It is quite likely that there was no intelligence involved in the creation of our species or even the simplest life forms on earth. Therefore one could say that we don't have a purpose. Nevertheless, I believe that one should aim to live a happy life and also make other people happier too. With all those problems in the world, a selfish life is a life without substance. Also, it would be awesome if science was able to make us live forever at some point in the future. Nanotechnology maybe.. ? I don't believe in a being that cares for us and intervenes in human affairs. There is the "problem of evil".