Nina Strohminger in Aeon:
A classic philosophical thought experiment poses the following paradox. Imagine a ship, let’s call it the Nina, whose planks are replaced, one by one, as they age. Eventually every original part is changed, resulting in a boat made of entirely new materials. Our intuition that this is the same ship becomes problematic when the builders reassemble all the Nina’s original parts into a second ship. The Nina’s identity is tied up inextricably with her physicality.
Personal identity does not work this way. As Nina-the-person ages, almost all the cells of her body get replaced, in some cases many times over. Yet we have no trouble seeing present-day Nina as the same person. Even radical physical transformations – puberty, surgery, infirmity, some future world where her consciousness is preserved on a hard drive – will not obliterate the Nina we know. The personal identity detector is not concerned with continuity of matter, but continuity of mind. As the cognitive scientist Daniel Dennett wryly observed in his essay ‘Where Am I?’ (1978), the brain is the only organ where it is preferable to be the donor than the recipient.
This distinction, between mind and body, begins early in development. In a 2012 study by Bruce Hood at the University of Bristol and colleagues, children aged five to six were shown a metal contraption, a ‘duplication device’ that creates perfect replicas of whatever you put inside. When asked to predict what would happen if a hamster were duplicated, the children said the clone would have the same physical traits as the original, but not its memories. In other words, children were locating the unique essence of the hamster in its mind.
For Nina-the-ship, no part of the vessel is especially Nina-like; her identity is distributed evenly across every atom. We might wonder whether the same applies to people – does their continued identity depend only on the total number of cognitive planks replaced? Or are some parts of the mind particularly essential to the self?