The best investigator of this question that I have found is Jordan Peterson.
The explanatory framework he develops for the evolution of the genetic and cultural defaults that deliver the unexamined purposes and a context of choice of purpose are the best I have found. His youtube videos of his lectures are worth the time.
And of course I think he has made a few errors, but he seems to be far closer to a useful model of something than most others who have made the effort.
For me, purpose is a choice, and for me it is individual life and individual liberty – applied universally.