Partner Selection in Tribal Communities

I would like to continue the theme of my previous post in a more speculative vein.

With the low probabilities of finding an ideal partner I showed in the previous post, one might wonder how people in small tribal communities of approximately 150 people* ever experienced emotional intimacy... And these are the conditions where human psychology evolved in the first place.

First of all, with a shorter life expectancy, we can suppose that not 1 in 4, but 1 in 2 people were of the right age range for an intimate relationship. But wait... due to the large number of children in tribal societies compared to our own, the proportion would actually be about the same as it is today, so we'll leave it at 1 in 4.

Next, because of the small size of communities and the inbreeding that was bound to occur, the IQ range present in any one community was almost certainly such that almost everyone was within "reach" of almost everyone else.

If we stop at this point, we have a chance of 1 in 256 for finding an ideal partner for members of tribal communities. This would mean that about every other person could find a potential ideal partner within his own community; the rest would have to settle for "next best" or look for a partner among neighboring communities. This is still assuming, of course, that every "ideal partner" is also available! We have not yet addressed the issue of eligibility ("marital status").

However, type distribution was almost certainly not uniform in tribal communities, which would have tended to develop a dominant quadra or set of types in order to remain stable. This non-uniformity would tend to be more pronounced in smaller communities. This means that for most people in the community, the chance of finding an ideal partner within the community would be higher, and for a minority the chances would be lower. Such people would be more likely to leave the community to find an ideal match or to remain single, which would perpetuate the quadra or type dominance already in place in the community.

So, what we get is a situation where a majority of people in the tribal community can find an ideal intimate partner within their community of roughly 150 people (whether or not that person is available for a relationship), whereas the rest must look outside their community for a satisfying intimate relationship.

We know that tribal communities were (are) never completely isolated, but had considerable contact with neighboring communities, just like any animal community. This increased the "dating pool," so to speak. However, it is safe to assume that most people's closest relationships were with other people in their own community; otherwise, these communities would have ceased to exist as a distinct entity. Most likely, a large portion (40-80%) of people also chose mates from among their own communities, while the rest "spread their genes."

As shown here, the search for psychological compatibility could have been one of the factors contributing to the interchange of genes between tribe, in addition to already recognized traits such as the "explorer instinct."

This may be even more speculative than the above, but it seems to me that the number of psychological types was limited by the size of human communities. If psychological compatibility is at all an important factor for survival and success, evolution could not have produced a situation where, due to the large number of psychological types (say, 256 instead of 16), only a small minority of people were able to experience it.

The size of communities was, in turn, determined by the economics of food consumption and cooperation. These "economics" determined the degree of psychological differentiation possible within human communities, as well as the minimum average number of compatible partners available to members of human communities. That average number cannot be much below 1 if compatibility matters at all to evolution.

* Note: read this article to learn where the number 150 comes from when estimating typical community size.