A report on Sub-replacement fertility and Income and fertility

However, in the last half of the 20th century it has become clear that the economic success of developed countries is being counterbalanced by a demographic failure, a sub-replacement fertility that may prove destructive for their future economies and societies.

This is part of the fertility-income paradox, as these high fertility countries are very poor, and it may seem counter-intuitive for families there to have so many children.