The New Atlantis - Acorns and Embryos - Robert P. George and Patrick Lee
The New Atlantis is a great and relatively new resource on the web. The latest edition contains this article on embryos and personhood as part of a symposium on the issue. I would encourage you to read through these essays thoughtfully if you have the interest to do so.
In my opinion, what Natualistic Darwinism and Evolution were to the 20th century, Bioethics will be to the 21st. (Not to the exclusion of the evolution issue...)
Robert P. George (quickly becoming one of my favorite authors/thinkers) and Patrick Lee have several insightful things to say about this debate. Here are a couple of snippits to whet your appetite:
Absent the appropriate framing of the issue, there is little likelihood of generating an illuminating public discussion.
If we were to contemplate killing mentally retarded infants to obtain transplantable organs, no one would characterize the resulting controversy as a debate “about organ transplantation.” The dispute would properly be characterized as a debate about the ethics of killing retarded children to harvest their vital organs. The issue could not be resolved by considering how many gravely ill non-retarded people could be saved by extracting a heart, two kidneys, and a liver from each retarded child. The threshold question would be whether it is unjust to relegate a certain class of human beings—the retarded—to the status of objects that can be killed and dissected to benefit others.
But are human embryos human beings?
Indeed they are, and contemporary human embryology and developmental biology leave no significant room for doubt about it.
I hope to get around to reading the entire symposium and commenting further on it in the future.