[mirkoadari]

If you look at it from the perspective of the entire species instead of an individual, it makes sense. Reproduce with the strongest genes possible. So if the body sees that this particular individual doesn't handle certain substances well, it terminates the line and avoids spreading that particular weakness in the species.

[rottyguy]

This sort of makes sense but now we're supposing that the individual, subconsciously, puts it's species ahead of itself. Is this the wide belief or is it that each person fights to keep themselves alive (again, subconsciously, as I believe some people will consciously sacrifice themselves for the greater good).

[baddox]

> This sort of makes sense but now we're supposing that the individual, subconsciously, puts it's species ahead of itself.

Not at all. The individuals (and the genes) don't need to have any goals or any notion of autonomy. It could just be that genes come about randomly, and the ones that are most successful at existing in the future will be the ones that cause a small portion of individuals to die when doing so increases the odds of survival of the rest of the individuals.