I used to think along the same lines, but I believe the harsh winter thing has been debunked. At least, Jared Diamond did a good job of it in Guns, Germs and St

I used to think along the same lines, but I believe the harsh winter thing has been debunked. At least, Jared Diamond did a good job of it in Guns, Germs and Steel. From what I remember, we are physically and mentally challenged to similar levels on all parts of the earth. Societal development was more hampered or aided by environmental factors. For example, Africa is a tall, narrow continent compared with Eurasia, which has serious implications for flora and fauna diversity, the time it takes diseases to circulate, among other things. I'd recommend the book if you haven't read it already; quite enlightening.