4. The Flood
PRIOR TO THE COGNITIVE REVOLUTION, humans of all species lived
exclusively on the Afro-Asian landmass. True, they had settled a few islands by
swimming short stretches of water or crossing them on improvised rafts. Flores,
for example, was colonised as far back as 850,000 years ago. Yet they were
unable to venture into the open sea, and none reached America, Australia, or
remote islands such as Madagascar, New Zealand and Hawaii.
The sea barrier prevented not just humans but also many other Afro-Asian
animals and plants from reaching this ‘Outer World’. As a result, the organisms
of distant lands like Australia and Madagascar evolved in isolation for millions
upon millions of years, taking on shapes and natures very different from those of
their distant Afro-Asian relatives. Planet Earth was separated into several
distinct ecosystems, each made up of a unique assembly of animals and plants.
Homo sapiens was about to put an end to this biological exuberance.
Following the Cognitive Revolution, Sapiens acquired the technology, the
organisational skills, and perhaps even the vision necessary to break out of Afro-
Asia and settle the Outer World. Their first achievement was the colonisation of
Australia some 45,000 years ago. Experts are hard-pressed to explain this feat. In
order to reach Australia, humans had to cross a number of sea channels, some
more than a hundred kilometres wide, and upon arrival they had to adapt nearly
overnight to a completely new ecosystem.
The most reasonable theory suggests that, about 45,000 years ago, the
Sapiens living in the Indonesian archipelago (a group of islands separated from
Asia and from each other by only narrow straits) developed the first seafaring
societies. They learned how to build and manoeuvre ocean-going vessels and
became long-distance fishermen, traders and explorers. This would have brought
about an unprecedented transformation in human capabilities and lifestyles.
Every other mammal that went to sea – seals, sea cows, dolphins – had to evolve
for aeons to develop specialised organs and a hydrodynamic body.
The Sapiens
in Indonesia, descendants of apes who lived on the African savannah, became
Pacific seafarers without growing flippers and without having to wait for their
noses to migrate to the top of their heads as whales did. Instead, they built boats
and learned how to steer them. And these skills enabled them to reach and settle
Australia.
True, archaeologists have yet to unearth rafts, oars or fishing villages that
date back as far as 45,000 years ago (they would be difficult to discover, because
rising sea levels have buried the ancient Indonesian shoreline under a hundred
metres of ocean). Nevertheless, there is strong circumstantial evidence to support
this theory, especially the fact that in the thousands of years following the
settlement of Australia, Sapiens colonised a large number of small and isolated
islands to its north. Some, such as Buka and Manus, were separated from the
closest land by 200 kilometres of open water. It’s hard to believe that anyone
could have reached and colonised Manus without sophisticated vessels and
sailing skills. As mentioned earlier, there is also firm evidence for regular sea
trade between some of these islands, such as New Ireland and New Britain.1
The journey of the first humans to Australia is one of the most important
events in history, at least as important as Columbus’ journey to America or the
Apollo 11 expedition to the moon. It was the first time any human had managed
to leave the Afro-Asian ecological system – indeed, the first time any large
terrestrial mammal had managed to cross from Afro-Asia to Australia. Of even
greater importance was what the human pioneers did in this new world. The
moment the first hunter-gatherer set foot on an Australian beach was the moment
that Homo sapiens climbed to the top rung in the food chain on a particular
landmass and thereafter became the deadliest species in the annals of planet
Earth.
Up until then humans had displayed some innovative adaptations and
behaviours, but their effect on their environment had been negligible.
They had
demonstrated remarkable success in moving into and adjusting to various
habitats, but they did so without drastically changing those habitats. The settlers
of Australia, or more accurately, its conquerors, didn’t just adapt, they
transformed the Australian ecosystem beyond recognition.
The first human footprint on a sandy Australian beach was immediately
washed away by the waves. Yet when the invaders advanced inland, they left
behind a different footprint, one that would never be expunged. As they pushed
on, they encountered a strange universe of unknown creatures that included a
200-kilogram, two-metre kangaroo, and a marsupial lion, as massive as a
modern tiger, that was the continent’s largest predator. Koalas far too big to be
cuddly and cute rustled in the trees and flightless birds twice the size of ostriches
sprinted on the plains. Dragon-like lizards and snakes five metres long slithered
through the undergrowth. The giant diprotodon, a two-and-a-half-ton wombat,
roamed the forests. Except for the birds and reptiles, all these animals were
marsupials – like kangaroos, they gave birth to tiny, helpless, fetus-like young
which they then nurtured with milk in abdominal pouches. Marsupial mammals
were almost unknown in Africa and Asia, but in Australia they reigned supreme.
Within a few thousand years, virtually all of these giants vanished. Of the
twenty-four Australian animal species weighing fifty kilograms or more, twentythree
became extinct.2 A large number of smaller species also disappeared. Food
chains throughout the entire Australian ecosystem were broken and rearranged.
It was the most important transformation of the Australian ecosystem for
millions of years. Was it all the fault of Homo sapiens?
Guilty as Charged
Some scholars try to exonerate our species, placing the blame on the vagaries
of the climate (the usual scapegoat in such cases). Yet it is hard to believe that
Homo sapiens was completely innocent. There are three pieces of evidence that
weaken the climate alibi, and implicate our ancestors in the extinction of the
Australian megafauna.
Firstly, even though Australia’s climate changed some 45,000 years ago, it
wasn’t a very remarkable upheaval. It’s hard to see how the new weather
patterns alone could have caused such a massive extinction. It’s common today
to explain anything and everything as the result of climate change, but the truth
is that earth’s climate never rests. It is in constant flux. Every event in history
occurred against the background of some climate change.
In particular, our planet has experienced numerous cycles of cooling and
warming. During the last million years, there has been an ice age on average
every 100,000 years. The last one ran from about 75,000 to 15,000 years ago.
Not unusually severe for an ice age, it had twin peaks, the first about 70,000
years ago and the second at about 20,000 years ago. The giant diprotodon
appeared in Australia more than 1.5 million years ago and successfully
weathered at least ten previous ice ages. It also survived the first peak of the last
ice age, around 70,000 years ago. Why, then, did it disappear 45,000 years ago?
Of course, if diprotodons had been the only large animal to disappear at this
time, it might have been just a fluke. But more than 90 per cent of Australia’s
megafauna disappeared along with the diprotodon. The evidence is
circumstantial, but it’s hard to imagine that Sapiens, just by coincidence, arrived
in Australia at the precise point that all these animals were dropping dead of the
chills.3
Secondly, when climate change causes mass extinctions, sea creatures are
usually hit as hard as land dwellers. Yet there is no evidence of any significant
disappearance of oceanic fauna 45,000 years ago. Human involvement can easily
explain why the wave of extinction obliterated the terrestrial megafauna of
Australia while sparing that of the nearby oceans. Despite its burgeoning
navigational abilities, Homo sapiens was still overwhelmingly a terrestrial
menace.
Thirdly, mass extinctions akin to the archetypal Australian decimation
occurred again and again in the ensuing millennia – whenever people settled
another part of the Outer World. In these cases Sapiens guilt is irrefutable.
For
example, the megafauna of New Zealand – which had weathered the alleged
‘climate change’ of c.45,000 years ago without a scratch – suffered devastating
blows immediately after the first humans set foot on the islands. The Maoris,
New Zealand’s first Sapiens colonisers, reached the islands about 800 years ago.
Within a couple of centuries, the majority of the local megafauna was extinct,
along with 60 per cent of all bird species.
A similar fate befell the mammoth population of Wrangel Island in the
Arctic Ocean (200 kilometres north of the Siberian coast). Mammoths had
flourished for millions of years over most of the northern hemisphere, but as
Homo sapiens spread – first over Eurasia and then over North America – the
mammoths retreated. By 10,000 years ago there was not a single mammoth to be
found in the world, except on a few remote Arctic islands, most conspicuously
Wrangel. The mammoths of Wrangel continued to prosper for a few more
millennia, then suddenly disappeared about 4,000 years ago, just when the first
humans reached the island.
Were the Australian extinction an isolated event, we could grant humans the
benefit of the doubt. But the historical record makes Homo sapiens look like an
ecological serial killer.
All the settlers of Australia had at their disposal was Stone Age technology.
How could they cause an ecological disaster? There are three explanations that
mesh quite nicely.
Large animals – the primary victims of the Australian extinction – breed
slowly. Pregnancy is long, offspring per pregnancy are few, and there are long
breaks between pregnancies. Consequently, if humans cut down even one
diprotodon every few months, it would be enough to cause diprotodon deaths to
outnumber births. Within a few thousand years the last, lonesome diprotodon
would pass away, and with her the entire species.4
In fact, for all their size, diprotodons and Australia’s other giants probably
wouldn’t have been that hard to hunt because they would have been taken totally
by surprise by their two-legged assailants. Various human species had been
prowling and evolving in Afro-Asia for 2 million years. They slowly honed their
hunting skills, and began going after large animals around 400,000 years ago.
The big beasts of Africa and Asia learned to avoid humans, so when the new
mega-predator – Homo sapiens – appeared on the Afro-Asian scene, the large
animals already knew to keep their distance from creatures that looked like it. In
contrast, the Australian giants had no time to learn to run away. Humans don’t
come across as particularly dangerous. They don’t have long, sharp teeth or
muscular, lithe bodies. So when a diprotodon, the largest marsupial ever to walk
the earth, set eyes for the first time on this frail-looking ape, he gave it one
glance and then went back to chewing leaves. These animals had to evolve a fear
of humankind, but before they could do so they were gone.
The second explanation is that by the time Sapiens reached Australia, they
had already mastered fire agriculture. Faced with an alien and threatening
environment, they deliberately burned vast areas of impassable thickets and
dense forests to create open grasslands, which attracted more easily hunted
game, and were better suited to their needs.
They thereby completely changed
the ecology of large parts of Australia within a few short millennia.
One body of evidence supporting this view is the fossil plant record.
Eucalyptus trees were rare in Australia 45,000 years ago. But the arrival of
Homo sapiens inaugurated a golden age for the species. Since eucalyptuses are
particularly resistant to fire, they spread far and wide while other trees and
shrubs disappeared.
These changes in vegetation influenced the animals that ate the plants and
the carnivores that ate the vegetarians. Koalas, which subsist exclusively on
eucalyptus leaves, happily munched their way into new territories. Most other
animals suffered greatly. Many Australian food chains collapsed, driving the
weakest links into extinction.5
A third explanation agrees that hunting and fire agriculture played a
significant role in the extinction, but emphasises that we can’t completely ignore
the role of climate. The climate changes that beset Australia about 45,000 years
ago destabilised the ecosystem and made it particularly vulnerable. Under
normal circumstances the system would probably have recuperated, as had
happened many times previously. However, humans appeared on the stage at
just this critical juncture and pushed the brittle ecosystem into the abyss. The
combination of climate change and human hunting is particularly devastating for
large animals, since it attacks them from different angles. It is hard to find a
good survival strategy that will work simultaneously against multiple threats.
Without further evidence, there’s no way of deciding between the three
scenarios. But there are certainly good reasons to believe that if Homo sapiens
had never gone Down Under, it would still be home to marsupial lions,
diprotodons and giant kangaroos.
