That's why I didn't give any examples. It's easy to ID these traits in hindsight, but I think it'd be presumptuous of me to make them in advance.

I hope I didn't muddy the waters too much by my use of "to" instead of "in". That was an error on my part.

if it doesn't make sense after amending that error in my statements, here's kind of what I mean:

X trait prevails under a selection pressure. For whatever reason, X trait allows for a greater survival of the species, through whatever means, under that selection pressure it's important to remember that that same trait may not be beneficial/selected for under another pressure. An example here might be sickle cell anemia. In an environment with a lot of malaria, sickle cell anemia decreases infection, outweighing the costs of the actual disorder. Outside of the environment, it's just a blood disorder and no longer beneficial. Thus, it is unsurprising that sickle cell anemia is only notably prevalent in regions where there is a great deal of malaria (or inhabited by people who come from such regions), and elsewhere, it is rare.

I am trying not to give specific examples, because I feel like I can't pick good ones to illustrate my point sufficiently. I'm not sure the latter one does either.

Does that make what I was trying to say more clear?