Mr. Saletan, you admit that embryo formation, although dotted, is the sharpest line we can draw in human development.

If that is so, then from an ethical standpoint, shouldn't it also be the point at which we make the distinction between human and non-human? Although imperfect, it is the clearest distinction that we can make based on what we know. To infer whether one is human at any point later in development would seem to me to be totally irresponsible. It's like saying because there is no definitive line, any arbitrary point in development would do just as fine. If you accept that reasoning then how can we defend ending the life of a fetus just prior to birth but not right after?

If science provides us with new facts that move the line either forward or backward in development then so be it. But given what we know, I think it is our ethical responsibility to make a decision based on the evidence we have. If I follow your logic to its end, then I don't see any reason why it wouldn't be morally wrong for me to end the life of anyone over the age of 0 days.

Furthermore, if we as humans are going to continue pushing the social and moral ideas of human rights, then it is incumbent on us to say what is human and what is not. Therefore, I fail to see why this distinction is not made at the point which we can identify as the sharpest line.

If there were no cost to drawing the line at the moment of conception, or of embryo formation, then sure, we could play it safe and assume that all embryos are human beings. Why not?

However, there is in fact a cost. If you draw that line there, then the logical conclusion is that abortion is infanticide; which imposes a substantial cost, to the women who will be forced to endure unwanted pregnancies, to the children who will result from those pregnancies, and to the rest of us who must live with the social consequences. It also imposes a cost on the people who might benefit from scientific research that is made illegal.

So it's incumbent upon us to think this through a little harder. If we're going to put the line at conception, we'd better be damn sure we aren't imposing those costs for nothing.

What makes a human being, human? The obvious answer is a human brain, which is the seat of consciousness, mind, and emotion. If you believe in souls, then they surely connect to the world through our brains. If you destroyed someone's brain but kept their body on life support somehow, it would be very hard to argue that that person was still a person in any meaningful way. On the other hand, if you replaced every one of a person's limbs and organs with mechanical substitutes but left the brain intact, that person would still have a claim to be human.

At the same time, a single neuron does not a brain make. So there must be some point in its development at which the embryo's nervous system crosses the line and becomes human. Exactly where does that point lie? That's a tougher call, and depends in large part on what you think the minimum functionality of a brain is before it can be called human. We will probably have to settle for a range; anything before date X is clearly not human, anything after date Y clearly is human, anything in between is a judgement call.

It's not a question with a clean, simple answer. But there is no justification for avoiding that question in the name of imposing a false clarity.

you admit that embryo formation, although dotted, is the sharpest line we can draw in human development.

If that is so, then from an ethical standpoint, shouldn't it also be the point at which we make the distinction between human and non-human?

The short answer for me is: no. Just because an event may be more or less clearly delineated doesn't mean it's the right place to ascribe certain properties.

I have no problem with the assertion that a five-second old fertilized egg has a good chance of developing into a human being. But to me it's clearly not a human being. I am positive it has no sensation (since it has no nerve cells), no awareness. And even awareness would not be sufficient for me; many lower life forms are aware of there surroundings, but we don't give them the same status as human beings.

Where would I draw the line? It's messy. It think personhood has a lot to do with how much an entity is "like us," which is a subjective determination where people's opinions may differ. But I have a tolerance for ambiguity. And I can say with high confidence that a fertilized egg, even an embryo several weeks or more old, does not meet my criteria of personhood. Equally, an eight-month old fetus almost certainly does. I think that sense conforms to most people's intuitions on the matter.

And intuition, really, is all we have. Science can tell us when certain things happen developmentally, but it can't tell us which, if any, of those things are significant for determining personhood.

Dausuul:

However, there is in fact a cost. If you draw that line there, then the logical conclusion is that abortion is infanticide; which imposes a substantial cost, to the women who will be forced to endure unwanted pregnancies, to the children who will result from those pregnancies, and to the rest of us who must live with the social consequences. It also imposes a cost on the people who might benefit from scientific research that is made illegal.

You are right, we must look for ways in which we can decrease the surplus population. This is a dangerous utilitarian argument. The conclusion is that any individual life must subordinate to the greater good. What happens is that those people who determine the way in which to measure the greater good ensure that they themselves come out on right side of the equation.

The moral tyrrany which you espouse is equally as dangerous.

There is a cost to amorality - consider if there would even be a Social Security deficit if thirty million abortions had not occurred in the past thirty years with less than 1% of all abortions attributed to rape or incest, this is a lot of abortions used as a birth control device. Consider the push for use of embryonic stem cells, when pluri-potent stem cells from adults are much more promising for therapies as one does not reject cellular material from oneself. The push to use embryonic stem cells is a prelude to human cloning and if that does not give one a moral pause, then you do not have a moral compass. Even the use of invtro-fertilization has a hidden cost as we are now perpetuating genetic lines of people who ordinarily would not conceive what does that mean in the long term?

Conception is at the "err on the side of life" end of the continuum. Viability and birth are towards the other end.

I see parallels between the Singer-ian attempt to broaden the applicability of "dignity" beyond the human species. These authors are looking at another dimension with the same basic impulse - to widen our conception of at what developmental stage we do the same with ourselves.