Eliezer Yudkowsky has been writing fascinating articles on various aspects of evolution. Here's the latest:
Sounds logical, right? If you take the hens who lay the most eggs in each generation, and breed from them, you should get hens who lay more and more eggs.

...

Selecting the hen who lays the most eggs doesn't necessarily get you the most efficient egg-laying metabolism. It may get you the most dominant hen, that pecked its way to the top of the pecking order at the expense of other hens. Individual selection doesn't necessarily work to the benefit of the group, but a farm's productivity is determined by group outputs.

Indeed, for some strange reason, the individual breeding programs which had been so successful at increasing egg production now required hens to have their beaks clipped, or be housed in individual cages, or they would peck each other to death.

...

And the fall of Enron? Jeff Skilling fancied himself an evolution-conjurer, it seems. (Not that he, like, knew any evolutionary math or anything.) Every year, every Enron employee's performance would be evaluated, and the bottom 10% would get fired, and the top performers would get huge raises and bonuses. Unfortunately, as GreyThumb points out:

...

"So Enron was applying selection at the individual level according to metrics like individual trading performance to a group system whose performance was, like the henhouses, an emergent property of group dynamics as well as a result of individual fitness. The result was more or less the same. Instead of increasing overall productivity, they got mean chickens and actual productivity declined. They were selecting for traits like aggressiveness, sociopathic tendencies, and dishonesty."