Catholic Evolutionism After Humani Generis
Catholic discussion of evolutionism did not end with the publication of Humani generis. Although it is not my intention to write a history of the three quarters of a century since publication of the encyclical, a few words about subsequent Catholic thought on the two issues that the encyclical addressed seem nevertheless to be appropriate.
The Evolutionary Origin of the Human Body
No subsequent document that has the authority of an encyclical has returned to the question of evolution and the origin of man. Reservations about the evolutionary origin of Adam’s body gradually faded. One can, to be sure, still find Catholics defending anti-evolutionist views. An English translation of Cardinal Ruffini’s book was published in 1957; a new edition of Carlo Boyer’s De Deo creante et elevante (still anti-evolutionist on this question) was published the same year. Michał Chaberek, OP, published his Aquinas and Evolution in 2017. Nevertheless, the view provisionally acknowledged in the encyclical eventually seems to have won general, if not universal, consensus among Catholics who addressed the issue.
One can take as a sign of this acceptance two statements made by St. John Paul II, and one issued by the International Theological Commission in 2004.
John Paul first addressed the question of evolution in his General Audience of April 16, 1986, where he said that
from the point of view of [Catholic] doctrine, there is no apparent difficulty in explaining the origin of man, as far as concerns the body, by the hypothesis of evolutionism. However, it must be added that that hypothesis puts forward only a probability, not a scientific certainty. [Catholic] doctrine, on the other hand, invariably affirms that man’s spiritual soul is directly created by God. That is, it is possible, according to the hypothesis just mentioned, that the human body, as a result of the order impressed by the Creator in the powers of life, was gradually prepared in the forms of antecedent living beings. The human soul, however, on which man’s humanity ultimately depends, being spiritual, cannot have emerged from matter.
He addressed it again on October 22, 1996, when, as part of the celebration of the sixtieth anniversary of the founding of the Pontifical Academy of Sciences, he gave an address (on evolution and on broader questions associated with the relation between science and religion) to a plenary assembly of the Academy. The particular question of evolution was one that it had chosen for some of its own work. St. John Paul began by recalling Humani generis. His address developed the work of his predecessor on one important point:
Taking into account the state of scientific research at the time as well as of the requirements of theology, the Encyclical Humani Generis considered the doctrine of “evolutionism” to be a serious hypothesis, worthy of careful investigation and reflection, equal to that due to the opposing hypothesis. . . . [But] today, almost half a century after the publication of the Encyclical, new knowledge has led to the recognition that the theory of evolution is more than an hypothesis. . . . The convergence . . . of the results of lines of work conducted independently of one another constitutes by itself a significant argument in favor of the theory.
There is, he went on to acknowledge, variation in detail between one scientific theory and another. More importantly for his purpose, there are various philosophical “readings” of evolution—materialistic-reductionist, as well as spiritualist. St. John Paul re-emphasized, in his own words, a point central to Pius: “In the case of man, we find ourselves faced with an ontological difference, one might even say with an ontological leap.” The intellect and the will make man a kind of being different from any other. The spiritual soul that underlies these powers could only have been created by God.
A few years later, the International Theological Commission addressed the question in its “Communion and Stewardship: Human Persons Created in the Image of God,” in which it emphasized that “Christians have the responsibility to locate the modern scientific understanding of the universe within the context of the theology of creation.” It reiterated St. John Paul II’s acceptance of scientific theories of the evolutionary origin of species, including man:
While there is little consensus among scientists about how the origin of this first microscopic life is to be explained, there is general agreement among them that the first organism dwelt on this planet about 3.5–4 billion years ago. Since it has been demonstrated that all living organisms on earth are genetically related, it is virtually certain that all living organisms have descended from this first organism. Converging evidence from many studies in the physical and biological sciences furnishes mounting support for some theory of evolution to account for the development and diversification of life on earth, while controversy continues over the pace and mechanisms of evolution. While the story of human origins is complex and subject to revision, physical anthropology and molecular biology combine to make a convincing case for the origin of the human species in Africa about 150,000 years ago.
The document also, of course, warned against “theories of evolution . . . of a neo-Darwinian provenance which explicitly deny to divine providence any truly causal role in the development of life in the universe” as well as “materialistic theories of human origins.” The document later emphasizes that the role given to chance by Neo-Darwinism is not per se incompatible with the doctrine of divine providence.
Monogenesis
Pius XII’s affirmation that the evolutionary origin of the human body was a theologically open question, even despite its cautious and provisional character, seems, for most Catholics, to have resolved the central question of the compatibility of the theory of evolution and Catholic doctrine, but the encyclical did not resolve every question. There was, after all, still the question of monogenesis. There Pius had reaffirmed, even if not definitively, a theological doctrine inconsistent with a presumptive consequence of the theory of evolution and, as it later turned out, some surprising similarities between chimpanzee and human genomes. Three points about the post-encyclical discussion of the question are worth noting.
The Clarification of Terminology
The first point concerns the gradual emergence of a uniform terminology for discussion of the question. Shortly before 1950, Catholic authors had already begun to make a more explicit acknowledgment that, however unified the concept of polygenism was in its rejection of monogenism, it came in two quite different scientific forms. Shortly thereafter, they began to use the “suffixes” -phyletism and -genism to distinguish theories about the number of first human groups from those about the number of first human couples in a way that clarified Catholic discussion of the issue.
The first step was taken in 1948, in two articles in the same issue of the Gregorianum. Vittorio Marcozzi wrote in his “Poligenesi ed evoluzione nelle origini dell’uomo” that:
Today the problem of polygenism can mean either of two things. The first meaning: Must the human races, living and extinct, be considered to be descendants of a single, already human, stock or must they be considered to have originated from diverse stocks? The second meaning: If it is proven that all the races are derived from the same stock, is it necessary to maintain that they were born from a single couple, or must one admit that there were originally many couples?
Heinrich Lennerz made the same point in “Quid theologo dicendum de Polygenismo?” Marcozzi went on to review geographical pluralism in some detail before returning his verdict: “There is not a single positive argument in favor of the simultaneous appearance of Man in multiple places on earth.” He then turned briefly to the second question, on which he wrote only a single paragraph, saying:
Whether many couples appeared in that center of origin, or only one, is not, in our modest judgment, a problem that can be resolved, at least not with certainty, with the resources of natural science alone since, in our opinion, one will never be able to know, from paleontology or biology, if there was only one couple or more than one at the origin of the species. The problem will have to be resolved by way of something other than the natural sciences.
Within a few months of the publication of Humani generis, Teilhard wrote (but did not publish) a short paper entitled, “Monogénisme et monophylétisme: Une Distinction essentielle à faire.” His introductory remarks—“one must insist once again”—suggest both that the distinction was not new and that not everyone was bothering to make it. Four points (of his) are important here.
First, “polygenism” should be defined by reference to a plurality of primitive couples; it has nothing to do with the question of how many distinct branches or phyla lay at the base of humanity. Polyphyletism, that is to say, stands in contrast to two forms of monophyletism, one polygenistic and the other monogenistic.
Second, since science (paleontology) can only see populations, mono- and polygenism are “purely theological” concepts. The scientific conception of the unity of man can be a matter only of phylogenetic unity (i.e., monophyletism), independent of questions of population size and morphology.
Third, the scientific indeterminacy with respect to population size leaves the theologian with a certain freedom with respect to whatever seems dogmatically necessary.
Fourth, all that we think we know about “the biological laws of ‘speciation’” renders monogenism “scientifically untenable.” Teilhard did not publish this note, though he may well have circulated it among his fellow Jesuits.
At that point, the now-standard Catholic terminological formulation of the trichotomy—polyphyletic polygenism, monophyletic polygenism, and monophyletic monogenism—was nearly in place. Marcozzi had distinguished two forms of polygenism; Teilhard, two forms of monophyletism. The combination of these two taxonomic categories appeared, shortly after the publication of Humani generis, in an article by another Jesuit, Guy Picard, whose article “La Science expérimentale est-elle favorable au polygénisme?” was published in Sciences ecclésiastiques. He wrote that “the name monogenism has been given to the doctrine according to which the present (actuel) human species has its origin in a single couple; and polygenism to the contrary opinion, which affirms many initially independent couples.” In a footnote, he added:
One can add another distinction. In fact, if a polygenistic origin began with several different species, it could be called polyphyletic; if came from a single species, it would be polygenistic in the strict sense. Polygenism is therefore a [logical] genus of which the [logical] species are polygenism (an [older] species producing several couples of a new species) and polyphyletism (several [older] species producing, by convergence, several couples of a single new species).
By 1960, a number of other authors had begun to make Teilhard’s “essential distinction” in a way that made the now-standard trichotomous taxonomy terminologically easy. Teilhard did so in print in his posthumously published Le Phénomène humain (1955). Léon Cristiani, priest, historian at the Université de Lyon, and popularizer, writing under the pseudonym Nicolas Corte, made it in his Les Origines de l’homme (1957), published as part of the Encyclopédie du catholique au XXème siècle. So did Frédéric-Marie Bergounioux in his La Préhistoire et ses problèmes (1958).
The distinction did not, to be sure, meet with universal approval. Jules Carles complained that distinguishing the “suffixes” -genism and -phyletism is “a subtlety whose only significance is to muddle a problem which is already a bit confused.” Other authors simply ignored it. Of those, some simply worked around the trichotomous nomenclature; others continued to use the term “polygenism,” in particular, as they always had done (in many cases, alas, imprecisely). Some of the resistance may have been connected to a fact noted by Léon Renwart of Louvain:
Theologians and scientists often use the words “monogenism” and “polygenism” in very different senses.
For theologians, monogenism is the doctrine that “all men now alive on this earth are descended from a single human couple, Adam and Eve.” For the scientist, the same word refers to the conception “according to which all hominids are derived from the same stock [souche], independent of the number of individuals, which had already attained the human level.”
Theologians define the term “polygenism” as meaning “that the origin of modern man is to be found in a multiplicity of first ancestors, while scientists use the same term for “the scientific conception in accordance with which human races come from parallel lineages which were detached from a common trunk before they had attained the human level.”
In 1960, Edouard L. Boné commented that, useful as adhering to the essential distinction would be, it still had by no means become general in the academic literature. Over the course of the next decade, however, it seems to have done so.
Evolutionary Monogenism After the Encyclical
The second point worth noting is that, in the years following the publication of Humani generis, there were several attempts to accommodate the populational account of human origins suggested by the scientific evidence with the strict monogenism of the encyclical. Muller’s attempt to do this was mentioned above. There were at least four others.
The first, appearing only a few months after the encyclical itself, was Swiss theologian (and later cardinal) Charles Journet’s brief Petit Catéchisme sur les origines du monde. Journet sketched two possible ways to imagine the origin of the human race.
First, from among the transitional beings (whose existence is uncertain), who are similar to man in their morphology and instincts but who, lacking a spiritual and immortal soul, are not philosophically human, God chose two, who became the first human couple. He made them in his image and likeness.
In his image: that is to say that He infused in them a spiritual and immortal soul which, entering into the body, made it a human body.
In his likeness: that is to say that He enfolded them with original grace.
His second, and more complex, possibility was that God infused spiritual and immortal souls into a larger number of these transitional beings (at different times and in different places). These philosophically human beings, made in the image of God, played some role in preparing for the arrival of Adam. It was from them that God would choose a single couple whom he formed in his likeness in order to inaugurate the order of grace. Only the descendants of Adam survived the catastrophes of prehistory; the rest became extinct. The idea that human beings are not descended from a single couple, but from multiple different couples, he said, would require separate original sins for each lineage and would require an interpretation of certain passages of Scripture different from those of the Church. He quoted from the encyclical and concluded by saying that science could not resolve the question of monogenesis. That view was neither scientific nor anti-scientific, but trans-scientific.
Camille Muller’s idea that, within a few generations, everyone within a small population that included Adam and Eve would be descended from them and thus tainted by original sin appeared again in a lecture at the Istituto de Paleontologia Umana dell’Università de Ferrara on July 7, 1962. In that lecture, Italian Jesuit Giovanni Blandino presented two alternative hypotheses (as well as a detailed mathematical proof of just how quickly descent from an Adam and Eve inserted into a larger population would become universal).
According to Blandino’s first hypothesis, the human race was the product of a gradual corporeal evolution from an earlier anthropoid population supplemented, at a certain point, by a general infusion of created spiritual souls. These first human beings were probably not able to exercise their intellectual powers to any great extent, but once they could do so, God raised two of them to a supernatural state by giving them sanctifying grace and revealing to them the fundamental truths of religion. He also subjected them to a test, which they failed. They and their descendants bred only among themselves and the co-Adamites gradually became extinct, leaving us with the entire species exclusively descended from Adam and Eve.
Blandino’s second hypothesis varies from the first by allowing interbreeding with the larger human population, with any descent from either Adam or Eve being sufficient for the inheritance of original sin and the promise of redemption.
Blandino thought that both hypotheses were consistent with the three dogmatic theses about original sin as one in origin, transmitted by generation, and present in everyone (anyway, “all men now being born”) at birth. He interpreted that “now” “broadly,” he said, but that breadth reached only as far back as the calling of Abraham. In a typescript tipped into at least some copies of the pamphlet, Blandino acknowledged that a more comprehensive version of universal guilt (as expressed, for example, in Humani generis) was inconsistent with his second hypothesis, but he expressed doubt that that encyclical was part of infallible magisterial doctrine.
Neither Muller nor Blandino succeeded in articulating a scenario in which all human beings (in the sense of beings with rational souls) are descended from the first couple. Both include co-Adamites that the encyclical said did not exist. A new hypothesis, one that did not include the kind of co-Adamites found in those earlier scenarios, was proposed by Josephite priest Andrew Alexander in 1964. On his account, a final crucial genetic mutation renders the body of pre-human beings suitable for the infusion of a rational soul without rendering them incapable of interbreeding with the other members of the pre-human population from which they emerged. If only descendants of Adam and Eve had that mutation, one would have a scenario that respected both the polygenism suggested by ordinary science and the monogenism required by Catholic theology.
Some years later, I proposed a variant of Alexander’s hypothesis, arguing that the genetic mutation that Alexander used to distinguish Adam and Eve from the larger population with whom they interbred, was not strictly necessary. The infusion of a rational soul into Adam, Eve, and all (or even most) of their descendants would be sufficient to make all fully human beings descendants of Adam.
Magisterial Silence
The third point worth noting is the relative neglect of the question of monogenesis in official statements on evolution and theology. The two documents mentioned above illustrate this.
St. John Paul II’s address to the Pontifical Academy of Sciences reemphasized the central point made by Pius forty-six years before, differing primarily in the greater certainty that he thought was due to the scientific argument in favor of evolution. The address did not, however, address a third point that was important to Pius, namely the monogenetic origins of the human race.
The second is the International Theological Commission’s “Communion and Stewardship.” With respect to the origin of man, the Commission asserted the “natural unity of the human race,” but in two passages seems open to polygenetic (though not polyphyletic) accounts of the origin of the human race. First, it concluded the long passage quoted above with the phrase “in a humanoid population of common genetic lineage.” Second, when it returned to the matter several paragraphs later, it referred to “the emergence of the first members of the human species (whether as individuals or in populations).” It did not propose a response to the problem of the original sin which had worried Pope Pius. Although some readers see in this parenthetical remark a new theological openness to monogenetic polygenism, that is perhaps too strong a conclusion. It can, in light of its failure to address the concerns raised by Pius XII, more plausibly be read to assert only that what the Commission was saying in that paragraph—“that that the emergence of the first members of the human species . . . represents an event that is not susceptible of a purely natural explanation and which can appropriately be attributed to divine intervention”—does not depend precisely on a monogenistic account of human origins.
EDITORIAL NOTE: This article is excerpted from The Origins of Catholic Evolutionism, 1831-1950 (The Catholic University of America Press, 2025). All rights reserved.
