THE puzzle of why men so often mistake the slightest sign of friendliness from a woman as amorous intent has been solved by social scientists.

Male overoptimism — often followed by a clumsy pass — is triggered by women sending out a series of subtle and highly deceptive flirting signals known as “proteans” when they first meet a prospective mate.

Although often interpreted as a “go” signal by the man, they represent nothing more than an instinctive attempt by woman to assess him and calculate whether he is worth pursuing. All potential mates, alas, are subjected to the same subconscious interrogation.

The proteus effect — named after the Greek river god who constantly changed his form to evade his enemies — is one of a number of courting rituals analysed in a study of flirting to be published by the Social Issues Research Centre (Sirc), an Oxford-based research organisation backed by the anthropologist Desmond Morris. Others include the “copulatory gaze” and the phenomena of “courtesy flirting” — a practice which works well among Europeans but one which can go badly awry if tried in America.

Kate Fox, the report’s author and the co-director of Sirc, said women tended to blitz men with protean signals in the first minute or so of meeting them.

“By sending erratic and ambiguous signals in the early stages of an encounter, women manipulate men into showing their hand,” said Fox. “It is not entirely surprising, given the levels of ambiguity and deception to which they are subjected, that males tend to become confused.”

Fox and her researchers questioned more than 1,000 people and organised a series of focus groups to test their findings.

Flirting proper was found to begin with what the researchers call the “copulatory gaze”, where intense eye contact is broken momentarily with occasional lifting or lowering of the eyes. This is followed by smiles, synchronisation of body movements, coy looks and head-tossing by the female. Men sometimes thrust their chests out like apes.

“Human flirtation involves sequences of gestures and expressions not unlike the courtship dances of birds and other animals that we see on wildlife programmes,” says the report.

Surprisingly, the researchers found that two-thirds of flirtatious encounters are initiated by women. They share the characteristic — known as “female proceptivity” — with other species, such as chimpanzees.

The report said: “Chimpanzee females, for example, actively solicit sex with males, going so far as to pull a resting male to his feet and insist on copulation.

“Among humans, female proceptivity is much more subtle. In fact, female solicitation is done so unobtrusively that most people think that men take the initiative in making advances,” says the report.

Nevertheless, the tactic seems to work. The researchers found that women are not simply initiating flirtatious encounters — something it has always been thought they have done — but are often going one step further and asking men out.

More than 30% of women who took part in the survey said they had initiated dates and only 1% reported being turned down. Of dates initiated by women, 51% lead to relationships lasting more than six months — an impressive rate of success.

The research also found that people often flirt simply for the sake of politeness. However, this so-called “courtesy flirting”, where the aim is to flatter rather than snag a mate, can also be misinterpreted, with embarrassing consequences.

The report said: “It is mainly practised by men, who engage in mild flirtation with women as a form of politeness. It is particularly common in Britain and Europe, and can be confusing for foreigners, particularly Americans, who mistake it for the real thing.”

Frequency of flirting was also measured in the study. Possibly reflecting the fact that men misinterpret protean signals for the real thing, 45% of the men surveyed reported flirting “in the past week”, compared with just 37% of women.

Fox said: “Our findings on British flirting support the view that we are a nation of flirts. In our national survey, only 1% of respondents said that they did not flirt.”

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