Human genetic modification is the direct manipulation of the genome using molecular engineering techniques. Recently developed techniques for modifying genes are often called “gene editing.” Genetic modification can be applied in two very different ways: somatic genetic modification and germline genetic modification.
Somatic genetic modification adds, cuts, or changes the genes in some of the cells of an existing person, typically to alleviate a medical condition. These gene therapy techniques are approaching clinical practice, but only for a few conditions, and at a very high cost.
Germline genetic modification would change the genes in eggs, sperm, or early embryos. Often referred to as “inheritable genetic modification” or “gene editing for reproduction,” these alterations would appear in every cell of the person who developed from that gamete or embryo, and also in all subsequent generations.
For safety, ethical, and social reasons, there is broad agreement among many scientists, ethicists, policymakers, and the public that germline editing is a red line that should not be crossed. Using germline editing for reproduction is prohibited by law in more than 40 countries and by a binding international treaty of the Council of Europe. However, in November 2108, a scientist named He Jiankui announced he had edited the genes of twin baby girls who had subsequently been brought to term. His reckless experimentation has been nearly universally condemned. This development has sparked new debate around human germline modification, particularly between parties who desire to push the technology forward and those who fear it could open the door to a new market-based form of eugenics.