[psranga]

My wife works in development. Her theory is insightful and simple: she says mortality from disease (even until age 20) is VERY high for poor people (I know of a poor 10-yr old who died of rabies in India, which is extremely uncommon among the middle-class of India). So they're being rational by having more kids.

Which is why development reduces fertility; people have higher confidence that their brood will survive into adulthood even if it's smaller.