The science of abortion: When does life begin?


In a recent interview, Senator Marco Rubio (R-FL) declared it is a scientific fact that “human life begins at conception.” He also said that “leaders on the left” who “wag their fingers” about the “settled science” of global warming are hypocrites when it comes to science, and someone should ask them if they accept the “consensus of scientists that says that human life begins at conception.”

Going further, the senator added, “I’d like to see someone ask that question. It’s never asked. And that’s not even a debatable thing, we can actually see that happening. I mean, that is a proven fact. And yet that’s a scientific consensus they conveniently choose to ignore.”

In the wake of these remarks, MSNBC reporter Irin Carmon and Washington Post blogger Philip Bump pushed back at Rubio, asserting that:

  • he made a “scientific blunder on abortion.” (Carmon)
  • “conception” and “life” “aren’t scientific terms.” (Carmon)
  • “the scientific experts we spoke with didn’t offer any consensus” on when life begins. (Bump)

However, as documented below, the facts of science support Rubio’s point and reveal that the claims of Carmon and Bump are scientifically baseless.

Science shows that life begins at conception

Contrary to Carmon’s allegation that “conception” and “life” are not scientific terms, both of these words are clearly defined in science dictionaries and widely used in scientific literature.

To cite just a few examples, the American Heritage Science Dictionary defines “conception” as “the formation of a zygote resulting from the union of a sperm and egg cell; fertilization.” (For reference, a zygote is the first stage of a human embryo.)

Likewise, the entry for “life” in the American Heritage Dictionary of Science states that life is “the form of existence that organisms like animals and plants have and that inorganic objects or organic dead bodies lack; animate existence, characterized by growth, reproduction, metabolism, and response to stimuli.”

Rubio’s statement that “human life begins at conception” is consistent with both of these definitions, because human zygotes display all four empirical attributes of life:

  1. Growth – As explained in the textbook Essentials of Human Development: A Life-Span View, “the zygote grows rapidly through cell division.”
  2. Reproduction – Per Human Sexuality: An Encyclopedia, zygotes sometimes form identical twins, which is an act of “asexual reproduction.” (Also, in this context, the word “reproduction” is more accurately understood as “reproductive potential” instead of “active reproduction.” For example, three-year-old humans are manifestly alive, but they can’t actively reproduce.)
  3. Metabolism – As detailed in the medical text Human Gametes and Preimplantation Embryos: Assessment and Diagnosis, “At the zygote stage,” the human embryo metabolizes “carboxylic acids pyruvate and lactate as its preferred energy substrates.”
  4. Response to stimuli – Collins English Dictionary defines a “stimulus” as “any drug, agent, electrical impulse, or other factor able to cause a response in an organism.” Experiments have shown that zygotes are responsive to such factors. For example, a 2005 paper in the journal Human Reproduction Update notes that a compound called platelet-activating factor “acts upon the zygote” by stimulating “metabolism,” “cell-cycle progression,” and “viability.”

Furthermore, the science of embryology has proven that the genetic composition of humans is formed during fertilization, and as the textbook Molecular Biology explains, this genetic material is “the very basis of life itself.”

In accord with the facts above, the textbook Before We Are Born: Essentials of Embryology and Birth Defects directly states: “The zygote and early embryo are living human organisms.” This may be controversial from a political perspective, but the sciences of embryology and genetics leave no doubt as to when human life begins.

ACOG is not an objective scientific authority

Bump’s article is entitled, “Marco Rubio demanded people look at the science on abortion. So we did.” Yet as far as the article reveals, the entirety of Bump’s “scientific” research consisted of speaking to a single organization: the American College of Obstetricians and Gynecologists, or ACOG.

While Bump’s article clearly shows that ACOG avoided the question of when life begins and attempted to change the subject, Bump did not articulate this to his readers. Instead, he used ACOG’s non-answer to conclude that life “is something of a philosophical question,” and “the scientific experts we spoke with didn’t offer any consensus” on this issue.

That is not “looking at science,” as Bump claims he did. Rather, it is cherry-picking the opinions of selected scientists and uncritically relaying them. It also presumes that the chosen scientists are unbiased and incontestable authorities on this issue, which is demonstrably not the case with ACOG’s leadership.

For instance, when a debate over partial-birth abortion was raging during the Clinton Administration. ACOG prepared a statement disclosing that a “select panel convened by ACOG could identify no circumstances under which this procedure, as defined above, would be the only option to save the life or preserve the health of the woman.”

Yet instead of releasing this information to the public, ACOG faxed it to the Clinton administration with a header that stated: “CONFIDENTIAL, NOT FINAL, DO NOT COPY, DO NOT DISTRIBUTE.”

This document came to the attention of a White House lawyer and policy advisor named Elena Kagan (later appointed by President Obama to the Supreme Court). She was displeased with ACOG’s conclusion and wrote a memo warning that its release would be a “disaster,” especially since ACOG opposed banning partial birth abortions.

Kagan then proceeded to edit ACOG’s statement by adding that partial-birth abortion “may be the best or most appropriate procedure in a particular circumstance to save the life or preserve the health of a woman….” Those words did not reflect the thrust or scope of ACOG’s findings, which Kagan clearly understood because she had detailed them in a previous memo.

Nevertheless, ACOG adopted Kagan’s words as its own, thus using the rhetoric of a Clinton administration lawyer in place of its own medical conclusions. Those are not the actions of an objective scientific authority but of an organization that is willing to place politics over science.

What is science?

There is a lot of posturing about science in the world of politics, but some of what is reported as “science” is actually just the claims of selected scientists, which happen to be at odds with the facts of science.

Science, in the words of Webster’s College Dictionary, is the “systematic knowledge of the physical or material world gained through observation and experimentation.” Notably, this does not entail parroting the assertions of someone with scientific credentials.

In the realm of science, what matters is facts and logically inescapable conclusions that flow from them—not opinions, no matter who voices them or how prevalent they are. A classic example of this is Galileo, who wrote that when it comes to the sciences, “the authority of thousands of opinions is not worth as much as one tiny spark of reason in an individual man.”

In this instance, Rubio is that man, and Carmon, Bump, and ACOG are substituting their ideology for science in the public debate over abortion.

James D. Agresti is the president of Just Facts, a nonprofit institute dedicated to researching and publishing verifiable facts about public policy.

To Top