Sir Joe, science uses a great many tools to figure things out. Using reasoning is a biggie and the process of elimination is part of the reasoning.
As I said, if you take a human sperm donor, a human egg donor, let them do their thing, the egg donor becomes pregnant, what the result would be is definitely not a mushroom, tree, or a cup of tea. The result would be an undeveloped human being after about the 40th day.
I agree Anna, it would be an undeveloped human being. That is a big advance anyway, now you have stopped referring to fetus as a human being (or did you ever do that? I don’t remember).
So I have no problem conceding that it is a potential or undeveloped human being. Now, an undeveloped human being obviously cannot have the same rights as a human being. That is why I draw the line at fetal viability. At the viability stage, it stops being an undeveloped human being, it can survive outside mother’s womb.