Evolutionizing human nature

New Ideas in Psychology 40 (2016) 103e114

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Evolutionizing human nature John Klasios York University, Toronto, Ontario, Canada

a r t i c l e i n f o

a b s t r a c t

Article history: Received 30 August 2014 Received in revised form 29 July 2015 Accepted 25 August 2015

Many have argued that the very notion of human nature is untenable given the facts of evolution and should accordingly be discarded. This paper, by contrast, argues that the notion can be retained in a coherent and modern way. The present account expounds on the view of human nature as a collection of species-typical psychological adaptations, and outlines how it can be understood in formally modeled computational terms. The view defended is also heavily developmental and connects directly with contemporary evolutionary developmental biology. Furthermore, the notion of human nature developed here allows us to abstract away from the obfuscating variability that manifests not only between individuals across ontogeny, but also cross-culturally and throughout time. © 2015 Elsevier Ltd. All rights reserved.

Keywords: Human nature Evolutionary psychology Adaptationism Darwin Homeostatic property clusters Developmental systems

The view that there is a coherent notion of human nature has been attacked by philosophers (e.g., Buller, 2005; Hull, 1986). Perhaps one of the most frequently heard criticisms of the notion of human nature is that it implies an essentialist rendering. And if what one has in mind by the notion of human nature is indeed something along the lines of a rigid essentialism, then such a notion is untenable in light of Darwinian evolution. In this paper, I aim to approach the issue from a different angle and defend an alternative notion. To this end, I will propose and explicate an EvolutionaryPsychological Notion of Human Nature (EPNHN) in the hopes that it can provide us with an evolutionarily-grounded definition of what the notion of human nature could mean. Specifically, a notion of human nature that is informed by Evolutionary Psychology and modern evolutionary science more broadly can provide a workable conceptualization that is unencumbered by the outmoded essentialist understandings that many argue render the concept problematic. In general terms, the view that there exists anything like a human nature was challenged once evolutionary thinking transformed our view of species. For one thing, evolutionary thinking upset the view of species as eternally fixed entities, replacing it with the view that species are instead mutable. The old view saw species as typological entities defined by a fixed set of traits. But the new evolutionary view of species held that there were no

E-mail address: [email protected]. http://dx.doi.org/10.1016/j.newideapsych.2015.08.004 0732-118X/© 2015 Elsevier Ltd. All rights reserved.

traits that defined species such that each and every member of a given species must possess all of its defining traits. For evolutionary mechanisms all but assured that there would always be one organism or more belonging to a putative species that did not possess one trait or more that typically defined that species. This new kind of “population thinking” therefore undercut the traditional view that species possessed fixed and clear-cut essences (Mayr, 2006). This had especially become apparent with Darwin's (1859) On the Origin of Species, if not prior to it with the work of Lamarck (1809). Evolutionary approaches to psychology have a pedigree that extends as far back as Darwin (1871), and a number of attempts to bring evolution to bear on the discipline have been attempted in the intervening period. Prominent historical figures in the field, such as Freud and Piaget, also attempted to integrate various evolutionary considerations into their theorizing. For instance, as will be discussed later, the notion of “relative bargaining power” recently utilized by Evolutionary Psychologists has an historical lix Le Dantec antecedent in the work of the French biologist Fe  de nuire” (ability to (1911), who spoke of a similar “capacite inflict harm). The present project attempts to continue the tradition of evolutionary approaches to psychology more generally, albeit in terms of the more recent approach of Evolutionary Psychology. The account developed here will be an attempt to spell out what Evolutionary Psychologists might mean when they speak of a human naturedthat is, insofar as they might aim to define and

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empirically discover our human nature. So, the EPNHN should also be viewed as a defense of what the overarching research program of Evolutionary Psychology ultimately might mean insofar as it speaks of, or alludes to, human nature. In developing and defending the EPNHN, the goal will not so much be to define a notion of human nature that coheres in every last detail with everything any Evolutionary Psychologist might have said about such a notion. Rather, the EPNHN should be seen as aiming to be at least broadly consistent with the general foundational tenets of the larger research program of Evolutionary Psychology (e.g., Pinker, 1997; Tooby & Cosmides, 2005). Moreover, most of the examples I give to illustrate the EPNHN will be similarly taken from Evolutionary Psychology. Interestingly, the EPNHN will also make some contact with the modular view of cognition advocated by some Evolutionary Psychologists. 1. Delineating human nature To a first approximation, I claim that the basic entities that comprise human nature will be all of the psychological adaptations, in the evolutionary-biological sense of the term, which all humans tend to possess. To put the point differently, the EPNHN aims to proverbially carve human nature at its ontological jointsdthat is, to provide a view of human nature in terms of its most basic psychological units. And as the EPNHN sees it, those most basic psychological units are psychological adaptations that have been designed by natural selection.1,2 This particular emphasis on adaptations can be construed as consonant with what Godfrey-Smith (2001) has dubbed “explanatory adaptationism”, which stipulates that the most striking feature of the biological world is its apparent design, as embodied by the adaptations of organisms. In what follows, I will elaborate on and refine this first pass definition of the EPNHN. 1.1. Human nature as a homeostatic property cluster of psychological adaptations The EPNHN can be viewed as an attempt to see human nature as a natural kind, and psychological adaptations, in turn, are to form the constituent components of that kind. Accordingly, we will need a framework of natural kinds, and to that end I propose to deploy the view of natural kinds as homeostatic property clusters developed by Boyd (1999). As it happens, this view of natural kinds has the added virtue of being a highly influential way of conceptualizing biological kinds. The homeostatic property clusters framework will illustrate what it might mean to say that psychological adaptations make up the basic constituents of human nature.3 By viewing natural kinds in this way, it will permit us to (1) advance a notion of human nature that sees it as a natural kind; (2) claim that the collection of psychological adaptations that all humans tend to possess comprises the cluster of properties that constitute human nature; and (3) absolve our notion of human nature from having to satisfy the outmoded, pre-Darwinian notion of essentialism. Moreover, the homeostatic property cluster (HPC) view of natural kinds would also permit us to view each constituent psychological adaptation

1 Use of intentional language at any point in this paper, such as the notion of “design”, is merely a pragmatic means of facilitating explication and should in no way imply foresight on behalf of the evolutionary process, or the existence of a designer. 2 I use the terms psychological adaptation and cognitive adaptation as essentially interchangeable. 3 In his defense of the notion of human nature, Samuels (2012) also makes use of the approach to natural kinds set forth by Boyd (1999).

as itself a natural kind, as each such psychological adaptation can in turn also be seen as comprised of a HPC. Crucially, as per the HPC view, it would not be necessary for all individual humans to develop all of the psychological adaptations that collectively make up human nature. For, very roughly speaking, an HPC rendering of human nature as a natural kind would assert that individual humans tend to possess the property cluster that makes up human nature in virtue of their belonging to the same species. As the HPC view would have it, individual humans would possess human nature because of the historical processesdspecifically, in this case, a deep history of natural selectiondthat made it such that each human tends to possess a cluster of relevant traits, each of which tends to covary with the others. As an upshot of this, developmental anomalies, physical insults, genetic mutations, and so forth, which might result in various individuals failing to possess one or more of the psychological adaptations that make up human nature, would therefore leave the status of human nature as a natural kind untouched. Similarly, an HPC construal of human nature as a natural kind would not require each constituent psychological adaptation comprising human nature to possess all of the same properties in each of its instantiations. For instance, a cognitive adaptation for language might vary with respect to a given property across individuals, with one or more individuals lacking a given property that the others possess. Similarly, two or more individuals could possess a given property, yet differ in various respects in just how that property is instantiated. For example, the property of language comprehension might vary between individuals along one or more of its dimensions. So, the existence of variation between individuals, such as the sort noted above, does not foreclose a given adaptation from being a natural kind, since the HPC view can accommodate such variance. Furthermore, a number of the psychological adaptations that make up our human nature as per the EPNHN could very well be largely or entirely conserved and therefore shared across various taxa (e.g., with our closest evolutionary cousins, the chimpanzees). Alternatively, a number of our species-typical psychological adaptations might be constituted in ways that are at least partially similardthat is, homologousdto psychological adaptations found in other species. In either of these casesdwhether largely or entirely conserved, or homologous to varying degreesdall such psychological adaptations would nonetheless constitute a part of the HPC that comprises human nature as the EPNHN sees it. For, the EPNHN aims to encompass all of the species-typical psychological adaptations of humans rather than only those psychological adaptations which are in some sense unique to humans. -vis alternative notions 1.2. The EPNHN vis-a Machery (2008) has recently proposed a nomological notion of human nature, one that he takes to counter various skeptical arguments.4 Since the EPNHN is fundamentally grounded in psychological adaptations, it will, broadly speaking, fundamentally issue in nomological regularities just like the account sketched by Machery (2008). As it turns out, both the EPNHN and nomological notion share in common the fundamental point that what counts as human nature are all those, and only those, nomological regularities that humans possess in virtue of those regularities having a selective history. That is, both views count as human nature all, and only those, nomological regularities

4 Machery's (2008) nomological notion aims to provide an account of human nature in terms of law-like regularities (hence the term nomological).

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that were selected for during the course of evolution. Conversely, byproducts, or traits that emerge as spandrels,5 do not, under the present view (and apparently Machery's view, for that matter), count as constitutive of human nature. Hence, the EPNHN, as well as Machery's notion, would encompass some subset of all the regularities evinced by humans. Accordingly, the EPNHN encompasses only a subset of the alternative “life-history trait cluster” notion of human nature presented by Ramsey (2013). Unlike the EPNHN and Machery's nomological notion, Ramsey's notion is much more permissive in what it counts as a part of human nature. In Ramsey's (2013) view, for instance, the hypothetical pattern that described “an antecedent ‘uncomfortable public-speaking event’ followed by ‘high cortisol levels’” (p. 988) would, if shown empirically to bear a causal relationship between the two variables at least to some degree, be a part of human nature. In contrast, the EPNHN rejects this permissive view, instead focusing on the nomological regularities that (1) stem directly from psychological adaptations, and (2) whose functions have been directly selected for. (Both of the foregoing points will be discussed in more detail later.) Of course, this is not to say that non-adaptationist-minded experimental work in the human sciences is unimportant or uninteresting. Rather, it is just to say that much of what appear to be nomological regularities do not properly count as parts of human nature as conceived by the EPNHN. Samuels (2012) also has recently developed a notion of human nature. In many ways, the EPNHN can be seen as both accommodating and melding the notions of human nature advanced by Machery (2008) and Samuels (2012). Unlike Machery's (2008) account but like the EPNHN, Samuels' (2012) proposal is anchored in the underlying cognitive basesdi.e., the structures and processesdthat give rise to the robust nomological regularities that are often taken as constitutive of human nature. Unlike the EPNHN, however, Samuels (2012) does not construe his proposal as defining human nature solely in terms of psychological adaptations per se. In this regard, and with reference to their underlying causal bases, Samuels' (2012) proposal apparently aims to accommodate all cognitiveepsychological nomological regularities, including the subset stemming from adaptations. But, to reiterate, the EPNHN is founded only on those nomological regularities that are caused by psychological adaptations, each of which carry out a specific naturally-selected function (or set of functions). So, another way of highlighting what is perhaps the central difference between Samuels' (2012) proposal and the EPNHN would be the following: While Samuels' notion is more indiscriminate in what it includes as a part of human nature (by counting all such regularities stemming from underlying cognitive structures and processes as part of human nature), the EPNHN, by contrast, is more restrictive and counts only those regularities that carry out the specialized functions of psychological adaptations. In other words, the EPNHN counts as a part of human nature only those psychological traits possessing specialized functions in virtue of having a selective history specifically for those functions. Additionally, the EPNHN appears to capture all four of the traditional criteria associated with the notion of human nature listed by Samuels (2012), and possibly satisfies the fifth, depending on how one construes the taxonomic criterion. As such, it can (1) delimit an area of inquiry the investigations of which speak directly to human nature; (2) describe what is constitutive of human nature; (3) provide a causaleexplanatory account of human

5 The term spandrel refers to any trait that emerges as a non-selected by-product of an adaptation (or as a by-product of two or more adaptations) (Gould & Lewontin, 1979). For a discussion of spandrels in relation to Evolutionary Psychology, see Buss, Haselton, Shackelford, Bleske, and Wakefield (1998).

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nature; and (4) capture the unique aspects of human nature (that distinguish it from other natures). So in this regard, it should be seen as on equal footing with Samuels' alternative. But since both the EPNHN and Samuels' notion employ the HPC view of natural kinds, it seems prima facie plausible that it could also satisfy the fifth criterion of the traditional notion(s) of human nature: as serving a taxonomic role. To sum up, the EPNHN, by orienting its construal of human nature specifically in terms of psychological adaptations, ensures the following: (1) that the focal nomological regularities that get picked out in virtue of serving specific naturally-selected functions are truly universal, rather than particular to specific and contingent cultural and ecological contexts, inter alia; and (2) that such nomological regularities persist across time, at least to a certain extent. With respect to psychological and behavioral differences occurring across space, the EPNHN, as will be seen later, specifically emphasizes the universal aspects of psychological adaptations which, at the very least, become apparent at some abstract level of analysis. Finally, an important caveat to note is that the homeostatic property cluster that constitutes human nature as per the EPNHN is in no sense a fixed property cluster that cannot change over evolutionary time. Hence, the EPNHN also has the resources for capturing the diachronic dimension of human nature. For new selection pressures can potentially change human nature. 2. The components of human nature Given that the present account of human nature sees it as a homeostatic property cluster of psychological adaptations, a treatment of how psychological adaptations feature in that account will be required. In what follows, I propose an approach to psychological adaptations that formally models them computationally. Just as importantly, however, psychological adaptations should be seen as being constituted bydthat is, physically subserved byddevelopmental systems embodied neurobiologically. So, the EPNHN should be taken to be in alignment with contemporary evolutionary developmental biology, which ought to be a virtue. Computationally modeling psychological adaptations as intrinsically developmental systems instantiated in the brain both highlights and captures the important fact that they emerge and are given expression throughout ontogeny. Importantly, the EPNHN stipulates that the developmental systems underlying psychological adaptations can be highly complex and quite open-ended. As such, viewing psychological adaptations as inherently developmental systems is quite congenial to the task of modeling them, since it is quite reasonable to expect that many if not most of them are complex and open-ended.6 In light of the above, then, the formal approach to modeling psychological adaptations adopted here should be seen as compatible with, and indeed embracing, recent developments in evolutionary biology, such as developmental systems theory and the extended synthesis more generally (e.g., Oyama, Griffiths, & Gray, 2001; Pigliucci & Müller, 2010). Indeed, meta-theoretical statements by prominent Evolutionary Psychologists (e.g., Tooby, Cosmides, & Barrett, 2003) also affirm the field's integrative orientation and therefore its theoretical compatibility with and embrace of such developments. Much confusion often accompanies the notion of “computation” in cognitive science in general, and Evolutionary Psychology in particular, so it will be quite helpful at this point to clarify the role it plays in the EPNHN. Essentially, only a very minimal notion of

6 Of course, the extent to which a given hypothetical psychological adaptation is complex, and if it is open-ended, the degree to which it is open-ended, are all ultimately empirical questions.

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computation is required: the rule-like (i.e., algorithmic) transformation of representations, both of which are instantiated in the brain. Compelling accounts in favor of the general view that some form of symbol-manipulationdviz., computationdis likely to comprise a central and important role in the brain have been advanced by Marcus (2001) and Gallistel and King (2010). In addition, Clark (2001) offers an elegant approach that attempts to reconcile and seamlessly integrate symbolic computationalism with the more recent rise of the “extended mind” perspective, the latter of which highlights the embodied, active, situated, and otherwise externally-enhanced nature of cognitive activity. Because psychological adaptations are to be modeled across ontogeny as well, models that are relatively fleshed-out will describe the computational dynamics of psychological adaptations qua developmental systems instantiated by brain systems. Formal computational models capture the functional nature of the psychological adaptations they model, but this is not to say that such formal models describe phenomena that float free of the neurobiological systems that embody them throughout development. In addition, formal computational models of psychological phenomena in general can be a theoretical and methodological boon, as they ultimately afford cognitive neuroscience the knowledge of what, precisely, the brain is doing in the first place, functionally speaking (Bechtel, 2007). The formal approach of computational modeling will allow one to remain open with respect to how psychological adaptations are precisely instantiated in human developmental biology and neurobiology. Relatedly, the developmental dynamics of representations and rule-like procedures postulated by formal computational models need not be discretely localized to neurobiological processes (i.e., they can be highly diffuse in their instantiations in the brain, as well as temporally extended). In addition, in investigating and modeling psychological adaptations, it will not be necessary to insist that every feature posited in a formal computational model will in fact turn out to correspond to real structures and processes found in brain development (or in the brain at any particular stage of ontogeny). For example, with respect to a hypothetical psychological adaptation, it may turn out that one or more of the representations or rule-like procedures postulated as part of its formally modeled developmental system will ultimately turn out to have no corresponding element(s) instantiated by developmental systems in the brain. In such a case, it would be necessary to excise the extraneous computational elements in the formal model.7 It is also worth mentioning that the EPNHN's computational modeling approach should not be seen as an alternative to more dynamical modeling approaches, whereby the latter might mistakenly be viewed as being able to capture aspects that the former cannot (Kaplan & Bechtel, 2011).8 In general, formally modeling psychological phenomena is a highly pragmatic if not necessary step in ultimately localizing such phenomena in the braindthat is, effecting a reduction of cognitive phenomena to their neurobiological bases (Bechtel, 2007). Moreover, in formally modeling psychological adaptations, one is fundamentally formulating “mechanism sketches” (Piccinini & Craver, 2011). Such mechanism sketches are intentionally incomplete or elliptical, and

7 For instance, advocates of the extended mind thesis argue that some or much of what standard computational approaches to cognition postulate in terms of representations and rule-like procedures have no correspondence in actual brains. Rather, such advocates believe that the embodied nature of organisms and external resources in the wider environment can, and frequently do, bear the cognitive burden that computational approaches presume to be met entirely by the brain. 8 See Bechtel and Abrahamsen (2010) for an example of a dynamical computational model.

they can be progressively filled in with more detail. Ultimately, a complete description of all the physical implementation details (i.e., structures, processes) will coherently map onto a complete description of all the functional details (i.e., representations, algorithms). And just as importantly, functional details and physical implementation details are mutually constraining, such that what functional properties a system exhibits must be instantiated somehow by physical mechanisms, and physical mechanisms, in turn, must constrain what the system can do, functionally speaking. In principle, computational modeling of psychological adaptations can be done at any point in development. Hence, one could model, say, our adaptation for folk physics as it functions at age 4 (at least in most children), or as it functions at any adult phase of life. At any rate, given the above considerations, we are in a position to sketch a first-pass definition of psychological adaptations according to the EPNHN: Psychological adaptations are developmental systems instantiated in the brain, and whose development and expression can be formally modeled computationally. 3. The functional design of developmental systems A psychological adaptation is a trait whose etiology traces to the effect(s) in virtue of which it was selected for. In plainer terms, psychological adaptations are selected for because of the effects they gave rise to ancestrally (although, strictly speaking, selection is more like a sieve that passively filters than it is an active “selector”). Moreover, the concept of adaptation can be seen as a concept of function, albeit one that defines function in the naturally-selected sense.9 In a very real sense, what natural selection does is filter less-fit variations in whole developmental systems. Since the EPNHN construes psychological adaptations as developmental systems embodied by the brain, developmental systems can be given functional descriptions.10 In addition, whole developmental systems, or at a more fine-grained level, structures and processes within a given developmental system, can in principle play a functional role in other developmental systems. Furthermore, since selection can co-opt a pre-existing trait for other functions,11 it should therefore come as no particular surprise if a developmental system, or a structure or process in one developmental system, plays a functional role in another developmental system.12 Hence, particular elements can have cross-cutting functionsdthat is, more than one functional role. This point will be elaborated on later, when the concept of modularity is connected to the EPNHN. As the EPNHN sees it, developmental systems are adaptations, and one of the hallmarks of naturally-selected adaptations, in turn, is functional design. Informal criteria diagnostic of functional design include (but are not limited to): the coordinated organization of structures and processes; functional specialization; and proficiency in solving some ancestral problem of survival and reproduction. To the degree that a trait evinces functionally specialized “design” (i.e., complexity, coordination between

9 Naturally, then, the selected effects concept of function (e.g., Neander, 1991) is at play here, rather than the causal role conception (Cummins, 1975). 10 Paralleling the view put forward in this section, Walsh (2006) also argues that evolutionary developmental biology vindicates Aristotelian “teleological essentialism”. 11 The term “exaptation” was introduced into the technical literature of evolutionary biology by Gould and Vrba (1982) to describe the process whereby natural selection co-opts pre-existing traits in the service of a new function (and perhaps while still serving the function(s) for which it was originally selected). 12 Indeed, mirroring the outlook of Jacob (1977), Marcus (2008) argues that the human mind is a “kluge” that shows signs of having evolved through processes of tinkering. Thus, one might expect on these grounds that models of cognitive architecture would reveal its jerry-rigged constitution. Hence, any given structure or process might be implicated in more than one psychological adaptation.

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constituent elements), the safer the inference will be that its origin owes to natural selection. This is because the second law of thermodynamics effectively shows that highly ordered physical states and processes are unlikely in proportion to the degree to which they are organized and functionally specialized, and because natural selection is the only known physical process that can generate such apparent “design”.13 In other words, natural selection is the only known physical process than can counter the (probabilistic) entropic “pull” toward ever greater disorder in the universe. Looking for signs of functional design, therefore, is a means by which adaptationsdand by extension their underlying developmental systemsdcan be identified.14 Correspondingly, the design features inhering within adaptations can permit for inferences of evolutionary function to be made. It is beyond the scope of the present paper to discuss the finer methodological and epistemological issues surrounding the discovery and reverse-engineering of psychological adaptations.15 For present purposes, the chief issue at hand is to provide an analysis of how the related concepts of adaptation and functional design are situated within the broader framework of the EPNHN. To be clear, the primary goal of the present paper is to set out a workable notion of human nature (and as it might be used in the larger research program of Evolutionary Psychology), rather than argue what the likelihood of actually identifying and reverse-engineering psychological adaptations is. Generally speaking, however, the discovery of adaptations and the reliability of functional hermeneutics are probably matters that must be examined on a case-by-case basis. So, for instance, an adaptation that evinced a more complex functional design (i.e., many coordinated design features) will probably be easier to identify (relatively speaking) than an adaptation possessing a lesser degree of complex functional design. Correspondingly, adaptations with higher degrees of complex functional design might also proportionally narrow the range of possible functional interpretations, whereas adaptations with relatively less complex functional design might be more ambiguous in this respect. For example, a functionally complex adaptation such as the eye is “well-engineered” for vision (its functional specialization), but not much else, if anything. In other words, the function of the eye relatively straightforwardly can be inferred from its form (viz., reverse-engineered). Doubtless, however, there are likely to be cases of real adaptations whose relative lack of functional complexity underdetermines our epistemic capacity to ascertain what their evolved functions are. Moreover, adaptations with relatively less functional complexity could very well make them difficult to identify in the first place. Identifying a particular psychological adaptation might prove to be extremely difficult, to say the least, if selection has cobbled together multiple preexisting adaptations and merely added to them slightly, and or altered them slightly. For instance, if selection forged adaptation1 by heavily relying on adaptation2, adaptation3, and adaptation4, all of which were preexisting, while only adding minimal new structure, say, such a state of affairs could very well pose a significant challenge to detecting the existence of that new functional adaptation, and also to inferring its function(s). Such a challenge might be ameliorated to some degree by careful attention

13 Interestingly, however, natural selection helps to increase overall entropy (in the global, universal sense) and is exactly what one might expect to emerge from a universe beholden to the probabilistic but ineluctable march toward greater entropy (Rosenberg, 2012). 14 Andrews, Gangestad, and Matthews (2002) discuss criteria for identifying adaptations specifically in the context of psychology. Likewise, Williams (1966) discusses informal criteria with respect to identifying adaptations in general. 15 For a negative case with respect to the merits of reverse-engineering biological adaptations in general and psychological adaptations in particular, see Richardson (2007). For more positive treatments, see Dennett (1995) and Lewens (2002).

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to the larger environmental context in which it was evolutionarily designed to develop and function (e.g., Lewens, 2002). 4. Evolutionary developmental biology, modularity, and cognitive flexibility This section will briefly survey some central ideas in contemporary evolutionary developmental biology and connect them to the EPNHN. It will be argued that evolutionary developmental biology helps to buttress the expectation of some Evolutionary Psychologists that the human cognitive architecture is modular in composition. Accordingly, a framework of cognitive modularity that is both evolutionarily and neurobiologically plausible will be briefly sketched. As we will see, the emerging view within contemporary evolutionary developmental biology is that life, too, is modular at a fundamental level. Granted, some key differences exist between the notion of biological modularity within evolutionary developmental biology on the one hand, and cognitive modularity within Evolutionary Psychology on the other. Cognitive modules are of course instantiated within the brain, and the working assumption for the purposes of the EPNHN is that they are therefore biological modules too. But since the framework of cognitive modularity is centrally a framework detailing the functional level of analysis rather than providing a biologicalephysical account of cognitive modules, it can for the most part remain open with respect to the precise neurobiological details that it ultimately maps on to. And since cognitive modularity is described in functional terms, the mapping of cognitive modules to brain systems need not, indeed very likely does not, correspond in a neat, discrete, anatomically localizable fashion (i.e., a module mapping onto a discrete chunk of neural tissue). Rather, cognitive modules are expected to be instantiated in a highly distributed manner in the brain (Barrett & Kurzban, 2006). One could argue that if the fundamental developmental units of biological life have evolved to be modular in constitution, then it leads one to believe that the brain could just as well be modular in constitution. Indeed, in ascertaining why biological organization itself has evolved to be modular, one can perhaps come to see what its selective benefits were throughout evolutionary deep time.16 As already alluded to, it is quite plausible to contend that evolutionary developmental biology largely vindicates the view that biological organization is modular in constitution.17 Evolutionary developmental biology is increasingly coming to show that biological modularity is itself a fundamental property of biological organization, and one that was itself selected for early in the course of life on Earth (Kirschner & Gerhart, 2005). One key reason why nature has opted for a highly modular approach to biological organization is because modularity permits for a high degree of evolvability.18 When developmental components of organisms are independent of one another to a relatively high degreedwhen they are more or less “semi-decomposable” (Simon, 1962)devolutionary change can commence with respect to a given component without affecting other components. When the development of organisms is largely non-modular, organisms are less disposed to evolutionary change, as the holistic nature of their developmental

16 This should not be taken to imply, however, that a comprehensive explanation of biological modularity will not invoke a variety of physical and biological constraints and contingent, path-dependent phylogenetic factors that were all implicated in its emergence. 17 For a general conceptual exploration of modularity in evolutionary biology, see Brandon (2005). 18 Wagner, Mezey, and Calabretta (2005) also discuss a number of theoretical models, in addition to models of evolvability, pertaining to the origin of modularity and survey relevant empirical research on the matter.

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processes tends to elicit multiple changes to the phenotype whenever a single, localized genetic change occurs (Schlosser & Wagner, 2004). More modular developmental processes permit for gradual evolutionary change, which incrementally builds on previous changes, simply because one genetic change can be more or less confined to a given local module without causing changesdparticularly negative, fitness decreasing disruptionsdto other modules (Schlosser & Wagner, 2004). This should not be taken to imply, however, that biological modules are not constrained in the manner in which they can evolve. To take stock, what is being contended, here, is that developmental systems are biological modulesdthat is, they are effectively equivalent, since developmental systems are physically instantiated by the developmental processes of biological modules. Another key strength of biological modularity is that the developmental processes of modules are more robust in the sense that they are better shielded against the effects of developmental processes occurring elsewhere in the organism. Hence, development of a given module can proceed in a more localized fashion. And although modules might hypothetically come to be designed such that their development utilizes the resources of other modules elsewhere in the organism, such utilization need not in principle affect the development of the modules from which developmental resources are drawn. In this sense, the collection of biological modules possessed by a species also constitutes an important part of the selective environment in which each constituent module evolves. And since biological modules constitute an important part of one another's selective environment, it should not be particularly surprising that they can co-evolve with one another. Yet another virtue of biological modularity is that since organismal development need not be orchestrated by a sort of “master homunculus” overseeing the entirety of development from the top-down, global order can emerge from relatively independent developmental processes occurring at a more local level (e.g., Kauffman, 1993, 2010). Once again, a key upshot of this brief survey of central themes in contemporary evolutionary developmental biology is that developmental systems are fundamentally biological modules. Selection acts on entire developmental systems (Oyama et al., 2001). So, when selection acts on psychological adaptations, it therefore acts on neurobiologically-instantiated modules as a whole. And those neurobiologically-instantiated modules, in turn, comprise the developmental systems that are tantamount to psychological adaptations. Importantly, since cognitive modules are instantiated by biological modules in the brain, each cognitive module can in principle evolve to utilize the cognitive resources of other cognitive modules, albeit only insofar as those cognitive resources are made available to the larger cognitive system. In addition, since biological modules constitute an important part of one another's selective environment, they can and often do co-evolve with one another as well. Another important upshot of the considerations presented in this section is that since psychological adaptations are developmental systems, and developmental systems, in turn, are instantiated by biological modulesdin this case, in the braindbiological modules are effectively what comprise the causalephysical bases that make up the homeostatic property cluster of human nature, as conceived by the EPNHN. It is well beyond the scope of the present paper to develop a fully articulated framework of cognitive modularity. Sophisticated, detailed, and empirically-informed frameworks of massive cognitive modularity have been developed elsewhere (Barrett, 2015; Barrett & Kurzban, 2006; Carruthers, 2006). Simply put, a massively modular cognitive architecture can be comprised by a collection of functionally-specialized psychological adaptations each of which is complex, dynamic, open-ended, and generative.

Furthermore, such psychological adaptations can develop and operate in parallel and interact with each other in ways that are, complex, non-linear, open-ended, and recursive. Because of the interactive nature of modular cognitive architectures, psychological adaptations can evolve to exploit the resources of existing psychological adaptations (insofar as they might be accessible). But in any case, the framework of massive cognitive modularity, when not hamstrung by unnecessary aprioristically-generated limitations, such as the insistence that all modules, central or peripheral, be defined in terms of strict Fodorian modularity (see below), appears to have the resources necessary to account for human cognitive flexibility and the evolved mind's capacity to deal with novelty. Of course, the details are a matter to be determined by empirical investigation (presuming the mind is modular in constitution). This brief sketch of massive cognitive modularity can also be construed as a “how possibly” modeldof how the cognitive capacities of humans can possibly be explained. It is worth underscoring the need to avoid placing a priori strictures on any theoretical framework aiming to capture the developmental and computational nature of the mind. What is important about a massively modular framework of cognition (keeping in mind, also, that cognitive modules are intrinsically developmental systems) is that it is an organizing frameworkdone analogous to the standard model of particle physics. For example, in the standard model of particle physics, concepts such as mass, charge, and spin apply to empirically discovered particlesdi.e., fermions and bosons. That is to say, such concepts are open parameters the values of which are empirically discovered with respect to each particle in the model. Likewise, with the framework of massive cognitive modularity conjoined to the acknowledgment that cognitive modules are instantiated by developmental systems in the brain, each module's particular parameters must be empirically discovered, and not, once again, determined a priori. Such parameters would include the extent to which a module possesses features famously described by Fodor (1983), such as the extent to which a module is capable of accessing information from elsewhere in the mind, or the extent to which its inner processes are accessible by other modules.19 Whereas in Fodor's original construal the properties possessed by modules took on a kind of one-size-fits-all characterization, more recent discussions of modularity, by contrast, leave each property to be determined on a case-by-case basis. For instance, only careful empirical research can reveal the extent to which a module is capable of accessing information from elsewhere in the mind, or the extent to which its inner processes (as opposed to its outputs) are accessible by other modules. In sum, however, whether we use the term “module”, “functionally-specialized psychological adaptation”, “mental gizmo”, or something else, is not so important. The modular framework is simply a useful organizing framework for conceptualizing the forms that psychological adaptations can take. Since the current paper advocates in favor of viewing modularity as an organizing framework, a critic who claimed that there is too much scope for ad hoc adjustments should also take issue with the standard model of particle physics. In principle, if enough observations said so, the mass and charge, say, of any number of particles would be adjusted in the model by physicists. Likewise, the properties of each

19 Fodor (2000) has argued that a modular, computational approach to cognition cannot be complete because, he alleges, it cannot for various reasons account for “central cognition”dviz., higher-order cognitive processes such as abductive reasoning and so on. However, Carruthers (2006, pp. 53e64) and Pinker (2005) counter with the charge that Fodor has seemingly overlooked forms of cognitive architecture and types of computational processes that very plausibly have the wherewithal of capturing central cognition in a computational, modular-like fashion.

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cognitive module must be determined in accordance with their precise, empirically determined nature. Furthermore, critics should aim to provide an alternative model that provides a better fit with empirical data. Perhaps the more interesting debate hereabouts, however, is whether a given psychological phenomenon results from an adaptation designed for that functionally-specialized purpose, or whether it arises as a by-product of one adaptation or more. In any case, the framework of modularity sketched here provides a useful way of conceptualizing the underlying cognitiveedevelopmental architecture that causes the psychological phenomenon in question. Having said all of this, however, perhaps an important qualification to make with respect to the identification of human nature with a homeostatic property cluster of psychological adaptations is to note the adapted nature, too, of the interactions between evolved cognitive modules. For on the massively modular framework of cognition, the flexibility of human cognition emerges from such a complex, interconnected architecture. Indeed, aside from the fact that psychological adaptations can be highly open-ended, such a complex, interconnected modular architecture can itself be seen as an adaptation to environmental heterogeneity, broadly speaking (viz., “complexity”dincluding social complexity). Indeed, it can be argued that environmental heterogeneity is what cognition most fundamentally is an adaptation to (Godfrey-Smith, 1996). As it turns out, this gloss on the interconnected nature of a massively modular cognitive architecturedthat it is adapted to environmental heterogeneitydis also in step with the well-known Machiavellian intelligence hypothesis. According to that view, human sociality was a centraldif not the centraldselection pressure that shaped the human mind throughout its evolution (e.g., Humphrey, 1976).

5. Human nature embedded in ontogeny It is generally the case (or at least we should plausibly expect) that cognitive adaptations are designed to unfold in open-ended ways, but open-ended ways that are nonetheless constrained or guided in a manner that has been designed by natural selection. For instance, we might very well expect the open-ended ontogenesis of various psychological adaptations to be conditioned by various types of input received during certain phases or junctures of development. To reiterate, as the EPNHN sees it, naturally selected psychological adaptations are ultimately developmental systems embodied by the brain. And as per developmental systems, cognitive modules can therefore potentially be highly “plastic”dor, to be more specific, can possess many open parameters in their design specifications. Many critics of Evolutionary Psychology (e.g., Fedyk, 2015; Lickliter & Honeycutt, 2003) mistakenly believe that modularity entails a rigid form of “nativism”. However, Evolutionary Psychologists largely eschew the label of nativism and the natureenurture dichotomy more generally, and many of its advocates embrace developmental systems theory in its full theoretical sense (e.g., Ellis & Bjorklund, 2005; Tooby et al., 2003).20 It is important to understand the nature of developmental systems in order to see how evolution can evolve adaptations that both emerge developmentally and which are highly open-

20 Incidentally, dynamical systems theory is also fully compatible with Evolutionary Psychology. Indeed, interesting theoretical connections between dynamical systems theory and Evolutionary Psychology have been developed by Evolutionary Psychologist Doug Kenrick and his colleagues (Kenrick, Li, & Butner, 2003; Kenrick et al., 2002).

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ended. Indeed, critics often argue that Evolutionary Psychology is a non-starter because its view (allegedly) runs afoul of what is known about the development, flexibility, and open-endedness of human cognition. With regard to the development of psychological adaptations, Barrett (2015) makes a crucial distinction between design space, which refers to the naturally-selected design of developmental systems, and phenotype space, which refers to the actual phenotypic outcomes of developmental systems.21 Very briefly, the design spaces of adaptationsdthat is to say, the naturally selected designs of developmental systemsdare a result of ancestral selection on populations of phenotypes. An extended explication of how design space is shaped is beyond the scope of this paper, but it is worth pointing out that the design spaces of adaptations reflect assumptions about the developmental environments in which they evolved. Thus, it is an open question as to how the design spaces of adaptations will develop and express themselvesdviz., what their precise outcomes will be in phenotype spacedoutside of the environmental conditions which ancestrally shaped those design spaces (Barrett, 2015). So, aside from the broader point that the developmental environment of psychological adaptations crucially determines what their phenotypic outcomes will be, the extent to which that environment deviates from the ancestral environmental conditions which shaped their design spaces is also important. Barrett (2015) also points out that both design space and phenotype space are massively multidimensional, in that both can have an extremely large number of dimensions along which variation in design or phenotype can occur. And the number of dimensions along which variation occurs depends on the particular trait in question. Furthermore, according to Barrett, the ways in which massively multidimensional design space are developmentally related to massively multidimensional phenotype space can be extremely complex and non-lineardalthough the exact nature of the developmental relations that obtain between design space and phenotype space again depends on the trait in question. Hence, the precise nature of developmental relations between design space and phenotype space is heavily contingent on the developmental environment in which an organism is situated. The developmental interaction between the environment (i.e., both endogenous and exogenous to the organism) and design space can give rise to a potentially wide range of phenotypic outcomes that the design space of an adaptation was naturally selected to produce. In other words, a potentially wide range of phenotypic outcomes can emerge by design. This point is worth emphasizing, since it underscores that there is no intrinsic tension between evolved adaptations on the one hand, and a potentially wide range of phenotypic outcomes emerging as a result of development on the otherdthat is, as a result of emergent design. Interestingly, although Evolutionary Psychologists generally eschew the notion of innateness, it is possible to argue that innateness is tantamount to the design space of organisms.22 However, one reason why we might wish to avoid using the concept of innateness is because many have construed innateness as implying that anything that emerges developmentally cannot be by designdthat is, as reflecting the functional rationale of an underlying adaptation (as reflecting its design space, in other words). For example, it would be wrong to insist that there is no underlying adaptation for acquiring language

21 This section's explication of the developmental and open-ended nature of psychological adaptations is heavily indebted to the work of Barrett (2015). 22 A number of philosophers have attempted to explicate and defend the notion of innateness (e.g., Ariew, 1999; Khalidi, 2007; Samuels, 2002).

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simply because, say, one population of children learns German while another population learns Cantonese. Neither population is born understanding and speaking either language, to be sure. And both outcomes depend on developmental processes and exogenous environmental input. But that does not mean that the underlying developmental system possessed by both populations of children does not embody a design space whose rationale is to acquire language per se (that is, a language, whatever it might be). Of course, in keeping with the homeostatic property cluster construal of human nature, even if we equate design space with innateness, various factors such as developmental anomalies, genetic mutations, environmental insults, and the like, can prevent adaptations from developing in accordance with their underlying design spaces. And equating the design space of adaptations with innateness also therefore allows various kinds of evolved, functionally-specialized learning processes, inter alia, to count as innate. Although many of the underlying cognitive adaptations that constitute human nature according to the EPNHN might be more or less discernible in some fashion during adult phases of ontogeny, some or many of them might be phenotypically expressed in species-typical ways only at earlier stages of ontogeny. In such cases, we would claim that the adaptation in question can develop along different paths, with the specific path taken being contingent on input from specific types of factors. Hence, viewing a psychological adaptation as it broadly unfolds and operates throughout ontogeny may reveal its species-typicalitydthat is, its design spacedwhereas such species-typicality might be obscured if one were simply to look at the adaptation as it operates at a later, adult stage of development. For instance, the psychological adaptation for learning and thinking about folk biology (Atran, 1998) might usefully be modeled at a certain stage of ontogenydperhaps at the stage wherein its species-typicality is most apparentdwith a description of its algorithms, representational formats, and so forth. Furthermore, examining the development of adaptations in many different individuals in a given socioecological context, and among individuals across different socioecological contexts, ought to make the underlying design spaces of psychological adaptations more apparent. On this note, Barrett and Broesch (2012) have found cross-cultural evidence among Shuar and American children (within the age-range 4-to-11) for a psychological adaptation tailored to learn about dangerous animals. Interestingly, the 4-to-6 year-old American children living in Los Angeles learned information pertaining to the dangerousness of certain animals in one shot, despite having relatively little exposure to such animals beforehand. In addition, like the Shuar children, when queried a week later the American children could recall the level of danger posed by animals better than information about the names and diets of the various animal stimuli. At any rate, it would stand to reason that such a psychological adaptation could be modeled computationally as it unfolds during ontogeny, with its critical design features being mappeddi.e., which specific inputs the overarching developmental system uses. Obviously, however, the postulated adaptation causes children in different ecologies to learn about different dangerous animals. So looking merely at the outcome of what the adaptation learns in particulardthat is to say, the particular animals that children learn to tag as dangerousdwould obscure the underlying features that are species-typical and that thus constitute the design space of the evolved adaptation. As with any psychological adaptation, however, filling in more of its developmental details will require a lot of careful (ideally cross-cultural) research with subjects of varying ages. At any given stage in the ontogeny of a psychological adaptation, one could computationally model its representations and rule-like procedures, and also its inputeoutput relations with other

psychological adaptations, inter alia. Various psychological adaptations might be designed by selection to develop in different ways, depending on environmental contingencies, and so highlighting their species-typicality will therefore require modeling, for instance, the crucial windows and or junctures during development that cause psychological adaptations to develop differently in different individuals. Doubtless many adaptations will turn out to be extremely flexible and capable of responding on very short timescalesdi.e., months, days, hours, minutes, and seconds. On the other hand, many psychological adaptations might just as well develop in a highly species-typical way right into adulthood. In such cases, although it would be legitimate to nonetheless model their developmental dynamics across ontogeny, one could also simply cast their explanatory focus on psychological adaptations as they operate in adults. For instance, Cosmides, Barrett, and Tooby (2010) argue that humans possess a psychological adaptation designed for detecting cheaters in contexts of social exchange. For the purposes of their explanatory goals, such a psychological adaptation can apparently be adequately modeled computationally as it functions in adults. Barrett (2007) has usefully employed the typeetoken distinction for the purpose of understanding how psychological adaptations can simultaneously be said to have functions which nonetheless possess open-ended parameters by design, including open-ended parameters that admit of evolutionarily-novel outcomes. Take the earlier example of a psychological adaptation designed to learn about dangerous animals in the local ecology, for instance. In such a case, dangerous animals per se would be the type of phenomenon that the psychological adaptation is functionally designed to learn about, though particular animals such as tigers and spiders would be individual token instantiations of that more general type. So, a computational model of a psychological adaptation for learning about dangerous animals in the local ecology should describe how tokens (i.e., tigers) of the underlying general type (dangerous animals) are developmentally generated. Fundamentally, however, the precise nature of the design space of any particular psychological adaptation is entirely an empirical question and cannot be determined in advance of careful and sustained scientific investigation. 5.1. The contingent manifestations of human nature A key virtue of the EPNHN is its capacity to pick out those aspects of human nature that are truly universal and that are therefore tantamount to the psychological design space of humans. For instance, one might imagine a state of affairs where a certain trait appears to be more or less universal among humans during a given point in historical time. In such a case, we might observe that humans perceive individuals in possession of a new Porsche 911 sports car to be of high status. We might also find in the course of empirical investigation that such a perception is generated by a psychological adaptation whose development comes to associate the Porsche 911 with high status. According to the EPNHN, however, it would be erroneous to view the function of the underlying psychological adaptation as imputing high status on those individuals in possession of a Porsche 911 per se. Instead, the EPNHN would guide one's attention to the function(s) of the psychological adaptation as reflected in design space, rather than its particular developmental manifestations in phenotype space per se. Specifically, and at least in a crude sense, we would instead take the imputation of high status on individuals in possession of a given type of object as the naturally-selected function of the focal adaptation. By computationally modeling the psychological adaptation

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across ontogeny, we might also come to learn interesting things about the properties that the individual tokens of the type must satisfy in order to count as objects indicative of high status (e.g., perhaps a reverse-engineering analysis of the design features of the adaptation converge with a separate analysis of the properties objects must possess in order for them to function as costly and therefore reliable signals [e.g., Miller, 2009]). In the current case, taking the ascription of high status to individuals in possession of a Porsche 911 per se to be the function of the underlying psychological adaptation would erroneously mistake the trees for the forest. That is, it would mistakenly take a contingent token outcome of the psychological adaptation as being its real function, when in actuality the real function is properly characterized at a more abstract level, namely in terms of a type. In this case, the function of the psychological adaptation would be to ascribe high status to individuals in possession of objects meeting certain criteria. Just to be clear, in this example, ascribing high status to Porsche 911 owners is a particular developmental outcome that resides in the phenotype space of the adaptation, but only the design space of the adaptation reflects its proper function: to ascribe high status to individuals possessing objects satisfying a certain criteria. Thus, there are many possible outcomes in phenotype space that developmentally emerge from, and are congruent with, the underlying function reflected in its design space. In any case, the key point would be that an EPNHN construal of what the true function of a psychological adaption is would be sufficiently abstract such that it would capture the truly universal aspects. That is to say, it would peel away the historically-, ecologically-, and culturally-contingent aspectsdwhich feed into the open-ended parameters of the adaptation that ultimately generate the tokensdand instead reveal the invariant aspects which actually constitute the function of the adaptation. As such, psychological adaptations might not necessarily be designed by selection to generate specific concrete tokens, even if those tokens are found at any given historical point in time to be very widespread, such as in the above example of Porsche 911s being ubiquitously processed as indicators of high status. Rather, to unveil the design space of a psychological adaptation, it is necessary to home in on the type of function(s) it is designed to facilitate (which in the above example would be to attribute high status to those individuals in possession of a certain type of object). 6. A database of human nature In light of the foregoing, we can begin to bring together elements of the EPNHN and envision what a database of human nature might ultimately look like. For each psychological adaptation that selection has forged, a computational model of its underlying developmental system could be provided. The functional rationale(s) of the psychological adaptationdviz., its design spacedcould also be described as well. The following discussion will attempt illustrate such a database by considering some examples of adaptationist hypotheses from within the literature of Evolutionary Psychology. To begin with, consider work by Lukaszewski and Roney (2011), who found evidence in favor of the hypothesis that extraversion levels are calibrated to some extent by an individual's physical attractiveness.23 Indeed, these findings have been framed as

23 Cross-cultural support for this hypothesis has also been found in a geneticallyinformative study of an Amazonian hunterehorticultural society (von Rueden, Lukaszewski, & Gurven, 2015).

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supporting an adaptationist hypothesis where extraversion levels are flexibly adjusted, at least in part, in proportion to one's physical attractiveness.24 Roughly speaking, higher levels of physical attractiveness yield self-assessments and or positive social feedback, which then serve as input into the adaptation. The input is then computed accordingly, causing one's disposition toward extraverted behavior to rise in proportion to one's overall physical attractiveness; lower levels of physical attractiveness, by contrast, has the opposite effect (via reduced positive social feedback and or negative self-assessments). In a human nature database, the entry for such an adaptation would include its naturally-selected rationale. Briefly, the description of its rationale would, amongst other things, state the following: (1) that it is a part of human nature to flexibly adjust one's level of extraversion contingent, at least partially, on one's level of physical attractiveness; (2) at least in ancestral environments, greater physical attractiveness (it is hypothesized) generally conferred increased success at attaining leadership roles, forming large social networks, and climbing status hierarchies (and so on); and (3) that an extraverted behavioral strategy was therefore adaptive under such conditions.25 Furthermore, in accordance with the EPNHN, the postulated psychological adaptation would be modeled in computational terms (both its development and operation), which would allow for its various design features to be explicitly mapped. A database of human nature might also be able to explicate the extent to which some sex-specific adaptations nonetheless share a common core.26 To illustrate, consider work by Sell, Tooby, and Cosmides (2009) which found experimental support for the adaptationist hypothesis that anger functions as a bargaining tactic. Sell, Tooby, et al. (2009) contend that humans possess an underlying adaptation which assesses the extent to which one's own welfare is valued by other agents within the context of interpersonal conflicts of interest. Furthermore, and correspondingly, Sell, Tooby, et al. (2009) also argue that humans appear to possess an underlying adaptation which computes the extent to which an individual can inflict costs and confer benefits on others. An individual's capacity to inflict costs and confer benefits on others is in turn taken to be cognitively represented by a regulatory variable, which is computed at least in part by an individual's strength and physical attractiveness. Moreover, the posited underlying regulatory variable governs one's anger proneness and sense of entitlement in having conflicts of interest settled in their favor. Sell, Tooby, et al. (2009), however, found that there were sex-differences in the postulated adaptation: upper-body strength had more of an impact on men's level of anger proneness and sense of entitlement in

24 In addition to physical attractiveness, this relatively nascent topic of research has found support for extraversion levels also being partly calibrated by other traits, including: physical strength; other condition-dependent traits, such as intelligence; and knowledge and skills valued by others. Such traits are also hypothesized to increase one's relative bargaining power (roughly, one's capacity to confer benefits and or inflict costs on others). The hypothesis holds that the benefits of extraverted behavioral strategies will be elevated, and their costs minimized, in individuals who possess such traits (i.e., high levels of attractiveness, strength, and intelligence). Evidence to date is consistent with the existence of a psychological adaptation flexibly calibrating extraversion levels in this manner (Lukaszewski & von Rueden, 2015; see also Haysom et al., 2015; Lukaszewski & Roney, 2015). The adaptationist interpretation of Lukaszewski and Roney (2011), it should be noted, is also quite consistent with the heritability of the Big Five personality trait of extraversion (e.g., Bouchard, 2004). 25 For a more detailed overview of this adaptationist hypothesis and supporting evidence, see Lukaszewski and von Rueden (2015). 26 A similar approach might also be applied, mutatis mutandis, to any relatively complex psychological adaptations that display differences between ancestrallydefined populations (e.g., Frost, 2011). This approach would also be in keeping with the HPC account of human nature and its constituent psychological adaptations.

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having conflicts of interest settled in their favor, whereas for women physical attractiveness played the larger role in calibrating the same dispositions. So one interpretation of these studies, so far as our database of human nature is concerned, would be to focus specifically on the aspects of the focal adaptation which are species-typical, as opposed to sex-specific. Accordingly, we might envision the entry for the adaptation in question as containing a computational model of those aspects common in both sexes. More specifically, the entry would spell out how the internal regulatory variable representing one's capacity to inflict costs and or confer benefits on others is expressed as increased anger proneness and sense of entitlement. Similarly, we might functionally describe the adaptation's rationale as governing the extent to which individuals feel that they can have conflicts of interest resolved in their favor, contingent on the extent to which they have the meansdviz., the ability to inflict costs and or confer benefitsdto enforce such favorable solutions. Similarly, a study by Lukaszewski (2013) supported the adaptationist hypothesis that a specific suite of personality traits (i.e., extraversion, fear of rejection, attachment styles) is flexibly calibrated by an underlying adaptation which computes an individual's “relative bargaining power”. Relative bargaining power refers, roughly, to one's ability to confer benefits and or inflict costs on others.27 For our current purposes, however, it need only be noted that a sex-difference was found in the manner in which the postulated adaptation computed one's relative bargaining power. Whereas both physical strength and attractiveness had independent effects on the postulated internal regulatory variable governing relative bargaining power in men, only attractiveness had such an effect on the same internal regulatory variable in women.28 Hence, an entry for such an adaptation in our database of human nature might focus only on the manner in which attractiveness in men and women serves as input into an internal regulatory variable computing one's relative bargaining power, which in turn flexibly calibrates the focal suite of personality traits (i.e., extraversion, fear of rejection, attachment styles). This approach would thereby ignore those aspects that are sex-differentiated (but they could be included in the part of the database that describes sex-differences). Fundamentally, the database entry would essentially focus on those aspects of the adaptation that are shared by both sexes, and which therefore constitute the homeostatic property cluster comprising this particular adaptation. Accordingly, the database entry for such an adaptation might describe its functional rationale as calibrating the personality syndrome in question in accordance with one's degree of relative bargaining power (again, roughly one's ability to confer benefits and inflict costs on others). On a more methodological note, it is worth pointing out that the studies of Sell, Tooby, et al. (2009) mentioned above also dovetail nicely with work by Sell, Cosmides, et al., 2009, who found experimental support for a psychological adaptation which assesses the strength and fighting ability of other individuals. For if humans possess a psychological adaptation tasked with appraising the extent to which they can inflict costs and confer benefits on others, it might be theoretically expected that they would also possess an adaptation for assessing the physical formidability of others as well. Such a complementary adaptation could serve as a

27 As Lukaszewski (2013) argues, much of the empirically documented covariance between multiple personality traits might be explained by viewing the covariance as arising through the effects of a common underlying adaptation, one which flexibly calibrates a suite of personality traits in coordinated and adaptively patterned ways. 28 For a detailed discussion of internal regulatory variables and how they might function in the evolved cognitive architecture of humans, see Tooby and Cosmides (2008).

basis for comparing, say, the two relative magnitudes of two underlying regulatory variables: one's capacity to inflict physical costs and or confer benefits, and the corresponding ability of another target individual to inflict physical costs. Such a comparative computation could then feed into decision-making processes carried out by the other adaptationdi.e., the extent to which the individual should exhibit anger proneness and a sense of entitlement in a given context characterized by a conflict of interest. As a general upshot of this methodological consideration, perhaps empirical investigation should have an eye for the functional integration and complementary nature of various psychological adaptations, since such a state of affairs might increase the confidence that one has indeed identified bona fide adaptations. That is to say, ceteris paribus, a higher degree of overall integrated apparent design increases the epistemic confidence that one has identified naturallyselected adaptations. An additional moral might be that evidence in favor of one adaptation could in turn spawn additional hypotheses of other adaptations that one might surmise as being functionally integrated with and complementary to it. For instance, evidence of a psychological adaptation for taxonomical cognizing about folk biology might motivate a hypothesis that humans also possess an adaptation for preferentially attending to animals (New, Cosmides, & Tooby, 2007).

7. Conclusion The kind of project pursued in this paper has affinities with what has recently become known as “naturalized metaphysics” (or scientific metaphysics) within the fields of philosophy of science and metaphysics (Ladyman & Ross, 2007; Ross, Ladyman, & Kincaid, 2013). This approach to ontology is quite often indistinguishable from science, save for the fact that it is frequently pursued by philosophers (but also scientists) and addresses questions that tend to be much more abstract, general, and fundamental than the ones typically tackled by workaday scientists (which of course does not impugn the important work undertaken by the latterdafter all, naturalized metaphysics is parasitic on their hard-won empirical knowledge). The project outlined in this paper has put forth a naturalistically grounded framework for what could quite plausibly be considered human nature. To that end, the framework takes seriously various important theoretical tenets in contemporary cognitive science and evolutionary biology, as well as recent scholarship within philosophy of science. The foregoing account has attempted to formulate a workable and non-essentialist notion of human nature. At its core, the EPNHN states that human nature is comprised of a homeostatic property cluster of psychological adaptations. Furthermore, the EPNHN holds that the set of species-typical psychological adaptations that constitute human nature can be profitably modeled in a formal computational manner. In addition, the approach views psychological adaptations as being tantamount to developmental systems instantiated in the brain. The EPNHN also allows us to home in on the actual nature of species-typical psychological adaptationsdtheir design spacesdwhile not being misled by the (oftentimes obfuscating) variability occurring between individuals. Similarly, the EPNHN allows us to properly identify the universal, invariant design spaces that underlie the manifest variability between populations and cultures, including variability exhibited by a given culture across time. Finally, I illustrated what a hypothetical database of human nature might look like, providing illustrations from extant research within Evolutionary Psychology. In sum, the EPNHN allows us to doff the outmoded strictures of essentialism while at the same time retaining a coherent and modern conceptualization of human nature.

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