ABSTRACT
Since great apes are promiscuous, paternity is never known, thus making it difficult to form nuclear families of father, mother, and offspring. Africa experienced a series of periods of cooling beginning about 12 million years ago, leading to episodic retreat of the forests in which great apes had evolved. The other strategy of blind natural selection and, later, increasingly cultural selection on hominins and then early humans was increasing the permanence and solidarity of groups in the face of selection pressures for tighter-knit group-level social organization, which was difficult because of the lack of bio-programmers for kinship and group structures in general that runs through the great ape line. In short, the selection that led to the ability to form stronger social ties, more permanent groups, and nuclear families were the result of Darwinian natural selection working blindly on great ape neuroanatomy and physiology.
