Sapiens: a brief History of Humankind

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, o spring 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.
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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

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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 rst 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 re 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 re, they spread far and wide while other trees and shrubs
disappeared.
These changes in vegetation in uenced 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 su ered greatly. Many Australian food chains collapsed, driving the
weakest links into extinction.
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A third explanation agrees that hunting and re agriculture played a signi cant
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 di erent angles. It is hard to nd 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