When I teach personal identity in Intro and Metaphysics, I often have a student suggest that what it takes to have the same person across time is for the persons to have the same DNA structure.
A good response to this has always been to point out that identical twins have the same DNA structure, but are not the same persons. That won’t work anymore. According to this article, we’ve discovered that we were wrong in thinking that identical twins have identical DNA structures.
Of course, I think there is still a pretty decent counterexample that would involved identical twins in the neighborhood. It turns out that identical twins differ only slightly in their DNA structure. So, imagine we discovered that there were twins who lacked those slight differences. I take it they wouldn’t be the same person. So the counterexample, isn’t completely undermined – but we do need to run it using nearby possible worlds. We can’t rely on something that’s actually true.
That seems interesting and worthy of note.
That is interesting; I’m not sure if it’s crucial to the identical twin counterexample, but it definitely does make it weaker because it takes away our ability to use abduction as an explanation for its plausibility.
Sameness of DNA structure isn’t sufficient for sameness of person, but maybe it’s necessary.
Hi Dennis,
I agree it’s not sufficient. The thought that it may be necessary is interesting. I’ve been attracted to that at times, but I’m worried about some kind of gene therapy case.
Suppose, my DNA structure is going to pretty much guarantee that I develop some kind of cancer, and the doctors develop some way to go in and turn off just that gene. Suppose that all newly generated cells in my body have DNA with that gene removed (or changed) and that after seven years or so, my DNA structure is different. That seems theoretically possible, but it’s a little counterintutive to say that this results in a different person.
If we want to say a person A at t1 is identical with person B at t2, what matters is that the person stage that is identical with person B at t2 bears the i-relation to the person stage that is identical to person A at t1. Duh.