I think part of the problem with the question is that you are considering the single-cell organism -- the egg right after fertilization to be the same as an unborn baby few minutes before birth -- calling both of them fetus.
I think most people here would agree that a baby few minutes before birth is pretty much human. However, the single-cell just-fertilized egg is far more controversial, hence the objections brought up regarding unfertilized eggs, as they are not so different.
The abortion laws in effect make exactly that distinction, they have rules about pregnancy length and/or fetus size to determine whether or not abortion is legal.
So I think the better question is: at exactly what point of development does a fetus become a human -- somewhere along the 9 months of development as it undergoes very significant biological changes, it crosses the threshold to "become" human, IMHO.
We have been discussing that. A definition of being human is still uncertain. A fertilized egg has the exact same genetics as an almost newborn baby. Yet, are genetics enough to define something as human?
Let me ask this, late term abortion is still legal. As I have mentioned before, in America a late term abortion is allowed for the most part about 7inches from being born. At this stage in the pregnancy, the definition of late term abortion includes the phrase calling the unborn baby viable. Viable means something like independent existence. If one allows late term abortion, they are saying 7inches from being born defines the humanity of a fetus. This is my problem with late term abortion.
As you have implied, looks like a fetus around after 20 weeks has very visible physical human characteristics.
So, how would you define when a fetus is human during the pregnancy stages and why? Right now, purely off genetics, fetus=human. On size, mental capacity, morality....etc, please read over the posts on these as these have been discussed on this thread before.
Don't worry, this part I have studied. Let's also not forget we are talking about this because someone earlier asked about if a procreated human is just as human from natural born baby. From other posts you have stated, you said 'Homo-Sapien' is not enough to define human or you said it doesn't matter (please remind me). Basically I think I was unclear. When I said something bothered me as I did in the Fetus thread, I was referring to what makes this thing human? Trees how would you respond to the post about procreation and human worth? If we started cloning people (like the futuristic movies or star wars) can we honestly say they are worth as much as people not cloned? If you say yes,ins't that saying only genetics define a human?
I did not mean a general biology college class. I meant a Cell Biology college class. (Junior biology level rather than Freshman non biology level)
I said Homo-Sapien is enough to define Human but not enough to define Moral Personhood. My position is there are a bunch of characteristics that people are trying to add onto the definition of human when they should be examining those characteristics individually rather than try to obscure both the characterisitic and the definition of Human.
Since I use Homo-Sapien as my definition of Human there are possible cases where Humans would be born to almost-but-not-quite Humans and cases where almost-but-not-quite Humans would be born to Humans.
However I see no inherent relation between being a Homo-Sapien and having Moral Personhood. I would refer to the ability to Reason, capability to Suffer or a similar trait as the necessary/sufficient condition of Moral Personhood.
Summary: Genetics determines humanity but humanity is not what makes it immoral to murder you.
If genetics determines humanity, what do you call an ape with 99.8 (or is it 98.9) % genetic similarities? They are capable of suffering and have the ability to reason. Chimpanzees even care for their young just like a human mom does.
Also, are you saying it is person hood that makes it immoral to murder? If so, what does that say to animal cruelty?
Chimpanzees are capable of suffering and have the ability to reason. However I did not list those as sufficient/necessary conditions of humanity. They are not Human.
Chimpanzees are capable of suffering and have the ability to reason. Those are the two candidates for sufficient/necessary conditions for moral personhood I presented. If correct then it is immoral to murder them.
Moral Personhood is the characteristic that the being deserves moral consideration. John Stuart Mills would claim Mice have this characteristic. Kant would claim Mice do not have this characteristic.
No oiffense, but I feel like we are going back around in a circle. Can fetus' reason and feel pain?
http://jmp.oxfordjournals.org/content/10/3/253.short here is an article bringing up the point a fetus gains some recognition since it has a brain...which occurs around the 7nth week.