Biologist Wilson. STU ROSNER

What can we learn from the natural sciences, and biology in particular, about the human condition? No matter how exalted we think ourselves, all that we can know and become has a material basis obedient to the decipherable laws of physics and chemistry. And no matter how intellectually far above the remainder of life we lift ourselves, and however technically proficient we become, we will stay a biological species, biological in origin, and thence adapted in mind and body to the living world that cradled us.

The persisting enigmas of the human condition--What are we? Where did we come from? What do we wish to become?--arise from two great gaps in that material comprehension. The first gap, encountered as we try to pass from biology to psychology and the social sciences, lies between brain and mind; and the second, which must be navigated from psychology to the social sciences and the humanities, is between mind and culture.

If the naturalistic conception is correct, the line between the great branches of learning is not a permanent epistemological break or, as a few scholars would like it, a Hadrian's Wall needed to keep the reductionist barbarians of science from high culture. It is instead a broad domain of largely unexplored phenomena awaiting cooperative exploration from both sides. That domain is now fully open to investigation. It is being penetrated at an accelerating rate by "borderland disciplines" that have begun to weave a skein of cause-and-effect explanations from brain to mind to culture, connecting the natural sciences with the social sciences and humanities.

One discipline within the borderland is cognitive neuroscience, which uses techniques of cell biology and brain imaging to trace the physical events of conscious experience. Another is human behavioral genetics, now closing in on the genes that affect mental and behavioral traits. A third such discipline of key importance is evolutionary biology, which is attempting to reconstruct the genetic history of human nature as it unfolded across hundreds of millennia--deep history, as it were. And finally, there are the environmental sciences, which define the physical and biological worlds to which the human body and mind have adapted during millions of years of evolution.

From the social sciences side, disciplines entering the borderland include cognitive psychology and biological anthropology. They have begun to anastomose with the natural sciences, adding to a thickening webwork of cause-and-effect explanation.

Why is this conjunction among the great branches of learning important? Because it offers the prospect of characterizing human nature with greater objectivity and precision, an exactitude that is the key to human self-understanding. The intuitive grasp of human nature has been the substance of the creative arts. It has been the underpinning of the social sciences, and it is a beckoning mystery to the natural sciences. To grasp it objectively, and explore it to its depths scientifically, would be to approach if not attain the grail of scholarship, and fulfill the dreams of the Enlightenment.

This morning, I will be so bold as to suggest a preliminary definition of human nature, as follows. Human nature is not the genes, which prescribe it. It is not the cultural universals, such as the incest taboos and rites of passage--they are the products of human nature. Rather, human nature is the epigenetic rules, the inherited regularities of mental development. These rules are the genetic biases in the way our senses perceive the world, the symbolic coding by which we represent the world, the options we open to ourselves, and the responses we find easiest and most rewarding psychologically to make.

Biologists and social scientists, by joining within the borderland disciplines, have begun to discover increasing numbers of such epigenetic rules. Many more, I am confident, will come to light as scholars shift their focus in order to search for these phenomena. I know that the conception of a biological foundation of complex social and cultural structures runs against the grain for many scholars. They object that higher mental processes and cultural evolution are too complex, shifting, and subtle to be usefully reduced in such a way. But the same was said by the vitalists about the nature of life when the first enzymes and other complex organic molecules were discovered. The same was declared about the physical basis of heredity even as early evidence pointed straight to the relatively simple DNA molecule as the carrier of the genetic code.

At long last we appear to have acquired the means either to establish the truth of the fundamental unity of knowledge, or to discard the idea. I believe we will establish it. The great branches of learning will meet this way, and if so it will be a historic event that happens only once.