The surroundings can have a drastic influence on a way an animal can evolve to be. For example, humans had a very crouched back and their hands had the same structure as its feet, so they hade 4 hands. As we are apes, and in the homos group (btw, its a classification), our ability to think, and brain sizes enlarged due to the daily struggle for food and shelter was upon them. An example why White and Black skin complexion evolved was due to climate. The Black complexion was the best in hot climates and humid areas, as the skin reflected the sunlight.

Hope it helps!

It is all in the plants and animal cells which are dead