This book examines Darwinian social science through the substantive topic of incest and inbreeding avoidance, a behavior forward by human sociobiology as the best example of sociocultural behavior naturally selected in humans. 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. Beginning with E. O. Wilson, sociobiologists have commonly claimed the genetic depression explanation for incest avoidance as one of the jewels - if not the canonical gem - in the sociobiological crown.
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. Although not all Darwinian theorists of social behavior deserve to be tarred with the same brush, Leavitt uncovers more than enough cause for dismay. To begin with, he finds that parts of the evidence used to support the inbreeding hypothesis do not warrant the weight placed on it; other aspects have been tendentiously (and sometimes incorrectly) interpreted; and yet other elements can be accounted for with more parsimonious explanations. Furthermore, although the cornerstone of sociobiological theorizing is the idea that genes or gene complexes generate complex, flexible behaviors, Leavitt points out that there is as yet no unequivocal evidence to support this proposition.
Of course, this hardly invalidates the thesis any more than, say, the absence of unequivocal evidence for the existence of energy strings and multiple dimensions invalidate string theory. The difference is that string theorists explicitly designate strings and multiple dimensions as hypothetical; they regard their existence skeptically; and they make constant efforts to test these basic propositions by deducing empirical consequences, by analyzing them for theoretical inconsistencies, and by examining how they conform with other, better substantiated theory. By contrast, Leavitt argues, sociobiology routinely hypothesizes the existence of full-blown, generative gene complexes behind incest avoidance, cannibalism, sacrifice, war, and other complex behaviors, yet it rarely tries to demonstrate or test the hypothesis. Too little consideration is given even to detailing possible intermediate steps through which such complexes might have evolved over time. A plausible explanation of how and why an inbreeding species might make the transition to outbreeding practice, for example, would go a long way to shoring up the inbreeding theory and might open up ways of testing it.
Yet, Leavitt notes, this has still to be carried out. To be sure, such an exercise is far from easy, but the difficulties can hardly be more thorny than those encountered by string theorists. 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. Where Leavitt has identified lacunae in the paradigm, these need to be addressed. Where the data have been misrepresented or over-interpreted, either further observational work needs to be done or the data have to be jettisoned from the debate.
If there are differences over the interpretation of the data, the empirical weakness needs to be acknowledged rather than sidelined or ignored. And - to admit a criticism that is inevitable, whether it is true or not - if Leavitt has misconstrued the arguments or the data, the error needs to be explained in detail, not dismissed offhand. In fine, Leavitt's work offers a rare opportunity for us to advance social science in a manner commensurate with that of the physical sciences. 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. These endeavors have permeated social sciences as far apart as cognitive science and political science, but it is perhaps most prevalent in anthropology. In cultural anthropology, the most familiar manifestation is Marvin Harris's 'cultural materialism'. For many years, Harris stipulated that cultural complexes were adaptive and that they had evolved through some kind of Darwinian process.
Not long before his death, he renounced this claim, but under the title of a "truly scientific archaeology" it is now ascendant in archaeology in the form of Robert Dunnell's 'selectionism'. Here, as in sociobiology, Darwinian theory is applied to the understanding of complex human behaviors, but the evolutionary vehicle is the action of natural selection on cultural traits, which are explicitly treated as analogs of genes. If the underpinnings of sociobiology are as tenuous as Leavitt argues, how much more tendentious must be those of selectionism? To the problems Leavitt identifies in sociobiological theorizing must be added the further difficulties associated with treating cultural traits as gene equivalents - not least the problem of identifying the mechanism that fixes 'successful' cultural traits in a population in the way that the physico-chemical properties of the universe fix 'successful' genes in a population.
The transmission and accumulation of adaptive genes down the generations is guaranteed by the properties of matter; nothing has yet been identified as the equivalent mechanism that, absent humanintention, would ensure the transmission and accumulation down the generations of adaptive cultural traits. The second issue on which Leavitt's work bears is the so-called 'cargo-cult' nature of theoretical development in the social sciences. As Thomas Kuhn observed quite some time ago, the social sciences have yet to move beyond a "pre-paradigm" stage of multiple schools of thought, characterized by division and polarization. In these disciplines, theoretical and methodological progress is characterized by frequent "crises", "critical moments", or "crossroads". New theoretical frameworks are welcomed with rapture or resisted with exasperation. Sociobiology is an instance in point - greeted as the end of social science by its adherents, and ridiculed (if not reviled) by unbelievers - yet it is hardly exceptional.
In the last half century, to take the sub-discipline with which I am best acquainted, cultural anthropology has seen structural functionalism, action theory, structuralism, symbolic anthropology, interpretivism, practice theory, and post-modernism come and go, not so much as an orderly theoretical progression towards more powerful theory but rather as a series of frameworks embraced with millenarian fervor, fitted out with all manner of data, and then abandoned to the litter of anthropological history when a new scheme appears. Why does this happen? Why don't the social sciences proceed in a less evangelical and more measured manner? Part of the problem lies in the complexity of our subject matter, the human brain, which far outstrips that of any other known physical phenomenon. Part of it lies in the greater ethical and practical difficulties of generating reliable data about the behavior of humans compared to those involved in studying matter. But part of the problem also lies in what may be the product of these difficulties: a progression of frameworks so grand and reductive that inevitably they must be asserted, not argued on the merits.
With the zeal of the converted, adherents create the discourse that learns and applies the new, embracing framework; with the antagonism of the unbeliever, critics want nothing to do with it beyond lobbing polemical grenades or moral accusations. The end result is a defensive attitude on both sides towards the infidels beyond the walls. Proponents end up talking to themselves and no-one else, and the critical questioning that should be the hallmark of scientific advance goes by the board. Fortunately for us all, Leavitt has tried to side-step this sad history: he assesses sociobiology on the merits. If sociobiology responds with a reasoned and empirical defense to the particulars of his case, there may be opportunities and lessons here for social science as a whole.