C: That’s well-said, but I have to deny the analogy. It’s true that tumors are made of cells with human DNA, but they’re no more human than an E. Coli in my gut which swaps for some human DNA with another, or a gorilla or chimpanzee who both have more than 90% of our DNA, or for that matter, rice and bananas with around 50%. No, the key attribute you’re missing is the potential. A fetus has potential to grow into something we both accept as human. No matter how many E. Coli you culture or tumors suffer to grow, you’ll never see one turn into a human being. They don’t have the potential.

A: So what would be your definition? Something is human if it’s a human being like you or me, or if it has human DNA and is going to become a human in the future?

C: Fair enough.

A: But fetuses still aren’t human. Most fetuses wind up being shed with the uterus’s lining, or just dying, or are so damaged they never come to term. There’s a chance they’ll become human, but the cumulative odds are low. Mother Nature is the greatest abortionist of all.

C: Many things in life are low odds. Let’s just say “is possible for it to become a human being”. That sounds reasonable to me. If you accept that, then you must condemn abortion!

A: I can’t be so enthusiastic. Let me offer a thought-experiment. Suppose we take a woman from her suburban existence. Let’s call her… “Sherry Tiavo”. So, we anesthetize Sherry, crack open her skull, and scoop until all that’s left is her spinal cord and brain stem. To be certain, we toss everything into the incinerator. Is Sherry (or her body) still human? Are we guilty of murder?

C: Well… the mind is irretrievably gone. You can’t regrow a brain. But people would still react to her as a human being—the issue is obvious to them—so I would say yes to both.

A: Suppose we then hired a mad plastic surgeon to transform her body into something nonhuman. Perhaps a humanoid cat. Now if they happened to come across it, her own family would no longer recognize her as human. Certainly they would not recognize her as their Sherry. What then?

C: I know the answer you expect—“No, since nobody treats her as human, and she has no future potential.”

A: Since the body is no longer human, but something “lower”, something animal at best, surely it follows we can do anything to it that we could do to an animal. We could conduct experiments on it, abandon it in the woods, kill it, butcher and eat it…

C: Stop, stop! Alright, maybe the obvious-and-potential criterion isn’t acceptable after all.

A: Well, how do you suggest we modify it? You can’t abandon the potentiality criterion without also abandoning fetuses, remember.

C: Then I’ll drop the “obvious” criterion. It was wrong of me to accept that in the first place: this very discussion is proof that what is human is apparently not obvious! Even a subset like deciding “gender” is hugely complex , so why not humanity as well? This criterion covers adults (as one must have the potential to ‘become’ human if one already is human), and fetuses, but excludes tumors and chimeric bacteria.

A: I am not normally a disagreeable person, but there must be something in the air today. Abandoning the appeal to social judgment as part of your personhood criteria seems to me to be quite as wrong as affirming it.

C: A strong claim. May I ask for an example of how “potential” on its own could go so astray?

A: Certainly. But I have some preliminary points. Now, you accept that on the level of individual cells and such-like, everything is determined by physical laws and starting conditions, yes?

C: Yes.

A: By which I mean, an embryo or zygote (which grow into the fetus) is an extremely complex agglomeration of chemicals or atoms in a particular arrangement. If I were to manufacture another such agglomeration, identical down to the molecular level, what I would get is a zygote or embryo which is very similar (if not identical) to the original?

C: Yes. No doubt there would be differences as the cells grew, ways in which the imperfect replication interacted with the varying conditions to produce varying results. If you were not artful enough, the agglomeration might not even be alive.

A: But if I were, it would grow and develop?

C: Yes. I am no mysterian who believes in an élan vital or New Age-y quantum magic or some such foolishness. You put the right ingredients in the right order, and you get life. It’s that simple. Why, we can synthesize simple living cells in laboratories! Synthesizing a fertilized human egg differs only in being much more difficult. It is doable in principle.

A: But do you suppose it would be more or less difficult to turn a random human skin cell into a fertilized egg than to synthesize a fertilized egg from scratch?

C: Less, I should think. The skin cell will have pre-constructed many of the necessary constituents; one wouldn’t have to construct all the common cellular structures like mitochondria or the cellular membrane and cytoskeleton. I believe I have read about skin cells which were made to become stem cells, and I understand stem cells can be made into any kind of cell. We can even convert skin cells to heart cells without converting to stem cells first!

A: Which finally brings me to my point: so isn’t it true, then, that any cell in the body has the “potential” to become a human? Even the lowly skin cell, shed after just 2 weeks, can aspire to personhood if placed in the right broth of chemicals.

C: To convert a skin cell to a zygote and grow it—that’s some broth.

A: But it can be done! And don’t your fetuses need quite a broth as well? Remember that most fetuses never become babies, after all. But to continue: you only mentioned possibility. Your possibility grants personhood to every cell of the body. I don’t think Walt Whitman meant “I contain multitudes” quite that way!