Note that the textbooks cited consider this fact so basic it is found on virtually the first page of all of them. There is no scientific debate over the question of when human life begins.
Code:
"Human development begins after the union of male and female gametes or germ cells during a process known as *fertilization* (conception).
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]
“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 time of fertilization represents the starting 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]
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]
Ender
Please reread my challenge. None of these textbooks reference an accepted convention. You know as well as I do, that textbooks are not scientific lierature (though good ones do reference literature).
In general, science sees no begining to life, just a transformation. The egg and sperm were both very much alive before conception.
Of course the bigger question, one that is much more philisophilcal, is if the zygote is an individual. Talk to an embryologist, and they will tell you that two zygotes can combine into one viable zygote. So it is pretty difficult to call them an individual. Conversely, one can split into two. Clearly, it is too early in development to call them individuals.
Nohome