I conclude by calling attention only to the findings I find most interesting. These are the distinctions between the seemingly identical differences of every individual with all others and the structural differences between all possible pairs in the population.The greater the heterogeneity among people, the greater are the chances that two people meeting will differ. But the greater the structural heterogeneity in a population, which is the mean difference between all possible pairs, the more likely are two people who differ to have any relation with one another, including marriage [Empirical tests confirm this for seven of eight differences, all but that in race (two versions of it: a dichotomous and multiple one)].Inequality between a people decreases the likelihood of friendships. But the degree of inequality in a social structure, based on the differences between all possible pairs, increases the likelihood of status different relations of all kinds, including marriages.