As a Human Evolutionary Biology (HEB) concentrator, I am honored to be able to use the lens of evolutionary biology to gain insight into the image of God, that is to say, you and me, humans! During my time in Harvard’s HEB department, I have learned through a comparative approach to understanding human biology and behavior. This approach involves studying human behavior in parallel with studying the behavior of other non-human species, especially our closest relatives, the great apes. One of the benefits of this method is that is allows us to determine which human traits are in fact uniquely human, setting us apart from the rest of the animal kingdom. Theologically, this is significant because humans are uniquely made in the image of God in a way that chimps, say, are not. Therefore, it behooves us to know what about us humans is actually distinct from chimps and other non-humans because we can infer that these traits are, in particular, reflective of God in a way that the traits that we share with non-humans are not.
In this article, I will focus on two ways we are unique from non-humans, the cognitive capacity for shared intentionality and in our social structure, and one way in which we are not distinct from non-humans, that is our propensity to inflict violence on one another in various settings. I will use biological data – some with direct citations, some of which I have accrued into my knowledge bank over my last four years at Harvard1 – to support my claims of the uniqueness (or lack thereof) of these human traits. I will ground my discussion of our biology in my interpretation of the theological relevance of these aspects of human behavior and cognition.
Among humans, teaching and learning as a collaborative activity is ubiquitous, and its effect is momentous, including enabling our extensive cultures. The particular fashion, frequency, and flexibility of human teaching and learning depend on the derived cognitive skill of shared intentionality, the ability to knowingly share psychological common ground during collaborative activities (Tomasello and Carpenter, 2007).
While shared intentionality evolved in the hominin lineage since our split from our last common ancestor with chimps and bonobos (LCA), the skill rests on the conserved cognitive foundation of theory of mind. Theory of mind is the ability to make inferences about the mental states of others, such as knowing what a conspecific knows on the basis of what his line of view permits him to see (Call, 2009). Subordinate chimps target food that is hidden from dominants. This is one of many examples indicating their capacity to infer the mental states of others (Hare, 2011). On the basis of parsimony, the LCA likewise possessed basic theory of mind. During human evolution, however, hominins have built on this social cognitive skill and now sport a large repertoire of derived cognitive abilities that we employ regularly in teaching and learning, the most of important of which is shared intentionality.
Juvenile chimps and human infants are both capable of following the gaze of a conspecific and engaging in joint triadic attention, which facilitates learning skills that involve external objects, such as cracking open nuts (Boesch, 1991). Compared to chimps and bonobos, 18-month-old humans spend much more time during the activity staring at the partner’s face rather than the object (Call, 2009). Tomasello and Carpenter (2007) interpret this as evidence that humans, unlike our closest ape relatives, have the derived motivation to demonstrate the shared psychological state of interest in the external object. This desire to share a mental experience motivates the process of teaching and learning itself, above and beyond the desire to achieve an end goal like obtaining a nut. For example, human children playing a game of hide-and-seek will hide an object again after it’s been found just for the sake of looking for it together a second time (Tomasello and Carpenter, 2007). In contrast to chimpanzees, which can emulate behavior but focus on the end goal (usually acquiring food) and skip superfluous steps, human children are invested in showing that they accurately observed and recall all the steps the teacher demonstrated (Tomasello and Carpenter, 2007). This is evidence of yet another way in which shared intentionality plays a key role in distinguishing human social learning from nonhuman social learning.
Teaching is not unique to humans, but we are the only species that regularly uses theory of mind, especially shared intentionality, to teach. Thornton and McAuliffe (2006) argue that meerkats, and probably many other species, teach their young. They define teaching as a modification of behavior only while in the presence of a naïve conspecific that provides no obvious benefit to the actor but accelerates the conspecific’s acquisition of knowledge or skill. Meerkats create opportunities for pups to safely practice hunting scorpions, a dangerous food source, by removing the stingers before giving the live prey to the pups. Teachers initially provide more dead and disabled scorpions but shift over time to providing more intact prey. This accelerates the acquisition of hunting skills at no obvious benefit to the teacher. Unlike in humans, however, there is no evidence that meerkats attribute the mental state of ignorance to pups. Rather, their teaching strategies change in response to the maturing vocal acoustics of pups’ begging calls, an observable action. Thornton and McAuliffe (2006) played audio recordings of older pups in a group with only young pups and vice versa. The teacher meerkats shifted their teaching strategies accordingly even though the actual age and skill level of the pups had not changed. Human teachers, by contrast, can consciously grasp the knowledge level of a particular pupil.
There have been rare instances of chimpanzee mothers at Tai creating opportunities for juveniles to practice cracking nuts with a hammer and anvil (Boesch, 1991)—in other words teaching, according to the definition that Thornton and McAuliffe (2006). Even if chimpanzees are cognitively capable of teaching, they do so very rarely. For example, termite fishing is an important foraging skill for chimpanzees living in Gombe National Park. Juveniles learn to termite fish by observing and emulating their mothers. There is no evidence, however, that mothers go out of their way to actually teach their offspring to termite fish, per se. They tolerate disruptions to their termite fishing by their offspring, but they do not actively facilitate juveniles’ attempts to replicate the behavior (Lonsdorf, 2006). By way of explaining the infrequency of teaching among chimps, I propose that, without shared intentionality, teaching is not a rewarding social experience for chimps as it is for humans. Shared intentionality is what propels humans to communicate purely for the sake of sharing a psychological experience. By age two, humans will gesture to point out interesting sights simply to share the psychological experience of interest (Tomasello and Carpenter, 2007) and engage in games of make-believe for the sake of sharing the same psychological common ground: this banana is not food, but rather a telephone (Leslie, 1987). Likewise, teaching is the transmission of a mental state of knowing.
Moreover, the known cases of nonhuman teaching, such as meerkats hunting scorpions (Thornton and McAuliffe, 2006) and chimps cracking nuts (Boesch, 1991), have occurred in the context of creating opportunities for a juvenile to practice a skill. Humans teach not only skills, but also abstract concepts that derive their existence solely from the minds of other human beings, such as symbols and conceptual models. By definition, the ability and motivation to teach and learn abstract mental states and representations depends on the derived human trait of shared intentionality.
Jesus was a great rabbi. His work on earth was grounded in teaching and learning. This is what he was doing when his mother found him answering questions in riddles (the common practice of the day) at the age of twelve (Lk 2:41-52). Jesus himself says that the reason “why I have come” is to “preach” (Mk 1:38, ESV), that is to teach about the Kingdom of God! Prayer, likewise, is an exercise in shared intentionality; at its best, we are able to have a share in the inner world of God Himself. Some have said that humans invented God as an overzealous application of our evolved mechanism of shared intentionality; I say that God used to the laws of biology to form us through the patient, gradual process of evolution by natural selection into beings with the capacity to attribute causality onto the natural world, in other words, to detect the hand of God working in history.
Beyond its application in teaching and learning, shared intentionality is key to compassion; this is the cognitive capability that allows us to see the world from the perspective of another and be moved by pity to act to alleviate the suffering that we detect through the application of shared intentionality. Jesus is frequently “moved with pity” to heal the sick (Mk 1:41, Mt 14:14, Mt 20:34, Mt 9:36, Mt 6:34) and we, in turn, beg for God’s mercy, implying that God’s capacity for shared intentionality – his ability to detect and respond to our pitiful mental states – is a particularly divine trait. And, indeed, biology tells us that this is, in fact, a uniquely human trait, and therefore reflects God. Naturally, God is much better at this than we are! This shouldn’t be surprising! Perhaps this explains God’s ability to hear silent prayers or His desire to live in close, loving communion with people the rest of us despise.
Without shared intentionality, there would be no instructor and no pupil participating in a joint endeavor. Teaching methods would only change in response to observed behavior, as in the case of meerkats (Thornton and McAuliffe, 2006), rather than address the actual knowledge state of the pupil. Learning through observation and emulation, meanwhile, would occur only incidentally, rather than being the product of an intentional joint activity (Hare, 2011). Without shared intentionality, neither would there be empathy and compassion, mercy and motivation to share common goals. The theological implications of these special human capabilities are hard to miss.
Violence, on the other hand, is not a unique human trait. Although ours is a warrior God, and there are numerous instances of God acting in the context of war in the Old Testament (don’t ask me to provide more detail because I know almost nothing about this!), using the comparative approach to study biology, it is clear that being violent is not the way in which human war images God’s way. Chimpanzees send out war parties to defend their territory. The males of a group even act cooperatively to defend their land. So engaging in violent conflict between warring groups defending resources is not uniquely human. But engaging in risky conflict for the sake of defending someone else is uniquely human; it would never occur to a chimpanzee to do something like this. Additionally, to the extent that just wars actually occur, the ability to engage in just war requires unique human cognitive abilities. According to the Catechism of the Catholic Church article 2309, four conditions must be met in order for a war to be just:
- the damage inflicted by the aggressor on the nation or community of nations must be lasting, grave, and certain;
- all other means of putting an end to it must have been shown to be impractical or ineffective;
- there must be serious prospects of success;
- the use of arms must not produce evils and disorders graver than the evil to be eliminated. The power of modern means of destruction weighs very heavily in evaluating this condition.
Exhausting diplomatic channels of course requires diplomacy, the cornerstone of which is cooperation. Cooperation requires sharing goals and mental states, attempting to see the situation from the perspective of those sitting across the table, and formulate compromises on behalf of the shared desire for peace. The idea of competing chimpanzee groups sitting down to hash out a plan for divvying up limited resources without resorting to violence is, of course, laughable. So war is not uniquely human but just war is uniquely human.
Another common form of violence is rape. Like humans, chimpanzees also rape females (as do subordinate male orangutans and many other non-human species). So we can safely conclude that rape is not part of the suit of traits that sets us apart from other animals and makes us uniquely made in the image of God. Actually, the fact that Mary provided her consent to be impregnated by the Holy Spirit – “Behold, I am the servant of the Lord; let it be to me according to your word” (Lk 1:38) – is part of what sets the God of Israel apart from, say, Zeus, who regularly went about raping women. The comparative biological approach substantiates the claim that, although humans do sometimes rape, this is an animal rather than a divine trait. It is not God-like. In fairness, the ability to provide consent for sex is also not unique to human females. But the comparative approach, even so, can shine light on how sexual relationships operate in human society in theologically significant ways.
Pair Bonds in Larger Groups
Our hominin ancestors evolved quite a few traits that make humans unique among the great apes: we live longer (Hawkes et al., 1998; Robson et al., 2006), give birth more often (Robson et al., 2006), take more time grow up (Kramer, 2010), eat astonishingly high quality diets (Carmody and Wrangham, 2009), habitually collect and prepare food to share (Durgavich, 2013), and affiliate with a large, flexible group of friends and family (Chapais, 2011). Of these derived traits, however, the behavioral suite that has been most critical in distinguishing us from other apes is the way we form families headed by pair bonds that live in larger groups that come together to care for dependent children during the extended period of juvenile dependence between weaning and full sexual maturation.
Humans have the longest life span among the great apes by multiple decades, but a similar age at reproductive senescence, giving rise to the derived trait of a protracted post-reproductive lifespan (Robson et al., 2006). With the oldest average age at first birth, human mothers are larger than most other great apes—besides gorillas— and have the longest gestation and largest neonates (Robson et al., 2006). Yet in spite of these slower life history traits, humans actually have the shortest inter-birth intervals among the great apes, as modulated by a relatively earlier age at weaning (Robson et al., 2006). The combination of late sexual maturation and early weaning combines to give humans the longest juvenile period of all the apes (Kramer, 2010). During this time, adolescents remain dependent on adults for provisioning (Kramer, 2010) even though their mothers can resume cycling and conceive again. This gives rise to the derived phenomenon of mothers stacking multiple energetically dependent offspring simultaneously (Robson et al., 2006). Because of the time and energetic demands, it would not be possible for a woman to be gestating, lactating, and provisioning another older offspring without help from others. Thus, our derived social structure and the opportunities for cooperative breeding that it affords are vital to offspring survival. Compared to other apes, humans have much more complex social groups uniquely composed of monogamous pair bonds embedded within larger multi-male, multi-female societies (Chapais, 2011).
There are other gregarious primate species that live in large coed social groups and even allonurse, such as capuchins (Perry and Manson, 2008), but these species all mate promiscuously. Other primates, like titi monkeys (Callicebus moloch), mate monogamously, forming lasting pair bonds, but these species live in small groups typically consisting of just the pair and its offspring (Gron, 2007). Only humans have the derived behavioral characteristic of forming pair bonds within a larger group (Chapais, 2011). The unique combination of flexible dispersal patterns and pair bonding facilitates exceptional intergenerational recognition of both matrilineal and patrilineal kin. This potentially played a role in the development of complex human societies comprised of families nested within multiple levels of larger alliances of kin, affines, distantly related family, and non-kin (Chapais, 2011). This means that mothers can receive assistance from a variety of individuals including a monogamous mating partner, other breeding adults in the social group, post-reproductive grandparents, and weaned older siblings who do not yet have their own offspring (Robson et al., 2006; Kramer, 2010; Hill and Hurtado, 2009). Arising from a combination of indirect reproductive investment, fathering, long-term reciprocal altruism, and mutualism (Hill and Hurtado, 2009; Kramer, 2010), food sharing within groups is extensive and ubiquitous (Hill and Hurtado, 2009). A study of two South American hunter-gatherer societies found that families receive critical help in provisioning their dependent offspring from non-reproductive adults and other adult males (Hill and Hurtado, 2009). The fact that we must process our food to survive (Carmody and Wrangham, 2009) means that we must bring it back to a central location to prepare rather than eating our spoils on the spot the way other primates do. This enables tolerated scrounging by parents with hungry children; whether the collecting, the processing, the scrounging, or the sharing came first or if they all emerged in concert, one thing is clear: for human children to survive, it is important not only that their parents form a bond and work together, but that their families live within larger groups of cooperating individuals. Single parents whose children make it to adulthood are a recent phenomenon, made possible by human innovations like grocery stores.
This unique human trait is theologically salient because it tells us something about the way a marriage ought to operate: a human marriage is not a self-contained unit, but ought to be outwardly directed. Marriages are missional; the most successful marriages acknowledge this, as both partners work together not just to get their own needs met, but also to benefit the larger community in which they live. Marriage is an important theological sign. Jesus is the bridegroom and his Church is the bride. Marriage reflects this relationship between Christ and his church in several ways: in its emotional and spiritual closeness, in its communion in the flesh (enacted in the act of receiving Holy Communion in the Eucharist), in its creative and pro-generative power, in its exclusivity and duration (although human marriages last only our lifespan on earth, the marriage between Christ and his Church lasts the duration of their lives, which is to say forever), but also in that union between Christ and the Church (this marriage) is embedded in a larger community of non-believers and exists to benefit not only the participants in the marriage but those outside the marriage. The marriage between Christ and the Church must be missional in its outlook. A comparative approach invoking evolutionary theory to study human marriage corroborates this view, which also finds support in 1 Peter. Peter writes that his readers are “are a chosen people, a royal priesthood, a holy nation, God’s special possession…” (1 Pt 2:10), but the upshot of this chosenness is that Christians ought to “[l]ive such good lives among the pagans that, though they accuse you of doing wrong, they may see your good deeds and glorify God on the day he visits us” (1 Pt 2:12). In other words, although God’s people are special in his eyes, as a wife is to her husband, the Church has a job to do on behalf of the “pagans” who are not participants in this marriage between Church and Christ, at least not yet.
A comparative approach to understanding humans, such as I have learned in Harvard’s Human Evolutionary Biology department, can be useful for gleaning more insight into how God works in the world and what he asks of us as the images of Him, given dominion over the earth. We have the ability to use shared intentionality to motivate shared goals and mental states, to facilitate teaching and learning, to enable empathy and compassion, to make possible complex compromise for the sake of the mutual good. This cognitive capacity operates in parallel with a biologically necessary complex social structure in which married couples are in the position to cooperate with one another and with the broader community to raise children, to build empires, to introduce our friends and neighbors Christ, to eradicate human hunger… with God’s help, anything is possible.
Jane Thomas ’15 is a Human and Evolutionary Biology concentrator affiliated with Pforzheimer House.
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- Note that large portions of the text for this article are borrowed from my own writing assignments from my Sophomore Tutorial in HEB, which I took as a junior in Spring 2014. ↩