Philosophers debate persistence conditions for personal identity because everything about us seems to change, including our cells, our memories, and our bodies. But DNA doesn't change and it codes for specfic traits in every cell of the human body. It's true that we experience changes in the way phenotypes are expressed in particular experiences or memories, but why not conclude that DNA is the ultimate source of personal identity? Philosophers don't seem to give this biological candidate serious consideration. Can you tell me why?

DNA cannot very well serve as a sufficient condition for personal identity over time, otherwise identical twins would each be identical with both their past and future selves. Can DNA serve as a necessary condition for personal identity over time? Imagine a futuristic machine that introduces a minute and meaningless change to your DNA (difficult, I realize!) at 4pm today -- a change that would not result in any noticeable changes in your feelings, memories, conduct, appearance, etc. Would it be credible to say that the person after 4pm is a different person from you? These are, I think, among the reasons philosophers would give for not taking DNA to be a good answer. But then good answers are not easy to come by for this question.

Has a person been wronged if they are cloned without their consent? Presume that the cloning process is non-invasive; a scientist simply picks up stray hair you left behind, and then makes a clone of you. Does that violate your rights? Do we have a copyright on our DNA?

This question is at the extreme end of a cloud of questions. The person who picked up your stray hair might use your entire genetic information (cloning) or any subset thereof. I don't think there is a general moral answer here about where to draw the line. There are some clues to a moral answer about how the line should be drawn in the law. Obviously, the less of your genetic information is copied, the less of a legitimate interest you have in preventing the copying. If they just copied the bit that controls hair color (I know, this isn't quite the way it works, but let me simplify a bit), then it is hard to see how you would become worse off by the fact that there is someone somewhere 20 years younger than you who has the same hair color. In cases where more substantial chunks or your genetic information are copied, you may well become worse off -- for example, because your talents, looks, or basic personality traits become less unique. In these cases, the more copies are produced, the...

Dear Philosophers (and especially Prof. Pogge), I can see why an empirical theory of DESCRIPTIVE ethics is possible, but can there be an empirical theory of NORMATIVE ethics? It seems to me that, in the final analysis, you cannot deduce "ought" from "is". If all people are born (have evolved) to be selfish and cruel, does it follow that we should be selfish and cruel? Shouldn't we be considerate and kind, even if we are not born with these attributes?

Just to clarify terminology. I would understand an empirical theory of ethics as one that explains the activities of a group of ethicists. An empirical theory of descriptive ethics would seek to explain the activities of those who describe ethical beliefs and practices; and an empirical theory of normative ethics would seek to explain the activities of those who justify or challenge ethical beliefs and practices. An empirical theory of normative ethics would not itself seek to justify or challenge normative-ethical propositions. Leaving terminology aside, I think what you mean to ask is whether an empirical account of how human beings behave has normative implications. In response, I would certainly agree that it does not follow from the fact that human beings tend to behave in certain ways that they ought to do so. Still, I would not think that empirical knowledge about human beings is normatively irrelevant. Two examples. If a morality is too complicated for human beings to understand or to...

Hi, I'm wondering what is the purpose of moral philosophy assuming that our moral intuitions are mere products of evolution. Evolutionary psychology seems to explain our moral roots (genes that coded for cooperation helped the organisms in which they resided reproduce and replicate those genes). Given this, our instincts that say we should behave in certain ways are merely adaptations that increased survival. It seems then that there is no objective answer to "What should I do?" and the entire field of normative ethics is premised on the delusion that there is. Wouldn't it be more honest for professors of moral philosophy to tell their students that they're merely looking for a consistent framework for decision-making that best coheres with our moral intuitions? And that outside of these intuitions (which arose because they increased survival), there is no warrant for believing in some absolute, metaphysical grounding of ethics--in other words an objective answer to the question "what SHOULD I do?" Thanks!

As happens often, also with professional philosophers, your word "then" marks the weakest spot in your argument. "Our instincts that say we should behave in certain ways are merely adaptations that increased survival. It seems then that there is no objective answer to 'What should I do?'." How does the second sentence derive support from the first? Our instincts may predispose us to get frightened by certain sights and sounds, and we may through evolutionary factors have become disposed to overestimate vertical distances and to underestimate horizontal distances over water. Does it follow that there is no objective answer to the question of whether those sights and sounds really are associated with danger -- no objective answer as to what these distances really are? I think your worry comes about as follows. You believe that what really goes on in moral philosophy is that people are "looking for a consistent framework for decision-making that best coheres with our moral intuitions (which arose...