Picasso joked that he painted with his penis. He died a wealthy man: his estate was worth $1bn. In his lifetime he created 14,000 paintings, 34,000 book illustrations, and 100,000 prints and engravings. He found time to father a child with his first wife, another with his mistress, and two with his second mistress. According to Geoffrey Miller, it is no surprise that one of the 20th century's greatest artists had a way with women.
Miller, an evolutionary psychologist at University College London, believes that the products of the human mind - from fine art to fine conversation - are inextricably linked with sexual conquest. "Evolution is more than the survival of the fittest," says Dr Miller. "Our ancestors had to do more than find food, they had to attract mates, and if they weren't able to attract mates, they didn't pass on their genes." This drive to be sexually alluring to the opposite sex led to the creation of more sophisticated sexual ornaments, which meant bigger brains to perform the increasingly complex mental tasks involved in artistic foreplay.
Charles Darwin's theory of natural selection explains how animals evolved: only those that were well adapted to their environment survived to pass on their traits to their offspring. However, Darwin had a hard time explaining how natural selection could produce the human brain and its intellectual spin-offs. Some scientists have postulated that we needed a large brain to survive; once our brains reached a certain size, other abilities arose as a by-product of this level of complexity. Miller argues that this is a weak answer: "It fails to explain why other large-brained species such as dolphins, whales and elephants did not invent paleontology or socialism." Darwin developed the theory of sexual selection to explain the evolution of certain "non beneficial" traits, such as the peacock's tail.
Miller argues that it could also explain the intellectual abilities of the large human brain. Sexual selection relies on the fact that most females choose the males they want to mate with, and it is female choice which has led to traits as seemingly maladaptive as the peacock's tail. Miller's "mating mind" hypothesis - outlined in a book of the same name published this week - is that the human brain is a sexual ornament as bright and brash as a peacock's tail.
Brains are complex and costly: they take a long time to grow and consume almost a quarter of our total daily intake of energy. "Every sexual ornament in every sexually reproducing species could be viewed as a different style of waste... male elephant seals waste a thousand pounds of their fat per breeding season fighting other elephant seals," Miller says. "Male humans waste their time and energy getting graduate degrees, writing books, playing sports, fighting other men, painting pictures, playing jazz and founding religious cults. These may not be conscious sexual strategies, but the underlying motivations for 'achievement' and 'status' - even in preference to material sources - were probably shaped by sexual selection," he says.
The peacock's tail and the overlarge human brain may not be such a waste of energy as they first seem. In the Seventies, an Israeli scientist, Amotz Zahavi, developed the handicap hypothesis in an attempt to explain why it is no bad thing for a female peacock to be attracted by a peacock's tail - which has no survival advantages. He argued that the tail is a handicap - it prevents males from escaping predators easily. The long tail could be advertising how fit and healthy the peacock is since a fit peacock will be able to escape from predators in spite of his tail.
Recent research suggests that the peacock is also displaying what good condition he is in, for only a bird with few parasites and a healthy immune system could sport a vibrant tail. Miller argues that the same may be true for the by-products of our brains. Human abilities, like cubism and jazz, do not look very adaptive to the environment our ancestors evolved in. But it is precisely these kind of abilities which vary widely between individuals, and which cost time and energy to practice and perform, that could have evolved through sexual selection.
The mind has been described as a computer, a cathedral, even a Swiss army knife. "Perhaps we could do better by picturing the human brain as an entertainment system... the mind as amusement park... the mind as a special-effects science-fiction action film, or romantic comedy... the mind as a Las Vegas honeymoon suite... dance club, cabinet of curiosities, mystery novel...." In other words, our brains evolved the way they did because our ancestors' brains were adapted to entertain other brains.
Miller believes that about 1.6 million years ago, when our ancestors evolved human-like traits, serial monogamy was the norm. This type of mating behaviour is common-place in hunter-gatherer societies and, increasingly, in our own. "Suppose that the level of fascination, happiness and good humour that our ancestors felt in another individual's company was a cue that they used to assess the individual's mind and character. If an individual made you laugh, sparked your interest, told good stories , and made you feel well cared-for, then you might have been more predisposed to mate. Your pleasure in his or her presence would have been a pretty good indicator of his or her intelligence, kindness, creativity and humour," says Miller.
Where males and females only stay together for weeks, months, may be years, but not for life, there would have been ample opportunity for affairs and new relationships. "The incentive for males to attract large numbers of sexual partners through public displays of physical and mental fitness explains why males are so much more motivated to produce such displays," he says. And although female hominids may have been choosing males for their story-telling, hunting or axe-making skills, it was likely they were at least as good at their partners: you need to have a sense of humour to understand that someone has just told a good joke.
In modern courtship, we take our dates to restaurants and pay chefs to cook them gourmet food, we go to the cinema where professional actors tell them stories, or to night clubs where musicians excite their auditory systems. "The chefs, musicians and actors do not actually get to have sex with our dates. They just get paid. We get the sex if the date goes well... to pay the professionals, we have to make money, which means getting a job. The better our education, the better our job, the more money we can make and the better the vicarious courtship we can afford."
The "mating mind" theory can, according to Miller, explain many of the traits we possess today, even the evolution of language. After all, we might pay to see a film, but the girl is not going to go home with you if you can't discuss it wittily afterwards. We have far more words that we need. Most people have a vocabulary of 60,000 words which is a little excessive given that 4,000 of them are used for 98 per cent of our conversation. Neither did our ancestors need a huge vocab to discuss mammoth-hunting tactics, or where to look for tasty tubers.
Instead, we evolved language to get lovers and to get physical. It takes approximately three months to become pregnant if there are no complications and no contraception is used: that's a million words to entertain one's partner long enough to produce a baby.
Our ancestors chose each other on the basis of who was most entertaining, kind, skilled at hunting, and good at making necklaces, or hand axes. Those males and females started choosing each other for their brains. Their brains did not invent television or literature - but they had the potential to.
This then is the latest explanation for Einstein, Eisenhower and Escher; Abba, Aristotle, Andre Agassi, and Absolutely Fabulous: the mind couched in 21st-century terms from entertainment system to business plan.
"Survival is like production, and courtship like marketing. Organisms are like products, and the sexual preferences of the opposite sex are like consumer preferences... animals [including humans] are not uniformly black Model T cars churned out by the assembly line of natural selection. They are self-advertising, self- promoting, self-packaging products adapted from the bottom up, from the inside out, from birth to death, to the demands of their consumers: the opposite sex," says Miller. "I believe our minds evolved through a million years of market research called sexual selection. From this perspective, we are walking, talking advertisements for our genes."
'The Mating Mind: How sexual choice shaped the evolution of human nature', by Geoffrey Miller, W Heinemann, £20Reuse content