We evolved more than two million years ago from pre-human ape societies to notably egalitarian hunter-gatherer groups. Then, with the advent of human settlements and farming and the resource surpluses that came with them, we reverted only 10,000 years ago - a flash in evolutionary terms - to social inequalities once again. What was going on and can we draw lessons for how to live today?
Such data will be picked over this afternoon by a social scientist, a biologist and an evolutionary psychologist at a Darwin seminar organised by the Centre for Philosophy of Natural and Social Sciences at the London School of Economics. It is an attempt by the LSE Darwinians to look at inequality through an evolutionary lens and thereby to shed some light on a subject which is usually analysed within a single discipline and not across several.
The inspiration for the event is the new book Unhealthy Societies: The afflictions of inequality by Richard Wilkinson, senior research fellow at the Trafford Centre for Medical Research at Sussex and a visiting professor at University College London. His message is that inequality kills. Countries like the US with big gaps between rich and poor have higher death rates than those with smaller gaps such as Sweden and Japan.
What seem to be more important than the physical effects of poverty are psycho-social factors such as how much control you have over your life. Being poor removes your choices and leads to a breakdown in social cohesion and trust. Research in the US has shown that people at the bottom of the heap experience their environment as hostile.
"Relationships with one's own species are absolutely crucial to welfare," Dr Wilkinson says. "Other species can compete for food supplies, but one's own species compete for everything - jobs, housing, sexual partners, the shirt off your back. But members of one's own species are also the greatest source of support and comfort. So, whether life is heaven or hell depends on your social relationships. I suspect through most of history that has been more important than physical environment to our health and is why in primitive societies there is such an emphasis on food-sharing, gift exchange, and an avoidance of clear opposition of interests."
What are the evolved mechanisms in the human body that lead the low-status to have worse health than their bosses? According to Dr Eric Brunner, a biologist and senior research fellow at University College London medical school who will also speak this afternoon, they are the same kind as those enjoyed by the baboons in Tanzania's Serengeti game park. (In a famous study he looked at Whitehall civil servants and found those with low status had worse health than their bosses - a classic sign that being bottom of the heap induces stress.)
We evolved with a powerful flight-or-fight response. If we were being chased by a lion or grisly bear, our bodies pumped adrenalin to ensure we were in a state of physical alert. Our blood became thicker in order to clot better and our blood pressure went up. (Our immune systems also shut down briefly.) We were ready to run a mile or climb a tree.
Similarly, when we are facing insecurities at work or anxieties in our domestic lives our bodies probably behave in the same way. Our blood pressure rises and we have higher levels of the blood-clotting factor fibrinogen. Only we don't run a mile or climb a tree. With repeated exposure to such conditions - but in the absence of historic ways of dealing with them - it is possible that our bodies suffer.
Enter the evolutionary psychologist. According to Andrew Whiten, a reader in psychology at the University of St Andrews in Scotland, it is generally agreed that our evolutionary past is as hunter-gatherers. With David Erdal, a colleague, he examined 24 modern day hunter-gatherer groups from four continents and found them to be broadly egalitarian - they shared food and power.
"You don't find formal leaders," he explains. "They are very democratic. Decisions are reached by consensus. Sometimes individuals are respected for their expertise but they won't have more sway when it comes to discussing when to move the camp or what to do about a local scandal." Although hunter- gathering groups are generally egalitarian, from time to time they do throw up dominant individuals, who are firmly put down. "The group as a whole manages to overcome an individual who starts to get uppity," he explains. Thus, the mind and body of the modern human have adapted to being a good hunter-gatherer. We have predispositions to behave in ways that seek to reduce conflict and maximise social harmony, at least in certain circumstances.
How, then, do we explain the brutishness and desire for power exhibited by so many around us? That, according to Dr Whiten, is the early non-human primate part of us struggling to get out. The great apes - chimpanzees and gorillas - compete for resources and have a rank order. They go in for inequality and hierarchical societies just as our ancestors are thought to have done.
The question of how we came to evolve from competitive non-egalitarian apes to egalitarian hunter-gatherers is a puzzle. The process was biological evolution, with an enormous increase in brain size a key factor, Dr Whiten says. Possibly it no longer became worth our while to continue to dominate and outmanoeuvre one another in small intimate groups. The evolutionary spiral reached a ceiling where the Machiavellian skills of the population were so refined that it was no longer strategically practicable to expend energy in an effort to dominate others physically. So, we flipped into a stable egalitarian state.
How we came to slip back into inequality is a different story - one not of biological evolution but of response to circumstances. When larger societies developed as we moved into settlements, resources began to be stored up. There were greater incentives perhaps for individuals to dominate others and our ancient pre-human tendencies were given freer rein. We therefore inherit a contradictory mix of early competitive juices overlain by egalitarian tendencies developed on the African grasslands. We might be happier, and healthier, if more people were aware of those facts.
`Unhealthy Societies: the afflictions of inequality', by Richard Wilkinson, Routledge, pounds 12.99.