The great beasts vanish

North America had an animal world on a par with Africa's today: mammoths, mastodons, ground sloths four metres tall, camels, lions, cheetahs, short-faced bears and sabre-toothed cats. Within a few thousand years three-quarters of all mammals over 44 kilograms were gone.

What was lost

**Mammoth and mastodon**

two unrelated elephant groups, one of the steppe, one of the forest

**Megatherium and relatives**

ground sloths the size of elephants

**Smilodon**

the sabre-toothed cat, with canines eighteen centimetres long

**Arctodus**

the short-faced bear, probably the largest land carnivore of its time

**Horse and camel**

both evolved in North America, both gone from it

Timeline

50,000 years ago

the fauna stands intact; La Brea captures it

16,000

people are documented south of the ice

13,000

Clovis points spread across the continent

12,900

the Younger Dryas: an abrupt return to cold

11,700

the Holocene begins; forests move north

10,800

the last secure mammoth dates on the mainland

4,000

dwarf mammoths still survive on Wrangel Island in Siberia

The argument

Two explanations have faced each other for sixty years. **Overhunting:** people arrived, and within a thousand years the animals were gone — the pattern repeats on Madagascar, New Zealand and Australia, each time humans appear. **Climate:** the ice age ended, the mammoth steppe vanished, and animals adapted to cold and grass lost their habitat.

The question is probably mis-posed. Climate fragmented the populations and left them small and separated; hunting took a fauna already under pressure. Large animals breed slowly, and a population halved by drought cannot also absorb a hunting pressure it has never met.

A third factor: these animals had no experience of humans. African megafauna evolved alongside us for millions of years and learned to fear us. American fauna met a new predator arriving fully equipped with spears.

What the absence did

The consequences are not only ecological. When the Americas met the Old World in 1492, the continent had no horse, no cattle, no sheep, no pig — no large draught animals at all. That means no plough, no cart in practical use, no cavalry, and — decisively — no dense livestock keeping and therefore none of the epidemic diseases that follow from it.

That imbalance explains much of what happened after 1492, and it was settled eleven thousand years earlier.