What makes us who we are?

Is it the society in which we live, or something more primeval? Robert M Sapolsky argues that all human difference - and human conflict - was shaped by the lives of our rainforest and desert-dwelling ancestors

A Swede and a Finn, two old friends, go to a bar. They settle down with their bottles of vodka and sit drinking in utter silence. Hours go by as the two drink away without a word. Finally, six hours into it, the Swede, moved by life, love, and friendship, raises his glass to his friend and says: "To your health." To which the Finn replies, "Look, did you come here to drink or to talk?"

The joke was told to me by a Swedish scientist at a conference in Stockholm where we Yanks teased the Swedes about their inexpressiveness: You think we're bad? You should see the neighbours. And yet why should Scandinavians be thought of as taciturn, and Mediterraneans as anything but?

All across the planet, where you live has something to do with the sort of culture you grow up with. Traditional tundra societies are more likely to have cultural patterns in common with each other than with tropical rainforest societies. High-altitude-plateau cultures are likely to differ in systematic ways from island fishing societies.

Some of the correlations between types of ecosystems and types of cultures are fairly predictable - desert nomads are not going to have 27 different words for snow. But some of the correlations are far from predictable and have had a tremendous impact on the type of planet we humans have produced.

Attempts to link culture with climate and ecology have an old history, but with the rise of anthropology as a discipline, those attempts became "scientific". Not surprisingly, the first attempts were often anything but scientific, and were instead howlers of white male racism. Every study seemed to generate irrefutable scientific proof that northern European ecosystems produced superior cultures, more advanced moral, technological, and intellectual development, and better schnitzel.

One of the pioneers of the new version of ecological anthropology was John Whiting of Harvard, who produced a 1964 paper entitled "Effects of Climate on Certain Cultural Practices". Comparing data from non-Westernised societies, he noted that, for example, cultures in habitats that produce protein-poor diets have the longest restrictions on post-partum sex. Whiting figured that with protein-poor diets, infants were more dependent on extended nursing, which placed a premium on keeping births far apart.

Other anthropologists produced ecological studies concerning cross-cultural patterns of violence, in papers such as "Statistical Evidence for an Ecological Explanation of Warfare" (1982), by Melvin Ember of Yale. Ember determined that certain ecosystems are sufficiently stable that family units remain intact throughout the year, farming their plot of land or hunting in the forest. In other, more unstable settings, family units are often split up. During dry seasons, for example, pre-industrial agriculturalists often have to divide their herds into smaller groups, with different family members scattered to distant pockets of grazing land. In situations like those, you're more likely to have age-set warrior classes. There are advantages to a communal standing army, in the event that enemies show up when the men of your family are away.

A radically different approach to cross-cultural research was pursued in the 1960s by Robert Textor of Stanford University, who collected data on some 400 different cultures from around the world and classified them according to nearly 500 different traits. Was a particular culture matrilocal or patrilocal? What sort of legal system did it have? How did its people make a living? Did they believe in an afterlife? When at play, did they prefer games of chance or of strategy? The result is his monumental book, A Cross-Cultural Summary, filled with table after table of what cultural differences are likely to be linked to ecological differences. Where else could you discover that societies that don't work with leather will very reliably only have games of skill? Amid all these different approaches, a basic dichotomy has emerged between two types of societies from very different ecosystems. The dichotomy carries some disquieting implications for the world we have created.

The dichotomy is between people who live in rainforests and those who live in deserts. Mbuti pygmies versus Middle Eastern bedouins. Amazonian Indians versus nomads of the Sahara or the Gobi. The sorts of cultures they generate have some consistent and permeating differences.

Some starters about religious belief. Who are the polytheistic animists, who are the monotheists? That one's easy. Rainforest dwellers specialise in a proliferation of spirits and gods, whereas monotheism was an invention of the desert. This makes sense. Deserts teach big singular things, like how tough a world it is, a world reduced to simple, furnace-blasted basics. "I am the Lord your God" and "There is but one God and his name is Allah" - diktats like these proliferate. In contrast, think of tropical rainforest people, in a world with a thousand different kinds of edible plants, where you can find more different species of ants on a single tree than you would find in all the British Isles. Letting a thousand deities bloom in the same sort of equilibrium must seem the most natural thing in the world.

What's more, when you do encounter monotheistic rainforest dwellers, they're much less likely to believe that their god sticks his or her nose into other people's business - controlling the weather and so on. And this makes sense, too. Rainforests define balance in both an ecological and cultural sense. If the forest pig evades your spear, there are endless plants to gather nearby instead. In contrast, in the desert, an oasis that dries up can be a death sentence, and a world filled with such uncontrollable disasters inspires the fatalism of desert cultures, breeds a belief in an interventionist god.

The next big difference emerges from the work of Melvin Ember. Desert societies, with their far-flung members tending cattle, are the classic spawning ground for warrior classes. And with them come all the accessories of a militaristic society: military trophies as stepping-stones to societal status, death in battle as a guarantee of a glorious afterlife, chains of command, centralised authority, slavery.

If you are a woman, you'd much rather stay away from those desert folks. The purchasing or indenture of wives is significantly less likely in rainforest cultures. Moreover, related women form the core of a community for a lifetime, rather than being shipped off to wherever marriage-making demands. Among desert cultures, women typically have the difficult tasks of building shelters and searching for water and firewood, while the men contemplate the majesty of their herds and envision their next raid. In contrast, among rainforest cultures, it's the men who are more likely to do the heavy work. And rainforest cultures are less likely to have cultural beliefs about the inferiority of women.

Finally, desert cultures are likely to teach their children to be modest about nudity at an earlier age than in rainforest cultures, and to have more severe strictures against premarital sex.

Which kind of culture would you prefer to get traded to? Desert cultures, with their militarism, stratification, mistreatment of women, and uptightness about sexuality seem pretty unappealing. And yet ours is a planet dominated by the cultural descendants of the desert dwellers. At various points, the desert dwellers have poured out of the Middle East and have defined large parts of Eurasian cultures. Such cultures, in turn, have passed the last 500 years subjugating the native populations of the Americas, Africa and Australia.

As a result, ours is a Judeo-Christian/Muslim world, not a Mbuti-Carib/Trobriand one. So now we have Christians and Jews and Muslims in the wheat fields of Kansas, and in the cantons of the Alps, and in the rainforests of Malaysia.

The desert mindset has proven extraordinarily resilient as it has been exported by conquest and diffusion. Sure, there's not a whole lot of those folks still living like nomadic pastoralists. But centuries, even millennia, after the emergence of these cultures, there is still the mark of those desert-correlated traits in the world they've fostered. The West's vanquished enemies, the Taliban, and our well-entrenched good friends, the Saudis, created societies of breathtaking repressiveness. And for an American educator with, say, a quaint fondness for evolution, the power of the Christian right in many parts of the US to dictate what facts and truths may be uttered in a classroom is appalling. Only one way to think, to do, to be. Crusades and jihads, fatwas and inquisitions, hellfire and damnation.

Unfortunately, most evidence suggests that the rainforest mindset is less hardy when uprooted. We have defoliated a world of forests, destroyed for farming, logging, clearing for cattle. This is an age that has not only seen an unprecedented extinction of species, but of cultures and languages as well. The demographer William Sutherland of the University of East Anglia has shown that the places on earth that have the most biodiversity have the most linguistic diversity as well, and those places where biodiversity is most threatened with extinction are where languages and cultures are becoming extinct at the highest rates. And thus the rainforest cultures, with their fragile pluralism born of a lush world of plenty, deliquesce into the raw sewage of the slums of Rio and Lagos and Jakarta.

What are we to make of these correlations between environment and cultural beliefs and practices? Think of us humans as the primates that we are, and it makes perfect sense. Go and discover two new species of monkeys, never before seen. Know nothing about them other than that one lives in the trees of an Amazonian forest and that the other walks the arid scrubland of Namibia, and a primatologist can predict with great accuracy the differing sex lives of the two species, who is the more aggressive, the more territorial, and so on. In that respect, we're subject to the influences of ecology, just like any other species.

Two big things make us distinctive, though. First, our exceptions to rules are far more numerous and dramatic than you find in other primates. After all, that same mean ol' Judeo-Christian/Muslim world has also produced Quakers and Sufis. In contrast, no baboon has ever opted for vegetarianism as a moral statement.

The second thing that's distinctive about human culture is that we're not just talking about ecological influences on the kind of arrowhead you make. What's at stake are some of the most central human issues. Is there a God? What happens when you die, and how do your actions in life affect your afterlife? Is the body dirty and shameful? If you want to understand how people find their answers to those questions, you're going to have to let some biology in through the back door. For example, we understand an extraordinary amount about the genetics, neurochemistry and endocrinology of depression, about how those factors influence whether a person views life as a vessel half-empty or half-full. And we are even beginning to glimpse a biology of religious belief itself.

To answer the question, "How did I become who I am?" we must incorporate a myriad of interactive factors - from the selective pressures that shaped our primate gene pool eons ago to the burst of neurotransmitters a microsecond ago. Maybe it's time to add another biological variable to the list: when our forebears pondered life's big questions, did they do so while contemplating a shroud of trees, or an endless horizon?

This article is adapted from the book 'Monkeyluv and Other Essays on Our Lives as Animals' by Robert M Sapolsky, Jonathan Cape, £17.99. To order it for the special price of £16.99 (inc P&P) call 08700 798 8897