1. The idea of evolution is popularly applied in various contexts. It is extended to the natural world generally, as when people speak of the “evolution” of the cosmos. In this wide sense, “evolution” simply means orderly process. Again, “evolution” is often used to refer to development in every sphere of culture and human life. This is a loose and inappropriate use of the term, for history is not a natural process but rather unfolds through human reflection, argument, and conflicts of power determined by human plans and choices. Popular usage aside, the only theory of evolution which is well established pertains exclusively to the unity and diversity of organic life.
The biological theory of evolution can be summarized as follows. Organisms reproduce; reproduction is not replication, but continuity with difference; differences which enhance reproductive potential tend to predominate; but what enhances reproductive potential differs under diverse conditions; therefore, organisms with common ancestors differ greatly under diverse conditions. Clearly, this theory applies neither to the natural world generally nor to human history, for they do not involve reproduction.
2. In light of these distinctions, one sees that only a pseudoscientific ideology supports the view that everything human can be accounted for in a single, all-embracing, naturalistic scheme of evolution. On the contrary, evolution as a biological theory can account only for the organic existence and attributes of humankind.
3. Intelligence and the capacity for free choice are not merely organic, however. As we experience and exercise them, these capacities involve self-reference and self-causation. These, in turn, presuppose the personal self which, in the natural world, only human beings possess. Nor can these capacities be accounted for as modifications of organically based functions. Thus evolution cannot account for human persons (see S.t., 1, q. 16, a. 2; q. 75, aa. 2–6; q. 82, a. 2).18
4. The capacity for free choice either is or is not present. One cannot have a partial ability to make a slightly free choice. It follows that, if one admits the spiritual reality of human persons including their capacity for free choice, one also must admit that their emergence in the world had to be a sudden event.19 Whether from the dust of the earth or from some group of subhuman primates, human persons had to be brought into being by a special act of the divine, creative power (see S.t., 1, q. 90, a. 2; S.c.g., 2, 87).
5. Following Genesis, Christians have usually thought of the human race as being descended from a single pair of individuals. This view is called “monogenism.” However, evolution theory points to the need for a sizable, interbreeding population at the origin of any organic type as complex as the human.20 This theory is called “polygenism.” Both Pius XII and Paul VI warn that polygenism, which evolution theory seems to demand, appears incompatible with the Church’s teaching. However, it is not clear that either of these popes proposed monogenism as the position to be held definitively.21 Hence, if a Catholic can show how polygenism is compatible with the essential elements of the Church’s teaching on original sin, then he or she may admit polygenism on the basis of the evidence in favor of it.
6. There is nevertheless no evidence requiring us to suppose that the present human race descended from more than one interbreeding population. Like Genesis, biological theory points to a single group at the beginning of humankind. Question F below will explain why the size of this group is not important.
7. Thus, there is no incompatibility between the Church’s doctrine concerning original sin and the scientific view that, insofar as they are organisms, human beings had subpersonal antecedents. Nor does the theory of evolution either require one to think or offer evidence for thinking that the first humans were semibestial or childlike, and incapable of serious sin. Whatever their antecedents, they were able to sin as soon as they were able to make free choices. If there were earlier, childlike, human beings, not yet capable of free choice, we have no social and moral solidarity with them.
Since anyone who accepts a Christian account of human persons must assume that they emerged by a sudden event inexplicable through natural causes alone, there can be no reason to suppose that the intelligence of the first person who was able to make a free choice was in any important way less than our own. In any case, one who can make a free choice can commit a sin; the Church’s teaching on original sin requires no more than this of the first persons. If they did not have this ability, then they simply were not persons relevant to our moral situation.
This last point is important to bear in mind when various data about human origins are considered. Fossil remains, even the remains of primitive tools, do not necessarily show that the creatures which left these remains were morally responsible persons. Subhuman primates today evidence some tool-making ability; extinct species might well have had more of this ability. Some species too advanced for our ancestors’ comfort may well have been extinguished by their competition.
18. Various naturalistic reductions (explainings away) of the nonnaturalistic aspects of human personhood are so common in contemporary opinion that even faithful Christians continually fall into this line of thought, completely incompatible with Christian faith. Those who engage in no Christian philosophical reflection but do read scientific works and theology are likely to miss the dogmatic and ideological character of all but the most technical writing about evolution. Except in purely scientific contexts, where they are harmless, evolutionist views express a speculative metaphysics of an indefensible sort. For an introduction to philosophical anthropology: James E. Royce, S.J., Man and His Nature (New York: McGraw-Hill, 1961); Mortimer J. Adler, The Difference of Man and the Difference It Makes (New York: Holt, Rinehart, and Winston, 1967). Against metaphysical reduction of the human person: Germain Grisez, Beyond the New Theism: A Philosophy of Religion (Notre Dame and London: University of Notre Dame Press, 1975), 230–40 and 343–56; Joseph M. Boyle, Jr., Germain Grisez, and Olaf Tollefsen, Free Choice: A Self-Referential Argument (Notre Dame and London: University of Notre Dame Press, 1976), 57–97.
19. This point often is overlooked in theological discussions. See, for example, J. P. Mackey, “Original Sin and Polygenism: The State of the Question,” Irish Theological Quarterly, 34 (1967), 106 and 110. Mackey also seems to confuse (112) polygenism (the evolution to human status of a substantial group, rather than a single pair) with polyphyletism (the origin of present humankind in two or more independent evolutionary processes, with later merging into a genetically unified species). The latter is not required by evidence and poses obvious biological problems of its own. See G. E. Kennedy, Paleo-Anthropology (New York: McGraw-Hill, 1980), 372–73; the possibility of different lines evolving into contemporary homo sapiens is “exceeding small” (373).
20. For a readable summary of the evidence, see Melvin Konner, The Tangled Wing: Biological Constraints on the Human Spirit (New York: Holt, Rinehart and Winston, 1982), 31–58, notes and references, 454–58; Theodosius Dobzhansky, Mankind Evolving (New Haven: Yale University Press, 1962); Claude Heddebaut, “Biologie et péché originel,” in La culpabilité fondamentale: péché originel et anthropologie moderne, ed. Paul Guilluy (Gembloux: J. Duculot, 1975), 153–64; but also see Jérôme Lejeune, “Adam et Eve ou le monogénisme,” Nouvelle Revue Théologique, 90 (1968), 191–96.
21. On monogenism: Pius XII, DS 3897/2328; Paul VI, “Original Sin and Modern Science: Address of Pope Paul VI to Participants in a Symposium on Original Sin,” The Pope Speaks, 11 (1966), 234 (58 AAS  649–55). Commentary: O. W. Garrigan, “Monogenism,” New Catholic Encyclopedia, 9:1063–64; Karl Rahner, S.J., “Evolution and Original Sin,” in The Evolving World and Theology, Concilium, 26, ed. Johannes Metz (New York: Paulist Press, 1967), 61–73. Dhanis and Visser, “The Supplement to ‘A New Catechism,’ ” 534–37, offer a speculative account similar to mine which renders the Church’s essential teaching on original sin and polygenism compatible. The teaching of Paul VI on polygenism ought not to be overstated; see Pozo, op. cit., 108–12.