I might suggest that in terms of medical guidelines, since we have ascertained that we judge moral consideration on the basis of moral agency, and since such is defined by conscious, executive function, that we might concentrate on looking at the neural development. Obviously that's not particularly helpful as after the central nervous system becomes differentiated (but not yet functional) at 3 weeks, it undergoes a constant process of development by which the various sensory modalities form. By a month, in fact, all of the basic organ systems are there, and by 3 months they start becoming interconnected.
So my father, operating without major chunks of his digestive and excretory systems, isn't alive?
However, we know that sensory input (esp. light and sound) is not necessarily appreciated until at least the second trimester. However again, even having said that, relatively complete visual acuity isn't acheived until a month post-natally and muscular control...you get the idea.
I get the idea. The blind and deaf are less than human.
The sticking point, to me, is do we really, truly want to push the envelope as far as possible. Do we as a society really want to say "it can conceivably not be murder at this point"? And draw the line there or do we want to draw the line further back, just in case we're wrong about what precise moment life occurs.
I'm sure you also realize that developmental biology is not an absolute. Every individual develops at their own pace. And the time progression is not a definite "mileston A happens at time B" situation.
And of course, silly as it sounds, doctors make mistakes when calculating gestational age.
I don't see why it is important to ride the line as closely as possible when setting the cutoff for when an abortion is not horrific. The only reason I can see is a coordinated effort to get people to accept more and more. "If we can get them to accept aborting a blastula, a baby that can't survive outside the mother isn't so bad. Once we get that, partial birth isn't so bad. Once we get that..."
Martyr:
You've either never been pregnant or you are just trying to be devisive. A much closer term than "parasitism" would be "sybiosis" as the mother does reap many benefits from pregnancy, including longterm increased resistance to many diseases and short term "happy hormones".
If it's murder after the baby is out of the mother, it's murder the split second before.
The only absolute, the only sure thing that we can say "it is before, it isn't after" in all cases is conception. Why are people terrified of this?