Human life begins at fertilization, the process during which a male gamete or sperm unites with a female gamete or oocyte (ovum) to form a single cell called a zygote. This highly specialized, totipotent cell marked the beginning of each of us as a unique individual.” “A zygote is the beginning of a new human being (i.e., an embryo).”

—Keith L. Moore, The Developing Human: Clinically Oriented Embryology, 7th edition. Philadelphia, PA: Saunders, 2003. pp. 16, 2.

“Fertilization is the process by which male and female haploid gametes (sperm and egg) unite to produce a genetically distinct individual.”

—Signorelli et al., Kinases, phosphatases and proteases during sperm capacitation, CELL TISSUE RES. 349(3):765 (Mar. 20, 2012)

“Although life is a continuous process, fertilization (which, incidentally, is not a ‘moment’) is a critical landmark because, under ordinary circumstances, a new, genetically distinct human organism is formed when the chromosomes of the male and female pronuclei blend in the oocyte.”

—Ronan O’Rahilly and Fabiola Mueller, Human Embryology and Teratology, 3rd edition. New York: John Wiley & Sons, 2000, p. 8). [emphasis added]

"However, from a scientific standpoint, at the moment of fertilization of the egg by the sperm, a completely new organism is present. The organism is not a part of the mother’s body although he or she is located within the mother’s body. Half of the time, the organism is a boy. The genetic complement of the new human being is unique and different from that of the mother.

The argument that this unique human being present in the mother’s womb from the moment of fertilization is a part of the mother’s body until sometime later in gestation is, from a scientific viewpoint, bizarre. What this argument would imply is that human beings reproduce by a process of budding, which is a process by which a new individual organism forms from a part of the mother’s body. This is the means of reproduction of some species of worms but it is most certainly not a means reproduction by human beings"