CloningGenetic engineering, altering the inherited characteristics of an organism in apredetermined way, by introducing into it a piece of the genetic material ofanother organism. Genetic engineering offers the hope of cures for manyinherited diseases, once the problem of low efficiencies of effective transferof genetic material is overcome.Another development has been the refinement of the technique calledcloning, which produces large numbers of genetically identical individuals bytransplanting whole cell nuclei. With other techniques scientists can isolatesections of DNA representing single genes, determine their nucleotidesequences, and reproduce them in the laboratory. This offers the possibilityof creating entirely new genes with commercially or medically desirableproperties. While the potential benefits of genetic engineering are considerable, so maybe the potential dangers. For example, the introduction of cancer-causinggenes into a common infectious organism, such as the influenza virus, couldbe hazardous. We have come to believe that all human beings are equal; but even morefirmly, we are taught to believe each one of us is unique. Is that ideaundercut by cloning? That is, if you can deliberately make any number ofcopies of an individual, is each one special? How special can clones feel,knowing they were replicated like smile buttons. "We aren't just our genes,we're a whole collection of our experiences," says Albert Jonsen. But theidea, he adds, raises a host of issues, "from the fantastic to the profound."When anesthesia was discovered in the 19th century, there was a speculationthat it would rob humans of the transforming experience of suffering. Whenthree decades ago, James Watson and Francis Crick unraveled the geneticcode, popular discussion turned not to the new hope for vanquishing disease

but to the specter of genetically engineered races of supermen and workerdrones. Later, the arrival of organ transplants set people brooding about aworld of clanking Frankensteins, welded together made from used parts. Already there are thousands of frozen embryos sitting in liquid nitrogenstorage around the country. "Suppose somebody wanted to advertise clonedembryos by showing pictures of already born children like a product," saysProf. Ruth Macklin, of New York's Albert Einstein College of medicine, whospecializes in human reproduction. Splitting an embryo mat seem a great technological leap, but in a worldwhere embryos are already created in test tubes, it's a baby step. The currentchallenge in reproductive medicine is not to produce more embryos but toidentify healthy ones and get them to grow in the womb. Using genetic tests,doctors can now screen embryonic cells for hereditary diseases. In the not todistant future, prenatal tests may also help predict such common problems asobesity, depression and heart disease. But don't expect scientists to startbuilding new traits into babies anytime soon. The technological obstacles areformidable, and so are the cultural ones. Copies of humans are identical, but are the people the same? Probably not. For a century scientists have been trying to figure out which factors play themost important role in the development of a human personality. Is it natureor nurture, heredity or environment? The best information so far has comefrom the study of identical twins reared apart. Twins Jim Springer and JimLewis, separated at birth in 1939, were reunited 39 years later in a study oftwins at the University of Minnesota. Both had married and divorced womennamed Linda, married second wives named Betty and named their oldestsons James Allan and James Alan. Both drove the same model of blueChevrolet, enjoyed woodworking, vacationed on the same Florida beach, andboth had dogs named Toy.