When Darwin discovered natural selection, he was quick and remarkably insightful as to how this might affect our understanding of our own species, Homo sapiens. Alfred Russel Wallace, the impressive co-discover of the theory, never agreed to its application to humans. He considered our mental faculties far too advanced to be accounted for by the same forces that gave rise to pond scum and even chimpanzees. The debate continues to this very day, and will not be resolved in the forseeable future.
Nevertheless, there is now little doubt but that we share many of our mental faculties with other species, including, as Marc Hauser shows us in this fine volume, some of our moral capacities. Even those we do not share with our evolutionary relatives, he claims, are clearly the product of biological evolutionary forces. I think his argument accurately reflects our current state of knowledge, and is impressive indeed. Sociobiology, which was roundly rejected and indeed excoriate by most behavioral scientists when first proposed by Edward O. Wilson in 1975, has been fully vindicated.
The past decade has seen a strong push for the notion that ethics is a part of science, and the philosophy of ethics, in principle, ought not to be that different from the philosophy of physics. In particular, our ethical notions do not come from some rarified Platonic realm, or the capacity to perceive synthetic a prioris, or our superior informational processing power, but rather from our evolution as a species that has spend most of its history living in small bands of mobile, propertyless, stateless, hunter-gatherers.
Hauser deals with our current understanding of virtally all aspects of the mental life of humans, cognitive, affective, and moral, and he consistently weaves an intellectual web in which the mental capacities of animals and humans are inextricably interwoven. His specific claim, and unique to my knowledge, is that we can understand human morality in much the same manner as we have come to understand human language, based on the work of Chomsky and his coworkers. Humans are genetically endowed with a universal moral grammar, a tool kit for building specific human moralities, the latter being the product of cultural specificity. Thus, just as we cannot understand a foreign tongue, so we cannot appreciate a foreign morality, even though we know it springs from the same basic human capacities.
I think the analogy of ethics with language is a fruitful one, and well argued by Hauser on the basis of the facts (e.g., people cannot defend their ethical beliefs any more than they can explain the rules of grammar that they follow, unless they have been trained to do so). I am less sure that it is true. This is because the actual content of ethical principles is largely the same across all societies, and certainly across major religious and cultural groups (see Donald Brown, Human Universals, and Hauser's discussion of religion, pp. 421ff). We humans certainly can amplify our petty differences (e.g., what to eat, what to call our God, when to wear what), and there are important non-petty differences (tolerance, gender equality, abortion and homosexuality), but these vary systematically with level of economic development, and are not the cocophony of human languages.
This book is written for the novice, and is a wonderful introduction to the recent liturature on the human mind, by an eminent researcher whose knowledge of "wild minds" (the title of his previous book) is unsurpassed, and who has enriched us all by turning his gaze to human primates.