These are good points. This one I'll have a stab at.

"The novel question to answer is why overeating - consuming more calories than you burn, and thus gaining weight steadily over long time periods - is so much more prevalent now than it was in previous decades."

Environment: more food, less exercise and incidental exercise. There is one intriguing idea, our bio flora (microbiota) is evolving and it's effecting us. ~ http://www.scientificamerican.com/article/how-gut-bacteria-h...