The Great Divide: History and Human Nature in the Old World and the New, By Peter Watson

The Great Divide is one of several recent books on the deep ecological roots of human history, a trend begun by Jared Diamond with Guns, Germs and Steel (1997). Peter Watson takes some leads from Diamond but goes much further in his attempt to rescue the pre-Columbian world of the Americas from the contempt and even hatred expressed by many at the time of the 2009 Aztec exhibition at the British Museum. One article called the artefacts on display "As evil as Nazi lampshades made from human skin".

There are many ways to look at the divide between the Old and New Worlds. Diamond pointed out the huge consequences that followed from the East-West orientation of Eurasia (the same crops and animals will thrive at similar latitudes; no bar to long distance trade routes) and the North-South orientation of the Americas, which had only one potentially domesticable large mammal, the llama. The consequences of this imbalance were devastating and in Diamond's famous formulation accounted for the fact that Pizarro captured the Inca Emperor Atahualpa rather than vice versa.

So colonisation began, and hence the "Columbian Exchange". Eurasia got tomatoes, potatoes, maize, rubber, silver, gold; South America got smallpox, malaria, bubonic plague, population decimation, slavery, ecological destruction. The exchange greatly enriched the globe but destroyed indigenous American cultures. As Charles Mann pointed out in 1493, globalisation began with Columbus over 500 years ago. There were a few negatives passing from New to Old – tobacco, syphilis and cocaine – but they hardly evened up the score.

Watson's technique is to explore the connection between myths and historical and natural events. In the case of the expulsion from the Garden of Eden (onset of farming) and the Flood (probably the sea level rise of around 6000BC) the connection seems well-founded. In South America, he attempts to explain pre-Columbian ritual killing: "Only extraordinary events can explain what is to us the barbarity yet universality of human sacrifice".

Effectively, the book is a history of the world from 15,000 BC to 1500AD, and there is much that is truly illuminating. The more we know about the emergence of agriculture, the more plausible the story of Adam and Eve as an allegory of the change from the hunter-gatherer life to settled farming. A passage from Genesis ("I will greatly multiply your sorrow and your conception; In pain you shall bring forth children") reflects the big changes that came with sedentism. Farming and a settled life allowed women to have babies every two years instead of the four usual in hunter-gatherer societies. There is evidence that the female pelvis is narrower in modern humans than in hunter-gatherers.

But Watson goes further and suggests that humans did not understand the role of sex in conception until they began to breed animals around 11,000 years ago. His argument sounds plausible until, over 150 pages later, he recounts the creation myth of the Tukanoans, an Amazonian tribe with no experience of animal breeding, in which "the male sun had fertilised the female Earth with its phallic ray".

Watson's rationale for the different religions that developed in the Middle East and South America does carry conviction. In the Old World, the regularity of the natural cycles meant that supplicative religions could be said to work. If your existence depends on the Nile flooding every year or the arrival of the monsoon, and you engage in rituals to implore these life-giving waters to return, and they do – the ritual is consolidated. But in the New World, the climate was extreme, with terrifying unpredictable events such as volcanic eruptions, tsunamis, earthquakes, violent storms. The gods were unappeasable and human sacrifice became the last resort. A reinforcing factor was the abundance of hallucinogens in South America; thanks to them, "the existence of the supernatural world was... more convincing".

In drawing together evidence from complex strands of archaeology, climatology, genetics and religious symbolism, Watson is compulsively speculative, but not every resemblance is meaningful. Too often, he leaps to improbable associative conclusions. His most elastic skein of speculation takes in the hallucinogenic herb Syrian rue, Nazi truth drugs, the red dye in Persian carpets, and concludes that Syrian rue might have "given rise to the tradition of the 'flying carpet'".

Watson makes a good case that South America was dealt a poor hand; but that does not mean we should find any virtue in the desperate practices resorted to: the hallucinogens, the shamans, the sacrifices. Pre-Columbian South America did not develop the full Western package of agriculture, domesticated animals, advanced technologies and monotheism because the materials were not to hand for them. The terrible violence inflicted by the Spanish was inexcusable but the most serious damage was done by the germs and ecological pests the Europeans brought with them. This was a tragedy but it was inevitable.

Peter Forbes is the author of 'Dazzled and Deceived: Mimicry and Camouflage' (Yale)