You know the saying don’t judge a book by its cover? Well, that’s pretty much what men are programmed to do with women: to judge their attractiveness and mating potential on the first glance. Woman, on the other hand, take much longer to evaluate the suitability of a man as a partner.
This difference is due to the fact that each gender looks for different attributes on a prospective partner. While men look for fertility – and good looking woman are deemed as more fertile – women search for a partner that can provide for her and her offspring as well as staying committed to the partnership.
You can read more about this here.