Deception is a very deep feature of life. Viruses practise it, as do bacteria, plants, insects and a wide range of other animals. It is everywhere. Even within our genomes, deception flourishes as selfish genetic elements use deceptive molecular techniques to over-reproduce at the expense of other genes. Deception infects all the fundamental relationships in life: parasite and host, predator and prey, plant and animal, male and female, neighbour and neighbour, parent and offspring.

Viruses and bacteria often actively deceive to gain entry into their hosts: for instance, by mimicking body parts so as not to be recognised as foreign. Or, as in HIV, by changing coat proteins so often as to make mounting an enduring defence almost impossible. Predators gain from being invisible to their prey or resembling items attractive to them - a fish that dangles a part of itself like a worm to attract other fish, which it eats - while prey gain from being invisible to their predators or mimicking items noxious to the predator.

Deception within species is expected in almost all relationships, and deception possesses special powers. It always takes the lead in life, while detection of deception plays catch-up. As has been said regarding rumours, the lie is halfway around the world before the truth puts its boots on.

But here I want to talk about self-deception. In the early 1970s, I busied myself trying to construct a social theory based on natural selection. When applied to social behaviour, natural selection predicts a mixture of conflicting emotions and behaviour. Contrary to widespread beliefs of the time (and even sometimes now), parent/offspring relations are not expected to be free from conflict, not even in the womb. At the same time, reciprocal relations are easily exploited by cheats, so that a sense of fairness may naturally evolve to regulate such relations in a protective manner.

The general system of logic worked perfectly well for most subjects I encountered, but one problem stood out. At the heart of our mental lives, there seemed to be a striking contradiction - we seek out information and then act to destroy it. On the one hand, our sense organs have evolved to give us a marvellously detailed and accurate view of the outside world - we see the world in colour and 3D, in motion, texture, non-randomness, embedded patterns and a great variety of other features. Likewise for hearing and smell.

Together, our sensory systems are organised to give us a detailed and accurate view of reality, exactly as we would expect if truth about the outside world helps us to navigate it more effectively. But once this information arrives in our brains, it is often distorted and biased to our conscious minds. We deny the truth to ourselves. We project on to others traits that are true of ourselves - and then attack them. We

repress painful memories, create completely false ones, rationalise immoral behaviour, act repeatedly to boost positive self-opinion and show a suite of ego-defence mechanisms.

Why? Surely these biases are expected to have negative effects on our biological welfare. Why degrade and destroy the truth? Why alter information after arrival so as to reach a conscious falsehood? Why should natural selection have favoured our marvellous organs of perception, on the one hand, only to have us systematically distort the information gathered, on the other? In short, why practise self-deception?

During a brainstorm on parent-offspring conflict in 1972, it occurred to me that deception of others might provide exactly the force to drive deception of self. Once I saw conflict over the offspring's personality, it was easy to imagine parental deceit and self-deception moulding the offspring's identity for parental benefit. Likewise, one could imagine parents not just practising self-deception but also imposing it - inducing it in the offspring - to the offspring's detriment but to parental advantage.

The general argument, outlined in my latest book, Deceit, is that we deceive ourselves the better to deceive others. To fool others, we may be tempted to reorganise information internally in all sorts of improbable ways and to do so largely unconsciously.

Why lie to ourselves?

Psychologists are fond of arguing that self-deception occurs because we all want to feel good, and self -deception can help us do so. The main biological objection is this: even if being happier is associated with higher survival and reproduction, as expected, why should we use such a dubious - and potentially costly - mechanism as self-deception to regulate our happiness?

Lying to ourselves has costs. We are basing conscious activity on falsehoods and in many situations this can turn around and bite us. Whether during plane crashes, the planning of stupid offensive wars, romantic disasters, or family disputes, time and again self-deception brings with it the expected costs of being alienated from reality - although, alas, there is a tendency for other people to suffer disproportionately the costs of our self-deception, while the benefits go to ourselves.

My central claim is that self-deception evolves in the service of deception, sometimes by saving on cognitive load during the act of lying. It also provides an easy defence against accusations of deception (namely, I was unconscious of my actions). In the first case, the self-deceived subject fails to give off the cues that go with consciously mediated deception, thus escaping detection. In the second, the actual process of deception is rendered cognitively less expensive by keeping part of the truth in the unconscious. That is to say, the brain can act more efficiently when it is unaware of the ongoing contradiction. And in the third case, the deception, when detected, is more easily defended against - that is, rationalised.

Learning to spot a liar

We talk of the innocence of children, but dissembling and lying show up at very early ages - both in everyday observations and in scientific studies. Children show a wide array of deceptive skills by the ages of two and three, and the earliest clear signs appear at about six months. Fake crying and pretend laughing are among the earliest. Fake crying can be discerned because infants often stop to see whether anyone is listening before they resume.

By eight months, infants are capable of concealing forbidden activities and distracting parental attention. By the age of two, a child can bluff a threat of punishment by saying "I don't care" about a proposed punishment when he or she clearly cares. Motives for children's lies seem broadly similar to those of adults. Lies to protect the feelings of others - so-called white lies - appear only by the age of five.

But lying can be cognitively demanding. You must suppress the truth and construct a falsehood that is plausible on its face, does not contradict anything known by the listener, and is not likely to be known. You must tell it in a convincing way and you must remember the story. People who are lying have to think too hard, and this causes several effects. Consider blinking. When nervous, we blink our eyes more often, but we blink less under increasing cognitive load (for example, while solving problems of arithmetic). Studies of deception suggest we blink less when deceiving.

Similarly, nervousness makes us fidget more, but cognitive load has the opposite effect: people often fidget less in deceptive situations. Men use fewer hand gestures while deceiving and both sexes often employ longer pauses when speaking deceptively. Efforts at controlling oneself can also reveal deception.

A nice example is pitch of voice. Deceivers tend to have higher-pitched voices. Tensing the body inevitably raises the pitch of voice, and this tensing will naturally increase the closer that the liar comes to the key word. Someone denying a sexual relationship with "Sherri" may find that her voice shoots up on mentioning the key person's name: "You think I am there with SHERri."

Another effect of suppression is the production of displacement activities. I once tried to slip a minor lie by a female friend at a bar and saw my left arm twitch involuntarily. Since we had by then been dating for some time, her eyes shot at once to the twitching arm. A few months later, the situation happened again, only with the roles reversed. If this had been a tennis match, the referee would have said on each occasion: "Advantage, your opponent."

The point about cognitive load is that there is no escape. If suppressing your nervousness increases pitch of voice, then trying to suppress that effect may only increase pitch further. If it is cognitively expensive to lie, there is no obvious way to reduce the expense, other than to increase unconscious control. Mechanisms of denial and repression may serve to reduce immediate expense, but with costs later on.

How do we deceive ourselves?

One useful way to look at self-deception in everyday life is in our use of language. Metaphor often flies just below the radar and may have important unconscious effects. Euphe­misms, for instance, may not just soften meaning but invert it. "Waterboarding" sounds like something you would like to do with your children on a Mediterranean holiday, and "stress positions" the perfect way to end a workout, while all of us could benefit from some good "sleep management".

But each of these refers to a form of torture: repeated near-drowning, long-term painful bending and stretching, wholesale sleep deprivation. In the same vein are terms such as "collateral damage" (civilians killed during military operations), "extraordinary rendition" (kidnapping followed by torture), "enhanced interrogation" (torture), "friendly fire" (death at the hands of your own soldiers) and "Final Solution" (the genocide of European Jews). There is also something that has been aptly called the euphemism treadmill, in which each new euphemism soon becomes tainted by what it refers to, so that a new euphemism must be invented to take its place. "Garbage collection" becomes "sanitation work", which morphs into "environmental services". "Toilet" turns into "bathroom" (so you are washing in there), which turns into "restroom" (so you are taking a nap in there).

It seems as if we are running from the negative connotations of words, with no net progress. The association is soon re-established, so we have to keep running.

On the other hand, humour can be seen as anti-self-deception. Comedy is often directed at drawing attention to the contradictions that deceit and self-deception may be hiding. These are seen as humorous. Reversals of fortune associated with showing off - usually entrained by self-deception - are often comical to onlookers. A staple of deceit and self-deception in silent films is the man strutting down the street, dressed smartly, showing off, with head held high, so that he does not see the banana peel underneath him, producing an almost perfect visual metaphor for self-deception.

Humour permits discussion of taboo topics and the views of disempowered groups. Also, people know self-deception is negative but necessary, so humour permits us to bring out this truth for enjoyment and consumption - we are all self-deceivers. Comedy permits a kind of societal-level criticism in which no one need be threatened. It is all just a joke.

Self-deception and sex

Few relationships have more potential for deceit and self-deception than those between the sexes. Two genetically unrelated individuals get together to engage an act that will generate a new human being - sex, an intense experience that is at best ecstatic and at worst deeply dis­appointing or, when forced, extremely painful and damaging.

Sex itself is fraught with psychological and biological meaning at every depth. Are we misrepresenting our level of interest, sexual or romantic, our deeper orientation towards the other, positive or negative, or our very sexual orientation?

I would have thought by now that scientific work would have shown a series of general differences in the sexes regarding deceit and self-deception. I would expect females to be better at seeing through males than vice versa, on grounds of social expertise and amount of time devoted

to social interactions, and I would expect males to be more self-deceived than females: they have more opportunities for benefit through self-

inflation and overconfidence. I believe that women often make a deeper study of deception in their relationships than do men; self-deception is always another matter.

Whether any of my speculations here is true, I have no idea, because there is no proper scientific research on this subject. There is no evidence of women's systematic ability to spot deception better or to propagate it more deftly. Nor is there a clear bias in self-deception when comparing the two sexes, except perhaps for overconfidence, where there surely appears to be a male bias.

Women more than men report being deceived about partner ambition, sincerity, kindness and strength of feeling. Only in willingness to have sex are women seen as more deceptive than men; hardly surprising, given men's interest in sex. Likewise, there is selection for females to simulate orgasm, but rarely a pressure (or necessity) for males to do likewise. Women fake orgasms to massage the male ego and to bring an end to unwanted sex. Some men are completely fooled, many probably at least some of the time.

One can, in turn, measure how much either sex is upset by particular deceptions of the opposite sex. As expected, women are more upset at male over-representation of resources and status than vice versa. But these are minor factors. Where women really get upset is in response to two related deceptions: men misrepresenting the depth of their feelings prior to first having sex and men failing to call or contact them after sex. That these behaviours may also involve self-deception, I have no doubt. As a young man in the early 1960s, I was conscious of something I called "false emotion". I would meet a woman, develop a strong attraction, wheel out my full show, feel I was in love, have sex with her two or three times and then find the entire attraction collapsing. The false emotion of romantic love must have been generated the better to induce the sex that ended it, but I was conscious of this only after the fact.

Conception and lies

A woman's biology changes in very interesting ways during her monthly cycle, with many implications for deceit and self-deception. Women are more attractive at the time of ovulation: they appear to be physically more symmetrical and their waist/hip ratio is slightly more curvaceous. They also derogate the looks of other women more than at other times in the cycle. Women appear to be more sexual in general at the time of ovulation but with a distinct bias towards more genetically attractive men and sex outside their relationships. In several clubs in Vienna where partners were studied over many months, a woman was less likely to show up with her partner near her time of ovulation but to display more skin (that is, to wear less clothing).

At time of ovulation, women's preferences for men's faces shift towards those that are more masculine and symmetrical, signs of genetic quality but not paternal investment. (Women's preference also shifts towards slightly darker men and less hairy ones.)

Wedded to lies

Is self-deception good or bad for marriage? There are two extreme forms of deception in a relationship where sex and love are concerned: the sex is great and you have to fake the love, or the love is real but you have to fake the sex. For the latter, we often invoke fantasy, a prior partner, an imagined partner, an imagined sexual act. Note that these relations are especially dangerous to the partner. If the partner is unaware of your own true reactions, he or she will be unprepared for the betrayal that so likely awaits. On the other side, it may be much harder to fake love when there is strong sexual interest. Low-love relationships are apt to be more volatile, open hostility coexisting with passionate sex.

The aphorism that you should go into marriage with both eyes open and, once in it, keep one eye shut captures part of the reality. When you are deciding whether to commit, weigh costs and benefits equally; when you have committed, try to be positive and not dwell on every little negative detail.

Consider first the positive form of self-deception. Couples last longer if they tend to overrate each other compared to the other's self-evaluation. This has an appealingly romantic ring: "I love you, darling, more than you love yourself, and thereby uplift you." Effects work on both sides. The more you overrate the other, the longer you stay together, and vice versa.

Evidence suggests that marital satisfaction declines linearly over time, but people have a biased memory - they remember early declines in satisfaction, but also more recent increases that offset the early decreases. In one study, both spouses reported steady increases in relationship satisfaction over two and a half years while none could be detected. By the end of the time, though, memories were readjusted so as to remember no improvement in the more distant past, only in the more recent.

In trying to predict which couples would stay together three years later, scientists enjoyed surprising success based on studying the interaction between the two people during recorded sessions. Those who rewrote history in a more thoroughly negative way were predicted to break up. On this basis alone, the scientists correctly predicted all seven marital break-ups, while incorrectly predicting three break-ups that did not occur. Other students of marriage claim to notice that when the ratio of positive to negative acts towards the partner drops below 5:1, the marriage is in trouble.

Fighting self-deception

Where does this leave us? The problem with learning from living is that living is like travelling on a train while facing backwards. That is, we see reality only after it has passed us by.

Before we begin, we may well ask whether we should bother fighting in the first place. Self-deception has been favoured by natural selection, the better to deceive others and ourselves, so why should we fight such tendencies in ourselves? They are advancing our own evolutionary interests. Surely it must be useful to adjust our self-deception strategically - towards situations where it is most likely to be effective - but oppose it in general.

My answer is simple and personal. I could not care less. Self-deception, by serving deception, only encourages it, and more deception is not something I favour. I do not believe in building one's life, one's relationships, or one's society on lies. The moral status of deceit with self-

deception seems even lower than that of simple deception alone, since simple deception fools only one organism - but when combined with self-deception, two are being deceived.

In addition, by deceiving yourself, you are spoiling your temple or structure. You are agreeing to base your behaviour on falsehoods, with negative downstream effects that may be very hard to guess, yet intensify with time. It is worth noting that we have also been selected to rape on occasion, to wage aggressive war when it suits us, and to abuse our children if this brings us some compensating return benefit, yet I embrace none of these actions, regardless of whether they have been favoured in the past. As one evolutionist told me, his genes could not care less about him, and he feels the same way towards them.

In my life, self-deception is often experienced as a series of minor benefits followed by a major cost. I will be overly self-confident, project that image and enjoy some of the illusions, only to suffer a sharp reversal later on, based in part on the blindness induced by this overconfidence. I believe this is a general rule in life, that the cost of ignorance takes a while to kick in, while the benefit of self-deception may be immediate.

So, how to tackle it? Imagine you are washing dishes and carelessly smash a wine glass against the sink bottom, splintering it. What were you thinking about while you did this? If you are like me, more often than not, you were thinking of something hostile and foolish to do to someone else. I have found this rule so often in my life that it is one of the few things I think I have learned, at least on a short-term basis: avoid carrying out actions that you have previously contemplated while you were screwing up during everyday life. As I age, I find myself scrutinising my errors more finely - not just broken wine glasses, but an unexpected lurch or tripping over the curb or some minor social failure - for deeper correlated mental mistakes.

What's more, it is possible consciously to correct for a bias in yourself that you have noticed. Sometimes you can correct your biases quantitatively. I long ago noticed that, when asked for my straight-from-the-heart, no-thinking estimate of a variable, I tended to overshoot by 30 per cent in the positive direction. So when I wanted to know the approximate truth, I just subtracted 30 per cent from my first estimate.

There are other outlets, too: meditation, prayer, disclosure of trauma, even if only to a private journal. Friends are also useful as commentators on our ongoing life. In general, try to avoid overconfidence and unconsciousness. Showing off is a special kind of behaviour in which we tend both to be overconfident and deliberately to exaggerate our behaviour to impress others: it is one of the most dangerous things you can do.

There is no doubt that self-deception and deceit - if they do nothing else - provide us with an unending extravaganza of nonsense, comedic and tragic, large and small. No human group has a monopoly of the disease, nor is anyone immune. How else can one explain that about 20 per cent of US citizens in 2011 claim to believe that their president is a Muslim and 40 per cent say he was not born in the US? Or that the argument can be seriously advanced (and believed) that the same president has a "deep-seated hatred of white people", when his mother was white and he was raised entirely by her and her family?

One nice feature of the study of deceit and self-deception is that we will never run out of examples. Quite the contrary - they are being generated more rapidly than we can deconstruct them. At least we can enjoy the never-ending extravaganza while trying to deepen our consciousness.

This is an edited extract from Robert Trivers's "Deceit and Self-Deception: Fooling Yourself the Better to Fool Others" (Allen Lane, £25)

© Robert Trivers, 2011

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