The evolution of evolution

Helena Cronin

This article originally appeared in the Time Atlantic Special Issue, 'The New Age Of Discovery', Winter 1997-1998

In one of my favourite cartoons, a hopeful patient asks his doctor, 'Have you got something for the human condition?' One cannot but sympathize with the hapless physician. Or so I used to feel. Now my urge is to leap into action crying, 'I'm a Darwinian; perhaps I can help.' For in the past decade or so evolutionary theory has yielded a mind-blowing discovery: it has pried open the neatly-arrayed toolbox that is our mind. Just as Gray's Anatomy laid bare the human frame, so Darwinian scientists are beginning to write the owner-occupier's manual to that hitherto most recondite of mysteries: human nature. Yes, human nature does exist and it is universal. Our minds and brains, just like our bodies, have been honed by natural selection to solve the problems faced by our ancestors over the past two million years. Just as every normal human hand has a precision-engineered opposable thumb for plucking, so every normal human mind enters the world bristling with highly specialized problem-solving equipment. And these capacities come on stream during development as surely as the toddler's first faltering steps or the adolescent's acne and ecstasy.

This mind-and-body-building is orchestrated by genes. But we're not merely their slavish puppets. Certainly, genes can do their work single-mindedly. However, genes - responding to different environments - also underpin the flexibility and variety that typify human behavior. All this apparent design has come about without a designer. No purpose, no goals, no blueprints. Natural selection is simply about genes replicating themselves down the generations. Genes that build bodies that do what's needed - seeing, running, digesting, mating - get replicated; and those that don't, don't. All the more wondrous, then, to discover what natural selection has achieved with human nature. The Darwinian exploration is still a fledgling science. But already it is yielding answers that we didn't even know had questions: What's the winning figure for ratio of waist to hips? Why are mother and foetus locked in irresolvable conflict? Why is fast food so addictive?

New though this science is, researchers are already pretty confident about some things. Fortunately, one of them is sex. Consider a familiar sex difference that emerged in a study of American college students. Asked by a stranger for a date, 50% of both women and men agreed. But asked 'Have sex with me tonight?' not one woman agreed - whereas men shot to 75%. And when students were asked 'How long would you have to know someone before having sex?' the questionnaire had to be rescaled for males requiring only minutes or seconds. Not only are men willing to have sex with a perfect stranger; they're more than willing with an imperfect one too. Another American study found that, for brief encounters, men (but not women) were willing to drop their standards as low as their trousers, ready to dispense with intelligence, humor, charm, honesty and emotional stability.

Why this difference between men and women? When natural selection shaped male-female differences, it didn't stop at muscles and naughty bits. It also shaped differences in our psychologies. Evolution made men's and women's minds as unalike as it made their bodies. Why? Think of it this way. Give a man 50 wives and he could have children galore. But a woman with 50 husbands? Huh! Generation after generation, down evolutionary time, natural selection favored the men who strove most mightily for mates - the most competitive, risk-taking, opportunistic. We are all the descendants of those winners. Females, meanwhile, faced nine months hard labor, breast feeding, rearing. A woman had to be far more picky about whose genes ended up partnering hers. Faced with the prospect of highly dependent offspring, she'd be on the lookout for someone who was not only fit and healthy but also had access to resources. Nowadays a Rolex or designer trainers provide cues. But for our hunter-gatherer ancestors roving the Pleistocene plains, what mattered were social resources - status, reputation, respect. Genes that built brains with tools for making these shrewd decisions were the ones that got themselves replicated.

Of course, natural selection doesn't download its strategic plans straight into our consciousness. Its instruments are emotions, priorities, desires. Behind each of these everyday human feelings are the calculations of natural selection, millions of careful years in the making. So, for example, men, without knowing it, tend to prefer women with a waist-to-hip ratio (WHR) of 0.7 - a waist that is 70% of the hips. Twiggy's skeletal form and Rubens' hefty muses share a 0.7 WHR; so do dumpy Paleolithic 'Venuses', figurines shaped by our ancestors 28,000 years ago. Why? It's an ingenious fertility-detection mechanism. Waists and hips are shaped by sex hormones, estrogen in particular. And the optimal hormonal mix for fertility also sculpts that desired ratio.

Both sexes have a predilection for symmetry. A body with matching right and left sides is an honest signal (because it is hard to fake) that the genes that built it are robust against invading pathogens. As for women's breasts, the larger they are, the more symmetrical they're likely to be. Why? Breast-building requires oestrogen; the larger the breasts the more the developing body must have been awash with it. But oestrogen suppresses immunity, making the woman vulnerable to pathogens. So breasts that are large and yet manage to be symmetrical signal that their owner's immune system is reliably robust. Facial symmetry, too, is highly attractive; beauty, far from being skin deep, is a Stone Age body scan, brimming with information about health and fertility. It's no surprise, then, that there's cross-cultural agreement on what constitutes a beautiful face; even two-month old babies concur.

Sherlock Holmes read the personal column 'because it is always instructive.' Yes, the instructions come straight from the Darwinian textbook. Turn to lonely hearts listings: man seeks young, good-looking woman; woman seeks older, financially stable man. Study sexual fantasies: men - anonymous multiple partners, thoughts of bare skin; women - someone familiar, tender emotions. Consider adultery (what Darwinians politely call 'extra-pair copulations': males go for quantity; females, having established resources within monogamy, go for quality, particularly high-quality genes. Across all its manifestations, human sexuality bears the stamp of evolved sex differences: always preferences diverge and always predictably. But it's not just sexuality. A funny thing happened on the way to divergent mating strategies. Natural selection created males and females so unalike that the differences don't stop at how fast you'll jump into bed; they pervade our psychology, shaping our interests, our values, our ambitions, our skills.

It's often said, for example, that men lack social skills. Don't believe it. It's just that their skills are, all too understandably, not what we call sociable. They are masters at status-seeking, face-saving, assessing reputation, detecting slights, retaliating against insults and showing off. They are more persistent and competitive than females, more disposed to take risks. Who causes most road accidents, climbs Everest, flies to the moon, commits suicide? Who are the alcoholics, motor-bike riders, scientists, child-abusers, CEOs, gamblers, smokers, bungee jumpers, murderers and computer nerds? Men, of course. Men outstrip women in deaths from smoking, homicide and accidents. Social scientists view these causes of death as 'life-style' as opposed to 'biology'. But, in the light of evolutionary theory, speeding to death in a flashy car is enmeshed in men's biology.

Put males and females in the same environment and their evolved psychologies trigger hugely different responses. Boys thrive in competitive exams; girls could do without. Boys play competitive games, big on rules and winners; girls play co-operative games with consensual endings. Men buy records to complete the set, women to enjoy the music. Rich, successful men go for ever-younger 'trophy' wives; top women go for men even richer, more successful - and older - than themselves.

After the enlightenment of the personal column, Sherlock Holmes would turn dutifully to the criminal news. This, he felt, was not instructive. Darwinian detectives do better. Consider the family. Criminologists are fond of remarking that it is the most dangerous place to be. If this were true, it would be a Darwinian scandal. Why? Remember that evolution is about genes getting themselves replicated. Sex is one way. Another is for genes to help copies of themselves in other bodies. One reliable way is to help kin - the closer the relationship, the more help is given. From this genetic reckoning, calculated by the blind forces of natural selection over millions of years, spring some of our most cherished human values. Whenever a mother braves hazards to save her child from drowning, whenever a brother donates a kidney for his sibling, 'kin selection' is at work. We are evolved to lavish altruism on our kin, not to abuse or kill them. So it's no surprise to find that the criminologists are wrong.

Take murder. For a start, most family victims are spouses - not genetically related at all. But what about infanticide? Children are cargoes of their parents' genes, 50% each, sallying forth into future generations. Infanticide is therefore a profound challenge to evolutionists - so profound that it sent intrepid Darwinians trawling through the statistics in Britain and North America to find out what proportion of murdered children died at the hands of their genetic parents. The researchers discovered that step-children are about 100 times more likely to be killed than genetic children. It's true what they say about Cinderella: having a step-parent puts a child at greater risk than any other known cause.

But where there is sharing, there also lies competition. When your children insist indignantly that your decision is not fair; when they squabble over a toy; when mother's keen to wean and baby resists - then bear in mind the following calculus of kin selection. A child's life is its sole bid for genetic immortality; and it values itself more than it values its brothers and sisters. Indeed, it is 100% related to itself but has only a 50% chance of sharing genes with siblings. But for a parent each child has the same value, a 50% relationship. The child will therefore always value itself, relative to its siblings, more than its parents do. The result is conflict. A child is evolved to want more than parents are evolved to give,

Pregnancy puts its own peculiar twist on this conflict because, at this point in the child's life, even the parents' interests diverge. Indeed, the womb harbors strife between mother and father that would make a divorce court look peaceable. 'He only wants me for my body,' women have cried down the ages. Darwinian analysis is now revealing that this is even more true after conception than before it. Fifty per cent of a foetus' genes come from its father. Our species cannot boast a history of reliable monogamy; so genes from that father might never borrow that womb again. Therefore paternal genes in the foetus have evolved to exploit the mother's body more than is optimal for her. The battleground is the placenta, an invasive network of plumbing that siezes control of the mother's blood supply, enabling the fetus to grab more than its (maternally calculated) fair share of nutrients. This has set off a maternal-foetal arms race, escalating wildly over evolutionary time. Occasionally, a mother succumbs to one of the typical illnesses of pregnancy, such as diabetes. Only in the light of Darwinian analysis have we at last been able to understand these recurrent pathologies; they are glitches in an irresolvable conflict.

Darwinian science is also beginning to discover how our ancient tool kit fares in the modern world. For 99% of human existence we lived as hunter-gatherers. Ten thousand years ago agriculture arrived. Our evolved bodies and minds were unchanged; but, placed in novel environments, triggered by cues they were not designed to cope with, how would they respond? For an inkling, go no further than your local fast-food joint. It is a monument to ancient tastes, to our evolved preferences for sugar, fat and salt. In our past, these finds were so scarce that we couldn't eat too much. Now our instincts are misled, resulting in the first epidemic of obesity that humans have ever known.

And we are processing not only food but also information that we weren't designed to digest. We have initiated a huge inadvertent experiment on human nature. Think of our devices for choosing mates - exquisitely fine-tuned but not, perhaps, to some of today's challenges. A recent study found that, when people were shown pictures of beautiful and high status people of the opposite sex, both women and men became more dissatisfied with their own partners. We were evolved to assess beauty and status, and to calibrate our satisfaction against a few hundred people at most. Yet we are all now exposed daily to images of the world's most beautiful women and richest and most powerful men, more beguiling than any our ancestors ever saw. Global communications amplify these invidious messages across the world.

Our species has been faced with unprecedented inequalities ever since agriculture enabled us to hoard resources. But in recent years the game has increasingly become winner-take-all. From the world's chess champion to the leading libel lawyer, the few places at the top command almost all the status; and, as rewards rise, the gap between top and bottom grows. Caught in this game are males who are evolved to value status. What impact might these novel inequalities be making on them? Might it be significant that throughout the developed world, countries with the greatest inequalities in income have the poorest health and earliest death.

What of the future? It is often claimed that human evolution has ended because technology cushions us from disease and death; and, equally often, it is claimed that human evolution is accelerating because technology favors balloon brains on puny bodies. Neither is true. Natural selection's pace is slow; genes are plodding on with building bodies and minds in much the same way as they have for a million or so years, and that's how they'll continue for a long time to come. The adaptations that we bear tell us about long-lost worlds in which our ancestors dwelt. But those same adaptations tell us about our future. For it is not to human nature that we should look for change but to the intriguing new responses, the innovative behavior, that changing environments will elicit from that nature. And this enduring thread of humanity reminds us that, however novel our environments, their most salient feature - for us and our descendants, as for our ancestors - is other human beings like ourselves, a meeting of evolved minds.

Further publications|