1976 "At the moment the sperm cell of the human male meets the ovum of the female and the union results in a fertilized ovum (zygote), a new life has begun."
[Considine, Douglas (ed.). Van Nostrand's Scientific Encyclopedia. 5th edition. New York: Van Nostrand Reinhold Company, 1976, p. 943]
1988 "Human development begins after the union of male and female gametes or germ cells during a process known as fertilization (conception)."
[Moore, Keith L. Essentials of Human Embryology. Toronto: B.C. Decker Inc, 1988, p.2]
1996 "Although 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 & Teratology. 2nd edition. New York: Wiley-Liss, 1996, pp. 8, 29. This textbook lists "pre-embryo" among "discarded and replaced terms" in modern embryology, describing it as "ill-defined and inaccurate" (p. 12}]
2003 "Zygote. This cell results from the union of an oocyte and a sperm during fertilization. A zygote is the beginning of a new human being (i.e., an embryo)."
[Moore, Keith L. and Persaud, T.V.N. The Developing Human: Clinically Oriented Embryology. 7th edition. Philadelphia: Saunders 2003, p. 2.]