Can modern science explain gender differences or our capacity for cruelty and kindness?

Aleading medical journal publishes a reverential tribute to a cat with an "uncanny ability to predict" when residents of a nursing home are about to die. A team of neuroscientists scan the brain of a dead salmon while showing it photos and asking it what emotions the people in the pictures must have been experiencing. Looking for insights into the differences between boys and girls, researchers ply monkeys with toy trucks and dolls. In their different ways, these reports all pose awkward questions about the relationship between nature and human nature. Onlookers might well wonder if this science is mad, bad, or dangerous to know.

For the primatologist Frans de Waal, animals are a profound source of comfort about the human condition. It is not that they are always comforting to observe. De Waal has documented chimpanzee violence in horrific detail: "All missing body parts were later found on the cage floor," he noted in a report on the "brutal elimination of a rival". He also set this aggression in the context of power struggles and alliances that he identified as "chimpanzee politics". These insights helped to shape a theory that human intelligence is "Machiavellian" in origin, evolved as an adaptation to life in complex societies full of other clever, manipulative primates.

Yet our ancestors wouldn't have needed to manipulate each other if they hadn't needed each other. The human condition is one of mutual dependency, relying upon and revolving around co-operation. In de Waal's latest book, The Age of Empathy: Nature's lessons for a kinder society (Souvernir Press, £18.99), he offers a plethora of examples to show that empathy, kindness and caring are as natural as violence and rivalry. When a chimpanzee is wounded or defeated by a rival, a friend or relative may console it with a hug. An arthritic old chimp may be helped up a tree by a sturdy junior. On occasion, adults in zoos have drowned trying to save young chimpanzees that have fallen into moats: chimpanzees cannot swim and dread water.

Such capacities are not exclusive to ourselves and our nearest relatives. Observers witnessed an agitated elephant's attempts to lift up a dying fellow using her tusks; in another incident, after similar efforts failed to save a shot elephant, one of her family tried to stuff grass into her mouth. These elephants showed both signs of concern about another's plight and a desire to do something about it, as well as some sense of what an appropriate response might be. They illustrate poignantly the central theme of de Waal's popular writing: that goodness is not a delicate invention recently applied by humans as a veneer over a pitiless and amoral nature, but a quality that arises from nature and has deep roots within it.

De Waal's writing is appropriately warm, engaging and empathic. His readiness to discern kind qualities in animals encourages the reader to be similarly open to the idea that we might learn to live better by considering ourselves as evolved beings, rather than ones who have risen above nature.

But in this latest essay his warmth has blurred his focus. He surmises that Oscar the cat, the prophet of death in the New England nursing home, is trying either to comfort himself when he curls up with people whose time has come, or trying to comfort them. Yet the journal report depicts Oscar as a cat who stalks the corridors like a haughty consultant, without a scrap of warmth for anybody not about to expire; nor do those he picks out appear to be actually suffering. He might be drawn to the dying by some terminal scent, or just their immobility. De Waal's preference for an explanation based on empathy, or even the germ of an existential awareness of mortality, inspires unease about his readiness to see kindness everywhere.

The cue for this latest account of his vision was the combination of the banks' downfall and Obama's advent. "Greed is out, empathy is in," he declares. It remains to be seen whether we have entered a new age of empathy or have just passed through the Obama moment. Today's Tea Party is a less kindly affair than those chimps in the zoo used to have. The prospect of a new epoch that "stresses co-operation" and puts the "emphasis on what unites a society" has provoked an opposite and possibly more than equal reaction.

Obama himself has spoken of an "empathy deficit". One of our society's most pervasive psychological beliefs is that this deficit is concentrated among males of our species; and one of its most pervasive psychological suspicions is that the shortcoming is innate. Glowing images are compelling, and popular accounts of cognitive neuroscience have seized upon brain-scanning experiments to proclaim, with liberal use of mysterious anatomical Latin, that male and female brains are differently "hard-wired".

Even neuroscientists themselves risk being mesmerised by the glowing lights – and this is where the dead salmon comes in. The scientists who conducted the deadpan exercise, which Cordelia Fine includes among many colourful studies she dissects in Delusions of Gender: the real science behind sex differences (Icon, £14.99), did it to remind their colleagues of the need to correct scans for false positive signals. By omitting to do so, they detected hints of empathy in a dead fish.

It was an apt choice of subject in a field littered with red herrings. Claims about differences between the brains of men and women – such as that the hemispheres of women's brains are more richly connected than men's, or that women's brains divide the processing of language more evenly between the hemispheres – have not stood up well to scrutiny. For Fine, a psychologist, the persistence of claims about sex differences in the brain despite the weakness of their empirical support is "neurosexism": the same old prejudice that prompted a neurologist in 1915 to remark that women's brains were not well organised for "political initiative".

Although such prejudices have been forced to stage a colossal retreat over the past few decades as women have proved them wrong by example, beliefs about the innateness of psychological differences between the sexes may actually have been reinforced by a generation that sought to refute them. Believing that they brought their children up without the baggage of old gender stereotypes, yet finding that those children avidly opted for pink or blue, they concluded that difference must be inborn after all.

Fine doubts, probably with good reason, that parents reject stereotypes as strongly as they like to think. She shows how vulnerable people are to conditioning about gender. Even the gentlest reminder can encourage them to conform to stereotypes.

In one test, men did better in maths, and women better on verbal skills, when the paper invited them to tick boxes to indicate whether they were male or female. Such priming effects are a powerful force – as she demonstrates by priming her discussion of sex-difference neuroscience with a hundred pages on culture and sexism. She makes ruthless sport with the shortcomings of the scientific findings, pointed up with ironic flourishes that give her critique a columnist's tone. Readers who feel threatened by biological explanations of psychological differences between the sexes will find all the reassurance they want in this book.

Lise Eliot, a neuroscientist, takes a similar view of the state of the science and the power of conditioning. But in Pink Brain, Blue Brain: How Small Differences Grow into Troublesome Gaps – and What We Can Do about It (Oneworld, £12.99), she accepts that there are subtle, inborn differences between male and female brains, upon which the forces of stereotype seize. She is ready to allow, for instance, that a wider spread of abilities might underlie the preponderance of males among the highest maths achievers. Fine prefers to highlight a few countries that defy this general pattern.

Eliot is confident that although such marginal differences are amplified and stylised under the pink-blue order that still prevails, they could be diminished and nuanced by quite simple techniques, such as helping boys develop the vocabulary they use to describe emotions. She tells her story authoritatively but modestly, with frequent references to her experience as a mother, and illuminates a very accessible pathway through the science.

The way the two scientists treat the case of the monkeys illustrates the difference between them nicely. A couple of studies have found signs that male monkeys prefer boys' toys and females prefer girls' toys. One of the preferences observed, among female vervet monkeys, was for a pot.

Fine pounces on this as an opportunity for an arch quip about how monkeys are not known to practise "the art of heated cuisine". The researchers themselves suggested that the preference was actually for the pot's red colour. Fine buries this point in a footnote, whereas Eliot cites the researchers' discussion to suggest that female monkeys are drawn to reds and pinks because those are the colours of newborn monkeys.

Fine points out that the monkeys' apparent preferences are not especially strong or clear. But the fact that there were any preferences apparent at all in such distant primate relatives is remarkable. These studies may have detected the germ of a psychological difference between males and females that takes a far more developed form in humans, just as compassion and co-operation in humans is far more developed than it is among chimpanzees and elephants.

Such possibilities are not as heartwarming as signs that kindness has a deep evolutionary ancestry, but they're the kind of scientific puzzle that tugs at the curtains of the imagination. And, as de Waal affirms, the more we learn about nature, the more richly we're able to imagine a better society.

Marek Kohn's 'Turned Out Nice: How the British Isles Will Change as the World Heats Up' is published by Faber & Faber