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.