THIS WAS A WEEK of cosmic triumph for biology, as scientists with the Human Genome Project announced they had mapped the landscape of the human genetic code, or what its directors termed, more biblically, "the Book of Man." This means they can pinpoint which of the 3 billion "letters" that make up the code determines eye color, or an enzyme important to the correct functioning of, say, the central nervous system. And our individual code exists on nearly every molecule of every cell of our bodies, so a bit of spit or hair and a special microscope is all they need to call it up. "The key to life," the scientists reveled; and yet hearing this, one couldn't help but feel a little alarmed, as though human beings were little more than machines programmed by, as National Human Genome Research Institute Director Francis Collins called it, the "instruction book for life."

In this week of tributes and parties, biologists were already lost in the future, the project's enormous potential for curing diseases, for determining our propensity for certain behaviors, for law enforcement. But there are already examples from current applications that give cause for humility and ethical concerns. One of the more fantastic promises is gene replacement therapy, in which abnormal copies of a certain gene are replaced by healthy ones. The field was sure it had its first success when two infant boys with an immune system breakdown seemed instantly cured. But as toddlers the boys developed a fatal form of leukemia last year and no one could figure out why, sending the whole cutting-edge field into confusion.

The DNA of one of Saddam Hussein's captured half-brothers will help identify the real Saddam Hussein should he, or his remains, turn up. DNA has helped find and convict many prisoners and free others wrongly imprisoned. This week the Bush administration proposed recording DNA profiles of all juveniles and adults who are arrested, even if they are not convicted. But we've already seen the first scandals of tainted DNA labs or unscrupulous expert witnesses who testify falsely to matches; DNA is only as good as the skills and intentions of its human handlers.

Some worry about a future of designer babies, of parents opting to raise their babies' IQs by 20 points. But those claims made by less responsible scientists seem far-fetched. Less than 1 percent of that massive genetic code turns out to be the actual blueprint for what makes up a person; the rest is called "junk," genetic memory, gibberish. From what they know, scientists can piece together a skeleton of what makes up a human, but it would be hubris to assume they could control qualities such as intelligence, creativity, musical ability or happiness. And more humble scientists say that they never will, that those will always come from the context in which genes are expressed, a body, parents, mentors. And only all those factors taken together provide the key to life.