This is a great question - because I think it has no answer! Humans have evolved to such an extent over the last 50-100,000 years that we have begun to think there is a reason for us being here, as if we are separate from all the other living things on this planet.
For some, religion answers this question because it brings meaning to those who would otherwise have meaningless lives, because they somehow feel they are "special" and distinct from other forms of life, or because they fear death.
Personally, I don't think we are here for any particular reason other than evolution and the outcome of probability on this very small planet. However, since we are here, I think we have a duty to be considerate to others, to promote sustainable evolution on this planet, and to learn to be better people.