Hominins, Apes, and the Imago Dei

The Swedish naturalist and botanist Carl Linnaeus caused a storm of controversy in the eighteenth century by classifying homo sapiens in the same genus (homo) as the recently discovered orangutan and by placing the genus homo within the order of primates. Linnaeus did not deny the unique dignity of human beings. He did, however, regard it as a matter for religion, not the naturalist whose method of classification—as Linnaeus practiced it—was based primarily upon similarities and differences in structural morphology. Calling it a “humiliating truth for humans,” the preeminent French natural historian, Georges-Louis Leclerc de Buffon, saw Linnaeus’s taxonomy as dangerously blurring the lines between apes and humans.

According to Buffon, morphological resemblances are not as important as are capacities such as reason or language. If we focus instead on the latter, then the morphological resemblances indicate only, in Buffon’s striking language, that the orangutan is “a pure animal, wearing a human mask.”[1] Language (or reason) renders us different in kind (or qualitatively different) from all other living beings. Such human exceptionalism found its greatest scientific challenge in the nineteenth century with the publication of Darwin’s Origin of Species in 1859 and his The Descent of Man in 1871. Ending his silence on human evolution in the latter text, Darwin famously argued for a difference in degree between humans and the other “higher” animals: “the difference in mind between man and the higher animals, great as it is, is certainly one of degree and not of kind.”[2]

We now, of course, have far more knowledge about human origins and our evolutionary relation to other species than Linnaeus, Buffon, and even Darwin possessed. But the issue of whether there is a difference in kind or degree between ourselves and other species continues to be fraught with scientific, political, ethical, economic, and religious controversy.[3] In fact—and as will be discussed in more detail below—the issue has become even more complex given the increased knowledge about the multiple extinct hominin species that we have gained over the past century or so. Most importantly for our purposes here, the claim that there is a difference in kind has long been central to what we may call the “capacities approach” to the imago Dei within Christian theology. Stated in its classical formulation, our possession of reason and will renders us different in kind from other animals and, in turn, renders us in the imago Dei. In Aquinas’s terse formulation: “things that do not have an intellect are not made in the image of God.”[4] For this capacities approach, clarifying the differences between humans and non-humans is intrinsic to its account of the imago Dei. In other words, it operates in an interspecies-comparative framework.

An increasing number of scholars within the humanities and sciences have, however, argued that it is no longer possible to uphold a difference in kind. According to the primatologist Frans de Waal, the belief in a difference in kind perpetuates because we have been habituated into the misguided practice of anthropodenial—that is, the rejection of human-like traits in other animals.[5] Indeed, for many, this practice implicates us in an anthropocentric-humanist tradition whose fruits have been ethically and ecologically catastrophic.[6]

Such claims—as well as developments within theology to be touched on at the end of this essay—cast a shadow of suspicion over the capacities approach to the imago Dei. But it seems to me that, while dismissals of the “difference in kind thesis” (DKT from now on), are quite common in both scholarly and non-scholarly works alike, such dismissals often operate without an adequate articulation of what “difference in kind” might actually mean or entail. In light of this, I want to explore the following question: what exactly does it mean to claim that human beings are different in kind from other animals and not simply different in degree? As I will suggest, there are different takes on DKT, what I call here the weak and strong versions. To be clear, it is not my intention to defend DKT. I only offer some clarifications concerning what these versions might entail and what a defense of them might look like for those who are so inclined. Having done so, I will dwell a bit in the conclusion upon what import any of this might have for those who adhere to the capacities approach to the imago Dei.

Challenges to the Difference in Kind Thesis

DKT faces two primary and interrelated challenges. The first we may call the Darwinian challenge. This challenge stems from the axiom in evolutionary theory that all evolutionarily relevant changes are incremental. With the combination of Darwin’s account of natural selection and the new science of genetics in the twentieth century, evolutionarily relevant changes came to be seen as only those that can be passed on genetically. These genetic changes are always incremental and, moreover, random insofar as they are not teleologically ordered toward a beneficial outcome for the organism.

For this to work as a challenge to DKT, the assumption must be that incremental changes are incompatible with there being differences in kind between species. By itself, the challenge amounts to very little. It is difficult to maintain that there is only a difference in degree between, say, an elephant and the earliest vertebrates living some 500 million years ago. An elephant is not simply more of the same as these earliest fish-like vertebrates. Both are, however, part of the same evolutionary process whose changes have been incremental. Genuine novelty can and does emerge within the evolutionary process where changes are incremental.

Already here the reader might note the ambiguity surrounding the phrases “difference in degree” and “difference in kind.” By “difference in kind,” do we mean something like “genuinely new”? In what sense exactly? Each species can be said to be genuinely new. But it does not seem correct to speak about every species as being different in kind from other species, especially when we are talking about species in the same evolutionary lineages. What about “difference in degree”? Does it mean that there are similarities? Similarities in what sense exactly? After all, an elephant is in certain ways similar to the earliest vertebrates.

Darwin is of some help at this point. Following his own logic in The Descent of Man, we might say that difference in degree is not just a matter of similarity but of a causal relation to a particular evolutionary lineage. As Darwin argued, the emergence of human morality—which he considered the most distinctively human characteristic—can be explained in purely naturalistic terms. We need only assume that our ancestors lived in highly social groups, had strong social instincts, and were subject to group selection. It is then possible to give an evolutionary-causal account of how human morality—or at least what Darwin understands by this—gradually evolved from non-human ancestors.

The Darwinian challenge can therefore be reframed in the following manner: there is an evolutionary explanation of the distinctively human capacities according to which they evolve gradually within a specific evolutionary lineage. There is no need to posit, say, a special divine act or something like an immaterial soul in order to explain how we became human.

This brings us to the second interrelated challenge to DKT—what I call the ethological-paleoanthropological challenge. The gist of this challenge is the following: a wealth of data has emerged from comparative ethology and paleoanthropology over the past few decades which demonstrates that other great apes and certain extinct species in our genus homo (e.g., homo habilis, homo neanderthalenis, homo erectus, and so forth) are/were capable of types of behavior long thought of as belonging solely to the human being. To name but a few: tool-use, foresight, culture, deceit, theory of mind, organized hunting, shelter construction, burial practices, and morality.[7] This second challenge to DKT therefore amounts to the claim that the presence of such capacities in certain other species to which we are closely related (evolutionarily speaking)—i.e., the great apes and the other extinct species in the genus homo—indicates that there is only a difference in degree between ourselves and these specific species. Given what we now know about the capacities of certain other species, we can now provide an evolutionary-causal account of how we got from non-humans to humans with even more confidence than Darwin could.

Two Versions of the Difference in Kind Thesis

Responding to these challenges requires making clearer what exactly such a defender has in mind when claiming that there is a “difference in kind” between humans and other animals. As I suggest here, we can make a distinction between a weak and strong version of DKT, the former of which is relatively uncontroversial and is in fact a position held by many scientists. The strong version is more controversial and is—I believe—what most have in mind with DKT.

The Weak Version

Let us begin with the less controversial weak version. The first thing to note is that, despite the regular publication of (often bestselling) books that emphatically assert our fundamental “ape-ness” (e.g., The Naked Ape, The Third Chimpanzee), claims about human distinctiveness in relation to the other great apes are in fact widespread in the scientific literature. As the anthropologist Robin Dunbar writes, “It is surely obvious to everyone that we are not ‘just great apes.’”[8] To offer but two examples: first, the discipline of cultural anthropology established itself upon a sharp divide between the symbolic human domain and the non-symbolic domain of the great apes.[9] Although this sharp divide is increasingly challenged within anthropology, the capacity for symbolism is still considered by many anthropologists to be distinctively human.[10]

Second and more recently, the extensively researched work of the comparative psychologist Michael Tomasello has demonstrated that humans possess a specific kind of intentionality—what he calls joint intentionality—that other apes lack. Joint (or “we”) intentionality—i.e., the ability to understand another as an intentional agent with whom I can share a goal and who can adopt a specific role in pursuit of it—is the key cognitive capacity for understanding the evolution of our genus homo. It undergirds the unique forms of collaborative, cultural, and moral activity that we do not find among the other great apes.[11]

Much of this literature can ground what I am calling the weak version of DKT. According to this version, humans are different in kind from the other great apes (and other mammals) in the following sense: despite our being primates and our sharing many morphological and behavioral traits with other great apes, humans are also members of a different evolutionary group (hominin) that originated some six to seven million years ago and that—depending on the authority being consulted—includes the genera of Homo, Australopithecus, and Paranthropus. We possess distinctive characteristics that emerged during the evolutionary history of this specific hominin lineage, both prior to and after the emergence of our own genus (homo) roughly two to three million years ago. How exactly these distinctive characteristics are defined and when they are said to have first emerged may differ among scholars, but what is shared is the claim that humans are not simply “more great ape.” We belong to a distinct group (hominin) and genus (homo) in which—for whatever reason—specific traits developed that are not possessed by the great apes. A Planet of the Apes scenario where the great apes are envisioned as being on the verge of attaining human modes of cognition and behavior is therefore misguided.

By focusing on our evolutionary relation to the other great apes, this weak version of DKT gives some specific content to “difference in kind.” It is, however, uncontroversial within the scientific community. It is also not uncommon among philosophical treatments of human distinctiveness, many of which focus on how language—as distinct from the expressive signals of other animals—renders distinct our mode of being in the world compared to other apes.[12] This weak version also borders on triviality, since it entails that all other living beings are different in kind from those they do not share a specific evolutionary lineage with. Human beings are therefore nothing special in this weak version of DKT.

The Strong Version

This weak version is not what many have in mind when claiming that humans are different in kind from other animals. Usually intended is what I call the strong version of DKT. In light of what we now know about other species in the genus homo, this version can be characterized as consisting of two claims: first, that, when it comes to behavioral and cognitive capacities, there is a difference in kind between not just ourselves and the other great apes but also other species in the genus homo.

Second, that homo sapiens represents something like a breakthrough to a new ontological domain (for lack of a better phrase). The difference between human beings and all other animals is framed here as akin to the difference between the plant domain and the animal domain. In more classical Aristotelian terminology that has been so influential on Catholic understandings of human nature, human beings alone have a rational soul. Other living beings possess only vegetative and/or sensible souls. In more recent metaphysical language articulated by, for instance, Max Scheler, the human being represents a breakthrough to the realm of “spirit” (Geist), while all other living beings remain in the realm of “life” (Leben).[13] Those who uphold this position can explain this breakthrough by means of either a natural-evolutionary process or special divine intervention.

These are more controversial claims. The first claim is, however, not in fact foreign to the scientific community. It is not possible to go back in time and see exactly what the other species in our genus were like. For those of a more speculatively sober disposition, this might rule out the possibility of any defense of the strong version of DKT. But perhaps this is an overly restrictive position on what we can or cannot say about these species. Based upon archaeological evidence, many paleoanthropologists do make inferences about the social lives and cognitive capacities of extinct species in the genus homo. Tool creation, for instance, is present in other species in the genus homo, but we find that some later tools are more complex and perhaps even give evidence of the utilization of aesthetic criteria in their construction. For some at least, this suggests the presence of different cognitive capacities in the species responsible for the more complex tools.

Furthermore (and as noted earlier), it is also a common position among anthropologists that symbolism is a distinctive mark of our own species (homo sapiens) who—genetically and anatomically speaking at least—emerges on the evolutionary scene roughly 300,000-150,000 years ago. Examples of early evidence of symbolism include bead technology and engraved objects. By 50,000 years ago, we find in the archaeological record what may be called a “symbolic (or ‘cultural’) explosion,” evidenced by, for instance, cave paintings and stone or wood figurines.[14] Moreover, strong cases have been made that language and symbolism co-evolved. This is, of course, a philosophical matter, since there is no way to go back in time to prove this. Nonetheless, if it is the case, then it suggests that we are the only species with language.[15]

Perhaps a defender of the hard version of DKT could make his or her stand here. That is, the defender might assert that, in relation to the other species in the genus homo, homo sapiens as a symbolic-linguistic species is something different in kind. To borrow from Ernst Cassirer’s formulation, homo sapiens alone is homo symbolicus.[16]

This position is not without its scientific advocates. It faces difficulties, however. For instance, the archaeological record is imperfect and ambiguous: imperfect in the sense that evidence of more sophisticated symbolism in other species may simply be lost to us; ambiguous in the sense that, depending on what one counts as “symbolic,” there is evidence of symbolic-like behavior going back roughly 400,000 years ago.[17] What are we to make of this deep history? Older indications of symbolism might not be as elaborate as, say, the cave paintings in the Chauvet Cave in France, but the more sophisticated indications of symbolism do not arrive de novo. The presence of symbolism does, moreover, not by itself indicate qualitatively different innate cognitive capacities.

This falls prey to what Kim Sterelny calls the “simple reflection model”—that is, an assumption that differences in cultural expressions in the archaeological record directly reflect differences in intrinsic cognitive capacities.[18] This is not always the case, however. Certain cognitive capacities (e.g., doing calculus) exist only in environments that support them; they do not say anything about innate cognitive capacities. Symbolism in the archaeological record therefore need not indicate the presence of qualitatively new innate cognitive capacities. Finally, other species in the genus homo must have possessed at least proto-linguistic communicative capacities that go beyond what we find in the great apes and other extant mammals. We can, of course, only conjecture, but these would have been bodily-gestural systems (akin to sign language) or spoken communicative systems that were more basic than our own linguistic systems. Either way, the point here is that these proto-linguistic communicative systems would not have been equivalent to the communicative systems that we find in, say, the great apes. Whatever they were like, it is much harder to draw a sharp divide between these proto-languages and human language.

Note that these considerations create problems for the second claim of the hard version of DKT—namely, that homo sapiens represents something ontologically new, indeed, something that might even require a special divine act in order to explain. But what exactly constitutes the ontological novelty, especially when we are viewing ourselves in relation to other species in our own genus? The boundaries between species is here highly porous. And for those who might want to resist a purely natural-evolutionary explanation of this breakthrough, why exactly does such an explanation not suffice in light of the clear continuities between ourselves and other species in the genus homo?

We might be tempted at this stage to say that a claim about an ontological difference is a matter of metaphysics or theology alone. This is correct to some degree, but it is also not quite true to the spirit of the harder versions of DKT as represented by the likes of Aristotle and Scheler, both of whom hold themselves accountable to the empirical data. In Scheler’s case (and to his credit), he developed his account of Geist in close dialogue with the latest studies on animal behavior in the early twentieth century. In light of this material, Scheler was very generous with what he grants certain other animals (e.g., chimpanzees) in terms of their capacities—for instance, that they exhibit practical intelligence (i.e., do not just act out of innate instinct), have proto-concepts, and make genuine choices.

The new data on animal behavior indicate to Scheler that what is distinctively human is not to be located in the practical domain and the mode of means-ends practical reasoning (Intelligenz) that governs this domain. Intelligenz is a mode of reasoning that we share with other animals. Rather (and here he follows Aristotle closely), what is distinctively human is the capacity to suspend our practical orientation toward the world and, corresponding with this, the capacity to grasp universals and attain knowledge of essences (or “metaphysical knowledge”). For Scheler, this represents a cognitive revolution that, so to speak, lifts the human being above (but not totally out of) the domain of (animal) “life.”

There is much in such accounts that remains insightful. The problem here, however, is that Scheler (and of course Aristotle) does not focus on the other species within the genus homo. The hard version of DKT often feels more intuitively compelling because we are thinking of ourselves in relation to the other extant animals (normally the chimpanzee). But things become far more complicated when we take into consideration the extinct species within our genus. It is difficult to imagine a creature who is, say, controlling fire, making tools and shelters, living in intensely social groups with a proto-language, and burying its dead as having merely animal reason (Intelligenz) and, indeed, as not having some system of human-like morality and conception of God (or gods). It seems fair to say that the classical philosophical and theological accounts of human distinctiveness are not adequate enough when it comes to dealing with the other species within the genus homo. Doing so requires the development of new categories and more fine-grained conceptual distinctions than what we find in classical expressions of the hard version.

The Imago Dei and the Future of Theological Anthropology

Let us return at this point to the theological issue at stake here—namely, the capacities approach to the imago Dei. What importance do the above considerations have for the capacities approach that—historically at least—has rested upon a hard version of DKT? There are perhaps four possible tactics with which to deal with the issues that have been raised here:

1. First, double down on the hard version of DKT. It is indeed defensible, but—as suggested above—it requires more careful work than what we find in the classical theological and philosophical accounts of human distinctiveness. Alternatively, one justifies the hard version solely upon, say, scriptural revelation.

2. Second, drop the hard version and claim that a difference in degree in relation to other species in the genus homo is all that is needed in order to limit the imago Dei to the human being. Those who adopt this tactic could perhaps remain agnostic on the question of what exactly demarcates the different degrees. Otherwise, defending this position would require some nuanced work on what exactly demarcates the different degrees and why another species that, say, buries its dead, has culture, uses tools, and so forth has not crossed the threshold that is needed in order to be in the imago Dei.

3. Third, extend the imago Dei to certain (or all?) other species in the genus homo. There is nothing intrinsically contradictory here. However, putting aside the difficulty of reconciling it with both scripture and tradition, the thought of multiple species in the imago Dei going extinct is an interesting challenge.

4. Finally, dismiss the capacities approach to the imago Dei, thereby rendering the data of no real significance for theological anthropology. To do so would be to move in the direction of developments in theological anthropology in the past few decades. Rejecting the capacities approach, many contemporary accounts of the imago Dei focus instead on, for instance, relationality, function, or Christology. Furthermore, many theologians have proposed that a biblically based approach to the image of God does not require an account of distinctively human capacities. Genesis 2:7, for instance, does not say anything about human reason or will. The breath of life that God breathes into Adam is not a special human soul but the same breath breathed into all other living beings. The New Testament places its emphasis on Jesus as the image and likeness of God and our transformation into his image. Contemporary theologians have also argued that the capacities approach creates problems for people with, say, cognitive disabilities. Do they image God in a lesser manner? Are they closer to other animals? Finally, some theologians argue that evolutionary theory has rendered the notion of an “essence” highly problematic and that the capacities approach presumes that such neatly defined essences exist.

For these types of reasons, many contemporary theological accounts of the imago Dei have critiqued and moved away from the classical capacities approach.[19] This has led to an enrichment of theological anthropology in multiple ways. But let me conclude here with this final—albeit underdeveloped—thought: perhaps this shift has come with a certain loss—namely, a loss of the consideration of animals and their capacities as an intrinsic part of theological anthropology? As indicated earlier, the capacities approach is interspecies-comparative in methodology and so always has other animals in its purview. What theologians who follow the capacities approach say about other animals may, of course, be superficial or mistaken, but this is not always the case. Here I think, for instance, of Aquinas’s subtle treatment of the estimative power in (certain) other animals and its equivalent in the human soul, namely, the cogitative power.[20] Perhaps one way to resist the habit of anthropodenial and to retrieve attention to other animals as an intrinsic part of theological anthropology would, then, be to re-adopt and reform the capacities approach to the imago Dei?[21]