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Comment by gte910h | Hacker News Reader

Omce birth control becomes free or affordable, and societites move out of agrarian only production, that is untrue.

Reliable birth control pretty much leads to voluntary replacement only reproduction

For a few generations. Eventually, the survival of the fittest kicks in, and those people who avoided birth control (from a stronger paternal feeling, etc) will restock the population.

This sounds like the same fallacy that the movie Idiocracy is based on – even if you pass on your genes, that doesn't mean you pass on traits like demographic fertility, or intelligence.

One of the best predictors of a woman's fertility rate is their level of education. Higher education leads to fewer children on average. This is largely independent of the fertility of their parents.

Also, if you look at the third world, there are actually some good economic arguments for having more children, related to infant mortality. Your children are your 'Social Security', so you want to ensure that some survive. Paradoxically, reducing infant mortality can actually reduce fertility. http://video.google.com/videoplay?docid=-5192204318056302269

> that doesn't mean you pass on traits like demographic fertility, or intelligence.

IQ is well known to be highly heritable. I would be very surprised if proper research came up with a null result on fertility heritability.

Evolution doesn't work that quickly.

And additionally, humans have a vast ideological landscape that is "contagious" among individuals, which also happens to limit breeding. This is not something evolution can control through reasonable means.

It's not just birth control: Even more important is education of girls, which is the number one factor reducing natality. Educated urban women (and educated urban families) just don't have the 8-15 children that rural peasant families do (before industrialization anywhere in the world, for thousands of years). Part of it is also that previously >50% of children died before age 5. Now infant mortality is extremely low in most industrialized countries.

Except for some insular subcultures (such as the Amish, to give only one example among many). These subcultures are continuing exponential growth unabated, and eventually this will affect national and world fertility rate statistics.

But such subcultures are still less than 1% of the population in the developed world, so even doubling their numbers every 20 to 25 years, it will take a while for them to have a statistically significant impact.

This appears applicable to whites in the west and Asians in east Asia. I'm not so sure this is universally true. You see big differences in fertility rates in different ethnic groups in the US.

And it may not even generally be true. It might just be how things appear right now given current circumstances. If you cut off immigration to the US, which is driving growth, I doubt the white fertility rate would stay at or below replacement. Wages for low skill labor would rise and fertility would go up. Who knows what the birth rate in Japan would be if their economic policy were not so incompetent.

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