All successful species have strongly developed instincts to maximize the probability of passing their DNA to children who can in turn do the same. For humans, birth timing and number of children are some of the most critical parameters in achieving this. Having too few, having too many, having them too soon, and having them too late, all lower the odds of success. The optimal parameter values depend on environmental risks, our abilities, resources, and our reproductive window.
If we expect a longer lifespan and higher odds of survival for potential children, our instinct is to delay reproduction and have fewer children in order to increase resources available per child.
This instinct developed over a very long period of time, but our technological advances have created a degree of safety and abundance that our instinct was never “trained” on and thus I suspect it is over-suppressing fertility. A longevity breakthrough will appeal to this instinct even more strongly than living in one of today’s highly developed countries. Consequently, I think our instinct will then suppress fertility even further.
Do people in America with one or two children really not have more because they think this is maximizing the expected number of grandchildren? This doesn't seem realistic to me. I think in American even the working poor commonly have children (often more than the wealthy).
It was meant to. My intent was to stimulate thought, not to conclusively prove. There’s great disagreement among researchers studying fertility, income, life expectancy, and such. These are merely my conclusions, which differ from those of many others.
> Do people in America with one or two children really not have more because they think this is maximizing the expected number of grandchildren?
Yes, but my argument is that this is more instinctive than it is conscious thought. For example, women are increasingly having their first child after 30 because they know it is possible to do so successfully and it gives them more time to establish a career and find the best mate. This increases expected resources available per child and expected genetic fitness. In essence, they are instinctively trying to maximize their probability of having children that successfully reproduce, but it tends to lead to fewer children than optimal because our instinct is poorly calibrated to today’s environment.
> I think in American even the working poor commonly have children (often more than the wealthy).
Correct. They also have shorter life expectancy than the wealthy.
If we expect a longer lifespan and higher odds of survival for potential children, our instinct is to delay reproduction and have fewer children in order to increase resources available per child.
This instinct developed over a very long period of time, but our technological advances have created a degree of safety and abundance that our instinct was never “trained” on and thus I suspect it is over-suppressing fertility. A longevity breakthrough will appeal to this instinct even more strongly than living in one of today’s highly developed countries. Consequently, I think our instinct will then suppress fertility even further.