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.

The definition of "illness" that you are using was originally developed by Christopher Boorse, and many others who have looked for an "objective" concept of illness have also adopted it. You are correct to say that on this view, all illness, including mental illness, is due to some dysfunction. And you are correct to note that we do not know (for most mental illnesses) whether or not there is a brain dysfunction. In fact, some have suggested that depression can be a functional response to failure and/or loss.

Different concepts of illness are worth considering here. For example, "subjective" concepts in which "illness" is defined as an undesirable or unwanted state. According to such definitions, there is mental illness when there is (serious)mental distress (since distress is undesirable or unwanted).

In practice, much can hang on whether or not something is labelled an "illness": medical treatment, insurance reimbursement, sympathy, excuses, responsibility, etc. That's really too bad, in my opinion, because "illness" is such a flimsy concept!

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 stronger your grounds to object.

Whether these grounds can be outweighed depends on the purpose and context of the genetic engineering. Suppose that, thanks to a rare combination of genetic traits, you have immunity against a nasty communicable disease. It's highly desirable that many in the next generation have such immunity. In such a case, the interest of society might outweigh your interest in preventing that, thanks to the use of your genetic information, many in the next generation are uncomfortably similar to you.

There's ample space for reasonable disagreement about how to weigh the competing interests here, and the decision should ultimately (once we get there, technologically, and thus have a better understanding of what is and is not technically feasable) be made by an elected legislature -- differently, presumably, in different jurisdictions. Such legislatures may also need to decide two further matters:

(1) who is allowed to extract and store genetic information, and for what purposes and with what safeguards (there are probably good reasons to make it illegal for any old hobby geneticist to collect stray hairs from people and to extract and store their full genetic information); and

(2) whether there should be (tradable or untradable) private property rights over genetic information and, if so, how these should be conceived.

While there is no good case for saying that persons have a natural right to veto the use of their genetic information, there are good reasons to be cautious in regard to legalizing -- especially commercial -- use of genetic information, even with the consent of the person whose genetic information it is.

You ask an interesting question about the process of evolution. Neo-Darwinians typically argue that species evolve by natural selection on random mutations. At any particular time, there is more than one kind of random mutation that is of selective advantage, and it is contingent which one of these (if any) occurs. So evolutionary history has a certain randomness and unrepeatability. If we recreated Neandertals and did not interbreed with them, they might evolve into yet another (new) human subspecies.

Some biologists have argued that some mutations are directed--i.e. not random and in response to specific environmental challenges. To the degree that this is so (and that environmental challenges repeat themselves) evolution might repeat itself. But this is a controversial theory and is not generally thought to account for much mutation.

This is a wonderful question, which goes to the heart of just what ethics is about. Some philosophers--such as Immannuel Kant--have maintained that ethics consists in universal principles of practical reason, which must therefore apply to all rational beings, including God, angels, devils, and any other rational being whatsoever. This 'universalist' conception of ethics obviously abstracts away from any other differences among beings to identify rationality and the capacity to be bound by ethical obligations. If, however, one thinks that ethics is about how agents negotiate their relations with one another, how they, as it were, 'get along', then it would seem that the sorts of differences that you point out would be relevant to shaping the ethical relations of these beings, and consequently, differences in biology, etc., might well lead to different ethical concerns. So what is ethics about? Is it about duties that apply to all rational beings? Or is it about how beings negotiate their relations with one another? Or is it about something else altogether? How one answers these questions will have deep and far-reaching implications, and these questions deserve further reflection.

There are two sorts of issues here.

Suppose that it is, in fact, extremely unlikely that reproduction should occur as it does. The universe is a vast place. For all we know, it occurs in billions of other ways in billions of other galaxies. Even on our own planet, of course, reproduction occurs in a dizzying variety of ways. That it happens to occur as it does among us might just mean we are the lucky ones. This is just a way of saying that astonishingly unlikely things do happen. The odds against someone being dealt, in a game of bridge, a hand consisting of 13 cards all of one suit are 158,753,389,899 to 1. But it does happen from time to time. And the universe has been around for a lot longer than we have been playing bridge.

Probabilities like the one just mentioned concern the probability that an event should occur on a single occasion. Every time a bridge hand is dealt, it is incredibly improbable that it will be a perfect hand. But the probability that such a hand should ever have been dealt is actually quite good, because so many hands have been dealt. So again: The universe is a vast place, and it is very old, and we have pretty good reason nowadays to suspect that life is quite common. So it just isn't clear whether it is unlikely that reproduction should at some time and in some place have evolved as we have it, even if we grant that it is very unlikely, case by case, and even if it is therefore unlikely that it should have evolved that way among us.

One might also question whether reproduction really does generally involve a beautiful relationship between two people. There are many societies in which such relationships between men and women are quite uncommon. Marriage in such societies is considered a largely economic and social transaction between families, one that has very little to do with the people involved, let alone with whether they love one another. That was so even in our own society until not very long ago. The ideal of romantic love, and especially the idea that marriage should involve romantic love, look to be very human creations that are not, in fact, very old, evolutionarily speaking.

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 follow with reasonably accuracy, then we might conclude that it is not the morality that human beings ought to try to follow. Similarly, if a morality is so demanding that we do not manage to educate most human beings to follow it, then again we would seem to have reason to conclude that it is not the morality human beings ought to try to follow. I see morality as solving the practical task of helping us live together peacefully and in a way that lets us flourish individually and collectively. On this account, we should be sensitive to empirical information and practical experience.

Should you be interested in more on this question, you might want to look at my exchange on this with Jerry Cohen (who takes the opposite view to mine). My response to his book -- Rescuing Justice and Equality -- is "Cohen to the Rescue!" in Ratio 21/4 (2008), pp. 454-75.

Yes, there is a book just out that you might like, called Philosophy for Everyone: Cannabis:

http://www.amazon.com/Cannabis-Philosophy-Everyone-Talking-About/dp/1405199679

The sub-title is quite fun: "What were we just talking about?"

That book, just published last year, should give you lots to consider.

Probably the most positive treatment of psychotropic drugs by a philosophically minded author is Aldous Huxley's The Doors of Perception.

Interesting question! We might distinguish between the 'general public' and the 'experts.' Don't you think there will always be 'experts' driving the technological process? Always innovating, always working, always moving 'forward' (or at least moving)? Such folks will always "know how to do things" etc. -- but then maybe you're right about the general public -- ie the more passive consumers of technology -- perhaps with advancement eventually people won't need to do anything, machines and technology will do everything -- (I'm reminded of the movie Wall-E, where the humans on the space ship just floated around on chaises longues getting fatter and fatter ....) --I suppose one could imagine a scenario in which humans create machines which not only do everything but ultimately control everything and thus leave humans behind .... Hm. But would that necessarily be a bad thing, Hollywood movie ideas excepted?

Yes. As far as I know, there is not a live debate in philosophy of biology (or philosophy more generally) regarding the viability of neo-Darwinian theories of evolution. There are lots of interesting debates about the details of the theories (e.g., levels of selection, how to understand the mechanism of natural selection, etc.), but no respectable philosophers I know of defend Intelligent Design as an alternative biological theory to evolution by natural selection. There are debates about how to treat the debate itself (e.g., whether ID should be taught--I like to teach Darwin vs. ID in my intro to philosophy class to teach abduction or argument to the best explanation), and philosophers still teach the teleological argument or Design argument for the existence of God (the new versions of these arguments that invoke the probabilities regarding the laws and constants being 'ripe' for a stable, evolution-friendly universe are interesting to discuss). But philosophers often teach such arguments as exercises in the history of ideas and in how to uncover what makes them unsound.

But again, the answer is yes, the consensus is that neo-Darwinian theory is the only viable theory that provides unifying and informative explanations of biological phenomena.