Biologists' Consensus on 'When Life Begins'

22 Pages Posted: 6 Aug 2018

See all articles by Steven Andrew Jacobs

Steven Andrew Jacobs

Northwestern Prizker School of Law; University of Chicago - Department of Comparative Human Development

Date Written: July 25, 2018


Many Americans disagree on ‘When does a human’s life begin?’ because the question is subject to interpretive ambiguity arising from Hume’s is-ought problem. There are two distinct interpretations of the question: descriptive (i.e., ‘When is a fetus classified as a human?’) and normative (i.e., ‘When ought a fetus be worthy of ethical and legal consideration?’). To determine if one view is more prevalent today, 2,899 American adults were surveyed and asked to select the group most qualified to answer the question of when a human’s life begins. The majority selected biologists (81%), which suggested Americans primarily hold a descriptive view. Indeed, the majority justified their selection by describing biologists as objective scientists that can use their biological expertise to determine when a human's life begins. Academic biologists were recruited to participate in a study on their descriptive view of when life begins. A sample of 5,502 biologists from 1,058 academic institutions assessed statements representing the biological view ‘a human’s life begins at fertilization’. This view was used because previous polls and surveys suggest many Americans and medical experts hold this view. Each of the three statements representing that view was affirmed by a consensus of biologists (75-91%). The participants were separated into 60 groups and each statement was affirmed by a consensus of each group, including biologists that identified as very pro-choice (69-90%), very pro-life (92-97%), very liberal (70-91%), very conservative (94-96%), strong Democrats (74-91%), and strong Republicans (89-94%). Overall, 95% of all biologists affirmed the biological view that a human's life begins at fertilization (5212 out of 5502). Historically, the descriptive view on when life begins has dictated the normative view that drives America's abortion laws: (1) abortion was illegal at ‘quickening’ under 18th century common law, (2) abortion was illegal at ‘conception’ in state laws from the late 1800’s to the mid-1900’s, and (3) abortion is currently legal before ‘viability’ due to 20th century U.S. Supreme Court cases Roe v. Wade and Planned Parenthood v. Casey. While this article’s findings suggest a fetus is biologically classified as a human at fertilization, this descriptive view does not entail the normative view that fetuses deserve legal consideration throughout pregnancy. Contemporary ethical and legal concepts that motivate reproductive rights might cause Americans to disregard the descriptive view or disentangle it from the normative view. However, these findings can help Americans move past the factual dispute on when life begins and focus on the operative question of when a fetus deserves legal consideration.

Keywords: human development, when life begins, abortion, scientific consensus, survey of Americans, survey of biologists, MTurk

Suggested Citation

Jacobs, Steven and Jacobs, Steven, Biologists' Consensus on 'When Life Begins' (July 25, 2018). Available at SSRN: or

Steven Jacobs (Contact Author)

University of Chicago - Department of Comparative Human Development ( email )

Chicago, IL 60637
United States

Northwestern Prizker School of Law ( email )

750 N. Lake Shore Drive
Chicago, IL 60611
United States

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