Germline genetic modification, CRSIPR, and human identity: Can genetics turn you into someone else?

Summary Genetic modification is no longer science fiction. Through CRISPR, genetic modification is rapid, inexpensive, and effective in an unprecedented way. The most controversial application is modifying the human genome so that the modification is inherited to future generations, so-called germline genetic modification. Germline genetic modification must be done at the sex cell or early on in the embryonic stages, before or in conjunction with the start of the existence of a human being. This article focuses on how germline genetic modification affects the identity of the human individual: will the individual become someone else than she would have been if the sex cell or embryo is subject to germline genetic modification? The question is about each human individual's numerical identity over possible worlds, or what the necessary conditions for being the individual one is. The few philosophers who have addressed the question have argued that germline genetic modification entails that another individual comes into existence as a result of that modification. In this article, I argue that this view is a mistake. Rather, germline genetic modification should be seen as analogous to genetic modification of an existing individual, which according to all plausible theories on human identity in most cases would not end the existence of someone. In other words, the person's numerical identity is not affected even though a significant modification has occurred. The metaphysical and normative implications of this argument are also discussed.