Different parts of it seem like bullshit (as do most things starting with "oh you see it comes from brain structure") but I'd buy that there's a There There once you start getting into analyzing the social structures.

link:

...es, KibbutzGo to:1. Introduction Although humans are capable of living in structurally diverse societies, our communities, even in the digital world, have a distinctive layered structure with successive cumulative layer sizes of 15, 50, 150, 500 and 1500 (Fuchs et al., 2014, Hamilton et...

Hard to take numbers as round as this seriously...

...es in hunter-gatherer societies: Lehmann, Lee, and Dunbar (2014) give values of 42.8 ± 18.0SD (bands), 127.3 ± 43.8 (clans), 566.6 ± 166.2 (mega-bands) and 1727.9 ± 620.6 (tribes) for 20 contemporary hunter-gatherer societies (see also Hamilton et al., 2007,...

42.8 +/- 18.0: a band

127.3 +/- 43.8: a clan

566.6 +/- 166.2: a mega-band

1727.0 +/- 620.6: a tribe

...19th American utopian communes. We plot the data on a log-scale because they have a strong skew with a long right tail. Excluding the extreme righthand...

But I feel like I can't read it because of that!

...03).bFrom Lehmann et al. (2014). Plotting community survival against size at foundation (Fig. 1b) allows two important conclusions to be drawn. First, religious communities survived significantly longer than secular ones (on average, 35.6 ± 32.5SD vs 7.7 ± 8.0 years: F1,81 = 35.5, p < 0.001). Second, the two types of community differ in the optima at which duration is maximised. Setting upper bounds to these distributions by quantile regression and then setting the first derivative to zero to find the maxima yields community sizes that maximise longevity of 64.4 and 171.1, respectively, for secular and religious communities (with corresponding mean durations of 15 and 100 years). These values mirror the band and clan levels of hunter-gatherer societies (Table 1). In sum, communities of around 50 or 150 at foundation seem to survive longer than those at other values. 3.2. Hutterite communitiesFig. 2...

Alignment around religious values allows for a larger structure to sustain itself.

...nd in hunter-gatherer societies. The Hutterites split their communities once they are above ~ 150 because, in their experience, this is the limit at which community cohesion can be maintained without the need for formal laws and a police force to maintain discipline (Olsen, 1987). Forge (1972) arrived at a similar conclusion from an analysis of settlement size and structure among New Guinea horticulturalists. He argued that, in these societies, 150 was a key threshold for community size because basic relationships of kinship and affinity were insufficient to maintain social cohesion when a community exceeded this size. It is perhaps relevant that, in natural fertility populations, the community of living descendants of a founding couple five generations back from the current offspring generation (grandparents' grandparents, or about as far back as anyone currently alive will have known personally) is ~ 150, and that no culture has kinship terms that identify relationships beyond this limit (essentially second cousins) (Dàvid-Barrett and Dunbar, 2017, Dunbar, 1995). In effect, natural kinship classifications seem to be mapped onto the typical size of natural communities. T he crucial implication of Forge'...

"grandparents' grandparents" as an important bound

...ifferent economic circumstances. With the exception of a few communes that required celibacy throughout their existence and did not adopt children, all of the communities we consider contain both adults and children. We may reasonably assume that the tensions that eventually give rise to community fission occur between adults, and hence that the effective functional group size is actually the number of adults. However, the routes by which conflict and stresses arise within communities can be complex. Evidence from primates, for example, suggests that the principal factor precipitating group fission may be stresses arising from female-female competition (Dunbar, 2017, Dunbar et al., n.d). Conflict between families over children, or at least conflict between the interests of one's children versus the interests of the community as a whole, may also be important for humans, and these can often be social (who has the right to discipline whose children). Since almost all analyses of social group size, in humans as well as nonhuman primates and other mammals, focus on total group size, we here simply follow common practice. In sum, analyses of the size and...

This is fascinating. "Conflict between the interests of one's children versus the interests of the community as a whole" seems like a huge yet little-stated dynamic in a decent amount of contemporary (American) political issues. Watch who wants their property taxes for schools to go to gifted programs for their kids -- watch who moves in order to access "better schools", accepting inequity and just trying to get on the good side of it.