The cranial capacity of Homo sapiens are responsible for their successful adaptation on earth. They have the cranial capacity of around 1400cc.
The major environmental conditions has changed but the complex human brain has helped him to sustain and understanding the nature. Humans are successful to sustain on this earth due to their complex brain.
Habitat isolation is a mechanism that prevents species from mating even if they don't have reproductive barriers. The differences in the habitat types may thus be sufficient to develop reproductive isolation between two (or more) populations
