To be fair, the last statement about extinction in the cold and explosive growth is largely due to the size of the brain. Humans figured out techniques to survi

To be fair, the last statement about extinction in the cold and explosive growth is largely due to the size of the brain. Humans figured out techniques to survive in the cold even while being warm blooded. No thick fur is necessary when we can just kill an animal and use its skin to get warmth. Then we discovered fire.