Like most people, libertarians tend to assume that we have an unconditional right to reproduce. In fact, many assume this right is even more fundamental than a right to free speech or property. After all, if we have any rights at all, we have to start with rights over our bodies, and reproduction seems like a natural extension of this right. Yet our reproductive choices have massive externalities – costs and benefits borne by other people who had no opportunity to accept or reject them. For many people, having children will be among the most socially significant choices they make.

This is true because the collective upshot of our individual choices shapes the gene pool for future generations, and because traits that are heritable impact people who share a common environment. The environment includes not only the air we breathe and the land we live on, but also the culture and political institutions we share, the technology that is created and transmitted through exchange, and the kinds of people who populate our planet.

Thomas Schelling wryly observed that “marriage and romance are exceedingly private activities, but their genetic consequences are altogether aggregate.” Because genes impact behavior by influencing our predispositions, facts about who has children, and under what circumstances, are arguably at least as important from a social standpoint as choices about how much time or energy people spend on parenting and schooling. Yet these facts are almost never discussed, presumably because of the common belief that even acknowledging them will resurrect movements toward state-sponsored eugenics.

But thoughtful people should be able to separate problems from solutions, and recognize that some problems can’t be solved through political institutions, if at all. For example, suppose that in developed countries around the world there is a negative correlation between fertility (the number of children people choose to have) and genetically-mediated traits like intelligence and impulse control. One question is whether this should worry us. Another question is whether we should do anything about it. The answer to the second question is much less clear, as I argue here.

We might frame the problem by asking which moral considerations determine our reproductive rights. I think the least controversial answer is something like the harm principle, but it has to be significantly hedged (not all harms count, and many harms – or “costs” – have compensating benefits). For example, the harm principle might imply that psychopaths and sadists should be dissuaded (or morally forbidden) from reproducing, since they are far more likely to produce children who prey upon other people. But the harm principle doesn’t offer much positive guidance for a future in which we have the ability to select which embryos we implant, or edit the content of our children’s chromosomes through genetic engineering. Many of these choices will produce both private and social benefits, some will create collective action problems, and nearly all of them will involve probabilistic costs.

I have argued that – to some extent – reproduction is a social act because it involves genetic and social externalities that disproportionately impact future people. I have not argued that we should always use political institutions to internalize externalities. Any attempt to do this will inevitably create new social costs and benefits. So, the question is this: to what extent do other people’s interests determine the scope of our right to reproduce? And when, if ever, is it appropriate to use political institutions to limit this right, or to alter the incentives that surround reproductive choices?