Social DNA: Rethinking Our Evolutionary Past

By M. Kay Martin

What set our ancestors off on a separate evolutionary trajectory was the ability to flex their reproductive and social strategies in response to changing environmental conditions. Exploring new cross-disciplinary research that links this capacity to critical changes in the organization of the primate brain, Social DNA presents a new synthesis of ideas on human social origins – challenging models that trace our beginnings to traits shaped by ancient hunting economies, or to genetic platforms shared with contemporary apes.

• Language: English
• Publisher: Berghahn Books
• Release date: Oct 19, 2018
• ISBN: 9781789200089

M. Kay Martin

M. Kay Martin has a diversified research, planning, and management background in the academic, public, and private sectors; she has taught at the University of California, Santa Barbara, and has since held executive posts in applied anthropology, environmental research, resource conservation, and other fields. She was the principal author of Female of the Species (1975, Columbia University Press) and has also published ethnohistorical and cross-cultural studies on foraging societies.

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SOCIAL DNA

SOCIAL DNA

Rethinking Our Evolutionary Past

M. Kay Martin

First published in 2019 by

Berghahn Books

www.berghahnbooks.com

© 2019, 2020 M. Kay Martin

First paperback edition published in 2020

All rights reserved. Except for the quotation of short passages for the purposes of criticism and review, no part of this book may be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system now known or to be invented, without written permission of the publisher.

Library of Congress Cataloging-in-Publication Data

A C.I.P. cataloging record is available from the Library of Congress

Library of Congress Cataloging in Publication Control Number: 2018040128

British Library Cataloguing in Publication Data

A catalogue record for this book is available from the British Library

ISBN 978-1-78920-007-2 hardback

ISBN 978-1-78920-757-6 paperback

ISBN 978-1-78920-008-9 ebook

To Eleanor Burke Leacock

1922–1987

Contents

List of Illustrations

Preface

Introduction   Some Givens

Chapter 1         Perspectives on Anisogamy

Chapter 2         First Families

Chapter 3         Paleoecology and Emergence of Genus Homo

Chapter 4         Paleolithic Dinner Pairings: Red or White?

Chapter 5         Signature Hominin Traits

Chapter 6         Kinship and Paleolithic Legends

Chapter 7         Kinship as Social Technology

Epilogue

Endnotes

Bibliography

Index

Illustrations

Figures

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.

1.1. Selfish-gene theory and the origin of female exploitation. By Drew Fagan.

3.1. Homo erectus lakeshore encampment in the Early Pleistocene. By Drew Fagan.

4.1. Lucius. By Emiliano Troco, oil on canvas, scientific supervisor Davide Persico, private collection.

4.2. Neanderthal Clan. By Emiliano Troco, oil on canvas, scientific supervisor Davide Persico, collection of Museo Paleoantropologico de Po.

5.1. Middle Pleistocene Homo heidelbergensis butchery site at Boxgrove, West Sussex, England. With permission of Getty Images.

5.2. A model of human society based on general systems theory. By Drew Fagan.

Tables

2.1. Principal assumptions about Pan-Homo social life in androcentric models.

2.2. Impact of ecological variables on female feeding strategies and primate social organization. Source data: Wrangham (1979, 1980).

Preface

I came to the field of anthropology under the mentorship of ethnohistorian Harold Hickerson, content to haunt the card catalogs and cavernous stacks of university libraries for early accounts of preagricultural peoples. My treasure hunts were aimed at uncovering glimpses of aboriginal social organization for hunter-gatherers on three continents and documenting postcontact change in these societies over time. The aggregate picture that emerged for foragers in their most pristine state was one of robust communities, diverse systems of kinship, and a broad spectrum of sociopolitical complexity. For most of these societies, however, their vitality and continuity was short-lived. Genocide, disease, atomism, and cultural dismemberment accompanied the unrelenting advance of European colonialism, leaving them depopulated, displaced, and a shadow of their former selves. Ironically, ethnohistorians, in their efforts to reconstruct the cultures of these peoples, often become the unwitting chroniclers of their sorrows.

During the mid to late 1960s, American ethnologists began to reinvent the concept of cultural evolutionism so roundly rejected by their discipline’s founding fathers. Neoevolutionary schemes inevitably commenced with portraits of small, atomistic family bands pursuing a meager living from limited resources in a harsh and unfriendly world. I was struck at the time by the incongruity of memorializing surviving hunter-gatherer societies in these models as living examples of Paleolithic life. Historic foragers, in my mind and experience, were arguably remnant or refugee communities, and unlikely avatars of our ethnographic past. Similarly, the characterization of early human kinship as inevitably male-centered did not square well with what I knew of the ethnohistorical and ethnographic records.

In 1975, I coauthored a book entitled Female of the Species with archaeologist and colleague Barbara Voorhies. An overarching premise of this work was that the human evolutionary journey carries the mark of our primate heritage, but that factors in addition to biology play a major role in shaping the gender behaviors and social institutions of both ancient and modern societies. The book presented the results of a cross-cultural study I completed for over five hundred societies that highlighted how ecology and history have influenced the nature and direction of cultural institutions through time.

During this same period, however, the pendulum had begun to swing toward biological explanations for human social origins and primeval kinship. Sociobiological theory placed primary emphasis on genes, and in particular the male genome, as the engine of human evolutionary development. A broadening schism on questions about early human social life developed between biological and social anthropologists, and it persists to the present day. Their at times intractable nature-nurture debates served to not only bifurcate the discipline into dueling camps, but to partition their respective areas of inquiry. Theories on the nature of early human society were largely co-opted by biological anthropologists. In contrast, their social anthropology counterparts, particularly in Great Britain, remained focused on ethnography and synchronic studies, and in subsequent years even moved away from kinship theory.

About this time, my career path detoured from academia to applied anthropology and public administration. It was not until my retirement about a decade ago that I began to revisit the theoretical questions about the nature of human kinship and our social origins that had so long fascinated me. How were male and female reproductive strategies aligned in the first human families? Were ancient hunter-gatherers cast from a single mold, or did these peoples have diverse economic and social forms? Why have societies throughout most of human history organized themselves into groups based on either uterine or agnatic affiliation? One of the interesting revelations upon returning to academic discourse after a somewhat lengthy hiatus was that these big questions had attracted few new answers. It is almost as if one camp had lost interest in asking them and the other camp felt that they had already been satisfactorily addressed.

In pondering possible reasons for this stalemate, I was struck by the way that the field of anthropology had metamorphosed in recent decades and how these changes have impacted communication and intellectual discourse. Those of us trained by second-generation American anthropologists were expected to attain a working knowledge of the four subfields of the discipline. Not uncommonly, one left graduate school with the ability to pass a laboratory practical exam in human osteology, record the spoken word in phonemic transcription, excavate a five-foot square at a prehistoric midden, and find one’s way around a kinship chart. One could also attend the annual national meetings of the profession and find concurrent sessions in these four basic subdisciplines; meet and academically engage, face-to-face, with more friends than strangers; and even locate the diminutive Margaret Mead on a crowded mezzanine buried at the proximate end of her notorious shepherd’s staff. I believe that this traditional training of anthropologists as generalists in many ways broadened their perspective on the human condition and served to open communication across disparate branches of science.

At the risk of sounding nostalgic, I still have fond memories of lively sit-down discussions and debates with some of anthropology’s great generalists on the subjects of evolution, early human society, and kinship systems. Exchanges with Leslie A. White, George Peter Murdock, Elman Service, Marvin Harris, Eleanor Happy Leacock, and Ward Goodenough did not always end in agreement, but always left me with a sense of awe about their breadth of knowledge, their openness to ideas, and their perpetual sense of wonder. Their voices, although past, still resonate, and have found their way into this book.

The age of generalist perspectives within the discipline, however, has been substantially diminished. We have moved from a community of generalists to a community of specialists. Whereas in years past professional anthropologists organized themselves into just a handful of subdisciplinary associations and related journals, today’s American Anthropological Association lists some fifty specialized sections and interest groups with focused memberships, and over twenty-five separate publications. This proliferation of specialized research foci, while perhaps a natural product of the discipline’s growth, also tends to create academic silos that both isolate and insulate their memberships. The trend toward increasing compartmentalization does not bode well for the cross-pollination of ideas. Is anthropology doomed to intellectual myopia and linear thinking?

Two hopeful countertrends provide a potential antidote to long-standing theoretical divides, such as that existing between biological and social anthropologists. First is the wellspring of new cross-disciplinary information that has become available since this debate began. Significant findings are emanating from the fields of primatology, paleontology, geology, paleoecology, genetics, and neuroscience that call for the reconsideration and modification of existing evolutionary theory. It turns out that while some of us were not looking, these parallel bodies of science were addressing many of the same big questions about human evolution, but from different vantage points. These alternative conceptual frameworks are adding key pieces to the puzzle of human origins and human sociality. We need only look. A second positive development is the sea change that has occurred in information technology. Over a relatively short span of time, we have graduated from a universe of typewriters, landlines, mimeographs, paper manuscripts, snail mail, and physical data repositories to personal computers, cell phones, the internet, email, electronic data files, the cloud, e-books, and virtual libraries. Thanks to the digital revolution, scholars of today have literally at their fingertips the ability to not only access an unlimited range of scientific data from their own and other disciplines, but to dialogue with other researchers, some of whom they may never meet, on questions of mutual interest. This is a powerful antidote to linear thinking, and presents both the means and the opportunity to usher in a new generation of generalists.

I have pursued the present work in this spirit. Over the past four years, I have read scores of books and literally hundreds of scholarly journal articles across multiple scientific disciplines. This diverse literature addresses a broad range of questions on hominin evolution and human sociality. The specialized technical data and scientific jargon in many of these sources were admittedly challenging, and some analyses were more difficult to digest than others. But the further along I got on this fascinating journey, the more apparent it became that the nature-nurture controversy in evolutionary theory presents a false dichotomy. New scientific findings inform the social anthropologist that human societies reflect our primate genomic heritage, including not only reproductive behaviors, but how hominid communities have been shaped in similar ways by selective factors in the environment. These findings also inform the biological anthropologist that genes are not the whole story. Their phenotypic expression is influenced by social learning throughout an organism’s lifetime. Recent evidence further suggests that phenotypic traits shaped by culture are at least partially heritable and therefore may have played an important role in the pace and direction of human evolution. In short, those who maintain that the human saga has been directed either by the genome or by culture alone are only half right. It is their interface—their complex, synergistic, and dynamic interaction—that accounts for the origins and trajectory of our genus.

Social DNA proposes to peel back the layers of nested hypotheses underlying popular theories on how our species evolved. It examines their interlocking assumptions about male and female natures, mating and intersexual dominance, Pliocene ecology, subsistence and family provisioning, and the extent to which contemporary primates may be taken as avatars of ancient social life. This book systematically disassembles these layers, evaluates the assumptions on which they are based, considers new or competing evidence, and develops alternative hypotheses that lead to novel reconstructions of human sociality.

This analysis is divided into three major parts. The first examines alternative perspectives on the nature of male and female Pliocene apes and how their mating and feeding patterns may have shaped early social groups. New climate and paleontological data are presented that connects early human occupation sites with more humid waterside habitats, greater resource densities, and evidence of dietary breadth, including reliance on aquatic flora and fauna. This reframing of Plio-Pleistocene ecology has profound implications for ancient social life, particularly when such variation in resource distributions is compared with social patterns observed among nonhuman primates. The second part of the book is devoted to a discussion of signature traits shared by members of both ancient and modern hominin lineages that distinguish them from contemporary apes, such as behavioral plasticity, dietary breadth and food sharing, social demography, and cognitive function. Social DNA entertains the notion that traditional academic emphases on phylogenetic chronologies, material culture, and gross brain or neocortex size has led to an underestimation of ancient hominin ingenuity, intelligence, and social complexity. A central theme of this discussion is that early hominins were, in some ways, like every other primate, but like no other primate. That is, while primates respond in similar ways to similar environmental cues, there are important threshold differences. Contemporary nonhuman species have evolved as specialists, bound by genetic platforms geared to specific niches, whereas hominins evolved as generalists who came equipped with a more diversified gene-culture playbook that broadened their ecological range.

The final section of this book returns to seminal questions about the essence of human kinship. It challenges current theories that tie kinship systems to innate dominance patterns, evolutionary stages, monotypic biograms, or phylogenetic continuity with chimpanzee-like apes. Instead, it proposes that the nature of human kinship systems is not preordained, but rather is the phenotypic expression of epigenetic rules (social DNA) that optimize the procurement and allocation of fitness-related resources in a given niche. Characteristic patterns of social group formation based on kinship alliance reflect rules for the regulation and distribution of resources critical to survival, such as energy, materials, genes, and information, that are adaptive in specific ecological settings. Matrilineal and patrilineal kinship systems are understood as variable social technologies for niche construction, with distinct architectures for structuring reproduction, labor, and political groups in relation to available resources.

Social DNA is distinguished from other titles on human evolution in its scope of inquiry. New cross-disciplinary research findings are brought to bear on fundamental questions about the nature of Pliocene ecology, Pleistocene subsistence activities, hominin brain evolution, hominin life history changes, and the relationship of inclusive fitness to primeval kinship systems. It is my hope that this book provides a fresh perspective on our biosocial origins and responds to current calls for the creation of an enhanced dialogue across academic and disciplinary boundaries.

I would like to extend special thanks to archaeologist Jon Erlandson, who graciously read and offered comments on parts of this manuscript. The ideas in this book are my own, but have benefitted from his insights on Pleistocene adaptations and the potential role played by aquatic resources in early human societies. Thanks are also due to my anonymous reviewers, who pointed out errors and omissions in the draft manuscript, and whose constructive comments resulted in improvements to this book. I’d also like to acknowledge ethnologist Isabelle Clark-Deces, who provided encouragement at the onset of this effort, and who left us all too soon.

I am grateful to paleoartists Mauricio Anton and Emiliano Troco for agreeing to share their wonderful portraits of early hominins to illustrate this book, and to artist and friend Drew Fagan for his creative genius, technical support, and good humor throughout this project.

Finally, I would like to thank my editors at Berghahn Books, Harry Eagles and Elizabeth Martinez, for their responsiveness and support during the book’s review and production.

Introduction

SOME GIVENS

This book revisits fundamental questions on the biocultural origins of human sociality. What set our ancestors on a separate evolutionary path from that of other apes? What was the nature of primeval kinship and mating? What roles have biology and ecology played in shaping human social groups through time?

Scholarly musings on such questions have populated library shelves for decades. Various theories have been proposed, debated, embraced, rejected, and periodically recycled. In recent years, the scope of inquiry on human origins has been enriched by pioneering research across multiple branches of science. The findings of such studies, however, have not always informed one another in a manner that encourages a re-examination of current evolutionary theory. In other words, establishment of an academic lingua franca that facilitates the creation of integrative models has been elusive.

A primary goal of the present work is to reach beyond traditional schools of thought and foster a cross-disciplinary dialogue on human social evolution. The task is to unravel the fabric of existing theories, explore new independent discoveries on the emergence of our genus, and tie together the myriad threads of this evidence in novel ways. This is arguably an arrogant undertaking, given the impressive lineup of experts who have already offered their insights on the subject. But experts currently disagree, both on the principal drivers of human evolution and on the nature of ancient social forms. Finding new answers to old questions often involves being a contrarian on some levels, and an adventurer on others. It also requires a measure of humility, since all accounts of human social origins are necessarily speculative.

Theories on the origin of society are neither new nor in short supply.¹ It is a subject that has fueled the imagination of both religious and secular philosophers for centuries. It has also spawned a robust body of scientific evidence, primarily in the fields of anthropology, paleontology, and evolutionary biology. Significant fossil and archaeological discoveries have provided the foundation for chronological reconstructions of our biological and cultural journey over the past 5 to 7 million years. Ancient material remains have shed light on the subsistence activities, technologies, settlement patterns, migrations, and cognitive abilities of archaic populations.

Insights into the evolution of human social behaviors, however, are constrained by the natural limitations of what bone and stone artifacts can tell us about the nonmaterial aspects of ancient sociality. How did our ancestors structure mating, labor, food sharing, kinship, and power relationships? To what extent did biology shape these behaviors? How did ecology influence the prevailing social architecture of human groups in both time and space? What role did primate brain evolution and the emergence of symbolic communication play in the trajectory of early social life?

Since we cannot travel back in time to the encampments of our forebears, answers to these questions have to rely on the construction of conceptual models. However, creation of models with clearly defined premises and measurable outcomes is particularly challenging when the task is to explain the origins of phenomena that are no longer directly observable. Interpretations of the fossil and archaeological records have therefore been traditionally combined with observations of contemporary nonhuman primate communities and of historic hunter-gatherers to paint a picture of what Paleolithic social life may have been like.

One of the earliest and most influential of these models was crafted over a half century ago. Commonly referred to as the hunting hypothesis, it proposes that the first apes to achieve a successful terrestrial existence on two legs established the social mold from which all subsequent forms of humanity were cast. The adaptation of our ancestors to a carnivorous life on the open savanna, it argues, served as a sort of primeval Petri dish for the germination of a distinct complex of traits—traits that predisposed early humans toward a uniform pattern of reproductive behavior, labor division, and kinship organization. Early sociobiological models argued further that this trait complex was so intimately connected to survival that it became genetically imprinted. In this view, the social life of Paleolithic peoples conformed to a standard template, one dictated by a biogram that not only was perfected by natural selection in ancient times, but continues to dominate the reproductive and social patterns of modern humans.

This monotypic model of human social evolution has enjoyed such popularity over the years that it is sometimes referred to as the standard narrative. The image of early humans organizing themselves into small male-centered family groups and wandering over parched landscapes in pursuit of sparse game is remarkable by its persistence, particularly in light of subsequent research. In recent decades, fossil, archaeological, and ethnographic records have expanded exponentially, along with our understanding of primate sociality. The hunting hypothesis and its implications for human social life have come under numerous challenges, but such debates have taken place largely within the confines of specific disciplines, such as anthropology and paleontology. Meanwhile, several ancillary branches of science, such as climatology, paleoecology, paleogenetics, and neurobiology, have been exploring their own avenues on the conditions affecting the evolution of our genus, many of which have significant implications for the nature of ancient social life. These new research findings are impacting traditional notions about what early humans ate, where they lived, how their brains evolved, and how ecology and the reproductive strategies of the sexes may have impacted the nature of social groups. In short, many of the fundamental assumptions of existing models are beginning to erode, but robust cross-disciplinary dialogue on these issues has lagged.

Rethinking human social origins is an exercise in collaborative inquiry. Such is the challenge of this book. Recalibrating current evolutionary paradigms is difficult, in part because it often requires a departure from academic comfort zones. Institutions of higher learning create disciplinary and subdisciplinary silos—each with their own legacies of specialized knowledge, jargons, and world views—that constrain the cross-fertilization of ideas. Experts don’t always talk to one another or, worse, become vested in their own viewpoints and stewardship of specific schools of thought. A major historical divide, for example, has existed between biological and social anthropologists with regard to the origin and nature of human kinship systems. If productive dialogue is sometimes constrained by banter and debate within individual disciplines, communication problems are compounded by the isolation created by institutional boundaries between them. The need to establish a more comprehensive dialogue on human social origins has recently been highlighted by Callan (2008) and others, such as Mills and Huber (2005), who have proposed the concept of intellectual trading zones to foster the communication of ideas across traditional academic disciplines.² In short, progress on theoretical questions such as the structure of ancient social life requires a lowering of technical and research boundaries and a more effective way to disseminate and integrate relevant data among scholars from widely disparate fields.

Progress on the refinement of conceptual models also requires a reassessment of cultural and individual biases. Scientific inquiry is an imperfect exercise. It assumes that the scholar approaches the examination of a problem dispassionately, developing insightful hypotheses and then objectively unraveling certain truths through a process of vigorous inquiry or testing. While some disciplines, such as mathematics, naturally lend themselves to the discovery of empirical proofs, others struggle to assemble fragmentary bits of information into some kind of formula or model that purports to explain extant conditions or end states. That assembly process often draws on an assortment of facts, hunches, and a priori biases, the segregation of which may be murky for both the scholar and the intended audience.

Ideally, authors of theoretical books such as this one should be required to devote their first chapter to a declaration of their underlying assumptions and predilections. This exercise would facilitate the author’s own awareness of the preconceived notions and agendas they bring to the table. It would also key the reader to factors that are likely to color the author’s focus of inquiry, selection of data, and conclusions drawn. An ancillary benefit of this early-warning system, of course, is that it would also provide an opportunity for the reader who disagrees with the book’s initial premises to return it to their retailer unread for a full refund. In most cases, however, it is a fair bet that readers would probably welcome a clear exposition of an author’s starting point and the opportunities for constructive debate that such honest dialogue provides. This introduction is written in this spirit.

The book thus begins with a summary of assumptions on eight general topics that have influenced this writer’s approach to the evolution of human sociality. This initial discussion draws attention to key issue areas in which recent cross-disciplinary research is both augmenting and redirecting our understanding of Paleolithic social life. Each will be discussed briefly, and an effort made to the elucidate how these baseline concepts are reflected in subsequent chapters.

Genes, Epigenesis, and Social DNA

The fundamental assumption of the current work is that modern humans (Homo sapiens sapiens) are the product of gene-culture co-evolution spanning at least the past 5 to 7 million years. Current knowledge about how the evolutionary process works has been advanced by three major milestones. The first was publication of Darwin’s The Origin of Species (1859) and The Descent of Man (1871). His revolutionary concepts moved questions about human origins from the realm of philosophy and myth to the discipline of science and established natural selection as the cornerstone of evolutionary biology.

The second milestone was development of the modern science of genetics. Genes were identified early in the twentieth century as the units of heritable traits, and seminal works, such as Dobzhansky’s Genetics and the Origin of Species (1937), laid the foundation for understanding gene flow through time and space. Discovery of DNA structure in 1953 revealed the molecular mechanics of how traits are transmitted. Later advancements in DNA sequencing in the 1970s and the 2003 reconstruction of the human genome are now allowing us to probe relationships among the ancient lineages of our family tree more deeply, often with surprising results.

The third source of enlightenment on evolutionary processes was the emergence of the field of sociobiology, officially launched in 1975 by E.O. Wilson’s Sociobiology: The New Synthesis, and its sequel, On Human Nature, in 1978. These works helped to establish an interdisciplinary approach to understanding the evolution of heritable physical and social traits in all animal species, including humans. The sociobiological movement overcame initial criticisms of biological reductionism and genetic determinism and went on to spur a wealth of new research that continues to flourish decades later.

The field of sociobiology hosted lively internal debates as well, not the least of which concerned the locus of natural selective processes. One school of thought places primary emphasis on the theory of kin selection. This concept, which originated in the earlier works of biologists Hamilton (1963, 1964), Trivers (1971, 1972), and Alexander (1974), proposes that individual organisms maximize their own reproductive success or inclusive fitness by behaving altruistically toward close kin, weighted by the degree of genetic relatedness. The theory, also known as Hamilton’s Rule, was supported by a mathematical formula that calculated that altruism will develop to the extent that the benefit to the recipient times the degree of kinship to the altruist is greater than its cost.

Kin selection as the principal driver of human social evolution gained widespread acceptance among biologists, including E.O. Wilson, for about four decades. Commencing in 2010, however, a series of coauthored papers by Wilson and others challenged the mathematical and biological validity of kin selection theory as an explanation for the evolution of advanced social behavior.³ In its place has emerged the concept of multilevel selection, in which the evolutionary dynamic is seen as operating simultaneously at both the individual and the group levels. As proposed by Wilson (2012: 162), individual selection is based on competition and cooperation within groups, and promotes selfish behavior by its members, whereas group selection is based on competition and cooperation between groups, which promotes internal altruism. Wilson views human evolution as a product of these conflicting selective processes in which the interests of the individual must be balanced against the interests of the larger collective.

Multilevel evolutionary theories assume that groups that develop internal structures for cooperative endeavors have adaptive advantages that accrue to their membership. Robin Dunbar (2008), for example, proposes that individuals enter into social contracts to enhance their prospects for survival and reproductive success. He goes on to caution, however, that multilevel selection should not be confused with group selection:

In kin selection, the final arbiter of what happens is the gene, not the group as an entity, and hence it requires no new mechanism of evolution other than standard Darwinian processes. . . . In multilevel selection again, the unit of evolutionary cost-accounting is the gene, and not the group. Group-level processes are intended to facilitate the successful replication of the individual member’s genes, not to facilitate the successful replication of the group. The distinction is subtle, but important. (Dunbar 2008: 147)

Richard Dawkins, in The Selfish Gene (1976) and The Extended Phenotype (1982), cast the gene as the sole protagonist in the evolutionary drama, discounting the role of both individual organisms and groups in the 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