One of the most intrinsic questions we have as human beings is where do we come from? The two main theories put forth are creationism and evolution. Creationism states that we were created about 10,000 years ago by God, in the form we are today, along with all the animals and Earth. Evolution, on the other hand, says Earth came to being several million years ago, and all life forms currently inhabiting it have descended from simpler beings. As the centuries went by, life forms got more complex and varied, with the weaker ones dying out and the strong ones passing on their traits to the next generation.
Obviously, the two are mutually exclusive, and the question educators and, lately, legislators, have been asking is: what do we teach in public schools? The short answer, to me, is both. While both theories of course have their detractors, I think this is an ultimately personal decision. The students should be told the various views, with the relevant hard data, and then left to decide for themselves.
However, due to the wisdom and foresight of various legislators and concerned citizens, evolution is the only theory to be found in most public schools. Citing the need for separation of church and state, creationism has been struck down by courts in several states. Neither theory can truly be completely proven, as we obviously have no witnesses to tell us what exactly happened, although there has been evidence to corroborate evolution.