By contrast, the post–World War II isolated nuclear family style was urban-based and, said Parsons, referred to a heterosexual, and parenting, couple only ever married to each other. Often, though not always, the households were situated in relative proximity and were frequently (although not always) engaged in shared agricultural pursuits. The extended style referred to an array of husband-wife households linked both by blood and a network of mutual support. Just as the West had evolved from the agricultural to the industrial age, Parsons reasoned that the post–World War II family style had evolved from extended into what he called isolated nuclear.

He called the process structural differentiation, and it coincided with the process of industrialization in the West. Parsons reasoned that the post–World War II isolated nuclear family style was the final culmination of a long journey-the end point of an evolutionary process that had been occurring for several hundred years.

The forms SF took in the 1950s and 1960s came almost exclusively from the imagination of Talcott Parsons (1955) these forms were elaborated by his students (Bell and Vogel 1960 Pitts 1964). And like those other primordial life forms, its survival is owed in part to its adaptive capabilities. To be sure, like other ancient life forms that have managed to survive, SF has mutated over time. Although virtually no one today would call her or himself a functionalist, SF stands unchallenged in terms of sway it holds over the realm of research and theory about families. Despite the range of theories that ostensibly replaced it (Doherty 1999 Vargus 1999), SF remains tenaciously in place. Indeed, there is no other single theoretical perspective that seriously rivals it. Its continuing influence on the ways research and teaching are carried out, and its impact on public policies for families, are as robust as ever before. Nevertheless, the fact that by the early twenty-first century SF was formally eradicated in no way diminished its potency. Subsequently, in today's articles and books about families, the explicit use of functionalist jargon has largely vanished. She did not, however, attempt to account for that contradiction and, in any case, by the 1970s, functionalist theory was overtly abandoned throughout the social sciences. Although only a relatively few researchers in the 1960s labeled themselves as SF-types, the great bulk of published work in the study of families was, she noted, shaped by SF assumptions, perspectives, and views of the social world.

Jennie McIntyre (1966) was the first scholar to discern the curious paradox of structural functionalism (SF) within the realm of research and theory about families.

Theory of structural functionalism