New technology reveals much about fetal development, including certain behavior occurring much earlier than previously thought. See also Evangelical Outpost and La Shawn Barber
ht and thanks to Tim Challies for posting on this early enough for me to find it first.
Most of these posts consider the relevance of this issue to abortion. I don't think this will affect in any way the insistence of pro-choice philosophers to list a bunch of properties not yet true of a fetus and to define personhood by them, then saying that moral status only comes when you have those properties. Since the argument is circular, they can just change whatever properties they'll insist are required for personhood, and you'll still come out saying mentally handicapped people aren't persons. You'll just have to say that more of them are. Once you allow circular arguments, you allow people to get away with such moves.
Still, what some of these posts are suggesting is right. 'Murder' is a legal term, and the law as defined by judicial activism allows abortion, so I don't see how abortion can be murder at this point, but it is the killing of a living human being, biologically distinct from its mother even if it's biologically dependent on her (which I think is a moral reason to presume against abortion rather than for the right to abort). I don't see why defining personhood to exclude this kind of human being should lower our estimation of the horror of such a killing.