Is it simply for the biological purpose of continuing the species?
This is a major misunderstanding of evolution and the universe in general. Biology has no purpose and neither does evolution. Evolution is just another scientific law. You put sodium and chlorine together you get salt. Not because somebody needs salt, or finds sodium or chlorine dangerous they are simply more stable as salt than separate. A species that is effective in filling an ecological niche has no purpose in filling the niche, but is a stable solution. The fact that filling the niche well increases the welfare and continuation of the species is a result not a purpose.
I have to find some other purpose in life than continuing the species because frankly a large part of my species is not worth continuing. Therefore I find purpose starting very locally. There are people whose welfare is integral with my own. They provide me with the intellectual challenge, love, sustenance and fun that makes my life worth living. By making my purpose to provide the same for those others I get a nice feedback loop that increases worth of all our lives. Although this starts locally, as one recognizes the importance of people outside of the face group ones purpose must expand as well to take into account the larger world one is a part of.