Originally Posted by Damian
What exactly happened in the 19th century to cause this then? Is it possible to revert back?

Increased wealth and increased living standards. Naturally there were people who lived like that even before, but this was for the wealthy. For the rest it was common for multiple families or generations to live under the same roof, including servants. During the 19th century survivability, better living standards, improvements in science and the industrial revolution etc made it possible for more to make their own income and afford their own house.

http://en.wikipedia.org/wiki/Nuclear_family

Can we revert back? Well, we already live in an era where people live in very different constructs even though the family construct is the most common.