How did humans come to dominate the Earth?

There are many reasons why humans became the dominant form of life on Earth, not the least of which is our ability to co-operate with each other. Current scientific thinking on the importance of co-operation is summarised by Frans de Waal, a professor of primate behaviour, in Scientific American (September 2014).

The traditional explanation of human success was that we aggressively beat off the competition by seizing land, hunting larger predators into extinction and wiping out other hominid competition, including Neanderthals. De Waal reckons that this scenario is very unlikely because early man was far too small and vulnerable on the open savanna to be aggressive, and lived in fear of pack-hunting hyenas and several kinds of big cats. He reckons we gained our edge through co-operation not violence. I will return to this point later.

Humans have the unique ability to organise and co-operate in large groups and have "a complex morality emphasising responsibility to others that is enforced through reputation and punishment". Such co-operation has deep evolutionary roots and De Waal and others have been studying this in chimpanzees and bonobos, our closest living relatives.

Studies of co-operation among primates reach three main conclusions. Firstly, primates co-operate widely with each other and not only with direct kin. Secondly, co-operation is often a reciprocal arrangement and favours received are remembered: a chimp is more likely to share food in the afternoon with another chimp who groomed him that morning. Thirdly, co-operation can be motivated by empathy. De Waal describes an interesting experiment: two monkeys sit together, and one selects a coloured token from a choice of two colours; one colour rewards only that monkey, the other colour rewards both monkeys. After a little experience of the game, the choosing monkey mostly picks the colour that rewards both monkeys.

De Waal sees the evolutionary origins of co-operative behaviour in the obligatory maternity care required of mammals. The young must be cared for or they will perish. This caring sensitivity and its underpinning hormonal and neuronal processes were then co-opted for other relationships – bonding, empathy and co-operation – within the larger society.

Co-operation brings great benefits. Mutualistic co-operation – working together for a goal that benefits all – is the most widespread form of co-operation, and it brings immediate benefits (for example, a pack of hyenas bringing down a zebra). Mutualistic co-operation encourages more subtle co-operation such as sharing; if one animal reaped all the rewards mutualistic co-operation would collapse. Animals and humans are very sensitive to fair sharing and De Waal quotes experiments showing monkeys, dogs and social birds rejecting rewards smaller than those offered to companions doing the same task.

Sensitive to public opinion

Human behaviour goes beyond that seen in other animals regarding our capacity to co-operate with strangers; other primates are normally competitive between groups. Humans also organise highly complex and hierarchical collaborations to carry out large-scale projects. There are mechanisms, not seen in other animals, to ensure human co-operation. We are very sensitive to public opinion (witness the power of PC) and loath to tarnish our good reputation. There is the well-known demonstration that people donate more money to charity if a picture of two eyes watching them is mounted on the wall. There are punishments for cheating the system. We don’t like freeloaders and we punish them in laboratory experiments.

I am not entirely convinced by De Waal’s hypothesis that co-operation played a far bigger role than aggression in helping humans to achieve dominance. De Waal rightly points to the modest physical attributes of early humans compared to dangerous animal species that would prey upon them.

However, humans have powerful compensating properties compared with other animals. We lack sharp claws but we can aim and hurl rocks. We lack powerful muscles but we can compensate very well by sharpening a stick or stone and impaling a foe. Humans made advanced spears 75,000 years ago. We can recognise patterns and anticipate and pre-emptively eliminate danger. Humans are fearsome killing machines and we have repeatedly demonstrated this capacity throughout recorded history.

[ understandingscience.ucc.ie ]