The possibility of intelligent life existing on other planets raises many interesting theological questions. Would these extraterrestrial beings be religious? Would they have been created in a state of Original Justice and then been infected with Original Sin? And if they were in need of redemption, would God become incarnate as one of their own to redeem them, or would God’s incarnation as Jesus Christ be sufficient to redeem them? These are among many questions that the Anglican theologian Andrew Davison considers in this book. In addressing these questions, Davison draws much inspiration from St Thomas Aquinas. Davison’s Thomistic approach is summarized in a quotation by Eric Mascall: ‘I do not consider “Thomas has spoken, the case is closed” as the last judgement to be passed on any theological problem; my approach might be summed up in the words “Thomas has spoken, the matter is begun”’. Davison is, therefore, not afraid to dissent from opinions that many Thomists would want to defend, but, nevertheless, by using Thomas as a starting point, Davison’s speculation on the existence of intelligent alien life provides an interesting context in which to engage with Thomas’s theology and philosophy. So even if one is highly skeptical about whether intelligent alien life exists, Davison’s book should still be of great interest to Thomists.

Davison begins by making a case for why we should take the possibility of intelligent alien life very seriously. Given the vast size of the universe, it would be surprising if there was not any life outside our solar system. In our galaxy alone, it is estimated that there are around two billion earth-like planets orbiting suns like ours, and our galaxy is one of approximately two hundred billion galaxies. So if there is some natural process by which life comes into existence when the conditions are right (an idea that many Thomists would be sympathetic to), then the chances of there being extraterrestrial life would seem highly probable.

Nevertheless, from a Thomistic perspective, it is still not obvious that one can conclude from this argument that intelligent extraterrestrial life is likely to exist as Davison supposes. As Davison notes later on in his book, Thomas thought that each human soul was created separately and individually by God rather than emerging in the natural process of things. Therefore, even if the secondary causes involved in the genesis of life on our own planet are at play on other planets in bringing life into existence, we would still have absolutely no idea whether God would choose to create creatures with rational souls on other planets. What we do know is that of the 7.7 million species of animals that have ever lived on the planet earth, only one species, namely our own (and possibly the species of our closest ancestors) can form the kind of linguistic communities in which rationality can express itself. Therefore, even though the current state of scientific knowledge suggests that it is very likely that there are species of life on other planets in the universe, we are still none the wiser as to how likely rationality exists among these species.

But if there were rational species on other planets, this does not necessarily pose serious challenges to the religious believer. According to Davison, non-religious people seem to overestimate the challenges that religious people would experience if faced with evidence of intelligent alien life. For example, it would be a mistake to suppose that such evidence would be a fundamental blow to Christian belief in humanity’s specialness. Similar erroneous claims have been made with respect to the discovery that the earth is not at the centre of the cosmos, or that human beings evolved from apes.

The fact is, Christianity does not teach that human beings are at the pinnacle of God’s creation. Rather, human beings are the lowest of God’s creatures that possess a rational nature. There is a whole angelic hierarchy of superintelligent beings above us. Davison devotes a chapter to angels in which he argues that the discovery of superintelligent life would not set a theological precedent, since the existence of such life has never been doubted in the Judeo-Christian tradition. Davison also notes that until the modern era, being at the centre of the cosmos was not thought to be a sign of human specialness. Rather, the centre was thought to be the least exalted of places – the ‘rubbish dump of the cosmos’.

There are, however, other challenges that the possibility of extraterrestrial life would raise, but the difficulties that Thomas had with extraterrestrial life resulted more from his erroneous scientific beliefs than from Christian theology. For instance, Thomas discounted the existence of other worlds capable of supporting life because he could not see how such a possibility was compatible with an Aristotelian picture of the cosmos with its concentric celestial spheres, and the belief that God in His ordaining wisdom had created the universe as a united whole of interrelated parts. But once one rejects this Aristotelian picture of the cosmos, it is not obvious that the existence of other worlds would pose a threat to God’s ordaining wisdom.

Another question that Davison takes very seriously is whether the Son of God might have chosen to become incarnate as an alien. Davison favours a Scotist-inspired theory in which the son of God would assume an alien nature for every intelligent alien species that existed, regardless of whether members of this species had sinned and were in need of redemption. Davison argues that this hypothesis need not contradict the content of Christian revelation. This question is discussed in Chalcedonian terms: Jesus Christ is the Son of God, He is one person with two natures, a divine nature and a human nature, and Jesus Christ became incarnate in our human nature in order to redeem our nature.

But although Chalcedon states that God became incarnate in one human nature, according to Davison, this does not rule out the possibility that God could become incarnate in other natures as well. In fact, as Davison points out, St Thomas argued that multiple incarnations could be possible, so maybe God could become incarnate in some alien nature in addition to our own in order to redeem it. According to Davison, the fact that there is no mention of multiple incarnations in scripture is not a sufficient reason to discount this idea, since the revelation of scripture is primarily concerned with human salvation, so other incarnations would not be relevant.

However, although the question of whether God might have become incarnate as an alien may seem irrelevant to human redemption given our current state of knowledge, that could all change if we were ever to encounter such aliens. If these aliens were rational animals, then they would be essentially human according to the Aristotelian definition of the human species. The acts of redemption of an alien Messiah would then seem very relevant to human redemption. Davison would deny this conclusion by rejecting the suggestion that intelligent aliens could be considered as belonging to the human species. But I think Davison’s counter argument would have to be much more compelling in order to convince me that multiple incarnations did not contradict divine revelation.

Another reason for being rather dubious about multiple incarnations is what this would mean for Mariology. If there are many incarnations, then presumably, there would be many mothers of God. Such a prospect seems to reduce the cosmic significance of the Blessed Virgin Mary. But Mary’s title as Queen of Heaven suggests that she has the greatest cosmic significance. Although her human nature is inferior to that of angelic natures, through the fullness of God’s grace, she has been raised up to be queen over the angels. Davison is far too ready to dismiss Catholic Mariology in his astrobiological speculations. Contra Davison, I don’t think we do well to set the language of Mary’s queenship aside.

Despite these criticisms, Davison’s book is a very scholarly engagement with St Thomas. Even if one is not convinced by all of Davison’s arguments, he asks the kinds of questions we should be asking about the theological implications of the existence of intelligent alien life.