To the thread creator:
You appear to work on the philosophy that "everything happens for a reason", implying that you have a very external locus of control. Yet you also say you are an atheist. If you believe in no "higher being", then where does the control originate? Thus, everything only happens for a reason if you subscribe to at least some form of spiritual identity.
I am an agnostic tending towards an atheist, and as far as I'm concerned, humans have no real purpose; the very idea of a "purpose" as such seems pretentious. Humans are in no way different to any other animal- the fact that we are intelligent is as arbitary as the fact that wasps are black and yellow. However, perhaps the presence of this intelligence puts the onus on us to use it- not because it is our responsibility, but for purely selfish means: to avoid the destruction of our species, and indeed our habitat, at all costs.