The relentless rise of Homo sapiens

We humans are members of the species Homo sapiens. Much is known of our evolutionary history, some of which is troubling. The story is brilliantly told by historian Yuval Noah Harari in his best-selling book Sapiens: A Brief History of Humankind (Vintage 2015).

A biological species is a group of organisms that can reproduce with each other, producing fertile offspring. Species evolved from a common ancestor are grouped together into a genus (plural genera). Our genus is Homo, meaning “man”, rather pompously qualified as sapiens (“wise”). Genera are grouped into families whose members can trace their lineage back to a founder. Homo sapiens are members of the great ape family whose living relatives include chimpanzees, gorillas and orangutans. Our common ancestor lived six million years ago.

The genus Homo arose in Africa about 2.5 million years ago from Australopithecus, an earlier ape genus. About two million years ago some of these humans migrated and settled in large areas of north Africa, Europe and Asia. These areas are climatically diverse, so, the human populations evolved along different paths. In Europe and western Asia, humans evolved into Homo neanderthalenis, adapted to the cold. Eastern Asia was populated by Homo erectus.

By 70,000 years ago Homo sapiens was evolving very quickly — the cognitive revolution

Meanwhile, new human species arose in Africa including Homo rudolfensis, Homo ergaster and eventually, about 300,000 years ago, Homo sapiens. So, between about two million years and 10,000 years ago, when Homo sapiens took over entirely, the world was home to several human species.

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By 70,000 years ago Homo sapiens was evolving very quickly — the cognitive revolution. Between 70,000 and 30,000 years ago Homo sapiens invented oil lamps, bows and arrows and needles (for stitching clothes) and boats and there is evidence of emerging religion, art, commerce and social layering. Sapiens began to communicate using a new type of language that, inter alia, facilitated the unique capacity to talk collectively about entities they had never seen — sapiens began to believe in myths. Harari believes this gave Sapiens the unique capacity to co-operate collectively in large numbers.

Homo sapiens first migrated from Africa about 100,000 years ago to the Levant, where Neanderthals lived but failed to gain a foothold there. However, about 70,000 years ago, African Homo sapiens again moved north and quickly overran the entire Eurasian landmass supplanting all other human species. Homo neanderthalensis and Homo erectus disappeared.

There are two opposing theories as to what happened Neanderthals and Erectus, the interbreeding and the replacement theories. Interbreeding means attraction, mingling, sex and merging. Replacement means incompatibility, friction and maybe genocide.

Harari points out that interbreeding would mean today’s Europeans are a mixture of Sapiens and Neanderthals and Chinese and Koreans are a mixture of Sapiens and Erectus with genetic differences between today’s Europeans, Africans and Asians going back thousands of years. This could provide evidence for explosive racial theories. Scientists have favoured replacement theory which has better archaeological backing.

However, recent DNA sequencing, using unearthed Neanderthal bones, reveals that 1-4 per cent of DNA in people with European or Asian backgrounds is Neanderthal whereas Neanderthal DNA is extremely low (0-0.2 per cent) in people from African backgrounds. This indicates that Homo sapiens and Homo neanderthalenis did interbreed to a small extent but not enough to support a full interbreeding theory.

About 45,000 years ago Homo sapiens reached Australia which supported a fantastic population of large animals

Neanderthals disappeared about 30,000 years ago. Homo sapiens may have driven Neanderthals to extinction by out-competing them in hunting and gathering — Homo sapiens were more effective hunters and had better social skills. A darker possibility is that the Neanderthals disappeared by genocide.

About 45,000 years ago Homo sapiens reached Australia which supported a fantastic population of large animals (megafauna) eg, a 200kg 2m-high kangaroo, flightless birds twice the size of ostriches, 5m long snakes, a 2.5-tonne wombat (diprotodon) and many more. This megafauna vanished within a few thousand years of man’s arrival.

Homo sapiens reached north America 16,000 years ago and by 10,000 BC had occupied the southern tip of south America. The same story as recounted for Australia unfolded in America — the megafauna quickly disappeared after Sapiens arrived.

Some scholars attribute megafauna extinction to climate change but Harari argues that there is good reason to suspect that Homo sapiens was, if not the sole culprit, also heavily involved. I hope that future research will tell a different story but it may be that Homo sapiens has been both a bad landlord on Earth (global warming) and a bad neighbour to other species.

• William Reville is an emeritus professor of biochemistry at UCC