But what about an englishman raised in the caribbean? You're talking about DNA and cultural upbringing so you need a good way to seperate the two as, otherwise, either one could be the culprit.
While there is definitely a general, overall element to heat tolerance, the fact that there are clear types and positions of burn would definitely suggest that it is possible to build more of a tolerance to one than another.
With my introduction to supers being what it was, my main resilience is likely to Scorpions, Nagas and, given my childhood, cinnamon. And indeed, while I seem to be in the majority in finding the intense mouth burn of my local chilli shop's Reaper sauce their hottest natural one, there are definitely those less used to a throat burn than me who struggle noticeably more with the Scorpion sauce below it.
Different people definitely react to different heat forms differently.
And then there's Hot-Headz's "Man the Fk Up!", which I think I may have had an underwhelming batch of
when I had it on video. It's a puree that was originally supposedly nothing but Reaper and salt but its maker swore blind that the second, Scorpion and Reaper batch was hotter.
Numerically, there is absolutely no way a blend of 2 peppers could be hotter than one but they do both hit different places, potentially lighting up more of the mouth. There is, at least in terms of perception, some merit to his claim.
And then god knows what goes on with browns. They do feel hotter than other colours of the same varieties and I have heard it said that this is because they produce more dihydrocapsaicin but I can see no reason why that would be consistent across every strain that has both brown/chocolate and non-brown forms. I would be far more inclined to believe that something in the brown colour affects perception but that seems like quite the claim as well.
I've heard suggestion that the browns contain terpines, loosely related to the active ingredients of cannabis and the wormwood in absinthe but that would technically, if as percievable as that suggests, make all brown peppers (and related vegetables like tomatoes) a mild psycho-active drug. Which seems insane.
I don't know the full details of what contributes to perception but I would certainly be interested to find out. I'm currently about to start some self experimentation with crystal menth (pure mint extract) to see how non-thermal hot and cold interact. I've heard that strong chewing gum can be pretty unbearable after super sauce so, if the same works in reverse, I may have something crazy up my sleeve in future.