Upon what do you base this? I know that my perspective is anecdotal, but I am curious how you reconcile your view with the current state of globalized society. If humans on average really needed multiple deep relationships, then how can the post-college doldrums be explained? Wouldn't people have created a greater abundance of ways to socialize? Isn't one's own family and occasional visits with relatives usually enough?
I'm not saying that I relate to this at all, despite that I am particularly solitary. I would like to have more deep and frequent connections with others, but my impression isn't that people actually want that. They might like the fantasy of having lots of deep friendships that don't interfere with their technological somnolescence or romantic satisfaction.
There are a bunch of studies that show that populations with the highest life expectancies tend to be those that not only benefit from high quality diets (usually seafood), in sunny areas, but also have strong family ties and sometimes live in multi-generational homes (Southern Italy, Spain, Okinawa).
I'm not saying that I relate to this at all, despite that I am particularly solitary. I would like to have more deep and frequent connections with others, but my impression isn't that people actually want that. They might like the fantasy of having lots of deep friendships that don't interfere with their technological somnolescence or romantic satisfaction.