Well unless we retained the ability to create small simple things such as camp fires, homes and fur clothing I doubt we'd be as spread out as we are. Humans are a pretty tenacious species but fact is we aren't made to handle the cold so without warmth either through fire,housing, or clothing colder climates would be much more avoided we'd probably have much higher populations in places like Greece, Spain, Mexico, Egypt Africa and so on with maybe a few dotted around areas were the weather either stays mild or warm. Given how fast we reproduce naturally without modern commodities I think the highest our species would number is weeping the 2-3 billion mark with the average lifespan ranging from 25-35 depending on location and natural predators. Part of why it isn't 'strange' to see sights of human construction and clothing is due to the fact we are raised around it. If you were raised in some commune were everyone lived in the same cave never had clothing and hunted their food a trip to a modern day city or even town would be a very alien experience.