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I鈥檓 going to eat this swing (Image: Michelle Gibson/Plainpicture)

In Snakes, Sunrises, and Shakespeare, evolutionary psychology pioneer Gordon H. Orians traces the roots of today鈥檚 human quirks in the minds of our ancestors

鈥淓VERY time you go away, you take a piece of me with you,鈥� sang Paul Young in the mid-1980s, creating for me a faintly disturbing image.

However, according toSnakes, Sunrises and Shakespeare by Gordon Orians, something similar happened to our out-of-Africa psychology. So much so that most of our reactions to sights, sounds and other stimuli come ready-made from a box of survival tricks tested long ago.

This idea is not uncontroversial, but Orians certainly has the background to link the intricacies and quiddities of animal behaviour to the environment that moulded them. His work on animal behaviour, especially red-wing blackbirds (Agelaius phoeniceus), produced respected and widely cited studies.

But by the mid-1970s, Orians was thinking more broadly about how behaviour and environment interact. He decided that the way humans think may largely be a legacy of where they developed. In one of science鈥檚 coincidences, several other researchers had the same idea and evolutionary psychology was born.

This is a nicely written introduction to the subject, which reads like a welcome meal made from landmark books The Selfish Gene and The Naked Ape, with Sociobiology for seasoning.

Orians outlines the key thesis: 鈥淥ur ancestors bequeathed to us鈥� responses to environmental challenges 鈥� unpredictable sources of food, ever-present predators, extremes of weather 鈥� [that] have moulded our emotional lives.鈥� Making the right decisions under pressure was vital, and it hardwired our responses, even when they no longer fitted our circumstances.

Orians uses this powerful thesis to explain surprising behaviour. For example, we prefer trees that are easiest to climb, look healthy and appear hardest for predators to access 鈥� and we like them savannah-tree shaped. But it is young girls, not boys, who like to climb them, and who spend more time on playground monkey bars, says Orians. And it is women, not men, who have the wider range of foot motions. Early female Homo sapiens were lighter, more agile: did they climb trees to escape predators, gather food and sleep, while males slept on the ground?

鈥淚t is young girls not boys who like to climb trees and who spend more time on playground monkey bars鈥�

Similarly, there is the tendency among small children to put everything in their mouths. However, they do so only while breast milk provides antibodies 鈥� it slows down at weaning, notes Orians. Like many things in this book, while it can鈥檛 be entirely proven, it makes you wonder.

But what about the snakes, sunrises and Shakespeare of the title? Not only do we dream more about primeval threats like snakes than pocket knives or climate change, but snakes are recognised unconsciously way before the brain consciously recalls any stored information on reptiles.

As for sunrises: they represent safety, signalling we survived the night, while sunsets are uncertain because we may not do so again. And Shakespeare? Here it is the rhythm and cadence that is in evolutionary play, where the displays of language and imagination 鈥� the conjuring of witches and ghosts in Macbeth, or Hamlet鈥檚 soliloquies 鈥� show great mental prowess in a prospective partner. By the way, we are not alone in responding to 鈥済hosts鈥�. Arctic moths have not seen bats and snakes for hundreds of generations, yet still respond defensively to them.

The only way to improve this neat, thought-provoking volume would have been a slightly more critical tone and examples of where evolutionary psychology collapses into speculative, just-so stories. Even so, it may just make you appreciate the origins of people鈥檚 behaviour, so you can be more tolerant on the bus or in the office.

This article appeared in print under the headline 鈥淥ut of Africa, or not鈥�