I suspect that on a global scale (and excluding China due to its "one child policy") this is true, but it may not hold up as well in the USA or "first-world" co

I suspect that on a global scale (and excluding China due to its "one child policy") this is true, but it may not hold up as well in the USA or "first-world" countries in general. Within the US I suspect there's a high standard deviation for the number of children in wealthy families, but it may be higher than for those where resources are highly restricted during reproductive years. Globally, I've seen references for years about high birth rates in poor countries, with (anecdotal?) indications that having multiple children was a requirement if you were going to have someone to take care of you in your old age. I suspect that also ties in heavily with youth mortality rates - you may have multiple children in hopes that some of them will actually make it through.