Social DNA. M. Kay Martin

set of biases on what constitutes basic human nature.¹⁰ What are the innate propensities that govern intra- and intersexual behaviors, reproductive strategies, social structure, and intergroup relations? As noted earlier, some inclusive fitness models see society as a collection of individuals who engage in cooperative and competitive actions solely in pursuit of their own ends. This portrait of human reproductive behavior congers images of situational loyalties, dominance, subordination, parasitism, deceit, and betrayal. Other origins theories attribute the darker side of human nature to adaptations thought to have accompanied the shift of early hominins from arboreal to terrestrial life. For example, some argue that hunting on the open savanna turned our ancestors into bloodthirsty killer-apes, fierce defenders of territories, and combatants in endemic warfare over mates and scarce resources. A penchant for aggression and violence has also been proposed as an enduring human trait by pointing to these behaviors in contemporary chimpanzees.¹¹

      At the other end of the spectrum are theories that suggest that cooperation had greater currency in the evolution of human sociality than competition or aggression. Namely, what separated our ancestors from those of contemporary apes was their liberation from primitive limbic system responses to external stimuli and the attendant modulation of hormonally driven behaviors. Current evidence suggests that cortical expansion and a reorganization of brain function was selected for among early hominins, along with the corollary evolution of behavioral plasticity. The increasing ability to interpret stimuli in light of past experience and to apply reasoned, nuanced responses provided hominins with the necessary social tools for empathic and cooperative behaviors. In short, the success of our ancestral lineages relied on the ability to create win-win rather than win-lose scenarios. As recently noted by Clancy (2017), the emergence of our genus may be more accurately described as “survival of the friendliest.” Survival and reproductive success came to those who learned how to get along and to modify their strategic alliances to meet the challenges of changing environmental conditions. This perspective will be favored here.

      While behavioral plasticity greatly expanded the social repertoire of early hominins, it did so without sacrificing the option for outlier responses. Humans are capable of both extreme empathy and extreme violence. Where threats to the welfare of offspring or access to critical resources present themselves, limbic system behaviors may rise to the occasion. Such responses, however, should not be regarded as the essence of human nature, nor as a rationalization for the inevitability of human aggression, warfare, or systems of inequality. What is innate is our ability to gauge responses appropriate to stochastic events. If negative or defensive behaviors have become more frequent in the Holocene and Anthropocene epochs, so too, perhaps, have the environmental conditions that trigger this ancient survival response.

      Science and Storytelling

      Theories on the nature of human nature and societal origins have always been an odd mix of empirical data and fanciful storytelling. I still have vivid memories of a lecture I attended in the 1960s in which my anthropology professor took a stumbling, bent-knee stroll across the stage to demonstrate the typical locomotion of ancient man. The fact that the speaker’s cranial morphology had strikingly Neandertaloid characteristics only served to add to the perceived drama and authenticity of the performance. Subsequent discoveries of additional, nonarthritic Neanderthal skeletons, of course, quickly put this misconception to bed. But not all notions on what life was like on the long road to humanity are so easily tested and modified. In fact, most theories are forced to address many open questions about the course of human evolution, the answers to which will probably remain unknowable.

      Why is this? The tangible evidence we have in hand to trace our evolutionary pathway is fragmentary, and may remain so. A tooth here, a tibia there, and if we’re lucky, a skullcap or a complete infracranial skeleton. Exceptional finds, such as the multiple skeletons recently unearthed from the Dinaledi Chamber, South Africa, while enlightening, often pose more questions than answers.¹² And so it goes with other sources of data. Geology and paleoecology tell us something about the earth’s past climate and physical environment, but also highlight the prospect that many ancient occupation sites may have been forever lost to rising sea levels. Stone tools give hints about how early humans made a living, but other components of ancient toolkits that could provide major insights, such as items made of wood, bone, and fiber, have long since turned to dust. Similarly, contemporary primates provide glimpses of ourselves and perhaps of a common ancestor, but differ from our proto-human forebears in ways we can only imagine.

      And imagine we do. Evolutionary biologists and paleoanthropologists struggle to assemble a complex human-origins puzzle that has unknown dimensions and many missing pieces. Consequently, scientists use their imagination and regularly make up stories (aka models) that paint a more complete picture from the fragments they possess. Multiple stories can be generated from the same evidence or set of facts, and the relative veracity of their competing plots is vigorously debated. A select few, however, are inevitably elevated to the status of academic dogma. These stories are told and retold for decades, and may gain traction for reasons beyond the evidence presented, such as the author’s reputation or the extent to which their conclusions correspond to prevailing cultural stereotypes or popular views of what constitutes “common sense.” But, ideally, dogma is eventually challenged and replaced with new ideas and syntheses that take us closer to an understanding of our roots.

      One of the primary challenges facing human-origins storytellers has been the intrepid duo of ethnocentrism and “anthropodenial.”¹³ Nothing offends scientists more than the suggestion that they approach their subject with less than an open mind. But scientists are human, and humans are creatures of their own culture. When it comes to visualizing what ancient peoples were like, theorists are notorious for casting them in their own image. Prevailing values, moral sentiments, and sexual stereotypes have had a way of creeping into not only our myths and folklore, but our scholarship as well. Cultural biases reflected in nineteenth-century evolutionary theories, for example, now appear quite obvious in hindsight. Ancestral forms prior to the emergence of anatomically modern humans were portrayed as brutish, stupid, oversexed, amoral, anarchistic, and speechless. As the story goes, the threshold of humanity was not crossed until when, thanks to the naturally diminutive libido and greater religiosity of females, males were roped into assuming the responsibilities of family heads, breadwinners, and protectors of dependent consorts and offspring. Thus, ancestral human temperaments and the pair-bonded family unit were perceived as not only mirroring, but rationalizing the Victorian ideal.

      Similar elements, however, have also found their way into more recent portraits of Paleolithic social life, along with the notion that these elements were genetically imprinted in the ancient past. This book will examine the extent to which Western European cultural bias has colored our perception of male and female natures, intersexual relationships, the evolution of sociality, the diversity of Paleolithic adaptations, and the antecedents of human kinship systems. In the process, the reader will be challenged to consider alternative viewpoints and interpretations of existing data.

      Humans as Chameleons

      The prevailing theme in the following chapters is that what set hominins off on a separate evolutionary trajectory—what made us human—was the ability to flex our reproductive and social strategies in response to stochastic conditions. This perspective directly contradicts prevailing monotypic models of Paleolithic life that rely on the genetic imprinting of trait clusters born in Plio-Pleistocene hunting economies. If there is such a thing as a human biogram, it is not a staid template that was perfected for all time in a single ancient biome, but rather the capacity of evolving hominins for plasticity—the ability to tailor their behaviors and adaptations to meet the challenges of changing environmental conditions. This represents a fundamental shift in our perception of human nature and of the hominin evolutionary journey.

      This book will argue that human lineages evolved in dynamic mosaic landscapes that selected for flexible rather than rigid adaptive responses. It explores new cross-disciplinary research that links the capacity for behavioral plasticity to critical changes in the structure and organization of the primate brain. Unlike contemporary apes, such as chimpanzees, early humans were equipped with a set of both hardwired genetic codes and “soft inheritance”