I agree with you about peer effects but I think you assume without cause that they are lasting. Twin studies, despite their flaws, would seem to be the best way to establish that, whatever their influence now, differing peer groups and adolescent environments will not lead to different adult characteristics. Any efforts that parents take NOW to improve children's peer groups, in order to improve current well-being, are valuable. But if the effect fades over time, then the harm is less than most parents think it is, and therefore on the margin children are less costly and Caplan's conclusion is warranted.

Downvoted- this is misleading. It might technically be true that we cannot sustain the population of Earth at US living standards currently, but the main reason is that a large portion of the population is nowhere near US levels of productivity. Even given this, we produce enough food for everyone on the planet with agriculture in Asia and Africa at productivity levels far below what could be achieved with common US technology. So if those people can generate enough prosperity to make houses and iPhones, which we did without the benefit of borrowing tech from more advanced societies, then the world can easily sustain many more people at US living standards.

There are certainly environmental problems remaining, but a child born today in almost any region of the world has the highest expected standard of living so far in history. As Caplan points out in the book, new people have large positive externalities, and their contributions more than make up for any drain on resources. And of course environmental problems tend to become less severe as societies develop.

A person enjoying life is an extreme good, overpopulation is really not an issue, so have more kids!

I've posted a few rationality quotes, so it sounds like time to introduce myself. I'm a 22 year old software project manager from Wisconsin, been reading LW since June or so when MOR was really going strong.

I've been a very rational thinker for my whole life, in terms of explicitly looking for evidence/feedback and updating behaviors and beliefs, but only began thinking about it formally recently. I was raised Christian, and I consider my current state the result of a slow process of resolving dissonance based on contradictions or insufficient/contrary evidence. I'm most interested in theory of government and achieving best results given the rather unreliable ability of voters to predict or understand outcomes of different policies.

I also think, though, that ethics is just as important as rationality- choosing the correct goals is just as necessary as succeeding towards those goals. I've seen appreciation of this within LW that, for me, really sets it apart, so I hope I can make a larger contribution. As someone once said, the choice between Good and Evil is not about saying one or the other, but about deciding which is which.

Our civilization is still in a middle stage: scarcely beast, in that it is no longer wholly ruled by instinct; scarcely human, in that it is not yet wholly ruled by reason.

Theodore Dreiser

I believe no discovery of fact, no matter how trivial, can be wholly useless to the race, and no trumpeting of falsehood, no matter how virtuous in intent, can be anything but vicious... I believe in the complete freedom of thought and speech- alike for the humblest man and the mightiest, and in the utmost freedom of conduct that is consistent in living in an organized society... But the whole thing can be put very simply. I believe it is better to tell the truth than to lie. I believe it is better to be free than to be a slave. And I believe it is better to know than be ignorant.

-HL Menken