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Pluralism and Process in Understanding Human Nature1 John Dupré The Centre for the Study of the Life Sciences (Egenis) University of Exeter Introduction Human nature is one of the most controversial topics in intellectual life. There is disagreement about what the concept means, whether any such thing exists and, if it does, what are its particular characteristics. These questions took an extreme form in the last decades of the twentieth century with the emergence on the one hand of sociobiology (Wilson 1975), a rather crude reduction of human nature to evolutionary biology on, and an influential school of cultural anthropology, which seemed to see humans as almost indefinitely variable and malleable, on the other (e.g. Geertz 1973). The latter view, to which my position in this paper will be closer, is often interpreted as holding that any attempt to describe human nature was misguided. However I do not want to deny the relevance of biology to understanding the human. On the contrary, my argument will be that it is our distinctive biology—though distinctive in degree rather than anomalous in kind—that is the key to understanding the remarkable flexibility, or plasticity, that is at the heart of human nature. This debate has been especially heated as it has widely been seen as closely connected with deep political differences. Critics of biological human nature have often accused its defenders of lending support to political conservatism: the immovable realities of human nature would inevitably undermine attempts radically to ameliorate the human condition. No doubt some supporters of sociobiology and similar positions were politically conservative. On the other hand some were certainly not and had good political reasons for their stance. The research leading to this paper has received funding from the European Research Council under the European Union's Seventh Framework Programme (FP7/2007-2013) / ERC grant agreement n° 324186. 1 1 Noam Chomsky, famous both for his claim that language was an innate feature of human nature and for his radical political views, has written: “The principle that human nature, in its psychological aspects, is nothing more than a product of history and given social relations removes all barriers to coercion and manipulation by the powerful” (Chomsky 1975). I will not discuss these important debates here. I mention them only as a reminder that while the topic of human nature is intellectually challenging and fascinating, there is more at stake than just getting things right. The dismissal of human nature is surely historically anomalous. Most thinkers have held that human nature was an essential and even neglected topic for study. Thus David Hume: “Human Nature is the only science of man; and yet has been hitherto the most neglected” (Hume 1888, p. 273). Thinkers as influential as Darwin, Freud and Marx have offered views about human nature and more recently it has been a topic for some practitioners of many scientific disciplines—psychology, neurology, physical anthropology, etc.—and, most notoriously, as mentioned, sociobiology and its successor, evolutionary psychology. These last, in particular, have agreed with Hume that ‘human nature is the only science of man’ and adding this to the view that science is the only source of knowledge, have taken their conception of human science to be the key to all aspects of human behavior, from competition and reproduction to art, religion and philosophy. There are many more specific, if less scientifically grounded views on the topic. Rather uncontroversially, according to the ancient Chinese philosopher Xun Zi “it is human nature to want to eat to ones fill when hungry, to want to warm up when cold, to want to rest when tired” (Ebrey 1993, p. 26); and more controversially, “Human nature is such that people are born with a love of profit” (Ebrey, loc. cit.)—though unlike many contemporary subscribers to a similar view, Xun Zi took this to illustrate that human nature was a bad thing. Perhaps this remark better reflects the way that references to human nature are used in everyday speech as an argumentative trope, a framework for generalisations that claim insight into, or just exercise wit about, the human condition. The Roman playwright Publius Terentius Afer, for example, is said 2 to have opined that “Human nature is so constituted, that all see and judge better in the affairs of other men than in their own”—a thought in which most of us will see a grain of truth. As a starting point for the present discussion, I shall understand ‘human nature’ as noncommittally as possible, to mean whatever is empirically true about humans. Such truths could be universal or culturally local. Surely Hume is right that we would like to know as well as possible what we are like. But if, as for example was famously argued by the existentialists, what we are like depends in crucial ways on our choices and decisions, then that is something that belongs in a proper account of human nature. What Human Nature Is Not Like all species humans are variable. Variability, as Darwin has taught us, is what makes evolution possible. Without it, we would not exist. A human essence, a property necessary and sufficient for anything to be human, is not something we should expect to find. This simple point, though important, doesn’t get us very far. It is not of the essence of an elephant to have a trunk: if some freak elephant were born with a snub nose we should not exclude it form the species from which it arose. Still, all or almost all elephants do have trunks, and this is certainly something we should include in an empirical account of elephant nature of the broad kind in which I am interested. It is important that we recognize that biological generalizations will always admit of exceptions, but this hardly makes generalization impossible. Debates about human nature, anyhow, are generally concerned with human psychology and behavior rather than physiology, and here the key idea is not so much variability as plasticity, of which variability is of course a product. This, I think, is what is most fundamentally lacking in the projects of sociobiology and evolutionary psychology2. The latter, in particular, supposes Here I mean specifically the project associated with authors such as Leda Cosmides, John Tooby and David Buss. Sometimes this project is referred to capitalized, as Evolutionary Psychology, to distinguish it from a range of other 2 3 that the human mind is composed of discrete modules, evolved during the Pleistocene, or late Stone Age, to solve specific problems posed by human life during that period. Of course evolutionary psychologists acknowledge some variability. There is the normal variability of the kind illustrated by the snub-nosed elephant: some people have abnormal modules. And more importantly, there is variability that comes from the interaction of modules with a variable environment. All or almost humans might have, say, a statusseeking module. But seeking status in a hunter-gatherer society in New Guinea no doubt calls for different behavior than it might for a fashion consultant in Milan. So evolutionary psychology allows for some variability in actual behavior, but the behavior is supposed to emerge from a broadly universal human mind, indeed essentially the same mind as might have been found in our Stone Age ancestors. This collection of mental modules is the universal human nature they assert, and it is a nature grounded on genetic determinism. Not, of course, the genetic determinism that sees people mindlessly emitting behavior as their genes give orders, but the determination by genes of the system that processes inputs from the environment and emits behavior in response. Like so much reductionist interpretation of evolution, the fatal flaw of this scheme is that it ignores, or black-boxes, development. In fact, however, the interaction of the environment with the mind does not begin after genes have somehow formed a standard and universal human mind; the environment interacts with the genes (and more) throughout the process of human development. So a different environment does not just produce different behavior in response to that environment; different environments produce different minds. The co-production of the organism by biology and environment is not something unique to the human mind of course, but is everywhere in the living world. The appearance of developmental homogeneity is as much a investigations of the historical trajectory leading to current human psychology. A standard reference for Evolutionary Psychology is Barkow, Cosmides and Tooby (1992). 4 consequence of the uniform circumstances in which organisms of a particular kind develop as it is of their identical or similar genomes. And part of the reason that organisms develop in homogeneous environments is that they often work hard to construct appropriate environments, a point that has been developed in recent elaborations of the idea of niche construction (OdlingSmee, Laland, and Feldman 2003). Birds don’t just happen to grow up in nests, for instance; these are painstakingly constructed by their parents. Looking beyond this appearance of developmental uniformity, we actually find an enormous amount of developmental plasticity, a phenomenon that has been documented in encyclopedic detail by Mary Jane West Eberhard (2003). This plasticity applies to physiology as much as to psychology. Famous illustrations of this are provided by quadrupedal animals that have had to learn to be bipedal. Where this has been from a congenital abnormality, as in the most famous case of a goat born without forelimbs and studied by the Dutch morphologist E. J. Slijper, the developmental accommodation to this disadvantage can be remarkable. This animal learned to walk quite comfortably on its hind legs and on post mortem examination was found to have radical changes in the anatomy of its legs and hips that accommodated these changes (West Eberhard 2003, pp. 51-2). Development is a highly integrated process, and changes to some aspect of it will often induce a range of compensatory changes in other features. That such plasticity applies to psychological development should hardly be surprising. Indeed, if there were no such plasticity the concept of learning would make no sense. It is, of course, possible that learning, or more generally the response of psychological development to environmental contingencies, could provide only a superficial filling in of details within a genetically determined framework. The physiological examples are intended at least to weaken the intuitions that favour such an understanding. In what follows I hope to offer a more positive account that provides further motivation for adopting a more radical view of psychological developmental plasticity. The central claim is this: the achievement of human evolution over the last few million years has not been the acquisition of a wider range of specialized 5 abilities to deal with specific problems, but rather the developmental flexibility to acquire a wide range of extremely complex behavioral repertoires. Humans as Processes In the previous section I have several times emphasized the importance of development in understanding human nature. Much of the tradition of discussing this topic has seemed to focus on the distinctive properties of an adult human in the so-called prime of life. In the past this adult was generally assumed to be male; now evolutionary psychologists spend a lot of time describing the differences between the nature of adult men and women. But as the developmental psychologist Alison Gopnik (2010) has remarked, “One of the best ways of understanding human nature is to study children. After all, if we want to understand who we are, we should find out how we got to be that way.” Children, surely, have just as much right to claim a human nature as their parents. In fact studying children has a particular advantage: differences in what happens to children can help us to explain the differences between adults. Humans, as we all know, go through a characteristic series of life stages: fetus, infant, child, adolescent, adult. These are not, of course, a series of discrete steady states separated by metamorphosis, as one might describe the life cycle of a butterfly—egg, caterpillar, chrysalis, butterfly—but rather a smooth progression from which these named stages are abstractions. Adhulthood, for instance, encompasses a gradual progression from youth to old age. The whole sequence amounts to the human life cycle. A central philosophical problem for centuries has been explaining our intuition that the stages of the life cycle constitute some single continuing entity, a person. Philosophers have divided over whether the identity of a person depends on persistent psychological features, notably memory, or whether the identity of a person is the same as the identity of a material thing, a human animal. Intuitions on the question are typically tested with thought experiments such as John Locke’s cobbler and prince who exchange minds, or more recently with imagined brain transplants. Is the prince the cobbler’s body with the 6 mind of a prince or the prince’s body with the mind of the cobbler? Intuitions tend to favour the former and, reflecting the widespread transition from Cartesian mind/body dualism to a largely similar brain/body dualism, some philosophers even make the bizarre claim that a person is identical to their brain. It is, at any rate, easy to see the problem. In what sense could a fetus be the same thing as an old man 80 years in the future? They are unlikely to have any matter in common, and their properties are quite different, both physically and psychologically. Even young people don’t remember being fetuses, and some old people, sadly, don’t remember anything. A natural thought here, much discussed in the literature, is that we should appeal to spatio-temporal continuity. But though there is surely something in this, it is clearly not enough. To take another ancient philosophical example, a block of stone is not the same thing as a statue, even though the two are spatio-temporally continuous. Or at any rate it is not the same statue, because the original block of stone isn’t a statue at all. This draws attention to the logical point that the kind of identity question in which we are interested is a question relative to a kind. The old man certainly isn’t the same baby as the baby he once was: spatio-temporal continuants can come to be or cease to be kinds of things. So to what kind do the fetus, the child and the old man all belong? The kind that motivates much of this philosophical debate is that of a person, but for my present purposes there is a more straightforward answer, that they are all part of a human life cycle. But, to get finally to the point, a life cycle is not a thing but a process. Of course we could insist on saying that they are all human, but this just restates the problem. How can all these very different entities be the same kind of thing? And the answer is that they are not; they are all parts of the same process. Humans are processes not things. Perhaps this still only names the problem. What is this distinction between a process and a thing? And what is it for a process (or for that matter a thing) to persist through time? I shall be very brief with the first question, though it is an ancient one, dating back to the pre-Socratic Greek philosophers. My very simplified answer is that a process is something to which change is essential. 7 For an ontology of things, change is a problem: what changes can a thing undergo and still remain the same thing? Answering this question has been one motivation for essentialism, the idea that there must be some essential property or properties that makes the thing what it is and the continued possession of which underlies its persistence through change. Processes, on the other hand, must change to continue to exist. For a river, a storm, a battle, cessation of activity is cessation of existence. It is the characteristic activity—flowing, blowing, or fighting—that constitutes the existence of these processes. This, I think, is the ontological category under which we should think of living beings in general and ourselves in particular. Let me turn in more detail to the second question, how do either things or processes persist through time? There has been a good deal of philosophical discussion in recent years about what constitutes the persistence through time of a thing. A major divide is between so-called endurantists and perdurantists (see Noonan and Curtis 2014). Perdurantists hold that things, often described in this context as “space-time worms”, exist in four dimensions and have temporal parts just as they have spatial parts. Endurantists object that, contrary to this view, when we encounter a thing we encounter it all, not just a small part of it. Sometimes the latter view is combined with presentism, the thesis that only the present really exists at all. With or without this corollary, it is evident that the endurantist will need to address a version of the problem I have been discussing, how, say, a fully present baby at one time can be the same entity as a fully present octogenarian eighty years later. The perdurantist, has an immediate answer to this question: they are temporal parts of the same four-dimensional thing, or ‘space-time worm’. The problem that most interests me from this perspective is a rather different one, to which I shall turn briefly below: how do we distinguish particular space-time worms from the tangle of interconnected entities that make up the biosphere. Without going much further into these deep ontological divisions, I would like to suggest that the whole issue looks much more intuitively tractable from the processual perspective I advocate. Everyone agrees that a process is 8 composed of temporal parts, and if one thinks of a human as most fundamentally a life cycle, surely a process, it is obvious that one should not expect, when confronted with a part of it, say an adult, also to be in the presence of its earlier (or later) temporal stages (for an explicit application of this perspective to the question of personal identity, see Dupré 2014). This observation leaves open the major question of what relations between stages of a process constitute these stages as parts of the same process, a problem exacerbated by the difficulty just mentioned of distinguishing a living process from multiple other such processes with which they are typically intricately entangled at various points in its history. But the core of an answer is reasonably clear nonetheless: the temporal parts of a process are connected by causation. The state of a battle, a storm, or a river at one time is caused by its state at a previous time (in interaction with other external causes). And the same goes for an organism. The organism is a sequence of such causally connected states. I should note in passing that I do not wish to subscribe to the standard version of four-dimensionalism. The dichotomy I have just considered contrasts views that give a special status to the present with those that treat all times symmetrically. My own view is that the proper dichotomy is between the past and the future: the past and present exist and the future doesn’t. The present has a special status as dividing the fixed past from the still unformed future. This is sometimes called the ‘growing block’ view of ontology: things grow as they move into the future and make real more of the past. This seems a view very well-suited to an ontology of processes, and has particular relevance to organic processes, notably human ones, as making room for the possibility of agency and even free will in the construction of the future. But this is not a topic I can pursue in any detail here (but see Dupré 2001, ch. 7; 2013). I have mentioned the problem of distinguishing a living process from the living context in which it is embedded. Actually I take it to be a major advantage of a processual perspective, that it not only recognizes this problem, but is also able to acknowledge that the division of biological reality into distinct processes is not always an unambiguous or even objective matter. Most of 9 life is more or less symbiotic, and the degree of integration between symbiotic partners is highly variable. We are generally comfortable with considering mitochondria, entities in cells that provide energy for the cell’s chemical reactions, as part of the organism, even though they have a distinct origin (in an ancestral bacterium) and reproduce independently. Their processes are entirely embedded within those of the organism in which they live. We are less sure about the trillions of symbiotic bacteria—90% of the cells that make up a human body, in fact—that line our gut and cover the surfaces of our skins, though many of these are also essential for our proper functioning. It is not clear that there is any fact of the matter as to whether these, or some of these, should be considered to lie within or without the boundaries of the human organism. And the process perspective may even weaken the hold on us of the individualism that has been such a dominant theme in modern Western thought, by reminding us that we are highly social organisms, and therefore parts of many social processes. But I will not suggest here that there is any problem in the intuitive assumption that individual humans are importantly separate, or at least conceptually separable, processes too. From a biological perspective what provides the coherence of such processes are, first a huge range of metabolic activities that maintain a complex organization in energetic disequilibrium with its environment and, more importantly for present concerns, a developmental process that carries a human through the various stages of a human life cycle. While it is certainly true that this developmental process follows a highly predictable sequence of stages (fetus, child, adolescent, adult, etc.), there are many aspects of this process that are highly variable. One reason for this is that far from being an internally closed causal process, development is equally driven by external influences. As I mentioned earlier, the appearance of human homogeneity is the result of shared environments as well as of similar biological processes. But as we extend our vision in both time and space environments change, and human diversity becomes more evident. Spatially we see the cultural diversity that has been documented extensively by anthropologists, a discipline one wing of 10 which has consistently repudiated on empirical grounds the human universals alleged by sociobiologists and their like. Temporally we see evolutionary processes at vastly higher rates than are possible from the perspective of genetic evolution still assumed by some to be the only possible basis for significant evolutionary change. The life of the Pleistocene hunter-gatherers so important to the ideas of evolutionary psychologists was very different from that of a contemporary city-dweller. Caves, wood fires, and dangerous beasts to be fled or eaten provided a very different context for the human developmental process than do city apartments, hospitals and schools. It is not surprising that the developmental process should take very different courses in such wholly different contexts, not least with respect to the development of the mind. A living developmental process is (more or less) adapted to the conditions in which it exists. Whether or not we want to say, as some do, that survival and reproduction are the ultimate purposes of a developmental process, we should be Darwinist enough to acknowledge that the developmental processes we find today are likely to be those that tend to lead to these outcomes. Organisms are very complex entities, and it is an amazing achievement to be a developmental process that leads reliably to survival and reproduction. It is a natural thought that the process should be very tightly constrained to produce outcomes that have a fair chance of meeting these desiderata. On the other hand a tightly constrained process will lead to a highly predictable outcome and one that is adapted to a very specific environment. As the environment changes the adaptedness generated by such a process will cease to be effective. Orthodox Darwinists respond to this problem by hypothesizing random changes in one determinant of the process, the genome, such that some of these changes will produce variations that adapt their lucky bearers to the changed conditions. I won’t try here to evaluate in any detail the general plausibility of this latter picture (for more detailed discussion, see Dupré 2012, ch. 9). I do want to insist, though, that it is not the only way in which organisms adapt to their environments. As already noted, another is through developmental processes 11 that can respond to the environment in ways that produce developmental trajectories that are more specifically suited to the outcomes they encounter. Such developmental flexibility abounds throughout the living world. To cite one important example, many plants change their shapes in highly plastic ways to accommodate to the availability of light, or their size to respond to the availability of nutrients. Clearly under appropriately varied conditions this is a better strategy than having a predetermined size and shape. It is sometimes objected that such a change cannot count as evolutionary because no difference is transmitted to the underlying cause of the change, the genome. But this is plainly question-begging, simply defining evolutionary change as genetic. Suppose for some reason the nutrient supply for a species of plant is permanently degraded. The plants grow smaller. As long as that change persists they will continue to be smaller. It is also possible that they become smaller through a selection of genetic causes of reduced size. Either way the species responds adaptively to the change. Why call one kind of change but not the other evolutionary? This is pure prejudice. In fact the only reason why the first scenario might be denied the status of evolutionary change is that it leaves the species able to revert to its ancestral state in case of a reversal of the environmental change, a blatantly question-begging insistence that evolution is opposed to flexibility. And this brings us back to the human. Humans have arguably pursued the strategy of adaptive plasticity to the greatest extent of any organism. Not only do humans have the ability to learn to live in a great variety of different environments both cultural and natural—from Inuit hunters in the frozen North to tropical city dwellers in Singapore or Rio de Janeiro; they have also evolved the ability to construct the environments in which they live. This is, like other extraordinary human capacities, not unique in kind to humans. One of the major insights in recent evolutionary thinking is that all organisms act on their environments rather than as, in traditional evolutionary thinking, merely adapting to it (Odling-Smee, Laland, and Feldman 2003). Classic examples are the dam building of beavers and, as explained in great detail by no less an evolutionist than Charles Darwin, the ability of the humble earthworm to transform the soil environment, and to do so in respects that suit its way of life 12 (Darwin 1881). But these are no more than striking examples, and all organisms have some effect on their environment; and thus their evolution is a dialectical interaction between them and the world in which they live. Once we recognize that a plastic phenotype and the ability of the organism to change the environment in which it develops provide a possible basis for evolutionary change, we see that just such a process permeates human evolution. Providing ourselves with heated homes and food-laden supermarkets has radically changed the conditions under which contemporary humans survive (and reproduce). It may well be that genetic evolution will eventually track these changes, making us more suited to heated buildings and less well adapted to the vagaries of the outside climate. But whether or not this happens, there is no reason not to count our development in a quite novel environment, and our plastic responses to this both physically and psychologically, as evolutionary changes. Technological innovation is, in this broader sense, a major driver of human evolution. Left to nothing but our biological endowment we are fairly slow and cumbersome creatures. With cars, trains, and planes, we are the fastest beasts on the planet. I have argued that generations growing up with mobile phones are developing a profoundly new conception of social space, one that is no longer fundamentally spatial. The fact that one’s circle of friends travels everywhere with one in cyberspace, often in continuous conversation, reduces the salience of physical proximity, a fact that notoriously provokes mutual incomprehension and even hostility (in Britain, at least) between people of different generations sharing train compartments. People, then, are developmental processes shaped by a variety of factors both internal and external. I shall summarize where this leaves the question of human nature at the end of this talk. But first I want to draw some connections with a different but related topic, pluralism. Pluralism in Understanding Human Nature 13 At the beginning of this talk I highlighted the polarized positions that dominate the discussion of human nature. A fascinating feature of the debate is that while almost everyone officially endorses a modest pluralism of causes, the view that human behavior must be explained in part by (more or less) universal features of human biology, in part by social forces, and in part by the idiosyncrasies of individual choice, both sides accuse the other of uncompromising reductionism, either to social influences or to a human nature grounded in the brain or the genes. And indeed, reading the works on either side of this debate it is easy to understand these accusations: having paid lip service to pluralism, most authors go on to wax lyrical about how much more significant and useful is their own preferred perspective. A slightly cynical explanation of this tendency is that is easier, or at least more attractive to the reader, to provide a theory that explains (almost) everything than to explore its limits. At any rate, this last remark locates one of my aims in this paper: to provide a discussion of human nature that acknowledge the multiplicity of causes, biological, social, and individual, that interact to produce human behavior. Methodologically, I advocate the necessity of a pluralism parallel with the pluralism of causes just mentioned. No single scientific approach can provide a complete understanding of human behavior. This should be clear enough simply from reflection on how science works in addressing highly complex phenomena, through abstraction. Most scientific models focus on a relatively small range of factors that are taken to be the most important in explaining a particular class of phenomena. The processual perspective that I have been describing adds a twist to this observation. Theories of human behavior generally not only focus on a particular set of causes, but they present a model of objects with a particular set of properties and dispositions. They thus involve both an abstraction from the full complexity of the causal nexus in which humans live, and a temporal abstraction from the extended process that constitutes the full human life cycle. There is nothing wrong in principle, for instance, with treating humans as consumers optimizing their utility in the face of a set of prices and a budget 14 constraint. It might turn out that for some economic models other factors affecting aggregate economic behavior come close enough to cancelling out to make such models effective and useful. For analyzing the market in pork bellies this is quite plausible; for predicting GDP probably less so. But however successful or unsuccessful such models may turn out to be empirically, no one really believes that humans are nothing but utility maximizing machines, though some people do seem to come alarmingly close to doing so. This kind of abstraction (or idealization—this important distinction can be ignored for present purposes; for discussion, see Thomson-Jones 2005) raises a well-documented dilemma between utility and realism. A relatively simple model may provide real insight into one important aspect of a situation far too complex to comprehend in all its gory details; but it may fall a long way short of providing an accurate fit with the complexity from which it abstracts. Bringing in further relevant factors should be expected to close this gap, but all the time reducing the insight into the real world dynamics. When maximum realism is important, for example in trying to understand and predict the dynamics of climate change, models are constructed of a complexity that no one can fully understand, and this no doubt contributes to the ease with which skepticism about their legitimacy can be promoted. In the case of humans, in certain respects far more complex entities even than the world’s climate system, we are interested in many perspectives on their existence and behavior, and sometimes very simple models can help us to understand aspects of these. The tragedy of the commons, for example, to return to the domain of economics, provides a simple and persuasive explanation of why, at a certain point in the development of human resources we will need a sophisticated and enforceable international fisheries policy. No boat, or fishing nation, has any motivation to reduce its catch given that other boats or nations are not expected to do so; and given an agreement, each nation is motivated to break it if they can get away with it. This does not tell us that some countries may not impose their own, altruistic controls on fishing, though it may suggest that these are unlikely to do much good. It certainly 15 doesn’t tell us how fish fit into the dietary or cultural beliefs of different nations, or which fish they prefer to eat, though these might in fact have a major bearing on the rate of collapse of fish stocks. But if we are interested in, for instance, how the collapse of fisheries will affect the lives of different peoples, these latter are just the kinds of things we will need to understand. The importance of partial perspectives on complex phenomena, provided by different models or theories that abstract from much of the less relevant detail of the phenomena is well understood in the philosophy of science. I have elsewhere argued in detail for its importance in understanding the sciences of the human, and also in avoiding dangerous exaggerations of the potential scope of some of these sciences (Dupré 2001), but this is not my central topic here. Now I want only to point out how inevitable this pluralism should look in light of the metaphysics of the human that I have been sketching. The individual human as he or she exists at a particular point in time is a stage in a process shaped by a partly unique biology and a highly idiosyncratic set of environmental conditions. Both the current properties of an individual and their future possible trajectories are shaped by this specific constellation of causes. This diversity does not at all imply that there may not be useful statistical generalizations about populations of humans, with a range of application depending on the topic in question, and with the potential to ground useful scientific models. But the idea of some account of human nature that could underlie a complete account of what humans do always and everywhere is a fantasy. Conclusion: Human Nature Again Theories involving well-chosen partial perspectives can be useful and even indispensible. But they also carry the obvious and serious risk that ignoring significant factors can cause major error. Surely the most dangerous example of this in the life sciences is the abstraction from environmental factors in purely genetic models of development and of evolution. Here we find a real asymmetry between the defenders of nature and nurture described at the beginning of this talk. No one imagines that development or evolution can be 16 explained entirely abstracted from genetics; that a human baby brought up by elephants will grow into an elephant, for instance; or that living among large expanses of bamboo will cause us to evolve into giant pandas in a few generations. But many people think that development can be studied more or less entirely as caused by genes; and though evolutionists will always see the environment as important in providing the conditions in which natural selection operates, they quite standardly treat it as a static background condition rather than a dynamic variable. Abstraction is always tempting as providing manageable and illuminating simplification. But in a topic such as that of human nature certain tempting abstractions can be disastrous, most notably the excessive focus on genetics. So what is human nature? Humans I have said are life cycles, a kind of process. The significance of this might be illustrated by considering the transhumanist dream of freezing human development for centuries at some preferred point in adulthood. If it is held that humans are a kind of thing, which takes a few decades to develop and then a few more to decay, it is a natural thought that one should do everything one can to retard this decay. From a processual perspective the envisaged change is a much more radical distortion of human nature, a complete reorganization of the life cycles that we are. The problems often noted with the reformation of the temporal relations between the generations of lifecycles that constitute the human reproductive lineage are perhaps even more significant. I don’t mean to say that any of this is necessarily bad; just that it is important to see what a drastic shift this idea involves in the kinds of beings we are. And perhaps the recognition of the extent of this change also suggests that it may be a lot harder to achieve even than some of its advocates imagine. Humans are highly flexible, developmentally plastic, life cycles. Evidence for this claim includes the geographic and historical diversity of human lives and societies and, perhaps equally important, the increasing realization that developmental flexibility is pervasive throughout the living world. The hypertrophied human brain is not a device for importing obsolete behavior patterns from the Stone Age, but rather for carrying behavioral plasticity to a 17 level unprecedented in evolution. The vast success of the human species, if admittedly not yet a very long-lasting success, suggests that this flexibility is highly adaptive. Flexibility is of course constrained by physiology. We cannot learn to fly or to swim in the deep oceans in pursuit of giant squid. If we want sonar we will need to build machines. And physiology constrains our psychology in deep though very general ways. Like all animals we care a lot about eating, and like most we care a lot about sex and raising children. We are a highly social species, a fact connected to our large brains that allow diverse and complementary specialization and division of labour, and our lack of especially impressive individual physical capacities. But what we eat, how we have sex and with whom, and how we raise our children are highly diverse. Similarly our profound sociality is realized in a hugely variable range of social systems, which provide a bewildering array of possible social roles. There are many species that are interested in food and sex, and many that are social; it is the developmental plasticity that is our peculiar distinction. A senior advisor to the UK recently announced publicly that research had shown that 70% of a child's performance is genetically caused. One supposes that he was referring to a measure of heritability, a claim that a certain proportion of the variation in educational outcome could be explained by genetics, a fact that says more about the variability of schools than about the causation of educational outcomes. The problem with such pronouncements from such a source is that they are of course intended to influence policy, for example by diverting resources from unsuccessful students, assumed to have ‘bad’ genes, supposed in turn to doom their possessors to poor outcomes. It is depressing to find these vulgar misunderstandings of genetics in the corridors of power, but perhaps the best way of addressing them is to promote better understanding of the open-ended and diverse processes that are human lives. Returning for a final time to the debate with which I began, I have said that my sympathies lie more with the deniers of human nature than its defenders; but I 18 prefer to say not that there is no human nature, but that human nature is uniquely plastic. Though there is of course something that humans are like, and that we should be concerned to describe and understand, the concept of human nature is generally used to circumscribe the range of human variation and possibility in ways that are ungrounded by the empirical facts about us. This does not mean, on the other hand, that I subscribe to the extreme existentialist view that we are entirely free to be whatever we choose. In fact human diversity and even the initial underdetermination of human life cycles is entirely consistent with the view that human lives are fully determined. It is just that the causal factors that will determine them are not settled in advance. A human life might be like the career of a stick floating down a turbulent river: no one could predict where it would end up, but this would not show that the stick had any choice in the matter. 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