In a 1996 address to the Pontifical Academy of Sciences entitled Truth Cannot Contradict Truth, Pope St. John Paul II said “the Church takes a direct interest in the question of evolution, because it touches on the conception of man, whom Revelation tells us is created in the image and likeness of God.”  Rather than dismissing evolution as somehow anti-Christian, the Pontiff embraced it as “more than an hypothesis.”  To be clear, the Holy Father never actually endorsed a specific theory of evolution, but instead says it is “more accurate to speak of the theories of evolution” because many of the so-called theories of evolution are wrong because they rest on a flawed metaphysical system.  This shows how the two areas, philosophical and scientific, must remain in dialogue with each other if we are to find the truth about man’s origins.  If the scientific community will turn its evolutionary glance towards the most highly evolved Ox, St. Thomas Aquinas, then he can point them only in the direction of those theories that rest on a firm metaphysical foundation.

Mostly as a matter of polemics, there is a false dichotomy that is often set up between creation and evolution.  But the two need not be mutually exclusive.  All too often a belief in creation is often lumped together with what is commonly referred to in Christian fundamentalist circles as “creationism.”  Creationism starts with the view that the six days of creation are meant to be taken literally and then posits that the earth is about six thousand years old.  Of course when science examines the question of the age of the earth, it comes up with a much larger number.  Since “truth cannot contradict truth” it is the scientific that wins out because it seems to be more in line with human reason.  What starts out as a defense of the Christian faith ends up making it look absurd.  St. Thomas warns about attempting to invoke arguments like these for “the Christian faith that are ridiculous because they are in obvious contradiction to reason” and only serve to provoke the irrisio infedelium, the mockery of unbelievers.

Along the same lines, a second dichotomy is set up in that creation means that the Creator had to make the world perfect.  If it is not perfect, then it must be one based solely on chance.  St. Thomas would reject both viewpoints.  In response to the latter, St. Thomas himself addressed the question as to whether chance could govern the world. St. Thomas countered the neo-Darwinists’ of his time called the “atomists” who saw the variety in the world as the result of a random interplay of matter by arguing that variety is precisely the intention of the Creator.  God “brought forth many and diverse creatures, that what was wanting to one in the representation of the divine goodness might be supplied by another. For goodness, which in God is simple and uniform, in creatures is manifold and divided” (ST, I, q.47 a.1).  In fact, if the purpose of creation is to show forth the Creator, then this diversity would be exactly as one would expect.  Just as no work of art can express or exhaust everything an artist has to say because it is always limited by its material framework, likewise no creature can entirely express the Creator.

In response to those who say the existence of a Creator necessitates that the world be perfect, St. Thomas would say that the world, because it is not an end in itself, is actually is a state of becoming, rather than already perfected.  In fact while St. Thomas affirms the goodness of everything that exists (this is called ontological goodness), this does not imply that everything is the best that it can possibly be.  In fact he even says that God could have created a better world (ST I, q.25, a.6, ad.1).  While the world may be journeying towards its ultimate purpose, it is not yet there.

It is the philosophical underpinnings of the response to this false dichotomy that gives us a Thomistic launching pad for philosophically valid theories of evolution.  The idea that each goodness is “manifold and divided” and each creature is limited is expressed by St. Thomas in his distinction between essence and existence.  What Aquinas teaches is that everything that exists (while allowing for a possible exception) is constituted by an inner structure of two metaphysical principles.  The first is the act of existence by which the thing is present is the universe of real things.  The second is the manner in which its existence is limited and that is its essence or type of thing.  Think of existence having two dimensions.  The vertical dimension is like a ladder in that the variety of things each have an increasing “amount of existence” that is determined by how much being its particular nature can hold.  There is also a horizontal dimension in which things can share the same nature or essential form and be multiplied because of matter.  Just as essence limits existence, so too matter limits the number of individuals.  So while two rose plants are identical in nature (and therefore being), they do not have the same level of being as say a bear.

Philosophically, St. Thomas would say that there is a dynamic principle that governs the change by relying on the Aristotelian notion of act and potency.  As things change, there must be a principle of continuity that acts as a means for the thing to receive a new mode of being.  This aptitude is its potency or potentiality.  Potency can be either passive which is the capacity to receive some actual perfection from without or active which is the capacity to act from within.  Creatures in essence shape themselves.  They have an active potency or inner force that is governed by their nature that shapes what they become.

It is also necessary to include as foundational the Principle of Sufficient Reason.  The principle of causality, as it is commonly referred to, states that every being that lacks the sufficient reason for its own existence in itself must have an adequate efficient cause. It seems then that the central metaphysical problem related to evolution is how to explain it without violating the Principle of Sufficient Reason, specifically the causal axiom that “no effect can be greater than its cause.”  Drawing upon what was said above about active potencies as the ability to act by some inner power, we can say that two beings already in existing in nature may have the active potentiality to combine with each other under certain conditions to form a new being.  For example, two hydrogen atoms and one oxygen atom, both of which are flammable, combine to form a water molecule which has the opposite property of putting fires out.  This viewpoint may explain evolution in the pre-biological dimension of our world in which all change may be a change in degree.  However this theory cannot explain those changes that require a step up the ladder of being without violating the principle of sufficient reason.

One final principle that needs to be articulated is the distinction between differences in degree and differences in kind.  A difference in kind refers to the fact that there could not possibly an intermediary between the two (called the law of the excluded middle) while a difference in degree admits this possibility.  Two things differ in kind if one possesses a characteristic totally lacked by the other or if one can do something that the other cannot while a difference in degree is a characteristic that one has more of it and the other less.

Any solution to the question of evolution would need to conform to the principle of sufficient reason.  This means that it must present creation as containing some points of discontinuities and cannot be a wholly continuous process that has been set in motion.  Non-living creation shares in existence to a lesser extent than creation that has life.  There is a further division within the realm of living beings.  All living beings have a soul, but they are different in kind and not just degree. These kinds of souls, delineated as vegetative, sensitive and rational, serve as animating principles for living beings.  All living things have vegetative powers in their souls, but only plants have a vegetative soul.  Likewise both man and the animals have sensitive powers in their soul, but only animals have a sensitive soul.  Only man, with reason and will, has a rational soul.  It seems natural to posit that the points of discontinuity would be reflective of these distinctions.  A Thomistic theory of evolution then could be developed by dividing the problem into four distinct areas.

The first would be evolution in the non-living universe from the beginning to the formation of the earth.  In order to satisfy the principle of sufficient reason all that seems to be needed is the infusion of a range of active potentialities (even if they are somehow dormant) in the universe.  This integration would require an Organizing Intelligence but would not require any further special intervention of the Creator (although there is room for such an intervention in theory).

Secondly we could speak of the evolution of plant life.  The principle of sufficient reason requires that an outside source of causality would be needed to move up the ladder of being from non-living to living.  The matter in the plants may have the passive potentiality to receive life, but that life would need to be supplied from an outside source.

Next we could speak of evolution of subhuman animals.  The presence of the sensitive powers must indicate a difference in kind because between the presence of these powers and the lack there are no intermediaries possible.  Therefore this suggests that there is a new level of being here as well.

It should be mentioned that the idea of microevolution within species presents no special philosophical problem because they could be the result of accidental changes with the same nature that produces beings that have only a difference in degree.  Many scientists such as Francis Collins have said that these accidental changes could be brought about by an active potentiality that consists in gene jumping in response to a given environment.  This may in fact become so cumulative that the later entities are no longer able to breed with the earlier and thus a new species is judged.  This however does not imply a qualitatively new level of being.

Finally, we come to the final step and that is the “evolution” of man.  Once again we find that man represents a jump up the ladder of being through the spirituality of the human soul.  The ability to form abstractions is attributed to man along with propositional speech, tool making for future use, and cumulative culture all mark a transcendence of the immediate environment.  These non-material powers cannot be explained by the combination of material causes and in fact would need the intervention of some outside non-material cause.

Notice that throughout the discussion we did not rely on Divine Revelation at all.  This is not because Divine Revelation has nothing useful to say or that we should ignore it.  It was simply beyond the scope of what was being proposed.  Science, philosophy and Divine Revelation are all reliable sources of knowledge and in an ideal world all three should be working in unison to come up with a unified vision of man’s origin.  This essay simply took a bottom up approach that would require no faith on the part of the scientist.  Followed properly, any reasonable person would begin to ask what (or Who) this non-material source might be.  In a future essay we will add the guidelines imposed by Divine Revelation to complete the full picture.