If Adam survived as only one twin, there would need to be a non-arbitrary reason to identify Adam with one twin rather than the other, but both twins are qualitatively identical to Adam, so no such reason exists.

References to identity in this debate come from objectors to this argument, who apply the argument from fission to a real life version of it, namely, twinning. An embryo might split any time generally before the two-week point in fetal development, and those two embryos could develop into fully formed infant twins. The question for the advocate of the above argument to consider is, in such a case, what happens to the original human being, the embryo we will call Adam? There are only three possib