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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.
*****
This
report is copyright, Brian Deer. Responses,
information and other feedback concerning this
resource homo erectus and the origins of the
human species are appreciated - via the briandeer.com homepage.
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