Princeton/Stanford Working Papers in Classics Evolutionary psychology and the historian Version 1.0 April 2013 Walter Scheidel Stanford University Abstract: New possibilities have been opened up for historians by a new wave of engagement with biology, or more particularly with human biology, for the study of human history, environmental history, health history, and the co-evolutionary history of humans and other species. This paper critically explores the uses and limits of evolutionary psychology for the study of history by focusing on the particularly intensely discussed phenomenon of incest avoidance. © Walter Scheidel. [email protected] “He who is the son says this to his mother: ‘Let us give (ourselves) in bodily intercourse so that we shall not have fear of Hell, and the sins we have committed will go from the account, and at the Cinwad Bridge [of posthumous judgment] we will be (pure in) heart, and a beautiful and seemly place will be ours, and we shall please Ohrmazd and cause harm to Ahriman.’ The mother says this to (her) son if she speaks righteously: ‘I give (myself) to you (in) bodily intercourse,’ even as that son said. The father says this to (his) daughter, the brother says this to his sister, (so) the sister says this to her brother.” 1 In the former Zoroastrian tradition represented in this text from around 900 CE, sexual relations between members of the nuclear family were not only to be encouraged but meant to result in progeny: “And there are those children who are born of a father and his daughter. Light flashes and glows and can be seen in course of time; and very fortunate and pleased is someone who has a child of his child (…). It is fitting that such sweetness and joy result from the son of a man whom he begets from his own daughter, a child who is a brother of the same mother. And he who is born of a son and his mother is also the brother of his own father: this is a way of much joy and praise, and the harm never exceeds the advantage, and neither do flaws exceed the beauty.” 2 At first sight, the global historical record appears to furnish us with actual instances of comparable behavior, most notably in ruling families from ancient Egypt and Iran to Inca Peru and more recently Laos, Hawai’i, and central Africa. In Egypt under Roman rule, even commoners are reported to have married and procreated with their full siblings. Yet, as we shall see below, reproductive marriages within the nuclear family are rarely unequivocally documented, and when placed in context even the breathless exhortations quoted above betray uneasiness about this conduct. 3 Why is that so? Notwithstanding notable differences in perspective, Émile Durkheim, Sigmund Freud, Bronislaw Malinowski, Talcott Parsons and Claude Lévi-Strauss all concurred in interpreting constraints of incestuous behavior as the result of a powerful “incest taboo” that had emerged through cultural evolution. The taboo’s perceived purpose was to prevent socially disruptive sexual relations among very close kin which, thought to be latently desired, were otherwise expected to occur. 4 This model presents historians with potentially serious challenges: if the avoidance of marriage and/or procreation by parents and children or full siblings arose from a cultural construct, global adherence to this principle would seem hard to reconcile with otherwise protean contingencies of cultural diversity and change over time. Conversely, observable exceptions to this norm ought to have triggered problems that the taboo was supposed to forestall, such as destabilization of the family unit or weakening of group solidarity. And in so far as sexual attractions existed within the nuclear family, socially sanctioned release from the taboo – as provided by Zoroastrian doctrine – might be expected to have become a popular measure. All these logical implications of a purely cultural model of “incest” avoidance are problematic to varying degrees. 5 Evolutionary Psychology (EP) offers a complementary way of accounting for universal constraints on reproduction within the nuclear family by positing a biological contribution to actual avoidance behavior. This approach is complementary rather than alternative in that it is fully compatible with the notion of cultural specific prohibitions (or the lack thereof, as in the Zoroastrian record): instead, it seeks to provide a more complete understanding of historically observed behavioral propensities. Among historians, engagement with the expanding field of EP has ranged from minimal to non- existent. Even those who tend to be indifferent to biology might be prepared to make an exception for the This paper was prepared for a forum on Biology and History. 1 The Pahlavi Rivayat Accompanying the Dadestan i Denig 8g1 (late ninth/early tenth century CE), translated by Alan V. Williams, The Pahlavi Rivayat Accompanying the Dadestan i Denig, Part II: Translation, Commentary and Pahlavi Text (Det Kongelige Danske Videnskabernes Selskab 1990), vol.2, 14. 2 Denkard 3.80 (early tenth century CE), adapted from the French translation by J. de Menasce, Le troisième livre du Denkart (C. Klincksieck 1973), 87-88. 3 For discussion and references, see below, nn.41-50. 4 Jonathan Turner and Alexandra Maryanski, Incest: Origins of the Taboo (Paradigm Publishers 2005), 14-52 provide a convenient survey of their and other theories. 5 The final implication conflicts with the Zoroastrian record discussed below (at nn.44-46). 2 notion that human behavior is influenced by inherited traits – by treating it with outright suspicion (or worse). Regardless of whether or not this attitude is justified, this particular approach should at the very least not be dismissed for the wrong reasons, based on generic polemics and reflexive misapprehensions about its agenda.6 Reduced to essentials, EP draws an analogy between the evolution of the brain and the rest of the body. Just like all organisms, the human body has been shaped by selective pressures. In response to these pressures it has developed thousands of adaptations, traits that were conducive to its survival and reproductive opportunities in the context of the physical and social environment which generated these pressures. 7 That is why we see, walk upright, and talk. There is no good reason why our brain, which accounts for 2 percent of our body mass but absorbs 20 percent of its energy, should have been exempt from this adaptive process: it is a product of selection just as any other body part. EP elaborates on these mainstream positions by hypothesizing that selection molded the brain in a way that created innate 8 propensities for adaptive behavior, defined as behavior that promotes transgenerational genetic survival. Because the evolution of such traits take time, any such adaptations would have emerged in response to conditions in what EP terms the “Environment of Evolutionary Adaptedness” (EEA), which is not to be thought of as a single concrete physical environment but rather as “the statistical composite of the enduring selection pressures of cause-and-effect relationships that pushed the alleles underlying an adaptation systematically upward in frequency until they became species-typical or reached a frequency-dependent equilibrium.” 9 In this respect, such traits would not be different from other adaptations in the human body, which likewise evolved under changing environmental constraints. This theory raises two simple questions: is it true that such inherited psychological adaptations exist, and if they do, how can they be identified? In a narrow sense, the only real counterfactual to the first assumption would be a “blank-slate” model of the brain that has long been discredited. What is open to debate is merely the degree of specificity of such behavioral traits: proponents of EP hypothesize a comparatively high degree, postulating the evolution of universal behavioral propensities that are directly germane to life-and-death matters such as mating behavior, parenting, and group living. Here it is important to note that even if such traits could be shown to exist, they would in no way result in “genetic determinism” in any strict sense of the term: inherited psychological adaptations would constrict human behavior no more than the anatomy of the human hand confines its use to tasks which sustained its evolution. Such traits can only be identified by testing hypotheses broadly and cross-culturally in order to control for the effects of environmental (including cultural) influence. Due to most EP researchers’ background in psychology and anthropology, existing work privileges interpretation of observed behavior over investigation of the underlying physiological mechanisms and processes down to the biomolecular level, even though the latter is in principle part of the overall program. EP-inspired scholarship has generated a large number of case studies designed to provide empirical support for and theoretical fine- tuning of its premises, which cannot be surveyed here even in the most perfunctory manner. 10 Suffice it to 6 For the ferocity of the earlier debate about “sociobiology”, which was both broader (by including animal behavior) and narrower (by focusing on social behavior) in scope than EP, see Ullica Segerstrale, Defenders of the Truth: The Sociobiology Debate (Oxford University Press 2000). More recent criticism of EP is addressed in the careful rebuttal by Edward H. Hagen, “Controversial issues in Evolutionary Psychology,” in David M. Buss (ed.), The Handbook of Evolutionary Psychology (Wiley 2005), 145-73. For an even-handed critique, see David J. Buller, Adapting Minds: Evolutionary Psychology and the Persistent Quest for Human Nature (MIT Press 2005). 7 Which is definitely not the same as saying that every feature is adaptive: cf. Stephen J. Gould, The Structure of Evolutionary Theory (Belknap Press 2002). 8 “Innate” propensities would be gene-based but expressed through interaction with exposure to environmental conditions, that is, epigenetic processes (see the paper by ###) and learning.