Scientists have demonstrated that male sexual preferences are largely determined by maternal influences in the early years of life - in other words if a woman looks like a man's mother he is more likely to find her attractive.
The study is based on observations of sheep and goats who were fostered by mothers from a different species but scientists believe the results could also be applied to humans.
Ever since Sigmund Freud proposed that mothers have an inordinately strong influence over their sons, cemented by a quasi-sexual bond, the question of whether the Oedipus complex is real has been the subject of controversy. Anecdotal reports have suggested that men tend to prefer women who look similar to their mothers but none has gained scientific credibility.
Keith Kendrick, a behavioural scientist at the government-funded Babraham Institute in Cambridge, describes in the current issue of Nature the results of an experiment to test the Oedipus hypothesis. He allowed new-born lambs to be fostered by female goats and likewise gave new-born kids to foster ewes. The researchers found that the male lambs and kids developed a lifetime preference for females of the opposite species.
"We chose sheep and goats because they form close bonds between mothers and offspring, just like humans. They can also recognise each other by facial characteristics, again like humans," Dr Kendrick said.
When the fostered animals became adults the male sheep continued to prefer female goats and the male rams continued to prefer ewes even though both sets had mixed only with their own species for three years.
The female lambs and kids also showed a slight preference for males of their fostered species but this proclivity did not survive being brought up among their own kind - suggesting that women do not share a biological preference for men who look like their fathers.
The researchers concluded: "The fact that male offspring are affected more than females ... is evidence that they are indeed more potently influenced by their mothers. This indirectly supports Freud's concept of the Oedipus complex."
Dr Kendrick said the results could not explain everything about why men fell in love, but acknowledged that in his own case it may have played a part: "My wife does have some similarities with my mother in her facial characteristics, although her hair and eye colour are not the same."