Human life begins at fertilization, when sperm and egg unite to form a genetically unique, living organism. Modern embryology and molecular biology confirm that the zygote is a distinct, totipotent human being capable of developing through all stages of life. **Scientific consensus holds that fertilization marks the start of human life.** # History Of Conception The understanding of human life and its beginning has evolved over millennia. In the 5th century B.C., Hippocrates recorded observations of embryos in incubating chicken eggs, noting parallels to human development, while Aristotle believed embryos arose from a formless mixture of semen and menstrual blood (American College of Pediatricians, March 2017, “When Human Life Begins,” Westchester Institute White Paper, P.O. Box 78, 582 Columbus Ave., Thornwood, NY 10594, p. 1–2; Moore KL, Persaud TVN. _The Developing Human_, 7th ed. Philadelphia: Saunders-Elsevier, 2003; Carlson BM. _Human Embryology and Developmental Biology_, 3rd ed. Philadelphia: Mosby-Elsevier, 2004, p. 2, 8–10, 31). By the 17th century, Hamm and Leeuwenhoek observed sperm under the microscope, though they initially thought sperm contained miniature humans (American College of Pediatricians, March 2017, p. 2; Moore KL, _The Developing Human_, 2003). In 1775, Spallanzani demonstrated that both the male sperm and female oocyte are necessary to create a new organism (American College of Pediatricians, 2017, p. 2). In 1827, von Baer discovered oocytes in the ovarian follicle and observed early embryos in the uterus, helping establish the developmental stages of mammals (American College of Pediatricians, 2017, p. 2). The advent of cell theory in 1839 by Schleiden and Schwann clarified that the embryo develops from a single-celled zygote, an independent, living organism (American College of Pediatricians, 2017, p. 2). By 1859, the American Medical Association recognized the zygote’s independence and opposed abortion, noting its life begins prior to implantation (Report on Criminal Abortion, _Journal of the American Medical Association_, Vol XII-6, 1859, p. 69–70; North American Medico-Chirurgical Review, Jan. 1859, p. 69–70). Modern embryology textbooks consistently affirm that human development begins at fertilization and continues as a continuous process through birth into adulthood (Moore KL, _The Developing Human_, 1974, p. 1; Moore KL, Persaud TVN, _The Developing Human_, 7th ed. Philadelphia: Saunders-Elsevier, 2003, p. 31; Carlson BM, _Human Embryology and Developmental Biology_, 3rd ed., Philadelphia: Mosby-Elsevier, 2004, p. 2, 8–10, 31). The American College of Pediatricians states that at fertilization, a genetically unique human being emerges, requiring only the proper environment to grow (American College of Pediatricians, March 2017, p. 1). Even authors who do not assign full moral status at the one-cell stage acknowledge that biologically, life begins when sperm and egg unite to form a zygote (Eberl JT. “The beginning of personhood: A Thomistic biological analysis.” _Bioethics_. 2000;14(2):134–157, p. 135). > [!faq]- Conception or Implanation? > Although the American College of Obstetricians and Gynecologists (ACOG) attempted in 1965 to redefine “conception” as implantation rather than fertilization, medical and English dictionaries before and after this redefinition continued to define conception as fertilization (ACOG Terminology Bulletin. Terms used in reference to the fetus. Chicago. ACOG No. 1. Sept 1965; The American College Dictionary, Random House, NY: 1956, p. 249; Stedman’s Medical Dictionary, Williams and Wilkins Co., 21st ed., Baltimore, 1966, pp. 352, 583, 586; Webster’s New International Dictionary of the English Language Unabridged, Merriam-Webster, Encyclopedia Britannica, 1986, pp. 469; Merriam-Webster Deluxe Dictionary, 10th collegiate Ed., Readers Digest, Pleasantville, NY, 1998, pp. 373, 677, 671; Tabor’s Cyclopedic Medical Dictionary, 14th edition, FA Davis Co., Philadelphia, 1981, p. 322). > > The rationale for the ACOG change likely stemmed from discussions at Planned Parenthood symposia: Dr. Bent Boving in 1959 argued for the social advantage of redefining conception to implantation so that birth control could be considered as preventing conception rather than destroying an established pregnancy (Bent Boving, “Implantation Mechanisms,” in _Mechanics Concerned with Conception_, ed. C.G. Hartman, New York: Pergamon Press, 1963, p. 386). Similarly, Dr. Christopher Tietze noted in 1964 that medical consensus would influence religious and legal authorities, reinforcing this strategic redefinition (Proceedings of the Second International Conference, Intra-Uterine Contraception, October 2–3, 1964, New York, ed. Sheldon Segal, et al., International Series, Excerpta Medica Foundation, No. 86, p. 212). Advances in molecular and cellular biology have reinforced the understanding that fertilization is the start of a distinct human organism. Studies show that sperm triggers egg activation through mechanisms such as Ca²⁺ oscillations and the “zinc spark,” signaling the beginning of embryonic development (Vjugina U, Evans JP. _Frontiers in Bioscience_, 13, 2, Jan. 2008, 462–476; Oren-Suissa Ω, Podbilewicz B. _Trends in Cell Biology_, 17, 11, Nov. 2007, 537–546; Cox LJ, et al., _Reproduction_, 124, 5, Nov. 2002, 611–623; Saunders CM, Swann K, Lai FA. _Biochemical Society Symposia_, 74, 2007, 23–36; Duncan FE, Que EL, Zhang N, et al., _Scientific Reports_, 26, 2016, 24737; Condic ML. _When Does Human Life Begin? A Scientific Perspective._ Westchester Institute White Paper, 2008, p. 3–5). Experimental studies in mice also demonstrate that sperm contributes to early spatial patterning and embryonic axis specification before the first cell cleavage, highlighting the zygote as a unique organism from its inception (Piotrowska K, Zernicka-Goetz M. _Nature_, 409, 2001, 517–521; Gardner RL. _Development_, 128, 2001, 839–847). Textbooks continue to define the zygote as the beginning of human life, and Merriam-Webster defines an organism as “a living thing composed of interdependent parts that maintain various vital processes” (Carlson BM, _Human Embryology and Developmental Biology_, 3rd ed., Philadelphia: Mosby-Elsevier, 2004, p. 36; Merriam-Webster Dictionary, [http://www.merriam-webster.com/dictionary/organism](http://www.merriam-webster.com/dictionary/organism), accessed February 23, 2017). Human life, once fertilized, may be lost through induced abortion, destruction of embryos, selective reduction in multiple gestation, or contraception that prevents implantation (Condic ML. _When Does Human Life Begin? A Scientific Perspective._ Westchester Institute White Paper, 2008, p. 5, paraphrased). This biological and historical evidence demonstrates that the zygote is a genetically distinct, living human organism from the moment of fertilization (American College of Pediatricians, 2017; Moore KL, _The Developing Human_, 2003; Carlson BM, 2004; Eberl JT, 2000; Condic ML, 2008). # Human Life Begins At Conception Here is a list of scientists from [Abolitionists Rising](https://abolitionistsrising.com/faq/) that affirm this. #### Fertilization is the Beginning of a Unique Human Being Scientific consensus across decades of embryology is that life begins at the moment of fertilization, when a male gamete (sperm) and a female gamete (ovum) unite. Keith L. Moore, a leading embryologist, writes: > “Human life begins at fertilization, the process during which a male gamete or sperm… unites with a female gamete or oocyte… to form a single cell called a zygote. This highly specialized, totipotent cell marked the beginning of each of us as a unique individual.” (Moore, Keith L., _The Developing Human: Clinically Oriented Embryology_, 7th edition, Philadelphia, PA: Saunders, 2003, pp. 16, 2) Similarly, Larsen notes: > “The chromosomes of the oocyte and sperm… 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) At fertilization, the genetic makeup of a new, unique human being is fully determined, including sex and hereditary characteristics (Kaluger, G., and Kaluger, M., _Human Development: The Span of Life_, St. Louis: The C.V. Mosby Co., 1974, pp. 28-29). From the mid-20th century to the present, a wide range of embryology texts consistently affirm that human life begins at fertilization: Moore, Larsen, Langman, O’Rahilly, Kaluger, Clark & Patten, Persaud, England, and Carlson all emphasize that the zygote is the **beginning of a genetically distinct human being**. > “Every human embryologist in the world knows that the life of the new individual human being begins at fertilization. It is not belief. It is scientific fact.” (Kischer, C. Ward, Ph.D., _When Does Human Life Begin? The Final Answer_, Human Embryologist, University of Arizona College of Medicine) #### The Zygote Represents a New Organism A zygote is not merely a potential human being—it is a distinct organism from the moment of its formation: > “A zygote is the beginning of a new human being (i.e., an embryo).” (Moore, Keith L., _Essentials of Human Embryology_, Toronto: B.C. Decker Inc, 1988, p. 2) > “It is the penetration of the ovum by a sperm… that constitutes the initiation of the life of a new individual.” (Clark, Edward, and Corliss Patten, _Human Embryology_, McGraw-Hill Inc., 1930) > “Zygote: This cell… represents the beginning of a human being.” (Moore, Keith L., Persaud, T. V. N., and Torchia, Mark G., _Before We Are Born: Essentials of Embryology and Birth Defects_, 4th edition, Philadelphia: W.B. Saunders Company, 1993, p. 1) The zygote is **genetically distinct**, totipotent, and capable of developing through all stages of human life if the environment supports it. #### Fertilization is a Critical Landmark in Development While human development is continuous, fertilization is the **first defining event**: > “Although life is a continuous process, fertilization is a critical landmark because… a new, genetically distinct human organism is thereby formed.” (O’Rahilly, Ronan, and Muller, Fabiola, _Human Embryology & Teratology_, 2nd edition, New York: Wiley-Liss, 1996, pp. 8, 29) > “Almost all higher animals start their lives from a single cell, the fertilized ovum (zygote)… The time of fertilization represents the starting point in the life history… of the individual.” (Carlson, Bruce M., _Patten’s Foundations of Embryology_, 6th edition, New York: McGraw-Hill, 1996, p. 3) Every human embryologist recognizes this as the scientific fact establishing the beginning of human life (Kischer, C. Ward, Ph.D., _When Does Human Life Begin? The Final Answer_, Human Embryologist, University of Arizona College of Medicine). #### Embryo Development Follows Directly from Fertilization The zygote enters a series of developmental stages, beginning with the embryo, which progresses until the fetus forms: > “Embryo: the developing organism from the time of fertilization until significant differentiation has occurred.” (National Bioethics Advisory Commission, _Cloning Human Beings. Report and Recommendations of the National Bioethics Advisory Commission_, Rockville, MD: GPO, 1997, Appendix-2) > “The development of a human being begins with fertilization… to give rise to a new organism, the zygote.” (Langman, Jan, _Medical Embryology_, 3rd edition, Baltimore: Williams and Wilkins, 1975, p. 3) > “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 edition, England: Mosby-Wolfe, 1996, p. 31) Thus, the zygote is not merely potential life—it is **actual human life at its earliest stage**, with all subsequent development depending upon it.