What is a person? Depends on who you ask. Some of the most common pro-choice claims are that you are not a person unless you are viable, or you are not a person until you are physiologically independent. I've never found these ideas remotely compelling. However, there is one definition of personhood that has always intrigued me: consciousness.
Some people assert that our consciousness--our level of cognition--is what separates us from other species and gives us our worth. They point out, for example, that when someone becomes brain dead--even as the rest of their body may function properly--we often consider them dead already. Their consciousness is gone. Some therefore assert that an embryo, which has no consciousness, is not a person either, and is therefore morally permissible to destroy.
Anytime people assert a definition of personhood that excludes the fetus (and, indeed, this seems to be the only time people distinguish "person" from "human being") I try to consider how their definition would apply to already-born people in similar circumstances. For example, if you must be physiologically independent to be a person, humans on respirators would not be people.
So are there any examples of humans we already consider people who do not have consciousness?
Coma patients always jump to mind. Damage to either the cerebral cortex (responsible for our awareness) or the Reticular Activating System ("RAS" - responsible for our sensory arousal) can cause a person to enter into a coma. Whether someone recovers varies depending on how the damage was sustained and how severe it was. In the meantime, the coma is considered a "state of profound unconsciousness."
So is a coma patient a "person"? Seems to me the answer to that question depends on whether the coma patient has a chance of recovery. If a patient has a high chance of recovery, society still considers that patient a person. If the patient becomes brain dead, there are those who argue the patient is no longer a person anyway.
This implies that the personhood of the coma patient rests on their future ability to have full consciousness. The same can be said of the zygote. Both the coma patient and the zygote are human; neither have consciousness.
I suppose the question is, then, what is the significant moral difference (if any) between a human being that will develop consciousness and a human being that will regain consciousness? What do you think?