When Does Life Begin?

DOWNLOAD IRL’s 2020 Report – Sources On The Scientific Consensus On When Life Begins

           While biologists’ consensus view that a human’s life begins at fertilization might be unexpected for some, it is expected given the underlying biological facts. Mammalian reproduction begins with the fusion of a male’s sperm and a female’s egg and results in a new mammalian organism. This new organism is a single cell called a ‘zygote’, and it is in the first stage of the mammalian life cycle. When a zygote is the result of a human sperm’s fertilization of a human egg, the zygote has a human genome that is distinct from both of its parents.[1] Therefore, based on its biological classification, rooted in its genetics and development in the human life cycle, the zygote can be described as a Homo sapiens zygote (i.e., a human) to distinguish it from a Felis catus zygote (i.e., a cat).[2] This is not controversial. However, there has been some debate on the uniqueness of a human zygote compared to other human cells.[3]

           Through gene expression, human cells differentiate to perform specialized functions in the body. A zygote is unique as it is a totipotent cell that often becomes “a fertile, adult individual” through generating all cells of a body and organizing them “in a specific temporal and spatial sequence”.[4] It is further unique in that it is the only single cell that is developing in the human life cycle. Accordingly, the biological stance on when a human’s life begins would succinctly state: ‘a human zygote is an organism with the human genome that is in the first stage of the human life cycle.’ This is a descriptive view based on observable traits[5], that recent findings suggest is a biological statement largely uncontested by the biological community.

           Just as important as ‘when life begins’ is Americans’ understanding of it. Americans were asked (1) when a human’s life begins, (2) when a biological human’s life begins, (3) when a fetus deserves legal protection, (4) when a fetus deserves legal protection outside of the abortion context, (5) when a fetus deserves constitutional rights, and (6) when surgical abortions should be illegal if an artificial womb were created; their responses to the questions were remarkably related.[6]

           This means that Americans have a very stable view of when a human’s life begins, whether one asks their biological view, their philosophical view, or their legal view. 82% of Americans believe it is an important question in the debate[7], 93% affirmed that a human’s life is worthy of legal protection once it begins[8], and 76% suggested that Americans deserve to know when a human’s life begins to be informed in their abortion positions and decisions[9].

           While half of pro-choice Americans believe a fetus should only be recognized as a human under the U.S. Constitution at viability or birth (51%), very few pro-life Americans do (6%)[10]. When asked how to resolve the question of when life begins, 80% of Americans suggested that biologists were most qualified to determine when a human’s life begins[11]; 91% suggested they made their selection because biologists are objective experts in the study of life[12]. When they were asked to anticipate what biologists would say, 23% of pro-choice and 54% of pro-life Americans anticipated that biologists would affirm the view that a human’s life begins at fertilization[13]. However, thousands of biologists were surveyed from over one thousand academic institutions around the world, and 96% affirmed at least one statement representing the view that a human’s life begins at fertilization.[14]


[1]Seisenberger, S. et al. “Reprogramming DNA methylation in the mammalian life cycle: building and breaking epigenetic barriers”. Phil. Trans. R. Soc., 2012.

[2]Wildman D.E., Goodman M. “Humankind’s Place in a Phylogenetic Classification of Living Primates”. In: Wasser S.P. (eds) Evolutionary Theory and Processes: Modern Horizons. Springer, 2004, p. 293.

[3]Anne, L. “Anti-Abortion Argument #1: It’s a Person”. Love, Joy, Feminism, 2012, available at: http://www.patheos.com /blogs/lovejoyfeminism/2012/09/arguments-against-abortion-its-a-person.html.

[4]Condic, M.L. “Totipotency: What it is and what it is not”. Stem Cells and Development, 2014, 23(8), p. 796-812, available at: https://doi.org/10.1089/scd.2013.0364.

[5]With recent technological advancements, biologists are now able to use observable genomic DNA to biologically classify a single-celled organism as a member of a species; modern biological classification methods make use of such genetic analyses in concert with classic methods that utilize morphological and phenotypical characteristics; see, for example: Kouduka, M., Sato, D., Komori, M. et al. “A Solution for Universal Classification of Species Based on Genomic DNA”. International Journal of Plant Genomics, Article ID 27894, 2007, 8 pages, available at: https://doi.org/10.1155/2007/27894.

[6]Jacobs, S.A., Balancing Abortion Rights and Fetal Rights: A Mixed Methods Mediation of the U.S. Abortion Debate (2019), p. 295, available at: https://knowledge.uchicago.edu/record/1883.

[7]Id.at p. 204.

[8]Id.at p. 205.

[9]Id.at p. 206.


[11]Id.at p. 208.


[13]Id.at p. 209.

[14]Id.at p. 250.