Not all changes of animals mean it has evolved. Animals have great genetic variety, to suit different environments. This is called natural selection.

Let's think of a simple example of changes by natural selection:

If the world were suddenly covered in snow, and polar bear-type predators invaded everywhere, it stands to reason that they'd be more likely to eat dark-colored animals which they could see more easily.

That would give an advantage to animals which, happened to be white. Animals of a usually black type which happened to be partly white might also escape the bears. They would then be most likely to breed, passing on the white genes to their offspring.

Over time, through breeding in a selective group, all animals would become white, as the ones least suited to their environment were weeded out. Some species which were unable, by chance, to adapt, would go extinct as the polar bears ate the lot of them.

So, humans have evolved in a different way than chimps, gorillas and orangutans because the requirements of the environment we found ourselves in were different. It was an advantage for us to go in the direction we went, just as it was for the other apes.

Natural Selection works towards the animal's specific needs. The mutation to create more hair in a cold environment would be in a specific population so some humans in the group would have more hair by nature (genetically). These individuals would in turn have a greater chance for survival in the cold environment. As they are selected for by nature their percentages will increase. More of the hairier humans will survive to reproduce and their children will be genetically driven to be hairier. That is just one of the marvelous and logical ways evolution in our nature world occurs. Natural selection is variations in genetic genetic variety that changes a species within itself. For instance, say a tribe of fair skinned people traveled to a very hot climate, those people with darker skin would be more likely to survive thereby passing on there dark skinned genes and eventually weeding out the fair skinned people.

Evolution only occurs when it is necessary. Some apes evolved into man because either they moved to a new environment or their existing environment changed, making evolution necessary for survival. So, the apes who needed to adapt to their new environment through evolution to survive either did so or were wiped out (apparently, they changed, creating the human race), or stayed in a friendly environment, making evolution unnecessary and therefore, nonexistent (the apes in these conditions remained apes).