In recent years, there has been much debate among Christian believers how to understand the imago Dei—the image of God in humans—in light of the evidence that humans have evolved from other life forms.1 In this post, I would like to contribute to this ongoing discussion by bringing the insights of the great medieval philosopher and theologian, St. Thomas Aquinas, into conversation with contemporary evolutionary biology.
For St. Thomas, the human person is made in the image and likeness of God in three different ways (cf. Summa Theologiae I.93.4). First, according to the order of nature, the human person is the imago Dei because of his or her ability to know and to love. Second, according to the order of grace, the human person is the imago Dei when he or she knows and loves God. Third, according to the order of glory, the human person is the imago Dei when he or she knows and loves God in heaven as God knows and loves himself. In the end, the Christian life, for St. Thomas, is a life of growing in perfection as God perfects the resemblance of the imago Dei in each one of us that begins in our human nature as rational creatures and ends in our glory as saints who have become partakers of the divine nature (cf. 2 Pet 1:4) and as such, have become like God.
At the heart of St. Thomas’s account of the human person as the imago Dei is his claim that the human person is made in the image of God because of his or her rational nature, i.e., his or her ability to know and to love. This is a profoundly Trinitarian insight because the acts of knowing and of loving are the acts that constitute the very persons of the Triune God (cf. Summa Theologiae I.93.6). In knowing himself, the Father speaks the Word who is his Son. In loving each other, the Father and the Son breathe forth the Holy Spirit.
Note that St. Thomas links God’s knowing with his speaking. This insight is critical and can also be applied to human persons: A rational creature is a linguistic creature, and vice versa, because language presupposes the capacity to know and to love as humans can uniquely do. To locate the evolutionary appearance of the imago Dei in evolutionary history, therefore, I propose that one has to identify that time and that place when anatomically modern humans evolved a capacity for language. It is not enough to equate our species with anatomically modern humans as many theologians do. We are anatomically modern humans who are behaviorally modern as well.
Biologically, this transformation from anatomically modern to behaviorally modern human beings is attributed to the evolution of brain structures that would have facilitated the use of language.2 Geneticists have calculated that it would have taken at most ten genetic mutations to explain the appearance of these capacities.3 Recent studies have uncovered uniquely human versions of genes involved in primate brain function that have been linked to the use of language including human versions of the genes, CNTAP2, ASPM, and MCPH1. Moreover, there is data that suggests that the human versions of these brain-associated genes have played an important role in human evolution because they bear the marks of strong natural selection in our species.
Notably, there is also data that suggests that this critical point in evolutionary history occurred around 100,000 years ago in southern Africa among a group of anatomically modern human beings, when a handful of individuals evolved the neurocognitive capacity for language.
How exactly this happened will always be a matter of speculation. If the biological capacity for language presupposes the acquisition of a package of pro-language mutations in the human genome, as biologists assume, then I can imagine a scenario where two anatomically modern humans, each with a subset of these pro-language genetic mutations, mated and conceived children.
Their children would have inherited the complete package of pro-language genes, bringing together the genetic advantages of each of their parents, and as such, would have acquired a novel capacity for language. They would be the first instances of behaviorally modern human infants surrounded by a tribe of closely related anatomically modern relatives who would not have full language capacity. They would be the first instances of the imago Dei.
Growing up together in the tribe, these infants would have spontaneously developed a new language that only they could speak and understand. A similar phenomenon was observed when fifty or so young deaf children were first brought together at a center for special education in Nicaragua in 1977. Within five years, the deaf children enrolled in this school and another school close by had invented a pidgin-like sign language that in time was taken to a higher level of complexity by the younger students. This more complex sign language is now known as Idioma de Señas de Nicaragua.
When these speaking children attained their maturity, it is likely that these behaviorally modern humans—these “speaking bipeds”—would have preferentially mated with each other because of their shared ability to speak a common language. Their children in turn would not only have inherited the capacity for language but would also have actually learned their mother tongue. Since language is clearly a beneficial trait for the survival of the species, it would not have taken long for these speaking bipeds to dominate and to outcompete their non-speaking anatomically modern relatives. These speaking bipeds would have migrated out of southern Africa and would eventually populate the rest of the continent and the globe.
Let me close by acknowledging that my speculative account remains exactly that, speculative. However, it is a plausible framework within which Christian believers could continue to think about our human origins and history. It is also a framework that can be easily reconciled with the theological datum that human beings are fallen creatures. As I have explained elsewhere, a theological fittingness argument can be made for the historicity of the fall and thus for original sin.4 In that light, it is easy to imagine a scenario where these original speaking bipeds, created in grace, disobeyed God and fell. In time, they and their descendants were redeemed by Jesus Christ, the Savior of the World, so that they may share in the inner life of the Trinity and as images of God in glory.