I like to believe we are more than the sum of our parts too. But all of the information for those parts comes into existence when a new human life is conceived, right. At any point along that continuum he or she is fully human and has all of the attributes he or she should possess for that stage of the human life cycle which begins at conception and ends at death. Which means it is not a potential human it is a human with potential.It is biology that makes us human beings. I like to think it is more than biology that makes us human. I like to think we are more than the sum of our parts.That is a shortcoming on your part.I can't distinguish what it is.
Our fundamental disconnect is that you see that zygote as a human being while I see it as the blueprint of a human being that it may one day become. To me it lacks the one thing that distinguishes it from any other animal, and that is a human brain. That miracle of nature.
Biology does not require that an organism have a brain. Especially at the first stages of that organism's life cycle.