Blame it on their genes, but men take just a fraction of a second to judge a woman on her looks and whether she will be a potential partner or not.
They weigh up potential partners based on their appearance because their "ancient" genetic preference for attractive mates leads them to, experts claim.
According to research, men take a woman with an attractive face to be fertile and able to continue the family line, which appeals to the man's survival instinct.
On the other hand, women take longer to decide their feelings for a man because they need to weigh up whether he will be a committed partner who will provide for them well - part of their survival programming.
Professor Mark van Vugt and Dr Johanna van Hooff, from the University of Amsterdam, and postgraduate student Helen Crawford, from the University of Kent, were behind the study.
They tested men and women's bias towards looks by conducting a series of tests on 20 women and 20 men, making them perform tasks while recording their brain activity.
While performing the task, the subjects were shown a series of photographs of faces of the opposite sex, ranging from attractive to ugly.
Men were easily distracted when they saw a pretty face but women stuck to the task.
"Men definitely have the most wandering eye but it is because they have evolved to pay attention to cues of fertility and one of those cues is facial beauty - it's not that men are shallow," the Telegraph quoted van Vugt as saying.
"But we found they do make snap judgments about women, much earlier than was previously thought. They make that decision on whether a woman would be a good mating partner in milliseconds.
"This is something very ancient and a way of helping men find the best mate to produce children.
"Women were not distracted by attractive male faces because women need more proof of whether a man is a good mate.
"Women make that decision on behaviour, whether a man is trustworthy and committed. They make their decision much later than men," he added.
The study will be published in the Oxford Journal Social ognitive and Affective Neuroscience.
