Nuclear Families

The nuclear family is not universal in humans, but the basic underlying processes of heterosexual bonding are. That is, an exclusively monogamous mating system that produces offspring who are full-siblings is not ubiquitous, especially if one looks at lifetime reproductive effort. This does not prevent the nuclear family from being presented as an ideal institution in many Western societies. Similarly, nuclear families exist widely, even in non-Western societies characterized overall as polygamous (that is, polygynous, polyandrous, or polygynandrous). No nuclear family has been found in any wild population of great apes, but it is the norm in the lesser apes (Hylobatidae) and in many other non-human primate species. Nuclear families of great apes artificially created in captivity seem to function satisfactorily.

The mismatch between mating system (monogamy) and family structure (nuclear) may cause analytical confusion, e.g. clandestine polygyny, serial monogamy, extra-pair copulation. Data on putative versus actual paternity show that a minority of purportedly monogamous relationships are not, although the manifest behaviour may be that of a nuclear family. This disconnect seems to apply to both humans and gibbons, but no study has tested this.

Much speculation exists on the evolutionary origins of the human nuclear family, given that none of the great apes presents a living model. Extent of sexual dimorphism is the usual proxy for mating system in the fossil record, given the positive correlation between degree of sexual dimorphism and the extent of polygyny, as it can be measured from skeletal and dental dimensions.