When I joined the Human Distinctiveness Research Project this summer, I found the Smithsonian’s interactive human evolution timeline to be a particularly helpful resource. The website locates early hominin species – complete with vivid artistic renderings – in the deep time of evolutionary history. It also records major human milestones, like the use of tools and fire, and important paleoanthropological discoveries.
One fascinating feature of the timeline is the visual juxtaposition of hominin evolution with climate fluctuation. As the graphic illustrates, changes in the earth’s climate have increased dramatically in the last six million years, and many of the most significant hominin adaptations coincided with periods of greatest climate fluctuation. Paleoanthropologist Rick Potts, curator of the Smithsonian’s human origins exhibit, argues that climate fluctuations have not simply been a catalyst for human evolution, but have also selected for plasticity as an adaptive strategy. Generally speaking, plasticity is a relatively common trait. Many organisms are capable of reacting to changes in their environment in order to aid survival and reproduction. Humans, however, take this phenotypic plasticity to a new level. Depending on environmental cues such as available nutrition, humans can grow to different sizes and reach reproductive maturity at different ages. Human lung capacity can develop according the individual’s altitude and oxygen availability. Plasticity is not merely physical, however. Distinctive human sociality, culture, and lifespan enable behavioral plasticity as well. Features like an extended childhood and hypersociality, for example, have facilitated learning. Humans are capable of imagining new ways to live in diverse environments and passing on successful strategies to future generations through social and cultural channels. In the process, we also actively construct our environment to make it more suitable to human life. As a species we are remarkably indeterminate and flexible, and these traits have enabled us to inhabit almost the entire planet.
An indeterminate human nature is also important for many theologians. For Kathryn Tanner in Christ the Key, human plasticity is essential if humanity is to be capable of receiving what it is not, namely the divine nature. More generally, notions of flexibility are presupposed in theological narratives of fall and redemption. It is somewhat central to Christian theology that human nature, as we encounter it right now, is not all that humans are capable of becoming. As the author of the letter of 1 John put it, “what we will be has not yet been revealed” (1 John 3:2). For theology, an indeterminate nature speaks to the human possibility for encounter with God and transformation in and through that encounter.
While the idea of a flexible nature is intriguingly present in both theological and evolutionary accounts of the human, we should be wary of overly facile identifications between the two. Does human plasticity actually mean the same thing in theology and anthropology? On the one hand, the conceptual overlap suggests that both disciplines can share a healthy skepticism of human essentialism. With respect to many human characteristics, behaviors, or social structures, particularly those that are destructive, we need not conclude that our apparent “nature” is unalterable. While such points of agreement are valuable, considering points of divergence between evolutionary and theological notions of human plasticity can also allow for fruitful interdisciplinary conversation. For example, theological analysis of a flexible human nature is not committed to any particular understanding of the mechanisms of personal or social change. From an evolutionary perspective, however, plasticity is inseparable from embodiment. It is enabled by very specific bodily and biological mechanisms. Such awareness can provide a vivid reminder to theology that discussion of God’s redemption of humanity might best proceed by attending to these bodily realities rather than attempting to sidestep them.
Can a theological perspective on human flexibility also be a fruitful source of reflection for scientists? Another major difference between the disciplines is the role (or lack thereof) of teleology. For Christian theology, a flexible human nature has the goal of imaging God, whereas in evolutionary accounts, human flexibility has no natural teleology. And yet . . . the distinctive way that humans engage their environment, consciously altering it, and charting new paths, raises the question of teleology in a new way. If we as a species are capable of not only constructing our niche (as many species do,) but doing so intentionally, with thought, imagination, and deliberation, can we avoid conversation about human intentions and goals? Are not these now part of the evolutionary story? And if this is the case, then it seems, as some anthropologists are already suggesting, that scholars of human evolution cannot dispense with a careful consideration of how humans think about and enact these ends – through religious belief, ritual, and philosophical reflection.