How does urbanization influence evolution?

[RuneJ]

Almost 100% of all humans lived in the countryside just a few hundred years ago, and cities were non-existing throughout most of our evolutionary history. A majority of the world population now live in cities, and we are clearly not adapted to this since this has never happened before.

How does this new situation influence the direction of human evolution?

[namo]

It reduces our overall health by keeping the sick and infirm alive and free to breed with the healthy. Just the other day I was watching a commercial where a little girl says her blood sugar is too high while riding in a car. This commercial had nothing to do with diabetes. It was just there. This is actually a reflection of our society today. Hereditary diseases are becoming more common than ever.

And by exemplifying pretty yet stupid people (i.e. Paris Hilton) as role models, intelligence is becoming less and less common (mostly because of nurture, but also with the nature aspect also).

And of course there is the sedentary, unhealthy lifestyle which is personified by the obesity epidemic. Almost every time I go outside I see an overweight person. It's sick.