Embryology quote of the week #4

"Although human life is a continuous process, fertilization is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is thereby formed. ... The combination of 23 chromosomes present in each pronucleus results in 46 chromosomes in the zygote. Thus the diploid number is restored and the embryonic genome is formed. The embryo now exists as a genetic unity."

(O'Rahilly, Ronan and Müller, Fabiola. Human Embryology and Teratology, 2nd edition. New York: Wiley-Liss, 1996, pp. 8, 29).

Is the recognition that the life of a human being begins at conception a religious belief or a fact based in science?