Social psychologists who research abortion attitudes typically associate pro-life views with sexism, opposition to gender equality, religiosity, conservative ideology, and right-wing authoritarianism.

That research, however, reflects liberal perspectives on abortion. Research measuring “conservative predictors” of abortion attitudes suggest beliefs about sexual morality and the sanctity of human life might better explain abortion attitudes than sexism, ideology, and religiosity. Using data from national polls on abortion attitudes, my fellow researchers and I assessed the significance of views on ‘when life begins’ in the U.S. abortion debate.

As shown in the table below, the percentage of adults who agree that life begins at various stages (e.g., fertilization, birth) roughly mirrors the percentage of adults who agree abortion should be restricted at that stage. These differences also relate to political identities: Republicans (72%) are more likely to believe ‘life begins at conception’ than Democrats (32%). Moreover, 59% of pro-life respondents said this view was a “biological and scientific fact,” whereas 58% of pro-choice respondents said it was a “philosophical or religious belief.”

In an online survey of 4,107 adults living in the U.S., a sample that was predominantly pro-choice (62%), liberal (63%), socialist (54%), and Democratic (66%), there were only small (and nonsignificant) differences between pro-life and pro-choice participants’ support of radical feminism (34% vs. 42%) and liberal feminism (80% vs. 90%). Similarly, there were virtually no differences between pro-life (91%) and pro-choice (93%) participants’ support of women’s rights.

Overall, these results suggest that pro-life attitudes are not driven by anti-women attitudes, which is consistent with polling that shows that women in the U.S. are more likely to identify as pro-life (51%) than men (46%). Instead, we found that the earlier a participant believes a human’s life begins, the earlier they believe abortion should be illegal. Indeed, 82% of participants reported that ‘when life begins’ is an important question in the abortion debate, 93% suggested a human’s life is worthy of legal protection once it begins, and 76% said Americans deserve to know when a human’s life begins to be informed in their positions on abortion and in their reproductive decisions.

When Does Life Begin?

In this same study, participants were asked to select the group most qualified to resolve the dispute on when a human’s life begins. The majority (80%) selected biologists, and most of those participants (91%) wrote that they made their selection because they view biologists as objective experts in the study of life. Thus, most believe that determining when a human’s life begins is a matter of biology.

So, we investigated biologists’ views by surveying 5,577 professors and postdocs in biology departments from 1,058 academic institutions around the world. In a predominantly non-religious (63%), liberal (89%), pro-choice (85%), and Democratic (92%) sample, most biologists wrote that a human’s life begins at fertilization (68%) in response to the essay question: “From a biological perspective, how would you answer the question: ‘When does a human's life begin?’”

An overall measure of biologists’ responses to five statements representing the biological view that a human’s life begins at fertilization was used to determine whether biologists agreed with that view (e.g., “In developmental biology, fertilization marks the beginning of a human’s life, since that process produces an organism with a human genome that has begun to develop in the first stage of the human life cycle.”; “From a biological perspective, a zygote that has a human genome is a human because it is a human organism developing in the earliest stage of the human life cycle.”). 96% affirmed at least one of the five statements, 86% affirmed at least half of the statements, and 64% affirmed all five statements.

Why Do Americans Disagree?

Despite differences in views on ‘when life begins’ among adults in the U.S., we found that most participants in the U.S. recognize fetuses as humans in non-abortive contexts. Presented with various scenarios in which conduct towards a pregnant person results in a fetus’s death (e.g., physical attack, capital punishment, drugging, negligent medical treatment, and drunk driving), 87% of pro-choice participants suggested such acts are unjustifiable homicides. In contrast, only 12% of pro-choice participants recognize abortion as homicide. Dan Kahan’s work suggests a potential explanation for this apparent inconsistency:

“[A]dopting the ‘wrong’ position in interactions with her peers could rupture bonds on which she depends heavily for emotional and material well-being. Under these pathological conditions, she will predictably use her reasoning not to discern the truth but to form and persist in beliefs characteristic of her group, a tendency known as ‘identity-protective cognition.’”

Some pro-choice individuals might fear that recognizing a fetus as a human could estrange them from their fellow supporters of abortion rights, on whom they might rely for social, emotional, and financial support. Therefore, they may be motivated to reject fetuses’ humanity, particularly in the context of abortion. If one experiences cognitive dissonance when thinking about a fetus as a human, and thus abortion as a form of homicide, one might distort their understanding of biology to protect their beliefs about abortion rights.

As shown in the table below, large majorities on both sides agree on the principles undergirding the abortion debate: a human should be protected once its life begins, all humans have rights and equally deserve rights, and the right to life is more important than the right to liberty.

The lack of agreement on ‘when life begins’ could be a byproduct of differences in abortion attitudes, but it could also be the result of an informational asymmetry. Indeed, many Americans believe that information about when a fetus is a biological human would influence abortion attitudes and behavior. Participants were asked about the possible impact of it becoming common knowledge that a fetus is a biological human: 90% of pro-choice participants said abortion rates would go down, and 83% suggested it could reduce support for legal abortion access.

However, as Dr. Maureen Condic, a board member of the National Science Foundation, has opined:

“[E]stablishing by clear scientific evidence the moment at which a human life begins is not the end of the abortion debate. On the contrary, that is the point from which the debate begins.”