Incest and Inbreeding Avoidance. A Critique of Darwinian Social Science

Author: Leavitt, Gregory C.

Nominated for the prestigious Adele Mellen Prize for Distinguished Contribution to Scholarship
This study is a sociological critic of Darwinian social science (human sociobiology), i.e., the application of Darwinian natural selection theory to complex human social behavior. More specifically, the manuscript examines Darwinian social science through the substantive topic of incest and inbreeding avoidance, a behavior forwarded by human sociobiology as the best example of sociocultural behavior naturally selected in humans. The sociobiology approach is now commonly presented in public forums and media leaving the impression on the general public that sociobiology and its many claims are scientific fact.


“I first encountered Gregory Leavitt's work while I was myself researching incest avoidance and the incest taboo. Like many anthropologists with limited expertise in genetics, I had assumed that inbreeding was securely established as a source of genetic depression. To be sure, anthropologists have commonly identified other factors as also having causative influences on incest avoidance and taboos, but I had presumed that the deleterious consequences of inbreeding had to be one-if not the ultimate--causative factor in a full accounting of the phenomenon. At around this time, though, Leavitt published in the American Anthropologist a cogent challenge to the conventional wisdom, and it seemed to throw everything back up into the air. Accordingly, in my own writings, it seemed best to side-step the issue, pending further research by those qualified to conduct it. In this book, Leavitt returns to the topic with an extended, systematic examination of the inbreeding theory. From lacunae in the special and general theory of evolution, through the ethological evidence commonly used to support the existence of inbreeding avoidance in sexual species, to the oft-cited kibbutzim data, he mounts what is surely the most comprehensive critique that has ever been addressed to a theory of incest. Marshaling a range of disparate, sometimes neglected sources scattered through several disciplines, he trains an impressive level of fire on what many have accepted as the standard explanation for the incest taboo.

Leavitt's treatment of the inbreeding and incest issue is neatly folded into a second, more encompassing focus: a rigorous critique of sociobiology … Tackling sociobiology at what it claims to be one of its strongest points, Leavitt uses his critique of the inbreeding argument as a point of departure for exploring broader inadequacies and weaknesses in sociobiology. In a theoretical field that prides itself for its "scientific" approach to social behavior, Leavitt finds a disturbing level of 'unscientific' sloppiness and an unsettling absence of 'scientific' skepticism.

Leavitt even musters a critique of Darwinian theory, a risky exercise given the difficulties of mastering such a specialized and sprawling field and the defensiveness that biologists no doubt feel in the face of the ill-informed attacks and sometimes deceptive tactics of creationists and proponents of intelligent design. Some of the critics he cites-Gould, Lewontin, and most especially Behe-have provoked controversy, and only evolutionists can judge the ultimate value of Leavitt's critique. For a social science audience, though, these chapters are useful reminders that evolutionary theory has yet to be nailed down in all of its particulars, and they are valuable summaries of the issues that are and are not still in dispute.

The real value of this book, though, lies in what it is not and in what it offers to sociobiology as well as to its critics. There can be no doubt where Leavitt stands on the issues, but what makes this book so exceptional is the absence of shrillness and polemic. There are no appeals to the standard and tiresome bogeys of chauvinism and racism with which sociobiologists are usually tarred. Nor is there resort to the tired claim that sociobiologists are uncritically externalizing western cultural assumptions (in contrast to the critics who make this charge, from whose eyes the cultural scales supposedly have fallen). Instead, Leavitt has done what is too rarely ventured, both within and beyond sociobiology. Rather than lobbing polemics, he has endeavored to engage sociobiology on its own terrain, to apply the critical eye that one wishes sociobiologists themselves had more rigorously applied. He mounts a strong and exhaustive case for the prosecution in a hearing that is long overdue, and social science and sociobiology will be well served if sociobiologists seize the opportunity and organize a detailed case for the defense.

There are two broader matters in social science to which Leavitt's inquiry also makes valuable contributions. The first concerns persistent attempts to apply Darwinian theory not to genes, as sociobiologists do, but to memes—culture … The second issue on which Leavitt's work bears is the so-called 'cargo-cult' nature of theoretical development in the social sciences … Fortunately for us all, Leavitt … assesses sociobiology on the merits.” – (from the Commendatory Preface) Dr. Paul Roscoe, Chair, Department of Anthropology, University of Maine

“The author displays impressive breadth of knowledge across the fields of evolutionary biology, sociobiology, and cultural and biological anthropology. To support his thesis he draws deftly on both classical and contemporary contributions to these fields … This book ably presents a solid cultural-materialist alternative to biologistic explanations catering to the perennial public appetite for simple answers … Contextualizing incest avoidance as a case study for examining “Darwinian social science”—a creative conception, engagingly executed! Bridging disciplines as it does, and with a fine foreword by Paul Roscoe, Professor Leavitt’s volume deserves a broad audience.” – Dr. Robert Bates Graber, Professor of Anthropology & Sociology, Truman State University

Table of Contents

1. Introduction
2. Theories of Organic Evolution
3. Natural Selection: A Critical Review
4. Darwinian Social Science
5. Darwinian Social Science: The Human Sociobiological Explanation of Incest/Inbreeding Avoidance
6. Inbreeding Effect
7. The Ethological Studies
8. The Human Community Studies
9. The Incest Taboo: A Look at Sociocultural Explanations