Social DNA. M. Kay Martin
natural selection process. He proposed that genes and their respective alleles act in their own self-interest, programming the organisms in which they reside to behave in a manner that optimizes their frequencies in the gene pool. Genes effectively hitch a ride on human “survival machines,” moving their hosts in directions that foster their own replication. In this view, adaptations represent the phenotypic effects of genes to reproduce themselves in future generations. All of this is seen as occurring beyond the conscious recognition of individuals, who are essentially temporary vehicles for gene replication. Dawkins also accounts for the role played by culture in human evolution with the parallel concept of “memes,” which are proposed as the units of cultural inheritance. Memes are crafted on the same genetic metaphor, competing with others in a meme pool. Like genes, memes have phenotypic effects, and are thought to be naturally selected by virtue of their successful replication.4
The significance of gene-centered theory for models on human origins is twofold. First, it proposes that sociality is (unconsciously) pursued by individuals largely on the basis of self-interest. Degrees of genetic relatedness become the floating calculus for cooperation and competition among individuals, who assemble and participate with others in a tit-for-tat world. Society thus defined becomes a collection of vying gene carriers—a procession of self-serving males and females, kin and non-kin, marching to the zero-sum drum of genomic replication. Second, some applications of gene-centered theory assume that characteristic reproductive strategies and associated phenotypic behaviors, such as dominance, aggression, or parasitism, have become imprinted into our DNA as a kind of species-specific biogram. In other words, ancient and modern humans, in their quest for self-replication, have been pre-programmed to favor certain behaviors and types of social organization to the exclusion of others.
While recognizing that the inclusive fitness of individuals rests on the replication of their genes, the present book will argue that the reproductive success of ancestral humans was not only enhanced by, but reliant on their ability to forge cooperative relationships and function effectively within social groups—communities that typically extended beyond the circle of immediate kin to include the broader membership of a breeding population. Humans are not solitary breeders, but group-bonded primates. Ancient human social groups were more than just a collection of individuals with whom to play out one’s genetic hand. The alliances and cooperative relationships on which they were based provided an internal division of labor for the acquisition and distribution of fitness-related resources that enhanced the reproductive success of all group members—a characteristic referred to by Wilson (2012: 133) as eusociality.
The process of evolution has been understood as involving the interaction of natural selection and genes that are either inherited through DNA or arise via random mutations. However, the recent discovery that an organism’s phenotype may be modified by a myriad of nongenetic factors, and that such phenotypic variants are themselves heritable, is transforming the field of evolutionary biology. The process by which this occurs, epigenesis, modifies the expression of genes without changing the underlying molecular structure of DNA. A new branch of theory, referred to as the extended evolutionary synthesis (EES), proposes that heredity is a developmental process influenced not only by genes, but by an organism’s cumulative interaction with its chemical, natural, and social environments. Epigenesis provides a source of nonrandom phenotypic variation once thought reserved for random mutations. Animal experiments have also demonstrated that epigenetic inheritance allows for the storage and transmission of learned information and provides the flexibility for organisms to modify their phenotype in response to rapid environmental change. EES proponents maintain that an organism’s niche construction (its selection and modification of its habitat and environmental resources) also affects the direction of evolution by modifying natural selective factors. In other words, the evolutionary process is more complex than simple genomic theories propose.
This perspective on the critical role played by epigenetic traits will find expression in the chapters that follow. What separated early humans from other apes was their gradual emancipation from purely hardwired responses to reproductive and subsistence challenges through a combination of epigenesis, behavioral plasticity, and cortical expansion. Instead of slavishly following an innate prescription or biogram for sociality, epigenesis provided a “soft inheritance system” that allowed humans to alter their behaviors and the structure of their social groups in response to stochastic environmental conditions. Wilson’s concept of “epigenetic rules” (2012: 193) parallels what is referred to here as social DNA. Social DNA consists of the underlying rules for characteristic human behaviors and social forms that have been selected and replicated over time by virtue of their role in enhancing reproductive success. While they provide a general framework for the human experience, the phenotypic expression of these rules is not unitary or preordained, but is sufficiently plastic to respond to external change.
One of the challenges in unraveling current conceptual models of human social origins is their tendency to meld ideas on evolutionary prime movers, reproductive strategies, sexual dominance, altruism, and social forms into a hardwired genomic platform. An effort is made in the succeeding chapters to deliberately separate these issues for closer examination and discussion.
Chronologies, Crania, and Traditions
Eugene Dubois’s unearthing of a million-year-old Pithecanthropus erectus skullcap in Java in 1891 inspired generations of paleontologists and amateur rock hounds alike to find the “missing link” connecting apes and humans. A century and a half later the growing fossil record has enabled a general reconstruction of human evolution (Figure 0.1). Fossil remains have typically been grouped into evolutionary chronologies based on their provenance, and on characteristics such as their skeletal and cranial morphology, dentition, estimated brain size, and associated stone tool traditions.
While resultant phylogenetic trees vary somewhat from one another, most scholars propose that hominins5 evolved in Africa between 5 and 7 million years ago (ma) from among a heterogeneous stock of bipedal Pliocene apes. Potential candidates for the earliest primates on the human family tree include a diverse clade of tool-using apes known collectively as australopithecines, as well as more ancient and less robust forms, such as Ardipithecus ramidus. Members of the genus Homo, distinguished by their larger bodies and brains and by their fully omnivorous diet, are generally recognized as emerging around 2 ma. These first humans are exemplified by fossils such as Homo habilis and by multiple waves of Homo erectus populations that radiated throughout Eurasia over the succeeding millennia. A prevailing view is that advanced forms of H. erectus diverged around 400–500 thousand years ago (ka) into separate lines in Europe (H. heidelbergensis) and Africa (H. rhodesiensis). These populations ultimately led to the parallel emergence of Neanderthals (Homo sapiens neanderthalensis) and anatomically modern humans (Homo sapiens sapiens), respectively, by at least 200 ka.6 This progression of hominin types is associated with evolutionary milestones such as refinement of the infracranial skeleton, increasing encephalization, dietary reliance on animal flesh, the invention of fire, and increasingly complex stone tool technologies.
Figure 0.1. Overview of human evolution (copyright John A. J. Gowlett) from Gowlett and Dunbar (2008: 22). With permission of John Wiley and Sons, Inc.
Such evolutionary reconstructions provide the essential backdrop for current theories on human social origins. Recovered fossil and cultural remains have been utilized as windows on the subsistence activities, cognitive abilities, and social organization of ancestral humans through time. A cautionary note, however, is that our perspective on Pleistocene lifeways is based on material records that are still quite fragmentary, and that are subject to revision with the next great find. Recent discoveries suggest that ancient hominins were much more diverse than previously realized. Fossil specimens do not always fit into the tidy boxes of existing chronologies. In short, when looking back, it is important to remain open to new information and new interpretations—to know how much we don’t know. There are points in this book where the reader will be asked to entertain alternatives