Singer also believes that we should not fear scientifically based programs of genetic improvement but instead ask how they might contribute to the greatest happiness. Genetic improvement, says Singer, holds out the prospect "of a new kind of freedom." After all, if human nature is the major obstacle to creating a better society, then the solution may ultimately lie in altering that genetically based nature.

What makes Singer so provocative is that he takes up the left's commitment to fighting injustice and at the same time urges scientists to pursue the knowledge and control of our biological makeup to the furthest reaches. He synthesizes, in a way, the determinism of Ridley with the social commitment of Lewontin. But, at least in this work, he doesn't clarify who'll be in charge of deciding which policies will lead to the greatest happiness for the most people -- a key question, particularly given Singer's controversial advocacy of euthanasia for those born with severe mental disabilities.

In Singer's preferred social order, molecular biologists like James Watson would be free to do what they wanted. To see why this is troubling, look to Watson himself and the other contributors to "Engineering the Human Germline: An Exploration of the Science and Ethics of Altering the Genes We Pass to Our Children." This book of essays, compiled and edited by UCLA neurobiologist John Campbell and the director of the UCLA Medicine, Technology and Society Program, John Stock, also contains the fascinating transcript of a 1998 panel discussion about how far we should go in modifying genes in the sperm and eggs we use to produce future generations -- what scientists call the "human germline." Currently, almost all clinical trials of genetic therapy are directed at specific parts of the body and affect only the patient involved; germline therapy would alter the genes passed on to all future generations. Earlier this year, the American Association for the Advancement of Science issued a report recommending that any effort to proceed with germline engineering, whether in the public or private sector, be regulated.

Watson, the co-discoverer of the double helix structure of DNA, appears in his catalytic prime here, casting aside what he views as the "prejudices" of social and moral concerns in order to advance science and medicine. Not only should we "try germline therapy without completely knowing that it's going to work," Watson says, but "if we could make better human beings by knowing how to add genes, why shouldn't we do it? What's wrong with it? Who is telling us not to do it? I mean, it just seems obvious now."

Watson suggests that just as we might find benefit from putting a Brazil nut gene in a soybean to enhance its nutritional value or an Arctic fish gene in a strawberry to help it resist damage from freezing weather, so too the human genome might be improved with the implantation of a plant gene or an animal gene or perhaps even an artificially devised gene. After all, Watson says, "we [molecular biologists] should be proud of what we're doing and not worry about whether we're destroying the genetic patrimony of the world, which is awfully cruel to too many people." While some voices in "Engineering the Human Germline" recommend a less ambitious approach to modification of the human genome, Watson's fellow panelists and many of the book's essays mostly echo his views.

Ian Wilmut, the leader of the team of scientists who cloned the sheep Dolly and a scientist who nearly equals Watson in stature, proposes a moral alternative. As coauthor of "The Second Creation: Dolly and the Age of Biological Control," Wilmut shows a humility in the face of our potential ability to alter the genome that's the opposite of Watson's brashness in every way.

Maya Angelou reads from "The Heart of a Woman"