Erika Jonietz

About the author: Erika Jonietz is an associate editor of Technology Review.

Researchers have been working on animal-to-human organ transplants —called xenotransplantation—since before 1984, when "Baby Fae" received a heart transplant from a baby baboon. Scientists now believe that pigs may be the most suitable animal organ donors, because of their similarity to humans in terms of both biology and size. Many problems must be overcome before pig-tohuman transplants become as routine as human-to-human transplants, but the promise of saving some of the thousands who die each year for lack of human organ donors is enough to keep researchers trying.

The numbers are grim. According to the United Network for Organ Sharing, more than three times as many people in the United States were waiting for heart, kidney and liver...