Truth can't contradict truth. Science can't contradict divine revelation - and divine revelation can't possibly contradict science.

Longtime readers will recall that I there rehearsed a proposal developed by Mike Flynn and Kenneth Kemp to the effect that we need to distinguish the notion of a creature which is human in a strict metaphysical sense from that of a creature which is “human” merely in a looser, purely physiological sense. The latter sort of creature would be more or less just like us in its bodily attributes but would lack our intellectual powers, which are incorporeal. In short, it would lack a human soul. Hence, though genetically it would appear human, it would not be a rational animal and thus not be human in the strict metaphysical sense. Now, this physiologically “human” but non-rational sort of creature is essentially what Pius XII, John Paul II, and the philosophers and theologians quoted above have in mind when they speak of a scenario in which the human body arises via evolutionary processes.

The Flynn-Kemp proposal is this. Suppose evolutionary processes gave rise to a population of several thousand creatures of this non-rational but genetically and physiologically “human” sort. Suppose further that God infused rational souls into two of these creatures, thereby giving them our distinctive intellectual and volitional powers and making them truly human. Call this pair “Adam” and “Eve.” Adam and Eve have descendents, and God infuses into each of them rational souls of their own, so that they too are human in the strict metaphysical sense. Suppose that some of these descendents interbreed with creatures of the non-rational but genetically and physiologically “human” sort. The offspring that result would also have rational souls since they have Adam and Eve as ancestors (even if they also have non-rational creatures as ancestors). This interbreeding carries on for some time, but eventually the population of non-rational but genetically and physiologically “human” creatures dies out, leaving only those creatures who are human in the strict metaphysical sense.

On this scenario, the modern human population has the genes it does because it is descended from this group of several thousand individuals, initially only two of whom had rational or human souls. But only those later individuals who had this pair among their ancestors (even if they also had as ancestors members of the original group which did not have human souls) have descendents living today. In that sense, every modern human is both descended from an original population of several thousand and from an original pair. There is no contradiction, because the claim that modern humans are descended from an original pair does not entail that they received all their genes from that pair alone.

Of course, this is speculative. No one is claiming to know that this is actually what happened, or that Catholic teaching requires this specific scenario. The point is just that it shows, in a way consistent with what Catholic orthodoxy and Thomistic philosophy allow vis-à-vis evolution, that the genetic evidence is not in fact in conflict with the doctrine of original sin. Naturally other Catholics and Thomists might reasonably disagree with it.

Back in 2011, when Flynn, Kemp, and I first wrote on this topic and the Flynn-Kemp proposal was getting a lot of attention in the blogosphere, some people objected that interbreeding of the sort in question amounted to bestiality. But of course, no one is suggesting that we should approve of the interbreeding in question. The claim is merely that in fact it may have happened, even if this was contrary to natural and divine law (just as Cain killed Abel even though this was contrary to the natural law, and just as Adam and Eve ate of the fruit of the Tree of Knowledge, even though this was contrary to divine law).

Nor would it be a good objection to suggest that no one would plausibly have been tempted to engage in such interbreeding. After all, the scenario in question would hardly be comparable to that of the average member of contemporary civilization being tempted to have sex with an ape, which would of course not be psychologically plausible. For one thing, the sub-rational but genetically and physiologically “human” creatures in question would not be like apes, or indeed like any of the non-human animals with which we are familiar. They would more or less look like us. Furthermore, they would even act like us to some degree. As I noted in a recent post, though a purely material system could never in principle exhibit true rationality, it might simulate it to a significant extent (just as if you add enough sides to a polygon you will get something that looks like a circle even though it could not really be a circle). The sub-rational creatures in question would have been sphexish, but a sufficiently complex sphexish creature might seem not to be on a superficial examination. Recall Popper’s distinction between four functions of language: expressive, signaling, descriptive, and argumentative. The sub-rational creatures in question would not be capable of the latter two functions (which presuppose rationality) but they might have exhibited very sophisticated versions of the first two functions.

Meanwhile, the earliest true humans would not have had anything like the modern civilizational accompaniments of sexual activity, especially given the effects of original sin. Obviously it would be absurd to think of their liaisons as involving smooth techniques of romantic seduction, contemporary standards of personal hygiene, etc. So, the cultural “distance” between primitive true human beings and the sub-rational creatures in question need not have been so great as to make the sexual temptation psychologically implausible. It might have been comparable to a very uncultured and unsophisticated person taking sexual advantage of an even more unsophisticated and indeed very stupid person. Not that it was exactly like that, since even a stupid person is still intelligent in the strict sense, whereas the sub-rational creatures in question wouldn’t even rise to the level of stupidity. The point is that the situation could have been psychologically close enough to that for the temptation to be real. (As I indicated, partly in jest, in one of the earlier posts, we might think on the model of Charlton Heston’s character “Taylor” being attracted to the Linda Harrison character “Nova” in Planet of the Apes -- not that the early sub-rational creatures would have looked quite that good!)

As for my view as an experimental chemist, the cell is an incredibly complex design, to suggest it formed by chance shows a lack of understanding about the complexity of the chemistry involved in its workings.