Sex and community

The emergence, of self-replicating matter, and the crucial revolution that produced sex to replace cloning. Sexual reproduction, plus dispersal, spontaneously produces the genetic variability natural selection needs to work on. If mammalian populations did not disperse, close inbreeding would result in a loss of such variability, and “hence mechanisms evolved to avoid it.
While primates have kin, they do not have in-laws. the dispersal of animal populations, the need for genetic variability and the origin of language, the last enabling social structures to form in time and space among men and women who have never seen each other and in some cases never will while enduring relationship between natal kin separated by marriage but linked by kinship, by descent from a common ancestor.”

At the same time too great a dispersal—so great that separated bands lost contact with each other—meant that beneficial features of kinship association might be lost. So it is that “organisms breed out to avoid losing variability, but not so far out that they dissipate genetic advantages.” Not too close, but not too far; that was the evolutionary Golden Rule and, of course, the plinth of tribal society itself.
To realistically understand the world of kinship obligations and tribal authority, one must first understand both history and social evolution. The domestication of Homo sapiens and his living arrangements has been a very drawn-out affair and requires a better grasp of tribal life than whatever the parents of a Baghdad bride or bridegroom might say to a visiting journalist:
Those tribal communities are the default system of human social nature. Humanity evolved that way for millennia after exiting the hunter-gatherer band stage of social life. Many of the planet’s diverse societies have since moved on toward becoming modern states, but not all of them have. And even for those that have, the shadowy emotional residues of the distant past remain; we never lose anything in evolution, but instead add new developments to older ones.