In a heroic effort to prevent the transmission of disease from mother to child, researchers from the United Kingdom reported last week on the birth of eight babies—each of whom was conceived from one sperm and two eggs.

Although the babies, thus far, appear mostly healthy, some are wondering if science has taken a step too far. Will tinkering with nature like this have lasting consequences? And what kind of human is the product of three distinct parents?

Development of the procedure, known as mitochondrial donation, has proceeded cautiously over decades . The aim has not been to create hybrid creatures, but to prevent a horrific disease linked to mitochondria , the microscopic power generators in the mother’s egg.

Mitochondrial disease is, in fact, devastating, affecting about 1

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