While we do observe a trend towards lower fertility rates as wealth/health/modernity increases, this isn’t universal. For example, there is a big gap between t

While we do observe a trend towards lower fertility rates as wealth/health/modernity increases, this isn’t universal. For example, there is a big gap between the fertility rates of religious and non-religious people in the arguably modern USA. It only takes one such group to carry on the tradition of exponential growth.