Excellent question, though I am not sure if it belongs to this thread. But, let’s hope that it does belong. I will present my opinion, which is only “binding” on myself.
First, I have to take exception with the description of “from non-human to human”. It is much too vague, I would like to you to clarify. The “entity” (to use such an emotion-free designation) is a human tissue (unless it is seriously mutant - and this opens up another scary can of worms!). But so is a malignant tumor. The difference is that under certain circumstances the fertilized egg
can grow into something (an infant) what we definitely accept as a human
being. One possible diving point is the “first breath”. Interestingly enough the word “
soul” is the derivative of the word “breath” in several languages. The point is that this is the time when the newborn starts his (or her)
biologically independent existence, when he is no longer dependent upon the mother’s biological resources. Anyone is able to provide the necessary nutrients and necessary care.
So a newborn is definitely a human
being{/b]. This brings up the obvious retort that one moment before the birth occurs, the fetus is exactly the same as he will be after the birth. So one can say that the act of being born is an arbitrary dividing point, and this objection has its own merit. But all such dividing points are somewhat “arbitrary”. A medical student cannot perform the duties of a licensed doctor one minute before she receives her diploma, even though getting that piece of paper does not add anything to her knowledge and ability to function as a physician.
During the ages the
cut-off point was debated and different solutions were offered. Taking the first breath was one of them. Then there was the moment of quickening. Sometimes the “viability” criterion was offered. All of these are arbitrary, no question about that. The approach of believers and materialists is different. The believers argue for the existence of the “soul”, but they are unable to give a coherent definition of what the “soul” might be, and how can one detect if it is “there” or not. Not even the church declares a point of “ensoulment”. So that is not a good solution. If even the proponents are unable to offer the exact criterion of the dividing line and are unable to offer a method to see if the “entity” crossed that line of not, then it is not much of a solution.
The best method is the presence of the electro-chemical activity of the brain. Death is declared when the brain stops working, so it is obvious that the beginning of this activity can be the marking line of declaring someone a human being. Mind you, there is no consciousness at that point, no “thinking” at all. It is just a point when the brain starts “working”.
Of course, this is also an “arbitrary” dividing line. It cannot be avoided. You can respond or disregard it at your convenience. Thanks for reading it. Best wishes.
From this it appears that you do not know when to draw the dividing line. Or are you pointing to brain activity as definitive - once brain activity starts, it would be wrong to kill. Is that your view? Earliest brain activity is very early, say 6 weeks, and it becomes more and more sophisticated from then onwards for quite some years.