1. Right...we are seeing maladaptation and infertility occurring in obese kids. That is a form of natural selection. Beyond that, in a natural environment, which humans do not exist in any longer, natural selection doesn't necessarily have to kill you before you procreate, just before you outprocreate that with the beneficial traits. If you die after having 1 child, who dies after having 1 child, who dies after having 1 child, ad infinitum while Ben lives to have 3 kids, who live to have 3 kids, ad inifinitum, whatever beneficial trait Ben has passed on will eventually overcome and outcompete your underperforming genes.
Note: the above story is not intended to insult anyone's DNA. The author has not examined the named subjects DNA.
2. Little adaptation has occured. It seems that most people have some level of gluten intolerance, obviously some exhibit overt symptoms and are hypersensitive. I would think those people are in a better situation than those that are slightly sensitive and damage their bodies for their entire life because "it doesn't bother me."
3. I think this is splitting hairs. If it knocks one out of the breeding cycle, whether at the cellular level or because you have short legs and can't outrun the tiger, it is natural selection at work.
Edit: Robb replied while I was posting...sorry for any duplications/discrepancies.