
start afresh by considering precisely the landscape
that had surfaced in my dream.
"If
you want to understand why human evolution took the
course it did, then you have to understand how
hominids articulated with their environment,"
Tom Plumber, a palaeoecologist from the University of
California, Los Angeles, working in western Kenya,
had explained to me the previous week. "They
weren't evolving in isolation from everything else.
They were part of dynamic ecosystems, which were much
like ecosystems that we see today."
By
this view, only once we have looked over the Garden
of Eden's flora do we zero-in on the two-legged
mammals. Although the fossil record is as full of
gaps as 36 exposures of the D-Day landings, we can
tell from bits of skull and bone that the rain forest
was home to so many types of monkey (which ran
horizontally through the trees), apes (which
clambered upright, or swung) and Dart's
australopithecines (which analyses of the famous Lucy
skeleton from Ethiopia suggest slept in the branches,
but waddled awkwardly on the ground), that the
features of each shaded into the next: a jumble of
evolutionary traits.
Even
using such names for countless related hominids
creates a misleading cartoon reconstruction, but
accepting Australopithecus as my dream's
knuckle-swinger from before The Dawn of Man,
and Homo erectus as the first step after the
sunrise (say, 2-2.5 million years ago), then
understanding why one died off and the other took off
might explain why in sleep my hands touched the
ground and awake they gripped a wheel.
Perhaps
another reason for my rainforest dream is that,
awake, I kind of envied Australopithecus. Although he
got by on a mere 450gms of brains, compared with my
possible 1400gms, in the lush, steamy vegetation
before today's Serengeti, he didn't have much to use
it for except eating, sleeping and sex. Males were
vastly bigger than females, and would have been able
to live much like gorillas do now: keeping harems
grouped near their favourite trees, where food was in
good supply.
This
was California Dreamin' without the property taxes,
and you can bet he didn't bludgeon his way out.
Instead, new technologies, analysing such things as
cores drilled from Arctic ice-caps and ocean beds,
reveal that between about 2.59 and 1.69 million years
ago, long-term climate changes would have shocked
Australopithecus like an eight-lane freeway down Main
Street. Variations in Earth's orbit threw the planet
into a cooler cycle - cutting atmospheric energy, and
therefore rainfall, and causing swathes of the forest
to wilt. First, patches of light woodland thinned the
lush canopy. Then came grassland, the dry savannah,
like parts of the Serengeti on which I drove.
This
change in itself had dramatic outcomes as many plant
and animal species went extinct. But the
environmental engine of our species' evolution was
also moving in another direction. Earth, then
celebrating its 4-billionth birthday, was also
shrinking, causing its crust to crunch and continents
to drift, throwing landscapes this way and that. As
earthquakes rumbled around the Pacific zone, a
6,000km fissure tore through east Africa (today's
Rift Valley, from the Red Sea to Tanzania's Lake
Manyara): creating a hotpotch of faults, buckles,
domes, basins, and all kinds of contortions in the
landscape.
Geological
surveys of sediment beds, sometimes hundreds of
metres thick, show that, over thousands of years,
local climates ebbed and flowed as mountains rose and
valleys sank. Lakes became rivers and rivers became
lakes, or sometimes both disappeared. Changing rain
shadows and drainage patterns turned forests into
woodlands and woodlands into grass, and sometimes
back into forests.
The
result was thousands of micro-environments, each
suited to different styles of life. "The eastern
Rift Valley and its surroundings had a mosaic of
vegetation types not too unlike those of today,"
wrote the late archaeologist Glynn Isaac in an essay
pasted in my notebooks. "A pattern in which
various types of dry thorn savannah and open
woodlands predominated, was interspersed with gallery
forests along water courses and perennial rivers, and
with evergreen forests on the major highland areas.
Substantial areas of grasslands occurred on
floodplanes and probably on high plateaux. Large
tracts of unbroken lowland forest probably did not
occur."
Analysis
in this chapter in humanity's genesis launched the
first big challenge to Dart. It has been clear to
specialists for at least a decade that the
environmental convulsions would have been quite
enough to cut the ground from Australopithecus,
without any armed New Enlightenment. With its small
brain (only about 50gms bigger than a chimp's) and
restricted locomotion, it would, for the most part,
have been too stupid to adapt to the stresses of the
changes in its habitat.
"The
shrinkage of forests at about 2.5 million years ago
created a crisis for hominids," wrote Steven M
Stanley, in the journal Paleobiology, which I found
on the shelves of the Nairobi library. "Most
populations should have experienced greatly increased
predation pressure. Many (perhaps most) died out,
while others abandoned obligate arboreal activities.
One population, whether it constituted a fraction or
all of the survivors of the ancestral species,
evolved into Homo."
Ironically,
today's investigations into this transformation are
often around sites that the household-name
palaeontologists have long since abandoned as barren.
At Olduvai, for instance, Robert Blumenschine,
professor of anthropology at Rutgers University, New
Jersey, is leading a team that is unearthing material
that the Leakeys could never have recognised. While
the white Kenyans' primarily focused on finding and
ascribing ancient dates to headline-grabbing bone
fragments, these new ventures are struggling to
reconstruct the landscapes and behaviours that would
have been seen nearly 2m years ago.
"So
much research in the past has been concerned with
finding hominid bones and making a case that they are
older or more important than anything else,"
Blumenschine told me. "But we are interested in
what the hominids were doing and why.
Only once we understand that can we seriously start
to tackle questions about why modern humans have the
peculiar traits that we do. These are the interesting
questions, but they have previously been restricted
to the realm of speculation and armchair
philosophising because the right kind of information
was not available from the fossil record."
Working
with scientists from the University of Dar Es Salaam,
he is investigating Homo erectus's takeoff around
what was once a salty lake. Unlike traditional
fossil-hunting, their studies mean digging in huge
areas of land, often far from where bones were found,
to cross-relate individual stone fragments,
fossilised vegetation, pollens and animal remains,
past geology and geography, and other clues to what
life was like. These are then combined with studies
of landscapes around the Rift Valley today.
With
similar work at other sites, this method is firstly
painting a picture of the end of the rainforest Eden.
Among the mosaic of new environments, the most
promising sported galleries of acacia, which lined
streams and dotted the flood-plains of fluctuating
lakes. Rainy seasons spawned short-lived herbaceous
plants, but otherwise the ground beneath the trees
was bare, and woodlands were surrounded by open
grass, only a little more fertile than today.
The
next task has been to decipher what was going on in
such transformed settings. Enough bone fragments have
been found at some east African sites to show that,
far from killing each other off, at least three
radically different kinds of hominid lived in close
proximity for more than a million years. Although
Australopithecus's rain-forest harems were wrecked by
the need to forage further afield, it clung on in the
woodlands until about 1.2m years ago, still sleeping
in the trees. And overlapping it in time and place
were the creatures evolving into Homo erectus, which
spent most of their lives on the ground.
Elementary
theory explains the spark for the transition.
"At the genetic level, evolution occurs by
accumulated substitutions of one nucleotide by
another in the DNA of the organism," is how a
1995 paper in Science puts it.
"Nucleotide mutations arise with constant
probability, but most are lost by chance shortly
after their origin. The fate of the rest depends on
their effects on the organism. Many mutations are
injurious and are readily eliminated by natural
selection... Other mutations are favoured by natural
selection because they benefit the organism."
Some
such mutations would have accomplished a task that
every parent today gives thought to. By comparison
with our ape cousins, human babies are, in effect,
born prematurely, with almost chimp-small brains
which then grow at foetal rate in the first twelve
months after birth. This unique feature reconciled
the narrow maternal pelvis with the big head that was
needed to be smart. Whose nucleotide mutations got
them there first will never be known, but it was the
next step on our path from the forest.
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