The Brave New World of Three-Parent I.V.F.

In August 1996, at St. Barnabas Medical Center in Livingston, N.J., a 39-year-old mechanical engineer from Pittsburgh named Maureen Ott became pregnant. Ott had been trying for almost seven years to conceive a child through in vitro fertilization. Unwilling to give up, she submitted to an experimental procedure in which doctors extracted her eggs, slid a needle through their shiny coat and injected not only her husband’s sperm but also a small amount of cytoplasm from another woman’s egg. When the embryo was implanted in Ott’s womb, she became the first woman on record to be successfully impregnated using this procedure, which some say is the root of an exciting medical advance and others say is the beginning of the end of the human species.

The fresh cytoplasm that entered Ott’s eggs (researchers thought it might help promote proper fertilization and development) contained mitochondria: bean-shaped organelles that power our cells like batteries. But mitochondria also contain their own DNA, which meant that her child could possess the genetic material of three people. In fact, the 37 genes in...