I think this is "one" way we can interpret our need and even acceptance of isolation. While what is discussed here could be true, we may also seek isolation as another way to thrive as well. It is not uncommon for early man to go out on their own and though they may have been rejected from the "group" that rejection doesn't necessarily mean, the end of survival. It could also mean an opportunity to thrive in a different way.
So these endorphines could be there to address the situation of either rejection or loss through some kind of trajedy to the group. So, in other words, if a group was destroyed leaving a survivor, these endorphines may be there to encourage the survivor to be "ok" in isolation until he/she can locate another group to connect with and again thrive and procreate.
So, what is discussed above is one way of looking at it, however, I believe there are more reasons than just what is discussed above.
Thank you for posting this di meliora, it is definitely something to ponder. I just want to make sure that people who truely struggle don't self blame and keep working on learning and growing inspite of being challenged. I think that it is important, we had to do that in early man as well.
Open Eyes