Dawn Eden points out that Planned Parenthood has helpfully defined when a person begins.
Q: My friend says that life begins when the egg and sperm join together. I say that it begins when a baby takes its first breath. Which of us is right?
"Most medical authorities and Planned Parenthood agree that it starts when a baby takes its first breath." [Source]
I guess once outside air is introduced into the babies respiration system it must mix with another component and personhood is spontaneously created. This works kind of like what occurs in a binary chemical weapon. This also means that if you gag the baby as it is born you can still kill it because personhood hasn’t occurred yet. Why go through the mess of partial-birth abortion when you can just strangle it before it takes its first breath.
Now we just need to know when rationality begins in a Planned Parenthood representative. Unfortunately there is not a known sample group on which to be able to do a scientifically measured study of.
If you want to read a truly sane explanation of when personhood begins read Peter Kreeft’s Human Personhood begins at Conception