Why do men say they like this type then go for that one?

This is a real quick survey that I´m hoping will shine some light on male behavior. Why is it that men say they like one type of woman and go for the complete opposite? I have seen it a ton of times and I´m a little baffled as to why this happens. The most common one I hear is that men like a low maintenance lady that can chug a beer and watch football. As far as looks, my male friends say they like brunettes with curves.

So what do I see next? They´re dating a pettite, skinny blond who rather watch Jersey Shore and drink a cosmopolitan. No offense to you skinnyblondJerseywatchingcosmodrinkers. You deserve love as well.

But, really, what is the reason behind this? It´s a very strange phenomenon.