Our instincts know us better than we know ourselves.
Women have a built-in instinct to be attracted to men that other women find attractive. (Pre-selection)
Because if other women find him attractive, then he is more likely to be a strong provider and therefore activates her sexually. (This is not rational. This is BIOLOGICAL.)
Men have a built-in instinct to be attracted to women with a youthful hip-to-waist ratio that signals the potential for child-bearing.
Because if she has such physical attributes, she is more likely to produce strong and healthy offspring. (This is not rational. This is BIOLOGICAL.)
Note to men: Even if you never want to procreate, this instinct is the impetus behind your attraction to the female form.