Even if we talk of a “traditional family”, the basic concepts which historically defined and described family relationships had been very fluid and connected to economy more than blood lineage or love.
Two models prevailed in Europe before the Industrial Revolution: the aristocratic one, where the main occupation was finding a way to kill time, and the agricultural-artisan one, in which production was necessary to survive. With the rise of a new class, bourgeoisie, came a different form of family, where the father provided with sustenance and the mother took care of the house and the offspring.
Other sociologists, such as Brigitte Berger, overturn the cause-effect link and think that was the nuclear family to start industrialization. To support this thesis they underline the fact that in England, homeland of the Industrial Revolution, married couples already left the parents house since XIV century. A thing that didn’t happen anywhere else.
So, couples got married later, only after reaching financial independence, changing some rules of domestic economy in the long term. As a consequence, the classic economic cycle based on self-sustenance turned into a more complex economic policy, on a social and public level.
Roles inside the family change as well. The father had still the leadership, but the distance with his wife and kids decreased, compared to the patriarchal model. In the same way the number of children diminished, because a huge labor force wasn’t needed anymore and there is more time for their education, managed directly by the parents (the mother) and not by the older members of the clan. There is less generational gap and that brought to a slow but constant progress.
The locution “nuclear family” was inserted in the Merriam-Webster dictionary only in 1947, though. The most conspicuous development is in the Sixties, thanks to the economic boom: higher wages and easier access to medication treatments. But this phenomenon wasn’t that new, not in England at least, as demonstrated by many studies conducted by Peter Laslett, Alan Macfarlane, Richard Smith, Lawrence Stone and Keith Wrightson.
The nuclear family looks like the normality, but it’s an exception. The extended family is more common around the world, for a simple reason: economic sustainability. When governments can’t or don’t want to provide sustenance, the older generations become an important safety net.
Nuclear families are still very common, sure, but in the minority, because of the social transformations. Single or not married parents, couple without children or with kids from previous weddings. And the youngest of them all, homosexual parenthood.
In the end, we can understand how, if we talk of tradition, the only one which is steadily carried on is the constant reshaping of the habits through time.