BRAVE NEW WORLD : EVERYTHING YOU WANTED TO KNOW ABOUT STEM CELLS, CLONING AND GENETIC ENGINEERING BUT WERE AFRAID TO ASK.

It was not by chance that President Bush's first televised address, last August, was about stem cell research, coming as it did at the height of a summer swirling with heated debate over the issue ("one of the most profound of our time," according to the President). That and other recent debates have raised questions not only about changes in science and medicine but about such profound issues as the nature and value of human life, and whether humans have the moral right to tamper with genetic material, on the one hand, or the obligation to develop technologies that would alleviate the suffering of millions, on the other. Such questions are important, but only by understanding the science involved can we begin to address the ethical conundrums coming our way.

With nearly every advance in medicine, from the smallpox vaccine to organ transplants, there has been controversy over how much we should be altering nature. When Louise Brown, the world's first test-tube baby (now a healthy 23-year-old), was born in England in 1978, some people called conception outside the body immoral and tried to have the technique banned.

Back in the 1970s, science made advances in two areas that seemed, on the surface, unrelated--but which have veered ever closer to each other. One was a growing understanding of, and ability to manipulate, deoxyribonucleic acid (DNA), the molecule that provides our genetic code. The other involved the advent of in vitro fertilization (IVF), the technology responsible for Louise Brown and nearly a million babies since.

IVF is a process by which eggs are removed surgically from a woman's ovaries and fertilized with sperm in a laboratory. After undergoing a few cell divisions, several of the resulting embryos are inserted into a woman's uterus where, with luck, at least one will develop into a full-term fetus. In any one trial of IVF, as many as 10 to 20 eggs may be extracted and fertilized, and the majority of the resulting embryos are often frozen at an early stage of development, in case they will be needed for later attempts at implantation in the uterus.

Though IVF offered new hope to many who could not otherwise conceive, it also opened up a slew of ethical questions, beginning with the status of those em-bryos that remain unused in the lab. Then there is the fact that the woman who donates the egg need not be the one who carries the embryo or who raises the child. It is, in fact, possible to have as many as five adults who could claim parenthood in an IVF scenario: the sperm donor, the egg donor, the woman who carries the fetus and a couple responsible for its upbringing.

Still, for all the potential issues it raises, IVF was in many ways just the beginning, a relatively simple manipulation of the natural order. The closer science has gotten to deciphering our genetic makeup, the more complicated the landscape has grown.

GENES AND DNA

By the middle of the 20th century, scientists had begun…