Robert G. Edwards's breakthrough development of in vitro fertilization, which led to the birth of the first "test-tube baby," Louise Brown, in 1978, gave humanity the power to do what previously was considered the province of God: create and manipulate human life.

In the ensuing decades, the pioneering techniques that won the British biologist a Nobel Prize on Monday have played a part in controversial scientific advances such as cloning and the creation of human embryonic stem cells while redefining fundamental social roles such as what it means to be a parent or a family.

"The impact on society has been profound," said Lori B. Andrews of the Chicago-Kent College of Law, who studies reproductive technologies. "The creation of a child outside the body for the first time has had scientific and personal implications far, far beyond the 4 million children who have been born through in vitro fertilization."

IVF has been crucial for human embryonic stem cell research because the cells are obtained from embryos left over at infertility clinics. At the same time, the techniques helped lay the groundwork for the 1996 cloning of Dolly the sheep, a procedure that could eventually be tried in humans.

"In exploring the fundamental mechanisms of how human reproduction actually works, Edwards unleashed a social, ethical and cultural tsunami that he could not have predicted and I don't think anyone at the time could have anticipated," said Arthur Caplan, a University of Pennsylvania bioethicist. "It opened so many doors that I'm not sure we even fully appreciate it today."

Edwards, who began his work in the 1950s and persevered with gynecologist Patrick Steptoe despite fears it would produce monstrously deformed babies and other problems, was motivated primarily by the desire to help infertile couples. Although the procedure remains controversial and is opposed by the Roman Catholic Church and others, it has become widely accepted.

"His achievements have made it possible to treat infertility, a medical condition affecting a large proportion of humanity," the Nobel Assembly at the Karolinska Institute in Sweden said in announcing the $1.5 million prize. "Today, IVF is an established therapy throughout the world."

The procedure involves taking an egg from a woman's ovaries, fertilizing it in a petri dish in the laboratory with sperm and placing the fertilized egg into a woman's womb to develop naturally. It is used to treat a host of fertility problems, including cases in which a woman's fallopian tubes are blocked, preventing the egg from being fertilized normally.

Edwards, now 85 and a professor emeritus at the University of Cambridge, was too ill to give interviews about the award. In a statement released by Bourn Hall, the infertility clinic he founded, Edwards's wife, Ruth, said: "The family are thrilled and delighted. . . . The success of this research has touched the lives of millions of people worldwide. His dedication and single minded determination despite opposition from many quarters . . . has led to successful application of his pioneering research."

But IVF has forced society to reconsider many assumptions. Using IVF, a child today can have one "mother" who donated her genes, another who donated her womb and another who raised him or her, for example. Family members have supplied eggs, sperm and wombs to relatives, scrambling traditional relationships. The procedure has also helped fuel the debate over gay rights by enabling same-sex couples to have genetically related children.

"The implications are just staggering," Caplan said. "Even some of the arguments about gay marriage spin out from the fact that IVF lets gay people have children."

The procedure also furthered the trend that started with the birth control pill by giving women greater control over their reproductive lives, leading more to delay childbearing to pursue education and careers.

"In the 20th century, you could argue the two developments that shaped human behavior were the birth control pill and IVF," Caplan said.

At the same time, because women are paid to donate their eggs or offer their wombs to become surrogate mothers, worries have arisen that the pricey procedure has turned reproduction into a commodity.

"It has led to some concerns about the commercialization - making childbearing into a business," Andrews said. "You have couples creating embryos in the U.S. and implanting them in women in the Third World, for example."

The law has also had difficulty keeping up with the technology, resulting, for instance, in legal battles over the custody of embryos.

"This has led to reconsideration of men's role in reproduction," Andrews said. "Prior to this, all the choices had to do with women. But now that the embryo is outside of her body, you have to rethink what reproductive liberty means. Courts are moving toward giving men more rights."

Because infertility clinics are largely unregulated in the United States, critics say many often push ethical boundaries. For example, some enable couples to choose the sex of their children.

"I would argue that IVF technology opened a door to a kind of control over human lives. Upon reflection now three decades later, I think we're seeing the very dark consequences of this," said the Rev. Thomas Berg, director of the Westchester Institute for Ethics and the Human Person, a Catholic bioethics think tank. "I think we're seeing the very questionable moral directions that this technology is taking us."

Another widely used procedure, known as pre-implantation genetic diagnosis, enables doctors to test embryos for specific genes. The process is used primarily to spot devastating genetic disorders, increasing the chances that couples will give birth to healthy babies. But combined with the constant flow of discoveries of new genes, the procedure has led to concern about "designer babies," in which couples might try to choose a host of traits, including eye color, hair color, height and intelligence.

"In the 20th century, I would argue the biggest debate in America in terms of reproduction has been abortion," Caplan said. "I believe in the 21st century, Edwards's discoveries will make the issue of designing our descendants - that is, trying to create children who are stronger, faster, live longer, that sort of thing - that's going to become the biggest issue in the first half of the 21st century."

For her part, Brown, now 32, a mother of a son she conceived naturally, welcomed Edwards's victory. "It's fantastic news," she said in a statement released by Bourn Hall. "Me and mum are so glad that one of the pioneers of IVF has been given the recognition he deserves."