>>13
I think that's the idea, yes.

The compassionate conservatives would have us believe that life begins at conception. A mammalian embryo depends upon its "host" mother for all of its existence, and cannot survive independently. Most importantly, it cannot be transferred to another host and survive. This last point is the difference between an exogenous and endogenous parasite -- exogenous parasites don't care what host they have, as long as it's compatible. Endogenous parasites are born from the host, and are dependent on that particular host with no exceptions. So cancer is an endogenous parasite, since you can't transfer cancer from one human (or any other animal) to another. Mammalian embryos are essentially endogenous parasites. They have different DNA from the host, as do cancer cells, but they depend on that particular host for existence. They are like nonfunctional organs which extract nutrients from the host and provide nothing in return, and can't be considered as an individual being. After birth they are physically independent of the host mother, and can be treated as a separate living being. So life as an individual can't begin at conception, since it's just a parasitical organ. It's only individual when it's born. And a human has the fundamental right (if you accept rights) to do whatever it wants to its body, including rid itself of unwanted portions of its body.

By this argument, other parasites can be individual beings because they are separable and transferrable. Free human cells, eg white blood cells, are not individual beings because they depend on the entire human organism for survival. They can be separated, but they die after a while and cannot replicate. Bacteria which can replicate and be independent of a human are certainly individual beings. Cancers can be taken out of the human body and cultured in a "fake" human environment, and by dint of their DNA they can replicate themselves, but you can't transfer them into another human successfully. Same goes for embryos. So they're not individuals, even though you can take them out of the body and put them on artificial life support.

Note that the argument in >>14 adresses two concepts, "life" and "individual". The concept of life is addressed fairly well at http://en.wikipedia.org/Life . The individual concept here is a biological application of metaphysical ideas of individuality, trying to find a dividing line between two separate living things. Some biologists don't believe that such a thing as an "individual" exists, since all life seems to be interdependent. I argue that it does, since we can make nearly everything necessary for our continued existence artificially (from nonliving substances and machines), although at such a high cost that it's cheaper to exploit other living things instead.