Sigh. I wish basic Evolution and Biology were taught in more schools. Both humans and apes evolved from earlier ancestors. These branches of the primate family were exposed to different environmental and genetic factors, and may have even started with DIFFERENT ancestors. All of these explain why they evolved into different species.

Darwin...must be turning in his grave...;-)

before the ape evolved it was a teenager

Wide Awakes answer is correct. Humans and apes share a common ancestor. In the case of chimpanzees and humans, this ancestor lived about 6 million years ago. Humans actually are apes, they belong to the biological genus "ape". Humans are closer related to chimpanzees than they are to gorillas. They share 98.4 percent of their genes with chimpanzees. The ancestor of humans and chimpanzees looked ape-like. Calling it ape would be kind of confusing, since apes are modern animals, and we´re talking about an animal that lived 6 million years ago. So this ape-like ancestor himself shared a common ancestor with all the monkeys (difference between apes and monkeys: Monkeys are smaller and they got tails). Their ancestor probably looked monkey-like. This ancestor evolved from screw-like mammals that lived at the same time as the dinosaurs. This screw-like organism evolved from reptile-like organisms. A reptile turning into a mammal sounds weird, but remember, ´reptile´and ´mammal´are modern terms. 100 million years ago, the distinction just newly emerged, and those animals looked very alike. Therefore, every time I use x-like, the ´like´ becomes more and more irrelevant, because the time the animal has evolved since then increases. So back to the story, the ancestor of the reptiles evolved from amphibians. The ancestor of the amphibians evolved from lungfishes. From this point on, I´m not sure what comes next (respectively prior to that). It might have been something wormy. And then a multicellular organism. Then a bacteria, and finally, a self-replicating macro molecule. To address the ´why´, species change only if the environment demands it. Animals have varying offspring. If a new ice-age arises, animals that are born with more fur tend to survive and reproduce more often. Therefore, genes ´for´thick fur tend to spread. Nature selects the good genes and the good mutations, while the bad ones die out. Evolutionary changes happen over very long periods of time. How do two different species evolve from one ancestor-species? This happens through geographical separation. If a group of early apes crosses some high mountains and finds itself in a new valley without other apes, there is no gene flow between the two population anymore. If there is no gene flow between the population for thousands of years, the populations evolve away from each other, partially because of different environmental circumstances (like climate, geography, predators, prey), and partially because of random genetic drift. Another important aspect is ´sexual selection´. If females have a preference for, say, colored males, any bird that has genes for bright colors will reproduce more often than dull birds. This way, the tail of the peacock evolved, and a convincing theory suggests that sexual selection played a big role in human evolution.

Wide Awake's answer leaves out that humans are actually still apes, in the biological sense. We belong to the same taxonomic group. So, to clarify, the theory of evolution holds (and supports) that humans and OTHER apes have common ancestry. We're related in the same way to every other living creature on Earth, too, just more closely related to the other apes. In exactly the same way you can be related to both your sibling and your cousin, but more closely to the sibling, even though you neither is your ancestor. The idea that the other ape lineages should evolve like humans did is probably based on the idea that humans are a superior species. But this is a very recent thing that we can attribute mostly to a few thousand years of technological progress. Before inventions like language, fire and agriculture, humans had a very hard time competing with other apes.

Simplest answer I feel is genetic mutation chooses the path certain forms go down based on the surroundings!

Humans and modern apes evolved from a common ape-like ancestor. In that this ancestor probably had hair all over, it would have looked more like what we currently call apes than modern humans, who have evolved the striking, but literally superficial, trait of near hairlessness. There is an implicit assumption in your question that evolution has a direction, and man has moved "further" along that line than modern apes. There is no such direction. Chimpanzees and gorillas evolved from our common ancestor to suit their environment, different kinds of jungle. Humans evolved for a different habitat, probably the open plains of Africa. This different habitat produced a number of changes - standing upright to see further and reduce area exposed to midday sun, losing hair except on top of head to cool easier, foot changing to run instead of climb. MOre conjecturally, needing to be in larger co-operating groups, needing a larger brain to keep track of more people in the group. Evolution acts all the time on all species. But may species are at a "local optimum" - they are wall adapted as they can be to the environment and lifestyle they have at the time, so they don't change much. But occasionally new opportunities occur, and evolution goes into overdrive, changing the species dramatically to take advantage of a new opportunity. That happened at some time in humanities past, and made us what we are now.

Because some apes weren't genetically altered by aliens

Well, if we must assume that all life on earth started from one single cell andthen became subject to genetic variation, then that is your most basic answer. However, I'm sure that is not what you are looking for. As we can see that apes are still here, but the Homo Erectus (for one), isn't, then we don't even know if the ape evolved from something that is still around. Odds are facing towards something that is no longer around, though. That's the problem with the theory of evolution. There are so many holes. Creation has no holes, but it has no basis or scientific evidence to phold the idea, so the only thing that can be said is that there are many things we dont know. Inquisitive minds such as myself, and clearly the author of this question, sometimes seek to find the answers to these holes, but, truth be told, there is really no way of knowing.

That is the question of all time! Man did not evolve from an ape, that's why.

The same way that different types of humans were created as we evolved and the bad types dies out. Just a branch in evolution, like monkeys and gorillas

A better question is whay are there no transitional species (other than extremely dubious examples) in the fossil records. There should be millions. The scant "evidence" would fit in a broom closet. Nothing is evolving into another species today.

Because not every creature goes through the same experiences. Ones that evolved into people went different ways and experienced different things than the ones that didn't. It's fairly simple when you think about it.