Even a tiny microscopic human being (organism) is still a human being. There is no size requirement. Is there?
Still waiting for the source that you think supports your claim that human beings morph out of something less than a human being that was the product of conception.
A conception, which looks like those of other animals, isn't a human being - it has human genetics. That's all.
To get from that to say, you, is a brutal process and most will not survive. That's life, fetus-lover. As I said, this is a legal and moral debate. Biology won't help you. Biology treats conceptions like bad candy it spits out, more often than not.