This is from The Power of Place, by Winifred Gallagher; she is quoting psychologist John Calhoun.
"For forty thousand years, the population has periodically doubled, which has meant more ideas, information, and creativity for our evolving culture. But each time our numbers double, the number of social roles and the effort it takes to maintain satisfaction with life also increase. That's one reason why India's caste system, which serves to reduce the number of social contacts, came about. We've become so overwhelmed by the roles, communication, and information produced by our huge population that we've had to become more impersonal. We've become dependent on machines, such as computers, to help us preserve order and complexity and keep us from disintegrating into chaos. These machines also make life so interesting that many people would rather concentrate on information than raising children. Eventually, the population level will fall."