First one:
http://en.wikipedia.org/wiki/Resiniferatoxin whether or not cap could do this if you where very sensitive, young, unaccustomed to it, and the pepper was hotter than normal is
possible but very unlikely. I had to type that in a hurry. Sodium was the wrong word, caused by being mildly conscious. The blistering effect caused by a natural defense mechanism in response to a fire, real or perceived, takes the top layer of cells with it. If this is repeated, particularly if a person is extra sensitive to it, permanent scarring could occur, and the person in question did, in fact, eat them for a prolonged period of time.
Second: Tiger attack was an example. Could have been plenty of other things, such as not vomiting out what limited food you could find, to the toughness factor to impress others in the village. If a hunter gatherer is in the middle of cap cramp, he's gonna have a lot harder a time fighting something off. Especially if he's never felt cap before. As such, the poor fool who consumed one prior to needing to defend himself/right after eating his one meal of the day is gonna have a much harder time surviving than someone who didn't. Even better, the guy who can eat them, get the nutrients, and not vomit them out would have several advantages. First, the other tribesmen would be impressed, thus increasing his social standing and therefore chances of procreation, and he would also be healthier. Civilizations took a good while to take root, just look at how close the American settlers came to perishing, and that was with the natives helping them. Imagine how much harder the first natives had in an environment they had never seen before. As such, a person with cap tolerance/immunity would do just marginally better so as to allow a small portion of the population would have immunity/increased tolerance.
Your last comment made me die inside. If you worded it poorly, you're forgiven. If not, I'm going to go break out the Punnet charts, even if they're not the most exact things out there. Genes have to mutate randomly, THEN the changes that they make in the organism can determine how well that gene is going to be passed down. If the gene that would produce a change allowing an organism to survive is present in no members of the population at the time it would be needed, it is not gonna show up. That organism is gonna die out completely.(again, forgive me if that is what you where trying to say. What you where saying seems to have been that the change in genome would manifest in response to the environment)
"1st off, "tolerence" is purely genetic. It is the upregulation and downregulation of neuroreceptors in response to the environment, giving rise to a need for greater stimulation to get the same effect as what was occurring prior to the changes. The DA pathway from the ventral tegmental area to the nucleus accumbens is sensitized, making the pleasure more efficient, which is the pathway of pleasure, obsessions, and addiction"
Are you trying to describe what tolerance is genetically, because if so you goofed. If not, than you are doing a very good job describing what adaptive tolerance is.