McGill, senior lecturer in Population Health at the University of Auckland, said humans were designed to maximize their energy intake because their large brains used about one-quarter of their total energy expenditure.

"Early humans sought energy-dense food with high levels of fats, starches and sugars. We are genetically programmed to find foods with these qualities appealing," said McGill.

I think that one can argue that the most evolutionarily successful humans are the Chinese. They aren't known for maximizing their intake of energy-dense foods. They (traditionally) mainly ate rice with small amounts of flavoring foods in addition.

I think the rise in obesity is mainly due to a couple of things:

1) People exercise less and less as their societies become more westernized. Exercise is very good at suppressing the appetite.

2) (As they say in other words) Inexpensive processed foods tend to be based on carbohydrates that aren't as satisfying to one's brain as foods that are more complex and take longer to digest. So we don't get the signals that we're expecting to stop eating. E.g. I think it's pretty easy to eat 16oz of Doritos as a snack but it's not so easy to eat a 16oz steak as a snack.

So, it's not evolution, it's sedentary lifestyles and lack of variety in foodstuffs. That's my feeling anyway - I can't back it up with a study at the moment.

Cheers,
Scott.