The titans existed before humans. They eventually vanished from the earth due to a terrible meteor crash that lifted dust into the atmosphere where they existed, cutting off their supply of sunlight. The humans then evolved from monkeys while the titans went into hibernation. Hundreds of years later, they slowly revived and threatened the human race as it is now.

The question is, if something, the titans in this case, existed before humanity and human history, do we even care where they come from? Can't they just be there?