Every time I teach abortion I get three or four papers that attempt to argue the pro-life position by appealing to every single fact about human development the author can look up. They generally go like this
Paragraph 1: State the thesis that full moral status is present at conception, thus making all abortion wrong.
Paragraph 2: State some facts about early embryonic development, along with several things that aren't facts. Say that this shows that all abortion is wrong.
Paragraph 3: Emphasize that the heart starts beating very early on. As a matter of fact, blood circulation can be present as early as 4-5 weeks, however students will place the date even earlier. I just read a paper that asserted the heart was beating at 18 days. Whenever the heart is asserted to start beating, this fact is then used to claim that all abortion is wrong.
Paragraph 4: Finish up the developmental cycle. Repeat thesis.
Paragraph 5: Conclusion.
This argument simply doesn't work. You cannot both assert that every stage of fetal development is morally significant and that full moral significance is present at conception. If you really felt that the presence of a beating heart marked the onset of personhood, than you would allow abortion before that event.
Now perhaps what the people who write this paper are thinking is that the *potential* for a beating heart is what brings moral status. But if that is the case, why focus on the potential for these minor events in development, and just talk about being a potential sapient adult?