Quantum physics was the most exciting scientific and technological frontier in the early twentieth century, as researchers made theoretical discoveries that ultimately gave rise to the atomic bomb, the nuclear-power industry, radiation therapy in cancer treatment, and the use of radioactive isotopes in medical diagnosis. After 1950, the biological sciences, especially molecular biology and genetics, produced the most stunning breakthroughs. But the same discoveries that deepened understanding of life also raised complex social and ethical issues.

For centuries, farmers had understood genetic principles in practical terms as a way to increase crop yield and breed fatter hogs and cows that produced more milk. Modern genetics dates back to the 1860s, when Austrian monk Gregor Mendel experimented with hybridizing pea plants.

The field of molecular biology arose in the 1950s. In 1953 Max Perutz of Cambridge University showed how x-rays could be used to establish the structure of protein molecules, the basic working elements of all living organisms. Modern genetics leapt forward in 1953-1954 when a young American scientist, James D. Watson, working with Francis Crick of Cambridge University and using data from Maurice Wilkins and Rosalind Franklin of King's College, London, established the double-helix structure of DNA (deoxyribonucleic acid), a mega-molecule essential in the transmission of genetic information. For their achievements, Perutz, Kendrew, Watson, Wilkins, and Crick all received Nobel prizes in 1962. (Franklin had died in 1958.)

By the end of the twentieth century, geneticists and molecular biologists were achieving breakthroughs on many fronts and applying their findings in unexpected ways. For example, DNA testing resulted in freeing a number of prisoners wrongly convicted of murder, including some on death row.

In 1986, with funds appropriated by Congress, the U.S. Department of Energy and the National Institutes of Health launched the Human Genome Project to determine the precise DNA sequence of all the genetic material in the forty-six human chromosomes. Establishing a significant precedent, Congress set aside 5 percent of the budget for studies of ethical and social questions raised by the project.

The task involved the computer analysis of massive quantities of biostatistical data. A private biotech company, the Celera Genomics Corporation, soon joined the race. In June 2000 the heads of the Celera and Human Genome Project teams jointly made a "working draft" of the human genome available to researchers. Some compared the achievement to the mapping of the vast North American interior in the nineteenth century.

In 1997 in Scotland, meanwhile, veterinary researchers successfully cloned a sheep, producing a lamb named Dolly. In other words, they created a precise genetic replica of a sheep by transferring the nuclei of its cells into an unfertilized egg from a female sheep, and then implanting the egg into the donor female, where it grew the way an egg fertilized by normal breeding would have. This soon lead to excited speculation about cloning human beings--a scary prospect that some scientists dismissed as science-fiction. Nevertheless, President Bill Clinton banned the use of federal funds for human-cloning research, and urged a "voluntary moratorium" on all such efforts.

More immediate concern focused on the medical applications of genetic research. By 2000 medical investigators had isolated defective genes that created a higher than normal probability that individuals would develop breast cancer, ovarian cancer, cardiovascular disease, dementia, cystic fibrosis, Huntington's disease (the neurological disorder that killed folksinger Woody Guthrie), and other ailments. In 2001 physicians began offering tests to expectant Caucasian parents to see if both carried the genetic defect linked to cystic fibrosis. (This

disease most commonly strikes Caucasians, with some thirty-thousand sufferers in America.)

The development of genetic-screening technologies to identify persons at risk for specific diseases offered the promise of early medical intervention, but also raised ethical dilemmas. While some individuals sought out such information so they could take precautionary measures, others preferred not to know. The danger that genetic information could fall into the hands of potential employers, insurance companies, and government agencies threatened patients' right of confidentiality.

Another troubling moral issue arose when James A. Thomson at the University of Wisconsin-Madison, along with scientists at other institutions, developed techniques for harvesting human stem cells from blastocysts (an early stage of embryo development) that had been frozen for the use of couples experiencing fertility problems. Typically, when a fertilized blastocyst is implanted in a woman's body and she successfully gives birth, any leftover blastocysts are discarded. Scientists proposed to use these "surplus" embryonic stem cells for research on diabetes, heart disease, and other illnesses. Stem cells are especially useful because they can develop into many different specialized human cells. But stem-cell research stirred controversy because it involved the destruction of early-stage human embryos, which some religious groups consider to be human life. Said one American Catholic leader, "We are talking about not only the direction of genetic science, but also [about]...questions of human dignity." In August 2001 President George W. Bush issued a compromise ruling allowing federal funding of research using existing stem-cell lines, but forbidding government support for research using human embryos dating from the period after his ruling.

In 2001 researchers converted cow skin cells into cow heart cells. If the same technique could be made

to work with human cells, it would be unnecessary to

use stem cells, and science would have resolved--or bypassed--this particular ethical dilemma.

These breakthroughs in human genetics opened new scientific horizons while raising profound ethical issues. Politicians debated; medical ethicists offered advice; and the American Medical Association set up websites to help physicians deal with the ethical dilemmas they faced as genetics increasingly affected medical practice.

As we have seen throughout The Enduring Vision, scientific discoveries and new technologies have vastly benefited Americans. But they have also had unanticipated cultural implications and posed troubling public-policy issues. As the twenty-first century unfolded, both the technological advances and their unexpected social consequences and ethical dilemmas seemed certain to continue.