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Human beings want to understand themselves, and in our time such understanding is pursued on a wide front by the biological, psychological, and social sciences. One of the questions presented by these forms of self-understanding is how to connect them with the actual lives all of us continue to lead, using the faculties and engaging in the activities and relations that are described by scientific theories.

An important example is the universal human phenomenon of morality. Even if we come to accept descriptive theories of the different forms of morality based on evolutionary biology, neuroscience, or developmental and social psychology, each of us also holds specific moral views, makes moral judgments, and governs his conduct and political choices partly on the basis of those attitudes. How do we combine the external descriptive view of ourselves provided by empirical science with the active internal engagement of real life?

This problem is posed and to some extent addressed by Jonathan Haidt’s The Righteous Mind, and part of the interest of the book lies in its failure to provide a fully coherent response. Haidt is a social psychologist, and he sets out his descriptive theory of the origins and nature of morality and of moral disagreement. But the book’s overall point is partly normative, not just descriptive. Haidt makes definite recommendations of a clearly moral nature, and he seeks to support them with the help of his descriptive findings about morality. These two aspects of the project do not fit easily together.

Haidt’s empirical theory, which he calls “moral foundations theory,” is an example of evolutionary psychology. It is the hypothesis that a set of innate “modules” of moral response were fixed in humans by natural selection, and that these responses, further shaped by cultural evolution in various more specific forms and combinations, underlie the widely divergent moralities that we observe not only across the globe but within pluralistic cultures like that of the United States. Specifically, Haidt argues that group selection—selection for genetic traits whose presence benefited social groups of early humans in competition with other groups, rather than individual selection for traits that enhanced the reproductive success of individuals in competition with other individuals—is responsible for the main moral dispositions. The existence of group selection is a highly contentious issue in evolutionary biology. Haidt defends it in this case on the ground that moral norms can include cheap enforcement mechanisms, such as forms of group pressure, that cancel the genetic advantage for any individual of trying to benefit from the group’s success while not following the norms—free riding, in other words.

Haidt distinguishes six basic types of moral response, which he likens to distinct taste receptors, so that different moralities are like different cuisines in the use they make of these responses. Each type manifests itself…