I assume for the sake of this thread that no one on RF would actually argue that human life begins at conception, and instead that people who appear to argue that human life begins at conception actually mean to say something along the lines of individual human life begins at conception.
If so, if individual human life begins at conception, then precisely what makes it an individual human life"? What does that word "individual" mean in this context? And what doesn't it mean?
And why is the presence of an individual human life a rational basis on which to oppose abortion?
Although this thread is in the debate section, I myself am not so much interested in debating this issue as I am interested in reading the sound answers, if any, that will be offered to those questions.
I think this subject boils down to realising that things exist in a continuum of ever gradual changes, with different stages identified and characterised by certain specifics, claiming no more nor less than those said defining features. Such that fertilisation is defined by this, implantation is that and so forth.
We must be clear what we mean when we say 'human life' in querying this continuum. What exactly are we asking? what answer are we fishing for?
Because 'human life' is not as clear and precise a term as the stages of development that we are trying to attribute it to. As such when trying to pin a broader definition onto a more narrow one, there is unavoidable loss of information, making the latter unavoidably inadequate in answering for the prior, in this case 'human life'.
Consider the question of when a hat becomes a hat? To try and pin point it onto a specific moment of the manufacture process is in vain, because ultimately no one point in the manufacturing can accommodate the greater definition of what it means to 'be a hat'.
Because what defines 'a hat' is broad, perhaps it refers to something we visually recognise? a specific shape, colour or design? Perhaps its anything that can be put on a head? and so forth. We might be confident in saying that 'I'll know one when i see one', but the larger connectome of information that defines the 'hat' cannot be effectively captured by some point of manufacture, and neither would it add to the understanding of 'hat' either.
When it comes to ethics, i think we need to be more specific in our questions, and thus allow us access to more meaningful answers. For example, quoting the stage of neuromaturation and pain perception in the development of a fetus has greater meaning to the question of bodily rights of the fetus regarding freedom from pain.