Political philosophers, arguably including Marx,1 have generally taken for granted the existence of a constant human nature which can be modified, but only to a certain point, through education and institutional reform. Rousseau, for instance, begins The Social Contract by committing to ‘taking men as they are and laws as they may be’.2 Following in his steps, John Rawls3 (p. 11) explicitly argues for a ‘realistic utopia’ that involves taking ‘people as they are (by the laws of nature), and constitutional and civil laws as…they would be in a reasonably just and well-ordered democratic society’. This commitment can have normative implications. For example, some have linked Rawls's commitment to taking men as they are with his acceptance of inequality-generating economic incentives as just (Cohen,4 p. 368).

Ingmar Persson and Julian Savulescu's Unfit for the Future breaks with this tradition by challenging the assumption that we must take ‘men as they are and laws as they may be’ in a liberal democracy. Instead, they propose that we consider morally improving human nature by biomedical means, such as drug treatment and genetic engineering. They also argue that, failing moral bioenhancement, our society would have to become less liberal because of the incapacity of liberal democracies to deal with environmental problems or security risks threatening our survival (Persson and Savulescu,5 pp. 7–8, 42–46, 73–100).

Unfit does not say much about how enhancement would be accomplished, and it is unlikely that populations that resist even the most urgent environmental regulations would allow themselves to be biomedically transformed into their willing supporters. But I shall here leave such matters aside and focus on the nature of moral enhancement.

What we believe to be right

Unfit associates ‘moral enhancement’ with increases in altruism and empathy (Persson and Savulescu,5 pp. 107–108, 121, 125ff), which is something we …