Philosophers debate persistence conditions for personal identity because
DNA does change. There are "point mutations", for example, in which say a single nucleotide changes, say from guanine to cytosine. . . . CTG TCA . . . becomes . . . CTG GCA . . . If there is a strand of DNA that suffers such a change, is it then not the same strand of DNA? This is exactly like the question whether persons become different persons if they lose say half a finger. And now we have the problem of DNA identity. When are two descriptions sufficiently similar to count as descriptions of the same strand of DNA? Anthony Quinton has the general issue right, in a 1962 article in the Journal of Philosophy called "The Soul": 'No general account of the identity of a kind of individual thing can be given which finds that identity in the presence of another individual thing within it. For the question immediately arises, how is the identity through time of the identifier to be established? It, like the thing it is supposed to identify, can present itself at any one time only as it is at that time. However alike its temporally separate phases may be, they still require to be identified as parts of the same, continuing thing.' By the way, 6% of identical twins do not have identical DNA, so the members some pairs of identical twins would be metaphysically identical and some would not.