Our bodies can cool themselves decently well by sweating. I think that if the climate was affecting you to the point where your brain was getting cooked, the symptom would probably be less "slightly dumber" and more "seizures and organ failure".

But I'm not a doctor or a scientist, so I could be completely wrong. Hopefully someone more informed will weigh in.

When diving to 90ft+ you get 'stupider' (nitrogen narcosis). Our instructor had us do simple math problems on a board underwater and timed us. We were doing them very very slowly but you don't feel that it is slower. It was an interesting experience meant to warn you that you won't realize that you are affected by nitrogen narcosis.

I've been there. It feels so good, you forget things and get unfocused

It'd make sense that there would be a mechanism for graceful degradation, no?

I think that sweating profusely and feeling thirsty is the graceful degradation. I don't think there's a way to gracefully degrade from "my brain is a burger patty now".

Well, getting hotter than you can handle is (at least sometimes) called heatstroke. And some of the symptoms include "Altered mental state or behavior. Confusion, agitation, slurred speech, irritability, delirium, seizures and coma can all result from heatstroke." At least some of those sound roughly like "getting stupider," though it should be a surprise that a complex system doesn't respond in a simple manner to going outside of its "design limits."

http://www.mayoclinic.org/diseases-conditions/heat-stroke/ba...

Don't worry you're not being racist, humans of all ethnicities are made of the same proteins after all. And getting too cold will affect brain function too.

Nope, we have that awesome homeostasis thing going on which is why our bodies (and brains) can live in such a wide range of climates in the first place.

If you get hotter than your behavioural adaptations (shade seeking, splashing yourself with water, turning on the air conditioner) plus your own inbuilt capabilities (vasodilation, sweating) can handle, then you pretty much overheat and die.

There's no association of human body temperature with latitude.

So endogenous human thermal regulation is efficient enough to deal with the normal range of terrestrial environments inhabited by humans. And when it can't (if you're naked in the arctic, for example), you die.

Wouldn't they not get noticeably stupider, because the observer would be getting just as stupid?

Does this also explain why people in Scandinavia+Finland seem to be so clever?