Personhood ethics goes like this: Membership in the human species is not enough to confer value on a human subject. Rather, one must be a "person"--that is, a conscious, self-aware being-- to count as a subject with rights. Embryos and fetuses lack the physical development to support consciousness, self-awareness, and the like, so they are not persons with a right to life. In short, we're told to distinguish between a person (the conscious self) and the body he merely inhabits.
As Serge and I have each written elsewhere, there’s a host of problems with the idea of personhood coming into existence only after some degree of bodily development. One is that you end up saying things like "I came to be after my body came to be." Or, "I inhabit a body that was once an embryo." At the same time, human/person dualism contradicts everyday experience. The same exact human being that sees a tree (a bodily action) also forms mental concepts about it (a decidedly non-bodily, non-material action).
Ramesh Ponnuru asks a great question: If membership in the human species is not sufficient to confer value, why are we allowed to kill animals with more cognitive ability than mentally disabled humans? Once you insist mere membership in the human species is not enough, it's very difficult to resist the logical pull of Peter Singer's case for infanticide or euthanasia.
Indeed, as Wesley J. Smith points out, Singer weighed-in on that question last Fall, urging that brain-damaged human beings be used in HIV research rather than chimps. "HIV research using chimps has not been very helpful as they don't seem to get the disease in the same way humans do," Singer explains. "So I don't think it's right and it's causing a lot of suffering and distress to beings who are sensitive animals--social animals who should be living in social groups and who suffer being in isolation and confined and that's wrong. If we need beings very like us to do this on, we should perhaps [turn to] the families of people who tragically have been brain-damaged and have no hope of recovery from persistent vegetative state who are totally beyond suffering because they are beyond consciousness."
Say what you want about Singer's conclusions, but once you deny human exceptionalism, it's really, really hard to say why he is wrong.
Next post: Robert George's 3 starting points.