A well known neuro-pharmacologist once explained that there are no free rides with drugs-- no brain enhancing drugs that don't have serious negative consequences but if there were I can't imagine what would be morally wrong with using them. Suppose, for instance, that these positive effects followed from eating a certain type of vegetable - would it be wrong to eat the plant? I don't believe so. Now, inasmuch as we often compete on the basis of mental performance, it would be nice to think that everyone had access to this drug. Suppose, for instance, that only millionaires could afford it. Would it be wrong to take it then? Maybe so. But the rich already enjoy vast advantages in the foot race of life, so I don't know that this would be any different. It would just add to the inequalities that we already live with in our society.

There are several sense to the word "life", which derives from a Norse word having to do with the body; in German we have Leib, body. (1) There is a biological sense, which used to be taken to say that things possess life only if they possess respiration, excretion, reproduction, growth, irritability - I like this one - and cells. Locomotion is also characteristic of animal living things. Physiological life is life in this sense. (2) Life can also be taken to be consciousness or psychological life, so that only conscious beings have life; but I think that this should be taken to mean that only conscious beings have a life. Grass is alive, practically eternal, but it does not have a life, and we do not say that the different kinds of grasses lead separate lives because they don't lead lives at all. A derivative sense here is a life, meaning a biography, as in "A life of Churchill". A life in this sense is a book. (3) "Life" can also mean "way of life", so habits, customs and attitudes, as in "the French way of life", and there is also the unappealing idea of a "lifestyle". "Life" here has a cultural and historical sense. "Life must go on", we say, after a war for example. (4) A life can also be a period of time. So my life started in 1951, and will probably end before 2051. "Life insurance" has to do with this sense, I think, though as we all know what you insure against is the thing insured, so that life insurance should really be called death insurance, as accident insurance is insurance against accident. (So-called house insurance is typically insurance against damage to a house and its contents.)

Perhaps it is only in the first of these four senses that there is anything which makes life to be life - as if it could be anything else! I mean that the seven characteristics (to which more recently are added an eighth characteristic - possession of DNA) are taken to make something which would otherwise be dead or non-living into a living thing. But it is not life which is made to be life by these things; rather it is a being or thing which they are said to make to be living.

In the other senses though what makes life life is just that it conforms to the definition, whatever that is. Though there would be no conforming to the psychological and cultural senses without living (unavoidable, more or less, in the psychological sense), there is an extended sense - living well - in which living badly is said to be no life at all. "Get a life", we say, and it can be a cruel saying or merely a hard one.

There may be as well a sense, though one very hard to grasp, in which "life" coincides with existence or world, so that the meaning of life has the sense of the meaning of existence. What I'm amazed at when I am amazed at the existence of life may be the existence of my life, but it may also be amazement at the existence of the world. 'The World and Life are one. Physiological life is of course not "Life". And neither is psychological life. Life is the world', Wittgenstein wrote in Notebooks 1914-1916. Here there is a sense of "true Life", the true Life, which means something one can live and participate in, no doubt, but more - what more is hard, or harder, to grasp.

I suggest that no matter how developed our brain sciences become, we will still have philosophy because the sciences themselves rest on philosophy, a scientific worldview. Without a concept of ourselves, causation and explanation, concepts of observation, and so on, we would not have any science. As for whether philosophers will have to be accomplished neurologists, I think that those philosophers working on human nature will at least need to have a general understanding of the methods and findings of the brain sciences and the general state of play in physics, chemistry, biology and psychology, but not to the point of actually being a scientist in any one of these domains. There are many issues that cannot be settled within the brain sciences themselves, including the nature of thought, emotion, desire, sensation, and so on. I suggest that whether or not machines can think or that human thinking is identical with brain processes is a philosophical matter that cannot be determined scientifically.

What is the difference between a living thing and a non-living thing? What is "vitality"? This is a difficult question. Once upon a time, it was widely believed that living things are distinguished by possessing a certain substance (an "elan vital") or perhaps by a certain force being present in them alone. This was a legitimate, testable scientific theory ("vitalism") that now appears to be false, since living processes can take place outside of living things (as when digestive enzymes can break down food in the test tube).

Another notable family of views on this question is that living things are alive in virtue of the fact that they carry out certain "life functions" such as growth, self-motion, metabolism, reproduction, and so forth. This view would account for the intermediate cases between life and non-life (such as viruses and whatever entities existed in the early stages of the origins of life on Earth). The intermediate cases could presumably carry out some but not all of the life functions.

Even if there were some sort of substance or energy that is possessed by all and only living things, presumably what makes that substance or energy able to give life is that it allows the living things to perform these characteristic life functions. That's another plus for the life-functions view.

However, it is notoriously difficult to specify these life functions in a way that all and only the canonical living things perform them. I set as a challenge for you to think of things that are not alive but can reproduce, respond to their environment, and undergo evolution by natural selection.

Another interesting complication here arises from the notion of "artificial life" -- not just life created by tinkering with DNA in living cells, but bits of software that behave like living things (such as computer viruses). Bits of computer code can reproduce, respond to their environment, undergo evolution by natural selection, and so forth. Are they alive (or even intermediate cases like biological viruses)? This is a controversial question. Some people think that if a bit of computer code simulates living things closely enough, it goes beyond merely simulating them to being actually alive. Other people think that this is an absurd result and shows that the life-functions view is mistaken.

Another option here is to say that what sets living things apart is not merely that they perform (many of) these life functions, but rather how they do so. Perhaps living things carry out these life functions "emergently": by bottom-up processes the precise outcomes of which cannot be predicted by some calculational short-cut. Some famous cellular automata are good examples of emergence (though they are not alive and perform none of the life functions).

There are many interesting examples in the history of science where the fact that something was alive was invoked to account for its behavior in much the way that an object's being copper can explain its properties and behavior. Whether these are genuine scientific explanations or not will ultimately depend on whether vitality turns out to have an essence or not. This remains an open scientific question.

And one might add that the cells themselves are hardly immune from "renewal" at the molecular level. So the short version is: If identity requires complete coincidence of matter, then essentially nothing but sub-atomic particles survive over any reasonable stretch of time. That does rather suggest, though the contrary view is certainly held, that identity over time simply does not require complete coincidence of matter. What it does require is not very clear, but that is no reason to despair.

Of course, the question didn't ask about complete coincidence of matter. But it's unclear why anything less might suffice. And, if it does, then you run into issues about transitivity: A might share much of its matter with B, which shares much of its matter with C; but A and C do not share much of their matter.

It's an interesting question, and to answer it, I'm inclined to turn things around. Let's start with what's clear: the fact that the rapist committed the rape seven years ago (supposing for the moment that this is the magic number) isn't a reason to let him off. In fact, the very way you pose the question makes the point. You ask about "the rapist" who committed "his crime" long ago. You've already take it for granted that we can say: this man is the one who committed the crime. And we can say it without worrying about how many cells have come and gone.

So yes: there is something more -- or something other -- to the notion of a person than just the idea of a collection of cells. The something needn't be anything spooky. After all, a corporation can exist for a hundred years, even though all the people have changed and all the buildings and equipment it owns have gradually been replaced. Although saying exactly what sameness amounts to here is complicated, it won't call for talking about anything strange. It will be a matter of various continuities and connections among perfectly ordinary agents, entities and events.

In fact, the word "agent" gives us a clue to the case of persons. John Locke famously observed that 'person' is a forensic notion. What he meant was that personhood has to do with accountability, agency and the like. To decide whether it makes sense to hold this human being accountable for what a certain human being did twenty years ago isn't a question that we approach by reviewing the history of the cells in his body, and someone who thought it did would show that they don't understand what was being asked.

Once again, detailed account will be complicated. But we can say at least this: when we ask whether a human being at one time is the same person as a human being at another time, we're asking about various kinds of connections and continuities. And what seems clear is that there can be enough of the right sorts of connections and continuities even if the cells that make up the present body are not the ones that made up the one from long ago.

Suppose there are two mutations that would allow a species of plant to gather more sunlight for energy, one that would make it grow taller than competing plants and another than would make it grow wider. The species happens to evolve to grow taller. It is true that it might have achieved the adaptive function of gathering more energy without growing taller (i.e., by growing wider instead). So, growing taller was not necessary (i.e., the only way) to achieve this function. Nonetheless, it would be a mistake to say that the plant's height is causally irrelevant to its capacities to gather energy from sunlight.

Similarly, it might be that a species (call them p-zombies) might have evolved that could gather and synthesize information about various features of its environment just as well as us but without being phenomenally conscious. But the possibility of such a species tells us nothing about whether phenomenal consciousness in us (and other animals) plays a causal role in gathering and synthesizing information about our environment. Consciousness may have been selected for even if p-zombies are possible. Consciousness may be the particular way (among many possible ways) that our ancestral species solved the challenge of gathering and synthesizing information about the environment and using it to guide adaptive behavior.

If your p-zombies are physically identical to us in every way, then we might wonder why consciousness evolved. But this already assumes that consciousness plays no causal role, since that's the only way that a physical duplicate of us without consciousness could still behave just like us. Once we recognize this, the conceivability of p-zombies becomes much more dubious (at least to me). I have a hard time conceiving of conscious states as causally inert, in part because I assume conscious properties are essential properties of certain underlying neural states.

(Another possibility is that consciousness was not selected for but was a side-effect of some other adaptation, but this still allows that consciousness eventually took on important roles in our behavior.)

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 because they increased survival)." You then say -- quite reasonably -- that the successful construction of such a consistent framework cannot count as the discovery of objective morality.

Why not? Here you might give two answers. One answer says that what our instincts dispose us to do is often wrong (e.g. when young males feel strongly inclined to take advantage of a safe opportunity to rape a female). But this answer would seem to presuppose rather than deny that there is an objective morality. Moreover, the fact that this answer is widely shared among moral philosophers shows that they do not count whatever our instincts urge us to do as a moral intuition. Our instincts may urge us to save ourselves from a dangerous situation, which we caused by our own negligence, through an action that is likely to kill innocent bystanders. But our moral intuitions tell us that this would be quite wrong.

The other answer says that history might have gone differently and might then have produced different instincts and moral intuitions. But since there can only be one objective morality, the moral intuitions that emerged in this history we actually happened to have cannot be a good path to discovering what this objective morality is. This answer makes some sense but, to reach your conclusion, you need to overcome two further hurdles. First, why cannot the morality that best accords with our moral intuitions be objectively right for our world even while another morality would have been objectively right if a very different history had shaped our moral intuitions differently? Second, are moral intuitions really the only basis on which an objective account of morality can possibly be established?

I think you are right to discern that the "playing God" objection to stem cell research/cloning is not what it seems to be. Those who offer this objection seem quite comfortable with the idea of "playing God" in well proven medical interventions e.g. appendectomy for appendicitis, C-section for obstructed labor, chemotherapy for leukemia. Of course there are some people (Christian Scientists, for example) who forgo most medical care on religious grounds. But the vast majority of those who worry about "playing God" with stem cell research/cloning are happy consumers of the best that health care has to offer. The question is, why don't they extend that happy consumer attitude to stem cell research/cloning? I am not sure of the answer to this, but I think it may have to do with the uncertainty that currently exists around these new technologies (will they work? will they produce monsters of some kind?). So it may be a risk aversive attitude of the kind "leave it to God, we don't know enough to intervene in this area." It expresses caution about experimenting with human beings, and modesty about our technological abilities, which is appropriate (if not taken too far).

Of course for every person who says that we shouldn't "play God" there is usually another person who says "God helps those who help themselves." Religious language can be used on both sides of this debate.

Your last sentence is correct, I think, with the exception of the word "improve," which I would replace with "modify" or "enhance." "Improvement" raises all the questions that critics of eugenics have raised about classifying human beings into better or worse.

By the way, we are already Transhumans, if you count glasses, sneakers, computers, etc. Perhaps the movement Transhumanism want the modifications integrated with our biology. But why would that be better?