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And so you began! Fertilization begins with the spermatozoon contacting the cells surrounding the oocyte and ends with the mixing of the 23 male and 23 female chromosomes. The result is a single-cell embryo called a zygote, meaning "yoked or joined together," and it is the first cell of the human body. Its the beginning of a new individual, never-to-be repeated and completely unique you!

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Life - when does it begin?

Human Life comes into existence in just a fraction of an instant. You have a human egg and a human sperm and their sole purpose in life is to meet each other and fuse, to create a one cell human being.

Within this single cell there is an elaborate and complete plan for development.

What do the experts say?

"The American College of Pediatricians concurs with the body of scientific evidence that human life begins at conception - fertilization…. Scientific and medical discoveries over the past three decades have only verified and solidified this age-old truth. At the completion of the process of fertilization, the human creature emerges as a whole, genetically distinct, individuated zygotic living human organism, a member of the species homo sapiens, needing only the proper environment in order to grow and develop. The difference between the individual in its adult stage and in its zygotic stage is not one of personhood but of development. The Mission of the American College of Pediatricians is to enable all children to reach their optimal physical and emotional health and well-being from the moment of conception."
When Human Life Begins, American College of Pediatricians, March 2004

"After fertilization has taken place a new human being has come into being...[this] is no longer a matter of taste or opinion, it is not a metaphysical contention, it is plain experimental evidence...." - Dr Jerome LeJeune, Professor of Genetics at the University of Descartes, Paris, discoverer of the chromosome pattern of Down's Syndrome, and Nobel Prize Winner, Report, Subcommittee on Separation of Powers to Senate Judiciary Committee S-158, 97th Congress, 1st Session 1981

If I could just make my way in here...

Scanning electron micrograph of a human spermatozoon (sperm)fertilizing an ovum (egg). The ovum is as thin as a hair at a size of almost 100 microns, and the microscopic spermatoz oon is only 3 microns. Courtesy of the film, Building Babies. (c) Mona Lisa

"An individual human life begins at conception when a sperm cell from the father fuses with an egg cell from the mother, to form a new cell, the zygote, the first embryonic stage. The zygote grows and divides into two daughter cells, each of which grows and divides into two grand-daughter cells, and this cell growth/division process continues on, over and over again. The zygote is the start of a biological continuum that automatically grows and develops, passing gradually and sequentially through the stages we call foetus, baby, child, adult, old person and ending eventually in death. The full genetic instructions to guide the development of the continuum, in interaction with its environment, are present in the zygote. Every stage along the continuum is biologically human and each point along the continuum has the full human properties appropriate to that point."
Dr. William Reville, University College Cork, Ireland. Quote from a letter to the Irish Independent.

Well now, that didn't take long, here I am 3 days old, all bright, new and shiny

... And from the literature...

"Development begins at fertilization when a sperm fuses with an ovum to form a zygote; this cell is the beginning of a new human being."
Moore, Keith L., The Developing Human: Clinically Oriented Embryology, page 12, W.B. Saunders Co., 2003

"In that fraction of a second when the chromosomes form pairs, the sex of the new child will be determined, hereditary characteristics received from each parent will be set, and a new life will have begun."
Kaluger, G., and Kaluger, M., Human Development: The Span of Life, page 28-29, The C.V. Mosby Co., 1974

"A new individual is created when the elements of a potent sperm merge with those of a fertile ovum."
Encyclopedia Britannica, "Pregnancy," page 968, 15th Edition, Chicago 1974

"Development begins with fertilization, the process by which the male gamete, the sperm, and the femal gamete, the oocyte, unite to give rise to a zygote."
T.W. Sadler, Langman's Medical Embryology, 10th edition. Philadelphia, PA: Lippincott Williams & Wilkins, 2006. p. 11

""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 Müller, Human Embryology and Teratology, 3rd edition. New York: Wiley-Liss, 2001. p. 8.

I just keep getting bigger and bigger, only 4 days old now

What you think, amn't I looking just fine... and only 40 days old

Human embryo in the amniotic sac at 40 days, showing the umbilical cord and the early development of the head, eyes, feet, and hands.

References and Sources

American College of Pediatricians: Human life begins at conception-fertilisation, 2004, http://www.acpeds.org/When-Human-Life-Begins.html
WebMD Conception Slideshow: From Egg to Embryo, 2012, http://www.webmd.com/baby/ss/slideshow-conception
Scientist : Human life beings at conception, fertilisation
Report of the South Dakota Abortion Task Force to Study Abortion, Submitted to the Governor and Legislature of South Dakota, December 2005 (see page 30 for testimony on life beginning at conception) https://docs.google.com/viewer?a=v&q=cache:aWT7EWOEj2oJ:www.dakotavoice.com/Docs/South%2520Dakota%2520Abortion%2520Task%2520Force%2520Report.pdf+&hl=en&gl=us&pid=bl&srcid=ADGEESh525eGzlANN8FeOTWTq_uDg8M2PqXlXUdkhzOv77LBTXau_YVzwC_3B5bH0DM_xgVRf-e9B2z8KM6G3CZp3tvg8xTY20TtykFDoT5XmsCUIWtqEDmwoU3wyzmZMMDxt3LuvzIx&sig=AHIEtbTtUJQonL9JmGPQv-vHuBtmHmAyKg&pli=1

When Does Life Begin