Our happy hour fact to amaze your drinking buddies with.

A man can't help but make a snap judgment of a woman based on her physical appearance -- it's the way he evolved.

Researchers from England and the Netherlands scanned the brains of 20 males and 20 females as they performed a complicated task. During the task, the researchers would show the subjects a series of photos of the opposite sex.

Upon seeing an attractive photo, the men would become distracted from the task, and display an almost immediate change in brain activity. On the other hand, a quick glimpse at a male hottie didn't affect the women's ability to stay focused.

Evolutionary scientists believe this is because men evolved to use facial attractiveness as a proxy for a woman's level of fertility. Women, on the other hand, need to know more information about a man -- in particular how reliable he is -- before they dedicate a good chunk of their brain power to figuring out a way to mate with him.

So when a woman stops traffic, it's all part of the process that keeps the human race going.