鈥淲OMEN don鈥檛 miaow and they don鈥檛 scratch at the door,鈥� says Randy Thornhill, 鈥渂ut they do have oestrus.鈥�
Most female mammals experience a hormone-induced oestrus or 鈥渉eat鈥�, but women are not thought to, and are not considered to be aware of when they are most fertile. Thornhill, a biologist at the University of New Mexico in Albuquerque, challenges that view.
He suggests we have mistaken the function of being on heat. 鈥淥estrus doesn鈥檛 indiscriminately increase sexual desire,鈥� he says. 鈥淚t functions to get good genes.鈥�
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He and colleague Steve Gangestad say there are many examples of mammals that don鈥檛 mate with just any male when on heat. Mice, for example, try to mate with males that have different immune systems from their own, while female elephants go for the most dominant male.
If women do experience oestrus, this would explain why in the most fertile phase of their cycle they also seem to prefer partners with 鈥済ood genes鈥�, such as taller men and those with more masculine or dominant behaviour. Outside their peak fertility they prefer men with traits indicating willingness to invest in child-rearing 鈥� even if this means the man might be raising another man鈥檚 child.
Thornhill believes applying the concept of oestrus to women resolves the apparent paradox that they are concerned with getting good genes at peak fertility, and outside of this time 鈥� when he says they are in a phase of 鈥渆xtended sexuality鈥� 鈥� they are concerned with getting material benefits. He presented his theory at the at Newcastle University, UK, last week.
鈥淭hornhill may have performed a service,鈥� says Manfred Milinski from the Max Planck Institute for Evolutionary Biology in Pl枚n, Germany. 鈥淚t needs someone to point out that there may be no paradox.鈥�
