Robin Hanson counters my views on human fertility

But as long as enough people are free to choose their fertility, at near enough to the real cost of fertility, with anything near the current range of genes, cultures, and other heritable influences on fertility, then in the long run we should expect to see a substantial fraction of population with an heritable inclination to double their population at least every century.  So if overall economic growth doubles less than every century, as I’ve argued it simply must in the long run, income per capital must fall over the long run, a fall whose only fundamental limit is subsistence; we can’t have kids if we can’t afford them

That is, growth is not forever and selective pressure will eventually cause population growth to pick up. I agree with the growth part.

Conditional on human’s not going extinct the population part is true as well. I didn’t recognize that when Robin first mentioned it in my comments but he is correct.

That is, if we survive long enough and if we are free to choose reproduction rates then high fertility will dominate. There are a few big ifs here.

First there is the, “if we don’t go extinct.”  When I was a kid one of the fist really gee whiz evolutionary stories I heard was the story of the Irish Elk (pictured above.) I don’t know if this is supported by current biological theory but so the story goes the Irish Elk was beset by opposing evolutionary forces.

On the one hand sexual selection was pushing for males with larger antlers. On the other hand larger antlers were unwieldy and required a large devotion of resources to produce. The Elk could not split the difference and went extinct.

Humans may likewise be beset with dual forces. We have these big brains, which are very useful. Mostly, I would argue, for playing the complex game of love. But, it also turns out that they can do other things, like blog, create birth control, video games etc. Bryan Caplan notwithstanding, these things are generally not conducive to reproduction.

So we have a adaptation that’s very good at satisfying our instinctual drives yet it is also good at avoiding the costs of those drives.  In particular the cost of raising children. These two forces are fighting against one another, and we may not be able to split the difference.

Second, is the free to choose “if”. Robin is ultimately saying that we will reach the carrying capacity of our neighborhood of the universe. Is it likely that society will allow this to happen? Understanding the costs, isn’t it likely that some type of future one-child (or 2.1 child) policy will be implemented?