"In the modern era, however, the relational milieu has collapsed. In 1850, the average household size in the West was six people - today it's three or fewer. A full quarter of Americans live completely alone. Hours and hours of television, educational ratios of 1:30 in school classrooms, mobile families, transient communities, nuclear families, broken families - all have contributed to reductions in the number and quality of relationships available to young children at the age when their relational needs are highest. Indeed, we now consider a ratio of one daycare worker to five children adequate! That is one-twentieth of the relational richness of a 'natural' hunter-gatherer setting."
-Introduction from Born For Love, why empathy is essential - and endangered.