Awesome post, by the way. I love it when people provide a number of details with which to proceed in the discussion.

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First of all, we have to agree on some premises. Most pro-choice folks I know will agree that human life is something to be protected. Some hard line pro-choicers try to make their stand here, saying this isnt the case. We can debate from that standpoint if you wish, but most people generally agree more or less with my premise.

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I agree, but for clarification, I'd say "human personhood" is intrinsically valuable, and should be protected (at least almost all of the time).

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Assuming that we agree on this, everything hinges around the question of personhood.

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Agreed. Specifically: "What criteria denotes personhood, or when does personhood begin (and end)?".

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The biological question isnt really debatable, just look at some embryology textbooks and see what their definition of the beginning of life is.

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From a biological standpoint, life does not have a beginning -- it's a continuum. Every living cell was formed from another living cell. Living cells produce more living cells, and later they die. The study of when life began, then, is a question regarding abiogenesis.

(Note: It is very probable that there are Biology textbooks that make the claim that "life begins at conception". This is a reflection of the religious/idealistic beliefs of the author(s) and not scientific.)

Here is a good read on this: http://www.devbio.com/article.php?id=162

Science can't tell us the answer to when "personhood" begins. That's a moral/social question. But, I think there is a rational answer if we really think about it.

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So where does personhood begin? Basically, asserting that personhood begins sometime after conception is asserting a dualistic concept of human existence, in other words that your physical being and your "personhood" (or soul or whatever word you want to use) are two distinct entities.

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If I cut off my finger, am I still a person? More or less the same person? Does my finger make me, me? What about my leg? Or my internal organs? What physical part of my body makes me, me? What is it that defines my personhood? Am I less of a person if I become a quadriplegic? I don't think so. So, at least these physical parts of my body are not "me" -- they are not what defines my personhood. But, I posit there is ONE physical part that DOES define my personhood: my brain. If I lose my brain, I'm no longer "me". So, this isn't dualistic, per se. I'm not saying there is a "me" that exists outside of my physical being. But, I am saying that a certain part of my physical being is what defines me. (Actually, it's the activity in the brain that creates my personhood... if my brain is not functioning, I'm no longer "me" either.)

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But this is a philosophically indefensible position. Human beings are an integrated unit, and thus no grounds exist for claimg that personhood doesnt begin when life biologically begins, which is clearly at conception.

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Again, life doesn't biologically begin with conception. Unless you are assuming some other criteria for "life". Like a unique set of DNA or something.

I'll go ahead and head off the DNA argument while I'm at it. Some will argue that a unique set of DNA constitutes personhood. So, when the egg & sperm fuse, a unique set of DNA forms, thus creating a new person.

One question: what about cloning?

(Aside: I wonder if this is at the heart of why a lot of religious people think cloning is bad?)

Anyway, I just read an article in Time, where they explained how Korean biologists cloned the first dog. They took a cell from the ear of an adult male. They removed the nucleus of an egg cell, and implanted the male ear cell into the egg. They "zapped it" with electricity to fuse the cell to the egg, and then implanted 10 or so into a female dog. 61 days later, out comes a healthy dog, genetically identical to the male that the ear cell was taken from.

So, when did the "doghood" of that new dog begin? Never was there new DNA. Never did 2 haploids join to create a diploid. To me, it's when the dog formed whatever it is that we claim indicates "doghood". I maintain it's the brain (activity). That is what gives the dog his personality, his desires, his memories, his emotions. To me, that is what "doghood" is.

Science fiction time: If we could implant a human brain into a dog body, what it be a dog or a human? I say human. Same for when we replace someone's heart with an artificial heart -- they are still a human person. If we replace their limbs with artificial ones, they are still a human person. If we replace their eyes, ears, nose, torso, every internal organ, and everything but their brain with artificial parts, I'd say they are still a human person. But, if we replace a human's brain with a computer -- all other body parts & internal organs remain -- then that is no longer a human person. It's a computer controlling a human body. We would not bestow human rights on that thing -- we could turn off the computer without feeling we committed homicide.

I look forward to hearing your replies.