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Sharon Kabel is a librarian, an independent researcher, and a Catholic.

She recently completed a project researching the signatories to the 1968 Scientists’ Statement on Birth Control Encyclical, which rejected the teachings contained in Pope Paul VI’s encyclical Humanae Vitae.

Kabel examined the history of the statement and catalogued the 3,097 signatures attached to it. She presents these primary sources, along with her reflections:


This week, the Church marks the 55th anniversary of Pope Paul VI’s promulgation of Humanae vitae.

The 1968 encyclical, which reaffirmed the Catholic Church’s teaching against contraception, was a bombshell, in part because documents had already been leaked showing that a papally-appointed commission examining the issue had advised Paul VI to change Church teaching. 

Dissent from the new encyclical was rapid and organized.

One week after the document’s promulgation, a dissenting statement with signatures from more than 80 theologians appeared in the New York Times, led by Father Charles E. Curran. The Canadian Conference of Catholic Bishops signed the ‘Winnipeg Statement’ rejecting the encyclical’s teachings that September. 

A petition from the short-lived National Association of Laymen amassed over 700 signatures

The New York Times, July 31, 1968, page 16. 

Beyond the protests of the dissenting theologians was a statement released in December, bearing the signatures of 2,600 scientists objecting to the encyclical.  

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Some scientists feared that Humanae Vitae would exacerbate the overpopulation crisis. Peter E. Hodgson, a Catholic scientist writing for New Blackfriars, declared that “the natural law arguments are insufficient to demonstrate the intrinsic evil of artificial birth control.” 

In the months following the promulgation of Humanae vitae, three biologists attempted to spearhead “a massive and unambiguous expression of scientific opinion” against it: Jeffrey Baker, Ernst Mayer, and Paul Ehrlich composed a 417-word letter, simply titled, “Scientists’ Statement on Birth Control Encyclical.”

The statement excoriated Paul VI, implicitly accusing him of starting another Holocaust, deeming him “unenlightened,” the encyclical’s consequences “evil,” the Church “antiquated and anti-human,” and the whole situation “repugnant.”

Baker, Ernst, and Ehrlich circulated packets by mail that included their statement, a cover letter explaining their goal, and sheets for signatures (Name, Department, Institution). The trio encouraged recipients to circulate to interested colleagues and return all signatures by December 20, to Baker at the University of Puerto Rico. 

The original plan was to collect signatures until December 20, 1968, and then issue a press release at the annual meeting of the American Association for the Advancement of Science (AAAS) in Dallas, Texas, December 26-30.

The AAAS vetoed both the press release and a request to set up a booth to collect signatures.

Nevertheless, Ehrlich, Mayr, and Baker released their statement to the press on December 30, 1968. To boost publicity, they wrote articles in the New Scientist and BioScience. As a result of those articles, and natural delays from mail, signatures continued to pour in, prompting an extended deadline.

The records pertaining to this statement are housed at Stanford University, where Ehrlich serves as an emeritus faculty member. The archives show just more than 3,000 signatures. 

It is unclear if anything significant was done with the signatures that came after December 1968. In page 293 of the archival records, there is a plaintive handwritten note from Baker to Ehrlich: “Paul - reassure me - These are being counted and filed, aren't they? Hope you plug them in your speeches. Jeff.”

In 1975, in the Bulletin of the Atomic Scientists, Baker reflected on the statement: 

Rather than waiting for action by such organizations, Paul Ehrlich (Stanford University), Ernst Mayr (Harvard University) and the author (then at the University of Puerto Rico), working with the help and support of Roman Catholic biologist John Thomas (Stanford University), drew up a strongly worded protest against the birth control encyclical. In less than 5 weeks, more than 2,600 signatures of biologists supporting the statement were collected. Included among the signers were five Nobel laureates and 26 members of the National Academy of Science. The statement was released to the news media on December 29, 1968, and received worldwide attention. 

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Dissent from the dissent 

Although Ehrlich and his companions had initially hoped for “a massive and unambiguous expression of scientific opinion,” they acknowledged in a November 18 letter soliciting signatures, “You will note that the statement is quite a strongly worded one. It was our feeling that a strong statement with fewer signatures would be far more effective than a watered-down one bearing many signatures.”

In fact, their open letter was met with objections from a number of theologians and scientists. 

At that AAAS meeting, Baker encouraged a “nationwide economic boycott of the Catholic Church to protest the papal ban,” Catholic News Service reported at the time.

But despite the three men’s best efforts, there is no mention of the petition or the encyclical in the AAAS meeting notes. 

On February 4, 1969, Ehrlich et al sent their Statement and signatures to more than 100 American Catholic bishops. They requested that Archbishop Joseph McGucken send a copy to Paul VI himself.

McGucken refused outright, saying, according to Catholic News Service, “It is a very impolite letter and not one you would expect scientists, or any educated man, to write…I wouldn’t dream of insulting the Pope by sending it to him.”

At least five scientists put their complaints about The Statement in writing: 

There have been some reservations and comments made on the statement which I shall briefly outline here. While purportedly a statement by scientists, it is more emotional in tenor than factual. Granted the facts have been stated many times, but the document would have been more forceful if it attacked the idea of the encyclical rather than the Pope himself. The document was clearly written by a non-Catholic who does not seem to realize (that in the eyes of a devout Catholic) that the Pope is more than an educated theologian, but is inspired by God. The encyclical may be “misguided” but the idea of its being “immoral” is very questionable. Also, why have a statement made up and signed if “hopes for change have been totally destroyed”? The signers of the document are less pessimistic. With these reservations in mind, the general intent of the statement is clear. What is to be done with the Scientist’s Statement? Thanks for your work and concern in this important field. [Thorston W. Henrich, Laboratory Instructor, Department of Biology, University of Victoria, June 13, 1969]

I cannot sign such an emotional pledge. Medical or biological evidence revealing the detriment of the encyclical would have been immeasurably more effective. It strikes me as a vague philosophical stand; instead of a constructive scientific criticism. [Stephen Manley, Canadian Forest Service]

I agree fully with the reasoning but, like J. Clark, I don’t like the tone of certain passages. The writer should have cooled down a bit before he wrote. [R. F. Morris, Canadian Forest Service]

Unable to sign this document. Arguments are inconclusive and do not present all sides of the picture. [E. G. Kettela, Canadian Forest Service]

Why give any attention to the Encyclical, anyway? [C. H. A. Little, Canadian Forest Service]

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Cataloguing signatories

While Baker asserted in 1975 that the statement had drawn more than 2,600 signatures from biologists, the reality is more nuanced.

An examination of the 3,097 signatures appended to the Statement in the Stanford archives shows that not all the signatories were biologists, or even members of the life sciences.

Science can be subdivided in any number of ways, and scientists may record their own discipline in various different ways.

Out of the 3,097 signatories, 79% said they worked in a life science.

About a third of the signatories hailed from the field of biology, while about 1 in 6 were in zoology.

All other fields had a much smaller representation, with fewer than 200 signatories each, making up 6% or less of the total.

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Full text of the Scientists’ Statement on Birth Control Encyclical

Scientists' Statement on Birth Control Encyclical

The undersigned scientists strongly protest the July 29, 1968 encyclical, Humanae Vitae of Pope Paul VI concerning birth control. More than half the world is hungry and our environment is deteriorating rapidly and perhaps irreversibly. The threat of worldwide pestilence increases as malnutrition and overcrowding increase and as transport systems make transmission of disease to the far corners of the Earth more rapid. Population pressures are contributing to political tensions and increasing the probability of biological or thermonuclear warfare. Any action which impedes efforts to halt world population growth perpetuates the misery in which millions now live and promotes death by starvation of millions this year and many more millions in the next few decades. 

How far removed must an individual be to remain innocent of the results of his actions? The realization that six million Jews were murdered in World War II stunned the civilized world into a more direct affixing of blame on those not directly involved in the actual executions. But what of the crippled lives or the slow and lingering deaths of an equal number of persons who do not get enough to eat? Does the fact that the Pope believes himself forced to his stand by personal religious convictions make these deaths any less horrible than those caused by political motives? We think not. It has been stated by Roman Catholics that the Pope is not evil, but simply unenlightened, and we must agree. But, whatever the motives, the evil consequences of his encyclical are manifest. 

The world has long tried circumspection with Rome in the hope that the antiquated and anti-human policies of the Church toward sexuality would be discarded. Humanity took heart when the Pope’s own birth control commission advised him to change these policies. Now hopes for change have been totally destroyed. 

It is high time, therefore, that we make our stand on the birth control encyclical perfectly clear. We pledge that we will no longer be impressed by pleas for world peace or compassion for the poor from a man whose deeds help to promote war and make poverty inevitable. The world must quickly come to realize that Pope Paul VI has sanctioned the deaths of countless numbers of human beings with his misguided and immoral encyclical. The fact that this incredible document was put forth in the name of a religious figure whose teachings embodied the highest respect for the value of human dignity and life should serve to make the situation even more repugnant to mankind. 


Cover letter from organizers 1968-11-18

November 18, 1968

Dear Colleague, 

The enclosed statement is sent to you either because one of the undersigned is personally acquainted with you, you were recommended to us, or because you have in your work given indication that you might be interested in signing it. 

As you can see, the statement protests the encyclical, Humanae Vitae, issued this past summer by Pope Paul VI on the topic of human sexuality and birth control. You will note that the statement is quite a strongly worded one. It was our feeling that a strong statement with fewer signatures would be far more effective than a watered-down one bearing many signatures. 

If you and/or some of your colleagues and graduate students would be interested in signing the statement, please do so in the space provided and return it by December 20, 1968. Feel free to put additional signatures on the back or on a separate attached sheet. The collected signatures will then be added to those gathered at the December 26-30, 1968 meetings of the American Association for the Advancement of Science (AAAS) in Dallas, Texas, and turned over to the press. Since support has already been given us by some Roman Catholic scientists, we are hopeful of gathering a large number of signatures even prior to the Dallas meetings. For this reason, we ask that you do not leak the news of this statement to the press before December 30, 1968. 

It is too late, of course, to prevent the Papal Encyclical. We hope, however, that it is not too late to lend a hand to those both inside and outside the Roman Catholic Church who are working diligently to nullify at least some of its potentially tragic effects. 

Yours very sincerely, 

Jeffrey J. W. Baker,
Professor of Biology,
University of Puerto Rico

Paul R. Ehrlich,
Professor of Biology,
Stanford University

Ernst Mayr,
Professor of Biology,
Harvard University

Return the statement with signatures, mailed so as to arrive BEFORE DECEMBER 20, 1968, to Jeffrey J. W. Baker, Professor of Biology, Estudias Generales, Ciencias Biologicas, Universidad de Puerto Rico, Rio Piedras - San Juan, Puerto Rico 00931

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