The following references illustrate the fact that a new human embryo,the starting point for a human life, comes into existence with theformation of the one-celled zygote:
"Development of the embryo begins at Stage 1 when a sperm fertilizes an oocyte and together they form a zygote."
[England, Marjorie A. Life Before Birth. 2nd ed. England: Mosby-Wolfe, 1996, p.31]
"Human development begins after the union of male and female gametes or germ cells during a process known as fertilization (conception).
"Fertilization is a sequence of events that begins with the contact of a sperm (spermatozoon) with a secondary oocyte (ovum) and ends with the fusion of their pronuclei(the haploid nuclei of the sperm and ovum) and the mingling of theirchromosomes to form a new cell. This fertilized ovum, known as a zygote, is a large diploid cell that is the beginning, or primordium, of a human being."
[Moore, Keith L. Essentials of Human Embryology. Toronto: B.C. Decker Inc, 1988, p.2]
"Embryo: the developing organism from the time of fertilization untilsignificant differentiation has occurred, when the organism becomesknown as a fetus."
[Cloning Human Beings. Report and Recommendations of the National Bioethics Advisory Commission. Rockville, MD: GPO, 1997, Appendix-2.]
"Embryo: An organism in the earliest stage of development; in a man,from the time of conception to the end of the second month in theuterus."
[Dox, Ida G. et al. The Harper Collins Illustrated Medical Dictionary. New York: Harper Perennial, 1993, p. 146]
"Embryo:The early developing fertilized egg that is growing into anotherindividual of the species. In man the term 'embryo' is usuallyrestricted to the period of development from fertilization until theend of the eighth week of pregnancy."
[Walters, William and Singer, Peter (eds.). Test-Tube Babies. Melbourne: Oxford University Press, 1982, p. 160]
"The development of a human being begins with fertilization, a process by which two highly specialized cells, the spermatozoon from the male and the oocyte from the female, unite to give rise to a new organism, the zygote."
[Langman, Jan. Medical Embryology. 3rd edition. Baltimore: Williams and Wilkins, 1975, p. 3]
"Embryo: The developing individual between the union of the germ cellsand the completion of the organs which characterize its body when itbecomes a separate organism.... At the moment the sperm cell of thehuman male meets the ovum of the female and the union results in afertilized ovum (zygote), a new life has begun.... The term embryocovers the several stages of early development from conception to theninth or tenth week of life."
[Considine, Douglas (ed.). Van Nostrand's Scientific Encyclopedia. 5th edition. New York: Van Nostrand Reinhold Company, 1976, p. 943]
"I would say that among most scientists, the word 'embryo' includes the time from after fertilization..."
[Dr. John Eppig, Senior Staff Scientist, Jackson Laboratory (BarHarbor, Maine) and Member of the NIH Human Embryo Research Panel --Panel Transcript, February 2, 1994, p. 31]
"The development of a human begins with fertilization, a process by which the spermatozoon from the male and the oocyte from the female unite to give rise to a new organism, the zygote."
[Sadler, T.W. Langman's Medical Embryology. 7th edition. Baltimore: Williams & Wilkins 1995, p. 3]
"The question came up of what is an embryo, when does an embryo exist,when does it occur. I think, as you know, that in development, life isa continuum.... But I think one of the useful definitions that has comeout, especially from Germany, has been the stage at which these twonuclei [from sperm and egg] come together and the membranes between thetwo break down."
[Jonathan Van Blerkom of University of Colorado, expert witness onhuman embryology before the NIH Human Embryo Research Panel -- PanelTranscript, February 2, 1994, p. 63]
"Zygote. This cell, formed by the union of an ovum and a sperm (Gr. zyg tos, yoked together), represents the beginning of a human being. The common expression 'fertilized ovum' refers to the zygote."
[Moore, Keith L. and Persaud, T.V.N. Before We Are Born: Essentials of Embryology and Birth Defects. 4th edition. Philadelphia: W.B. Saunders Company, 1993, p. 1]
"The chromosomes of the oocyte and sperm are...respectively enclosed within female and male pronuclei. These pronuclei fuse with each other to produce the single, diploid, 2N nucleus of the fertilized zygote. This moment of zygote formation may be taken as the beginning or zero time point of embryonic development."
[Larsen, William J. Human Embryology. 2nd edition. New York: Churchill Livingstone, 1997, p. 17]
"Although life is a continuous process, fertilization is a criticallandmark because, under ordinary circumstances, a new, geneticallydistinct human organism is thereby formed.... The combination of 23chromosomes present in each pronucleus results in 46 chromosomes in thezygote. 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}]
"Almost all higher animals start their lives from a single cell, thefertilized ovum (zygote)... The time of fertilization represents thestarting point in the life history, or ontogeny, of the individual."
[Carlson, Bruce M. Patten's Foundations of Embryology. 6th edition. New York: McGraw-Hill, 1996, p. 3]
"[A]nimal biologists use the term embryoto describe the single cell stage, the two-cell stage, and allsubsequent stages up until a time when recognizable humanlike limbs andfacial features begin to appear between six to eight weeks afterfertilization....
"[A] number of specialists working in the field of human reproduction have suggested that we stop using the word embryoto describe the developing entity that exists for the first two weeksafter fertilization. In its place, they proposed the term pre-embryo....
"I'll let you in on a secret. The term pre-embryo has been embracedwholeheartedly by IVF practitioners for reasons that are political, notscientific. The new term is used to provide the illusion that there issomething profoundly different between what we nonmedical biologistsstill call a six-day-old embryo and what we and everyone else call asixteen-day-old embryo.
"Theterm pre-embryo is useful in the political arena -- where decisions aremade about whether to allow early embryo (now called pre-embryo)experimentation -- as well as in the confines of a doctor's office,where it can be used to allay moral concerns that might be expressed byIVF patients. 'Don't worry,' a doctor might say, 'it's only pre-embryosthat we're manipulating or freezing. They won't turn into real humanembryos until after we've put them back into your body.'"
[Silver, Lee M. Remaking Eden: Cloning and Beyond in a Brave New World. New York: Avon Books, 1997, p. 39]
