What are the factors that make a given person more or less likely to have children? How important are income, education, and optimism about the future? Is it true that “development is the best contraceptive,” as demographers like to say? And is the global population really going to double by the next century? (Probably not — in fact, one U.N. estimate finds that the population in 2100 could be lower than today.)

These are some of the questions we ask in this week’s episode, “Why Do People Keep Having Children?” (You can subscribe to the podcast at iTunes, get the RSS feed, or listen via the media player above. You can also read the transcript, which includes credits for the music you’ll hear in the episode.)

You’ll hear from Brown economist Emily Oster, who appeared on an earlier podcast talking about her research on Huntington’s Disease. (She is also writing for FiveThirtyEight these days.) Oster walks us through the various factors that seem to drive high and low fertility; she tells us that fertility rates (research here) can be linked to some surprising behaviors:

OSTER: When people get access to cable TV, which really lets them watch soap operas, it actually decreases their fertility, and one interpretation of that is that people see the people on TV, they have fewer kids, and they have this really fancy life, presumably because they’re on television. But you know, maybe if I had fewer kids I could … have that also. DUBNER: I guess another interpretation might be that soap operas are not as sexy as previously thought? OSTER: No, true, and also people are too busy watching TV to have sex is another interpretation we considered.

Among demographers, one important question is how people’s view of the future — whether optimistic or pessimistic — drive fertility. How do events like war, economic depressions, and natural disasters affect population change?

We go after those questions as well, taking advantage of fascinating research by Elizabeth Frankenberg, a demographer and sociologist at Duke. Frankenberg has been studying population dynamics in Indonesia for more than 20 years. So when the brutal Indian Ocean tsunami struck in 2004, killing more than 150,000 people in Indonesia (including a great many children), Frankenberg and her colleagues had an opportunity to determine fertility in the aftermath. Their findings may surprise you:

FRANKENBERG: So we looked at whether losing a child in the tsunami predicted a birth after the tsunami, and the answer to that question was yes. Women who had lost a child in the tsunami were about ten percentage points more likely to have another birth after the tsunami than women whose children had survived.

The podcast also looks at the optimal fertility rate to keep an economy humming these days, and how drastically the fertility rate has fallen even in some of the world’s poorest countries.