One of the fundamental tenets of evolutionary psychology - the discipline that claims that certain cultural phenomena are universal because they have a hard-wired neurobiological basis-is the sanctity of female chastity. Evolutionary psychologists argue that males the world over set great store by it in order to minimize the possibility of wasting their paternal investment on someone else?s genetic material.

But it turns out that the culture of female fidelity is not universal after all. Several peoples in lowland South America, India and Polynesia, the American Association for the Advancement of Science annual conference heard, believe instead in ?partible paternity?. This is the concept that every man who sleeps with a woman while she is pregnant makes a biological contribution to the child she is carrying.

And this belief makes all the difference to the fate of the woman and child. All the fathers are expected to share in parenting - which usually amounts to providing food - once the baby is born, and so it comes as no surprise that having multiple fathers is a distinct advantage to the child.

A multiple-fathered child of the Bari of Venezuela, explained Stephen Beckerman of Penn State University, Pennsylvania, is 16% more likely than a single-fathered child to survive to the age of 15, probably due to improved nutrition.

For the Ache people of Eastern Paraguay, having multiple fathers is also desirable, as in this case they appear to protect children from violence, the main cause of infant and child mortality. According to Kristen Hawkes of the University of Utah, the death or divorce of a child?s primary father increases the child?s mortality risk three-fold.

The Curripaco of the Northwest Amazon value fidelity and yet believe that one act of copulation is not sufficient for a woman to get pregnant, Paul Valentine of the University of East London reported. ?The Curripaco say that making a woman pregnant is hard work,? he added. This belief is also shared by another Amazonian tribe, the Canela, according to William Crocker of the Smithsonian Institution. Unlike the Curripaco, however, they don?t require just one man to do all the hard work.

Since they believe that a child will bear most resemblance to the man or men who contributed the most semen, Canela women have the chance to amass several desirable fathers for their children.

?A pregnant woman seeks affairs with the men, besides her husband, whom she wants her child to be like, ?Crocker explains. ?Besides being handsome lovers, great orators and popular sing-dance leaders, they must be good providers.?