Among the mammals that have both familial and social drives, we invariably notice that during those periods in which the former predominate, that is, during the period of pairing off and mating, the latter decline significantly. The union of parents and offspring is also tighter if the number of young is smaller. I will cite only one distinctive example: within the class of fishes, those whose offspring are left entirely on their own lay countless millions of eggs, whereas among the brooding and nesting fish, where the beginnings of a familial cohesion are found, few eggs are produced.

XREF: Connects to life-history tradeoff theory: r/K selection and parental investment strategies in biology.

Georg Simmel, on individuality and social…, loc. 626