Evolutionary psychology in the round
Abstract and Keywords
This article makes two general points on evolutionary psychology. First, the evolutionary approach enjoins a broad disciplinary perspective to the subject. Second, an evolutionary view does not commit to any particular assumptions about the genetic determination of behaviour. Indeed, learning, and by extension cultural transmission, play an especially important role in the behaviour of humans, and one will never be able to understand human behaviour without understanding culture and the way it influences what humans do. The important consideration in the present context is that the theory of evolution provides a framework within which a diverse range of intellectual questions can be integrated. The significance of this is well illustrated by the role it has played within biology. Evolutionary psychology, the article argues, is not a new and separate sub-discipline within psychology, but rather a framework theory that allows psychology's many diverse sub-disciplines to be integrated into a unitary whole.
Although the closing decades of the nineteenth century witnessed a great deal of interchange between psychology and evolutionary biology, the hasty departure of James Baldwin from the American psychological scene in 1908 (thanks to the scandal of being caught in a brothel) triggered, for reasons that are more political than scientific, the virtual severance of contact between the two disciplines (Plotkin, 2004). Psychology became more heavily influenced by its alternate roots in physiology and the neurosciences, on the one hand, and the social sciences, on the other. Evolution played no significant role in psychology for the better part of a century. Indeed, the 1950s in particular witnessed a somewhat tetchy quarrel between the comparative psychologists (with their feet firmly planted in behaviourism and an experimental paradigm) and the ethologists (with their roots in evolutionary biology, and a focus on the observational study of an animal's behaviour in its natural environment).
In part, this drift away from biology reflected an increasing focus within academic psychology on questions of mechanism (with a broad focus on stimulus-response processes, motivation, cognition and, later, neuropsychology) and development. For the ethologists, these constituted just two of what eventually came to be known as ‘Tinbergen's Four Why's’—the four kinds of questions that biologists can ask, the other two being questions about function (a teleonomic question that is, ultimately, about the genetic consequences of behaviour) and phylogeny (the evolutionary history of how a behaviour came to have its current form). Tinbergen (1963) pointed out that all four provide appropriate answers to the generic question ‘Why does an animal do X?’; all must in the end be answered for a full understanding, but each can be asked and answered independently. That is to say, our answer to one does not necessarily commit us to any particular answer for any of the others.
We want to make two general points in this chapter. First, the evolutionary approach necessarily enjoins us to take a broad disciplinary perspective to our subject matter (which, following Heyes (2000), we might refer to as ‘evolutionary psychology in the round’). Second, an evolutionary view does not—and should not—commit us to any particular assumptions about the genetic determination of behaviour. Indeed, learning, and by extension cultural transmission, play an especially important role in the behaviour of humans, and we will never be able to understand human behaviour without understanding culture and the way it influences what humans do. These issues are explored in more detail elsewhere in this volume, but our main concern here is to provide a framework within which the chapters that follow can be understood.
(p. 4) 1.2. Asking the right questions
The important consideration in the present context is that evolutionary (or Darwinian) theory provides a framework within which a diverse range of intellectual questions can be integrated. The significance of this is well illustrated by the role it has played within biology. A century ago, biology consisted of half a dozen or more quite separate disciplines (anatomy, zoology, botany, genetics, physiology, microbiology, biochemistry, etc.) that rarely interacted. The gradual acceptance of the theory of evolution as a central organizing principle has made it possible for these diverse interest groups to talk to each other in a common language in a way that had rarely been possible in the past.
Our claim here is that an evolutionary approach can and should do the same for psychology. Evolutionary psychology, we argue, is not a new and separate sub-discipline within psychology, but rather a framework theory that allows psychology's many diverse sub-disciplines to be integrated into a unitary whole. It is not our intention to demonstrate this claim here by showing how different psychological approaches could relate more effectively to each other. Rather, our aim is simply to make it clear that a developmental stance, for example, is not different from, or in intellectual opposition to, an evolutionary approach. Rather, an evolutionary perspective adds to a developmental approach by offering new ways of seeing development, prompting novel questions for empirical study, and, more broadly, allowing developmental psychologists to integrate their findings with those of neuropsychologists, cognitive psychologists and others. Life history theory, for example, is major feature of contemporary evolutionary ecology, with enormous relevance both to reproductive decision-making and to development. Yet, its implications have only recently begun to be explored. Several of the chapters in Section V draw on it in their explorations of different aspects of human reproductive behaviour.
In this context, it is particularly important to understand that an evolutionary approach does not commit us ipso facto to genetic determinism. To assume that it does is to commit a classic category mistake by failing to distinguish two of Tinbergen's Four Why's—functional questions versus ontogenetic (i.e. developmental) questions. Questions about genetic determinism belong to the realm of ontogeny (how the individual acquires its capacities during the course of development), but the core to an evolutionary approach lies in function (questions about the evolutionary goal-directedness of these capacities and the behaviour they make possible).
Of course, as an essentially biological question, the primary focus of functional questions lies in how an organism's behaviour maximizes its genetic fitness. But the fact that an individual acts so as to maximize its fitness does not mean that its behaviour is genetically determined, merely that it has a set of genetically inherited motivations (or goal states) that it seeks to satisfy. How it achieves those goal states will, at least in neurologically advanced species, depend on the individual's assessment of the costs and benefits of acting in one way rather than another, given its experience of the world. In evolutionary biology, every decision is a contingent one that depends on the details of the context. That context will obviously include many features of the physical environment, but in highly social species like humans it will also include the social environment. We return to this point again below. The issue here, however, is that the genes that are passed on from one generation to another need be not the genes for a particular behaviour, but may, rather, be the genes for a brain that is large enough, and complex enough, to make the decisions about how best to act in order to satisfy its motivations (thereby maximizing fitness). Questions about the roles of genes and the environment in the production of those brains, or any other aspect of the system, are of course interesting, but they remain quite separate, and are unaffected by the extent to which an individual can be shown to be maximizing its fitness.
The issue of ontogeny is, of course, an important one that has been the focus of yet another long-running debate within psychology in particular (the so-called nature/nurture debate). Biologists have largely accepted, since the 1960s, that this distinction is arbitrary and, worse still perhaps, misguided. We cannot separate genes from the environment in the simple-minded way implied by this dichotomy. Both nature and nurture are deeply implicated in the processes of development, even though it may be possible to (p. 5) discuss the magnitude of the relative contribution of genetic versus environmental effects to the differences between individuals. Nonetheless, no aspect of an organism's biology or psychology can be said to be wholly (or even mainly) due to its genes or the environment in which it grows up.
The distinction, nonetheless, is important in one key respect. If we recognize that questions about the mechanisms of inheritance are separate from questions about the evolutionary function of behaviour, then the way is opened up for the evolutionary study of culture as an important phenomenon in its own right. Self-evidently, culture depends on learning—specifically the social transmission of beliefs or rules of behaviour—but learning is simply another mechanism of inheritance in the grand evolutionary scheme. Biologists' perennial focus on genes (and, more recently, DNA) as the mechanism of inheritance is, perhaps, to be expected given their interest in the more hard-wired aspects of biology, such as anatomy. But it is crucial to remember that neither Darwin nor Mendel (widely considered to be the founding father of genetics) actually knew anything about genes or DNA. Both the Darwinian formula that underpins the theory of evolution by natural selection and Mendel's laws of inheritance that provide the modus operandi for Darwin's theory refer only to fidelity of copying (in other words, the similarity or correlation between parents and offspring). The evolutionary consequences work equally well whether the basis of that copying is genetic transmission or cultural learning. Of course, there are some differences in the details of how cultural and genetic evolutionary processes work, but their role in the bigger scheme of things is sufficiently similar to warrant them being treated as being equivalent [a point also emphasized by Mameli (Chapter 3) and Laland (Chapter 4); see also Barrett et al., 2000; Dunbar et al., 2005].
The fact that the nature/nurture debate has been so entrenched within psychology for so long perhaps provides us with an explanation for the recent history of evolutionary psychology. Our reading of the history of psychology suggests that, during the 1970s and 1980s, the environmentalists (the nurture-folk) began to win the nature/nurture debate, especially within developmental psychology—to the point, in fact, where the nature-folk were reduced to a minority rump on the periphery where they continued to focus on somewhat arcane topics like intelligence and personality theory. The rise of evolutionary ideas in the study of animal behaviour during the 1970s (originally in the form of a sub-discipline that named itself sociobiology, but which later adopted the alternative name behavioural ecology) seems to have been viewed by the naturists as offering something of a bulwark against the nurturists, in part at least because it seemed to imply some form of genetic basis for cognition and behaviour.
This may, in turn, provide us with a way of articulating the equally fractionated sub-disciplines of evolutionary psychology. Since the mid-1990s, evolutionary psychologists have been embroiled in what might seem like an internecine war between those whose intellectual tradition lay within behavioural ecology (who sometimes refer to themselves as evolutionary anthropologists) and those whose intellectual tradition lay within psychology (who originally referred to themselves as Darwinian psychologists, but later co-opted the term ‘evolutionary psychology’). In our view, this dispute is properly seen as being between two of Tinbergen's Four Why's, specifically between the functional approach (represented by the behavioural ecologists) and questions about proximate (mainly cognitive) mechanisms (represented by the evolutionary psychologists sensu stricto). Hence, we endorse the view advocated by Mameli (Chapter 3) that both together constitute the proper domain of evolutionary psychology sensu latto (which he signals with lower case initial letters).
It is equally important to appreciate in this respect that an evolutionary perspective does not of itself necessarily commit us to the claim that the mind is entirely organized on modular principles, even though some have argued trenchantly for such a case. Full-scale modularity is just one of a continuum of possibilities. Indeed, we do not doubt that the mind has some degree of modular structure, but it is a purely empirical question as to exactly what form this modularity takes, and how many modules there are. The issue cannot be resolved on a priori philosophical grounds, since evolution neither entails modularity nor requires it. It may well be that, in the adult, cognition behaves as though it were (p. 6) modular, but we have yet to establish whether that level of modularity is present at birth (or develops willy-nilly during childhood, irrespective of experience). More importantly, it may well be that many of the cognitive scripts that we see in adults behave like modules (may, indeed, even be hardwired in neural circuitry), but in fact arise by the switching of cognitive mechanisms from conscious thinking (where a lot of hard cognitive work has to be done ‘up front’) to more automated (subconscious?) processes once the phenomenon has been cognitively processed often enough during the course of development (there is, indeed, now neuroimaging evidence to support this suggestion).
Although this is an interesting issue in the developmental psychology of cognition, we do not see it as an evolutionarily interesting question: evolution is indifferent as to whether the mind is modular or not, since that is simply a matter of history (the stages through which the human mind evolved). We can, of course, ask questions about the efficiency of the mind's design, but there is equally no guarantee that evolution will always produce the most efficient design: there are too many examples of poor design in biology, of Heath-Robinson adaptations of existing components for new purposes for which they were not originally designed (a process biologists sometimes recognize by the term exaptation). Nor, on this point, do we find the concept of the environment of evolutionary adaptedness (EEA) especially convincing or helpful. It may be possible to explain, ex post facto, why modern humans and their minds have come to be the way they are by reference to past circumstances, but it is rarely possible to identify past circumstances with such precision as to be able to predict (prospectively) the outcome of any selection process (Strassman and Dunbar, 1998). Moreover, the historical process by which a particular behavioural or cognitive trait is acquired is often so complex and convoluted, it is often hard to know exactly what came when, or which particular time and circumstances played the seminal role. This is well illustrated by the evolution of speech and language. In addition to the need for fine motor control, the capacity for speech depends on anatomical capacities associated with bipedality (a flattened chest, the freeing of the chest wall muscles from the pressure of walking) which have a very ancient origin at the very root of the hominin tree some 6 MYA (Aiello, 1996). Without these preadaptations, it would be impossible for modern humans to sustain the long exhalations that are required for speech. Were these components of the story more or less important than the social or technological circumstances that created the functional demand for communication when language itself evolved in the late Pleistocene? The answer is not always as obvious as it might seem.
However, to take such a view does not, of itself, mean that we have to dismiss the evolutionary psychology sensu stricto approach in its entirety, a mistake that has frequently been made by its opponents (many of whom have not always taken the trouble to investigate its claims at first hand). There has been much empirical work of considerable worth carried out under this rubric, and its value should be recognized. The reality is that some aspects of our cognition and physiology do predispose us to behave in certain ways, or at least to have such behaviours as our default condition. For us, the more interesting issue is the fact that our brains allow us the luxury of being able to fine tune our behaviour more subtly in the light of circumstance: that, after all, is why large brains evolved. In all likelihood, we probably do come to the world with a set of default cognitive options, but our cognitive capacities—and the processes of cultural transmission that these make possible in addition to simple trial-and-error learning—allow us the option of fine tuning our behaviour to the circumstances in which we happen to find ourselves in what are often very subtle ways. Voland (Chapter 28) argues cogently, from a very detailed review of the evidence from historical demography, for exactly this interpretation. Rather, we take the view that these disputes are arcane and of the past. We should begin with a clear canvas and set about building a more integrated science that draws on all relevant perspectives.
1.3. Taking the broad perspective
Although the evolutionary approach was initially applied mainly to questions of cognition within psychology [prompting Cosmides and Tooby's (1992) (p. 7) generic design-of-the-mind approach], recent years have witnessed a dramatic growth in areas traditionally associated with social psychology (for recent overviews, see Schaller et al., 2006; Forgas et al., in press). Indeed, there are good grounds for seeing the behavioural ecology approach as being traditional social psychology with an evolutionary backbone, and the evolutionary psychology sensu stricto approach as being conventional cognitive psychology with an evolutionary backbone.
Our view, and the one we have tried to promote here through our choice of contributions, is a more balanced one that takes a broader perspective. In selecting topics for inclusion in this volume, we have endeavoured to give weight to both the central importance of individual topics and the balance across the sub-disciplines that currently constitute evolutionary psychology. Our aim has been to work towards a synthesis of approaches, in the expectation that the range of topics which can be exposed to scrutiny from an evolutionary perspective will encourage a wider range of psychologists to take note of the evolutionary approach. Our message, more than anything else, is perhaps that the evolutionary approach enables us to ask questions that are both wide-ranging and interesting: more importantly, it prompts us to ask questions that are not conventionally asked. The fact that evolutionary theory provides a very powerful, well-articulated and thoroughly developed body of theory has enormous heuristic value because it allows us to make strong predictions about how individuals might be expected to behave if a particular hypothesis is true. The main benefit of evolutionary theory, therefore, is that it provides a fine scalpel for hypothesis-testing.
Despite our insistence on the importance of intellectual breadth, there is one area that has remained resolutely on the sidelines of evolutionary psychology, namely culture. Though a strong research programme developed in the study of gene-culture co-evolution during the 1990s, this has remained highly mathematical in focus, and rather peripheral to the main developments within the broader discipline. Its attention has been focused mainly on the mechanisms of learning and the dynamics of gene-culture co-evolutionary processes. Yet culture plays an important role in everyday human behaviour, both as a conduit through which we acquire knowledge about how to behave and as a framework that itself creates many of the costs and benefits of social life. Plotkin (Chapter 2) develops this theme in more detail, so we will not elaborate further on the broader question of the importance of culture. However, one point he makes is worth emphasizing in more explicit detail because it provides the basis for some major new developments in evolutionary psychology. And this is the fact that humans, like most primates, live in large, multilevel societies.
For the past four decades or so, evolutionary biologists and behavioural ecologists (and, following their lead, evolutionary psychologists sensu stricto) have tended to view the individual in isolation, making decisions about how to behave in his/her own best interests. The reality, of course, is that human (and, indeed, many mammal and bird) individuals are members of societies that exist for the individual's benefit. We ought not to view an individual as acting in isolation in quite the way we have done traditionally because every behavioural decision an individual makes has consequences for every other member of the community within which it is embedded, and those consequences will in due course feed back on the individual. In actuality, this is nothing new in behavioural ecology: it is, in effect, the lesson of Hamilton's Rule. Although Hamilton's Rule was originally proposed as an explanation for the evolution of altruism [Hamilton's (1964) famous theory of kin selection], it has since come to be seen, rightly, as the fundamental theorem of behavioural ecology. In a nutshell, Hamilton's Rule states that a gene for altruism will evolve to stability whenever the benefit to the recipient (in terms of number of additional future offspring born), when devalued by the coefficient of relatedness between recipient and altruist, exceeds the cost to the altruist (when measured as the number of future offspring lost). While strictly speaking just an approximation to Hamilton's original finding (Hamilton termed this ‘neighbour-modulated fitness’), even so simple a formulation reminds us that the consequences of one's actions reverberate around the population, and feed back on one's own inclusive fitness (the composite fitness of a trait that results from summing one's personal fitness with the kinship-devalued fitnesses contributed by everyone else in the wider (p. 8) community). If I help you, I cannot so easily help someone else, and I have to balance the loss that I accrue as a direct result against all my other gains.
This becomes significant when individuals live in interdependent communities whose persistence and success is a product of the effectiveness with which individuals work together. In these cases, actions that destabilize the group's coherence—and the fragile social contract on which its existence is premised—ultimately risk adversely influencing the fitness of the individual decision-maker. Social (or even physical) ostracism inevitably has disastrous consequences for an individual, especially in small-scale societies. Cultural rules may provide particularly powerful mechanisms for enforcing social conformity, not least by creating a sense of group identity. From an evolutionary point of view, this may seem to result in individuals behaving in ways that are sub-optimal when seen from the individual's purely selfish point of view. But a wider perspective may reveal that the individual's net lifetime fitness is higher if he/she accepts some losses now in the expectation of receiving greater returns in the future.
The need to integrate culture into the story has been added extra impulse in recent years by two recent developments. One is the concept of multi-level selection, and the other niche construction theory. The principal issue behind both is that fitness may be influenced in a rather complex way by the fact that an individual's actions reverberate through the layers of the biological system. This has quite explicit implications in the case of niche construction theory, which argues that organisms can (and often do) alter the environment they live in by their own behaviour. Beavers and their dams are an obvious and familiar example. But social groups themselves are a form of niche construction—indeed, they are perhaps the most complex form of this phenomenon, especially when kinship is part of the process. In effect, the social groups of many monkeys and apes (and, by extension) humans are implicit social contracts: individuals collaborate to solve the problems of everyday survival and successful reproduction more effectively than they can do on their own. Ensuring that the group functions effectively as a group has crucial feedback consequences for the fitness of its individual members. It may also create tensions within the group when individuals' preferred ecological, social or reproductive strategies differ.
The importance of multi-level selection, especially for understanding human behaviour, has been stressed for many years by Wilson (1975; this volume), but its implications have received very little attention. It has acquired particular significance in the light of the finding that human societies are themselves multi-level constructs. Seen from the individual's perspective, human social networks appear as a series of concentric circles (the so-called ‘circles of acquaintanceship’) whose sizes have a surprisingly constant scaling ratio of three (Zhou et al., 2005). Although there is considerable individual variation in the size of these circles, nonetheless the typical sizes seem to be constant across a wide range of cultural and socio-economic circumstances (from hunter-gatherers to modern post-industrial societies). Each circle corresponds not only to quite discrete numbers of individuals, but also to particular frequencies of contact and feelings of intimacy (Hill and Dunbar, 2003). We do not, as yet, understand why human societies should have this form (though it may well be a trait characteristic of many mammals with complex social systems). Nonetheless, the different groupings seem to have social and ecological functions that are a critical component of our personal life-history strategies. Since group-living is costly, we benefit from living in communities of this kind only if they work effectively. Hence, ensuring that the group functions as a coherent unit and is not destabilized by individuals' actions becomes an essential component of our sociality. The tightly integrated nature of human social groupings means that each of us is deeply embedded in a complex network of relationships: as a result, the consequences of whatever we do inevitably reverberates through the layers of the system and has ramifications for everyone with whom we have to live.
The fact that societies exist as collaborative ventures itself raises an issue of considerable importance that has very much come to the fore within the past few years in evolutionary studies of human behaviour. This is the issue of social cooperation. If we are to maintain—and thus benefit from—socialities of this complexity, an intense form of prosociality is necessary since (p. 9) group members must compromise on at least some of their self-interest. But any such social contract is always at risk of being destabilized by freeriders (those who take the benefits of the social contract, but decline to pay all the costs). Social cooperation, and the behaviours that derive from it (freeriding, altruistic punishment, second-order public goods problems) have emerged as a particularly fruitful area of collaboration between evolutionary biologists, evolutionary anthropologists and those who now refer to themselves as evolutionary economists. Though most often investigated in isolation, these have to be seen within the broader picture of both the evolution of multi-level social systems and the role that culture plays in creating the environment within which cooperation games are played out in real life. Some of the chapters in Section VII will develop these themes in more detail.
1.4. Evolutionary psychology of the future
We end this introductory chapter with two brief observations about the future. The first is that evolutionary psychology is now clearly here to stay, notwithstanding the rather negative press it has received in recent years. (We are reminded somewhat wearily of the equally negative responses that greeted sociobiology in the later 1970s: contemporary forecasts of its imminent—indeed, actual—demise proved to premature.) However, its future, we are convinced, will depend on our capacity to integrate the various strands that have developed over the past decade or so. We hope this volume goes some way to initiating that process. The second point is, we believe, even more important, at least for the human end of evolutionary psychology. Embedding human behaviour into the cultural matrix within which humans live is, we believe, a particularly important and crucial challenge. In our view, some of the current puzzles that bedevil the study of human behaviour may well evaporate when humans are seen as operating within a more complex multi-level social environment.
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