Why is it that of all the living creatures on earth, people are the only ones that can't survive extreme temperatures or climate changes without an unnatural source of protection? For instance, I live in a place where the summers are hot and the winters are pretty cold. Why doesn't my body naturally adjust like a bear or a rabbit? It can't be that we have evolved over the last thousands of years with enough sense to make some clothes, otherwise why weren't 'the cavemen' wiped out before they figured it out?

I am not looking for a religious answer. "Because God said...." or "It is in the Bible...." will not suffice as an actual answer. I am looking for well thought out, scientifically plausible answers.