From the information given in the passage, it is clear that ....... .

Scientists believe that today the number of people who are carrying defective genes is increasing.
Part-of the explanation for this is that more people are being exposed to damaging radiation,
chemicals and other environmental hazards from the side-effects of technology. Another reason
may lie in generations of poor nutrition. Medical advances, however, have made it possible for
those people with inherited diseases and other deficiencies to live longer, marry and to produce
children. Each year increasing numbers of genetic defects are being defined, the ways in which
they are transmitted are better understood, and methods for identifying carriers of such defects
are being improved. The controversial field of generic surgery, in which harmful genes are
altered by direct manipulation, is also being studied.