The announcement in June that the Human Genome Project and Celera Genomics have assembled a nearly complete sequence of the chemical "letters" in the human genome is certain to encourage proposals to use this information to refashion human biology. The most profound application would involve genetically engineering human embryos. By deliberately introducing DNA changes early in development, the characteristics of an individual could be greatly altered. What's more, the alterations could be passed on to that individual's descendants in perpetuity.

The drive to improve the human species biologically -- eugenics -- is a pernicious but recurrent theme in human history, leading to abuses ranging from discrimination to forced sterilization to the gas chambers. Embarking on programs of genetic improvement will, in due course, lead to the social exclusion of those unfortunates who are born without the benefits of the best genes money can buy. Whether in its authoritarian or its free-market forms, eugenics poses societal risks of the most disturbing kind.

For these reasons, most scientists and medical professionals have long opposed suggestions that the genetic manipulation of early embryos be permitted. In just the past three years, however, some scientists and others have begun a vociferous campaign in support of such procedures.

They look forward to a world in which parents select their children's genes, literally from a catalogue, to give them an edge in the quest for success. With little sign of real concern, they acknowledge that such practices could lead to profoundly greater inequality. One widely discussed scenario anticipates humanity eventually segregating into genetic castes or even into separate species.

Advocates of such a future include scientists such as Lee Silver of Princeton University and James Watson, former head of the Human Genome Project. It is unfortunate that prominent members of a profession that thrives on the public's trust and its resources would use their prestige and authority to argue in favor of using genetic engineering to divide humanity into separate and unequal castes.

Current technology for making genetic changes in developing mammals is extremely primitive. Animals with altered genes introduced during early stages often have unexpected properties such as dramatic increases in cancer rates in subsequent generations. The death of 18-year-old Jesse Gelsinger as a result of an experiment using the related technology of tissue genetic engineering was accompanied by reports of the resounding lack of success of hundreds of such attempts and should give us pause about proposals to engineer our offspring.

But even if such procedures were capable of being performed reliably in animals, biological differences among species would guarantee that the first attempts in humans -- or the first hundred attempts, more likely -- would be very much hit-or-miss operations. This means that the genetically modified individuals could grow up with developmental aberrations, birth defects introduced solely by the procedure. In many cases, the nature and magnitude of such conditions would not be known for several generations.

And to what end? There is no medical need for genetic engineering of human embryos. Though often presented as a means to prevent gene-related disease, genetic manipulation for such purposes is rendered pointless by the existence of prenatal and pre-implantation genetic testing. Other options, including adoption and artificial insemination, are also available. Embryo genetic engineering would be the technology of choice only if the goal was so-called genetic enhancement, that is, the creation of a "super-human."

Acknowledging this, some advocates of genetic engineering of human embryos have dropped any pretense that their interest in the procedure is limited to therapeutic applications. James Watson stated at a 1998 UCLA symposium: ". . . if we could make better human beings by knowing how to add genes, why shouldn't we?" And in a statement before the British Parliamentary and Scientific Committee last month, Watson added, ". . . if scientists don't play God, who will?"

The inevitability of adverse outcomes alone will not prevent would-be genetic engineers and their commercial backers from promoting and attempting to implement these technologies. The hyperbole surrounding the announcement of the human genome sequence -- scientifically unjustified claims that the sequence is a "blueprint" or a "rule book" for constructing a human being -- serve only to fortify these ambitions and to mislead the public.

Genetic manipulation of future generations is a path we as a species have not yet taken. Science and history provide us with ample reason to refrain from implementing a technology that will be portrayed by some as desirable or inevitable, but in fact would be both perilous and irreversible.

Printed in the St. Loius Post-Dispatch, Tuesday, July 25, 2000

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