The abortion debate is not framed around the concept of the continua. It is framed around the beginning & end of *human* life. Would you say that a human corpse is alive? If so, how is it alive? If not, when did it start living?
I think you're correct in saying that life is a continuum, but *human* life is not. The human body has a definite end to its life and has a definite beginning, although we aren't able to scientifically say when that beginning is.
Did you read the comment I posted with the article?
Ultimately, there is no specific beginning and ending of human life. A human corpse is not alive, but there is no meaningful instant that separates alive from dead.
Biology is almost entirely about continua, and human biology is no exception. Conception is a continuous process which ultimately has no meaningful specific dividing time for any property, including rights.
It is not that we aren't able to say scientifically when the beginning is; it is that scientifically, there is no beginning. Science recognizes the fact of continua in almost all physical observables. This is so fundamental to science that it is usually presumed to be understood, despite language about specific dividing times.
It's conception. The penetration of the egg by the sperm that BEGINS the sequence that 9 months (or so) later produces what is legally called an infant. Sort of a mini big bang.