Altered fish's weak offspring.

• Position: Genetics

The genetic modifications that improve animals for human consumption also could doom populations if released into the wild, warn scientists from Purdue University, West Lafayette, Ind. Biologist Rick Howard and his colleagues have discovered a paradox that crops up when new genes are inserted into a fish's chromosomes to make the animal grow larger. While the genetically modified fish will be bigger and have more success at attracting mates, they also may produce offspring that are less likely to survive to adulthood. If this occurs, as generations pass, a population could dwindle in size and, potentially, disappear entirely.

The most common question posed about genetically modified organisms (also known as GMOs or transgenics) is whether they are safe for people to eat. When GMOs first were made commercially available in 1996, many food crops, such as corn and soybeans, were altered to produce substantially more yield than they do in nature. The debate on transgenics in supermarkets has yet to be resolved, and Howard indicates it could be drawing attention from an equally important issue: whether they are safe for the planet.

"With all the concern over whether transgenic food is safe for humans, the environment has been more or less left out of the picture," he points out.

As a step toward resolving this issue, Howard and his colleagues set out to examine the risk transgenic fish...