What Darwin Got Wrong is a remarkable book, one that dares to challenge the theory of natural selection as an explanation for how evolution works—a devastating critique not in the name of religion but in the name of good science.
Jerry Fodor and Massimo Piattelli-Palmarini, a distinguished philosopher and a scientist working in tandem, reveal major flaws at the heart of Darwinian evolutionary theory. Combining the results of cutting-edge work in experimental biology with crystal-clear philosophical arguments, they mount a reasoned and convincing assault on the central tenets of Darwin’s account of the origin of species. The logic underlying natural selection is the survival of the fittest under changing environmental pressure. This logic, they argue, is mistaken, and they back up the claim with surprising evidence of what actually happens in nature. This is a rare achievement—a concise argument that is likely to make a great deal of difference to a very large subject. What Darwin Got Wrong will be controversial. The authors’ arguments will reverberate through the scientific world. At the very least they will transform the debate about evolution and move us beyond the false dilemma of being either for natural selection or against science.
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Jerry Fodor is a professor of philosophy and cognitive science at Rutgers University.
Massimo Piattelli-Palmarini started his academic career as a biophysicist and molecular biologist and is now a professor of cognitive science at the University of Arizona.
WHAT DARWIN GOT WRONG
PART ONE THE BIOLOGICAL ARGUMENT 1 WHAT KIND OF THEORY IS THE THEORY OF NATURAL SELECTION? Introduction The (neo-)Darwinian theory of evolution (ET) has two distinct but related parts: there's a historical account of the genealogy of species (GS), and there's the theory of natural selection (NS). The main thesis of this book is that NS is irredeemably flawed. However, we have no quarrel to pick with the genealogy of species; it is perfectly possible -in fact, entirely likely-that GS is true even if NS is not. We are thus quite prepared to accept, at least for purposes of the discussion to follow, that most or all species are related by historical descent, perhaps by descent from a common primitive ancestor; and that, as a rule of thumb, the more similar the phenotypes of two species are,1 the less remote is the nearest ancestor that they have in common.2 However, although we take it that GS and NS are independent, we do not suppose that they are unconnected. Think of the GS as a tree (or perhaps a bush) that is composed of nodes and paths; each node represents a species, and each species is an ancestor of whatever nodes trace back to it. The questions now arise: How did the taxonomy of species get to be the way that it is? What determines which nodes there are and which paths there are between them? In particular, by what process does an ancestor species differentiate intoits descendants? These are the questions that Darwin's adaptationism purports to answer. The answer it proposes is that if, in the genealogical tree, node A traces back to node B, then species B arose from species A by a process of natural selection, and the path between the nodes corresponds to the operation of that process. We will argue that it is pretty clear that this answer is not right; whatever NS is, it cannot be the mechanism that generates the historical taxonomy of species. Jared Diamond in his introduction to Mayr (2001, p. x) remarks that Darwin didn't just present '... a well-thought-out theory of evolution. Most importantly, he also proposed a theory of causation, the theory of natural selection.' Well, if we're right, that's exactly what Darwin did not do; or, if you prefer, Darwin did propose a causal mechanism for the process of speciation, but he got it wrong. There are certain historical ironies in this because it is the Darwinian genealogy, and not the theory of natural selection, that has been the subject of so much political and theological controversy over the last hundred years or so. To put it crudely, what people who do not like Darwinism have mostly objected to is the implication that there's a baboon in their family tree; more precisely, they do not admit to a (recent) ancestor that they and the baboon have in common. Accordingly, the question doesn't arise for them how the ancestral ape evolved into us on the one hand and baboons on the other. This book is anti-Darwinist, but (to repeat) it is not that kind of anti-Darwinist. It is quite prepared to swallow whole both the baboon and the ancestral ape, but not the thesis that NS is the mechanism of speciation. The argument for the conclusion that there is something wrong with NS is actually quite straightforward; to some extent, it's even familiar. Not, however, from discussions of Darwinism per se, but from issues that arise in such adjacent fields as the metaphysics of reference, the status of biological teleology and, above all, in the psychology of learning. Bringing out the abstract similarity-indeed, identity-of this prima facie heterogeneous collection is a main goal in what follows. But doing so will require a somewhat idiosyncratic exposition of NS. In the first place, we propose to introduce NS in a way that distinguishes between: (1) the theory considered simply as a 'black box' (that is, simply as a function that maps certain sorts of inputs onto certain sorts of outputs); and (2) the account that the theory gives of the mechanisms that compute that function and of the constraints under which the computations operate. This is, as we say, a somewhat eccentric way of cutting up the pie; but it will pay its way later on when we try to make clear what we take to be the trouble with NS. In the second place, we want to develop our exposition of Darwin's account of evolution in parallel with an exposition of B. F. Skinner's theory of learning by operant conditioning (OT). Some of the similarities between the two have been widely noted, not least by Skinner himself.3 But we think, even so, that the strength of the analogy between NS and OT has been seriously underestimated, and that its implications have generally been misunderstood. In fact, the two theories are virtually identical: they propose essentially the same mechanisms to compute essentially similar functions under essentially identical constraints. This raises a question about which prior discussions of NS have been, it seems to us, remarkably reticent: it is pretty generally agreed, these days, that the Skinnerian account of learning is dead beyond resuscitation. So, if it is true that Skinner's theory and Darwin's are variations on the same theme, why aren't the objections that are routinely raised against the former likewise raised against the latter? If nobody believes Skinner any more, why does everybody still believe Darwin? We're going to argue that the position that retains the second but not the first is not stable. Natural selection considered as a black box As just remarked, one way to think about NS is as an account of the process that connects ancestral species with their descendants. Another (compatible) way is to think of it is as explaining how the phenotypic properties of populations change over time in response to ecological variables.4 By and large, contemporary discussions of evolution tend to stress the second construal; indeed, it's sometimes saidthat this sort of 'population thinking' was Darwin's most important contribution to biology.5 Whether or not that is so, 'population thinking' is convenient for our present purposes; it allows us to construe an evolutionary theory abstractly, as a black box in which the input specifies the distribution of phenotypes at a certain time (the GN [Generation N] distribution, together with the relevant aspects of its ecology), and in which the output specifies the distribution of phenotypes in the next generation (GN+1). This provides a perspective from which the analogies between NS and OT become visible, since OT is also plausibly viewed as a black box that maps a distribution of traits in a population at a time (a creature's behavioural repertoire at that time), together with a specification of relevant environmental variables (viz. the creature's history of reinforcement), onto a succeeding distribution of traits (viz. the creature's behavioural repertoire consequent to training). We therefore propose, in what follows, to indulge in a little 'population thinking' about both NS and OT. Operant conditioning theory considered as a black box If we are to think of the Skinnerian theory of learning in this way, we will first have to decide what is to count as a 'psychological trait'. Fortunately, Skinner has an explicit view about this, which, although by no means tenable, will serve quite nicely for the purposes of exposition. Let's stipulate that a creature's 'psychological profile' at a certain time is the set of psychological traits of the creature at that time.6 For Skinner, a psychological trait is paradigmatically a stimulus-response (S-R) association; that is, it is a disposition to perform a token of a certain type of behaviour 'in the presence of' a token of a certain type of environmental event.7 Skinner takes S-R associations to be typically probabilistic, so a creature's psychological profile at a certain time is a distribution of probabilities over a bundle of S-R associations. Correspondingly, OT is a theory about how the distribution of probabilities in a population of S-R connections varies over time as afunction of specified environmental variables (including, notably, 'histories of reinforcement'). The picture is, in effect, that the totality of a creature's dispositions to produce responses to stimuli constitutes its psychological profile. These dispositions compete for strength, and environmental variables determine which dispositions win the competitions; they do so in accordance with the laws of conditioning that OT proposes to specify, and of which the so-called 'law of effect' is the paradigm. We've been describing OT as a kind of 'population thinking' in order to emphasize its similarity to evolutionary theory (ET): both are about how traits in a population change over time in response to environmental variables ( ecological variables; see footnote 5). That is, we suppose, a mildly interesting way of looking at things, but if it were all that the ET/OT analogy amounted to, it would warrant only cursory attention. In fact, however, there is quite a lot more to be said. Both theories postulate certain strong constraints (we'll call them 'proprietary' constraints)8 on how the empirical facts about population-to-population mappings are to be explained; and in both cases, the choice among candidate theories relies heavily on the imposition of these constraints.9 Some proprietary constraints derive from (what purport to be) general methodological considerations;10 but many of them are contingent and substantive. They derive from assumptions about the nature of evolution on the one hand and of learning on the other. The substance of the analogy between Darwin's version of evolutionary theory and Skinner's version of learning theory consists, in part, in the fact that the proprietary constraints that they endorse are virtually identical. Proprietary constraints (1): iterativity OT and NS are both formulated so as to apply 'iteratively' in their respective domains. That's to say that psychological profiles are themselves susceptible to further conditioning, and evolved phenotypes are themselves susceptible to further evolution. Iterativity is required in order that OT and ET should acknowledge the open-endednessof their respective domains: ET implies no bounds on the varieties of phenotypes that may be subject to evolution, and OT implies no bounds on the variety of behavioural profiles that may be modified by learning. The effect of this is to permit both theories to begin their explanations in medias res. ET presupposes some presumably very simple unevolved self-replicators with phenotypic traits to which the laws of evolution apply in the first instance; OT presupposes some presumably very simple repertoire of S-R associations to which the putative laws of conditioning apply in the first instance. In both cases, there are serious questions as to exactly what such 'starting assumptions' a theorist ought to endorse. In OT, the usual view is that an organism at birth (or perhaps in utero) is a random source of behaviours. That is, prior to operant learning, any stimulus may evoke any response, although the initial probability that a given stimulus will evoke a given response is generally very small. In ET, a lot depends on what kind of self-replicator evolutionary processes are supposed to have first applied to. Whatever it was, if it was ipso facto subject to evolution, it must have been a generator of heritable phenotypes, some of which were more fit than others in the environmental conditions that obtained. Proprietary constraints (2): environmentalism What phenotypes there can be is presumably determined by (among other things) what genotypes there can be; and what is genotypically possible is constrained by what is possible at 'lower' levels of organization: physiological, genetic, biochemical or whatever. Likewise for the effects of physiological (and particularly neurological) variables on psychological phenomena. It is, however, characteristic of both ET and OT largely to abstract from the effects of such endogenous variables, claiming that the phenomena of evolution on the one hand and of psychology on the other are very largely the effects of environmental causes. A striking consequence of this assumption is that, to a first approximation, the laws of psychology and of evolution are both supposedto hold very broadly across the phylogenetic continuum, abstracting both from differences among individuals and from differences among species. (In the darkest days of conditioning theory, one psychologist claimed that, if we had a really adequate theory of learning, we could use it to teach English to worms. Happily, however, he later recovered.) Likewise, it is characteristic of evolutionary biologists to claim that the same laws of selection that shape the phenotypes of relatively simple creatures such as protozoa also shape the phenotypes of very complex creatures such as primates. It's clearly an empirical issue whether, or to what extent, such environmentalist claims are true in either case. It turned out that OT greatly underestimated the role of endogenous structures in psychological explanation; much of the 'cognitive science' approach to psychology has been an attempt to develop alternatives to OT's radical environmentalism. In Part one we will consider a number of recent findings in biology that suggest that analogous revisions may be required in the case of ET.11 Proprietary constraints (3): gradualism ET purports to specify causal laws that govern transitions from the census of phenotypes in an ancestral population to the census of phenotypes in its successor generation. Likewise, OT purports to specify causal laws that connect a creature's psychological profile at a given time with its succeeding psychological profile. In principle, it is perfectly possible that such laws might tolerate radical discontinuities between successive stages; gradualism amounts to the empirical claim that, as a matter of fact, they do not. This implies, in the case of ET, that even speciation is a process in which phenotypes alter gradually, in response to selection pressure.12 'Saltations' (large jumps from a phenotype to its immediate successor) perhaps occur from time to time; but they are held to be sufficiently infrequent that theories of evolution can generally ignore them.13 In OT, gradualism implies that learning curves are generally smooth functions of histories of reinforcement. Learning consists of a gradual increment of the strength of S-R associations and not, for example, in suddeninsights into the character of environmental contingencies. Strictly speaking, according to OT, there is no such thing as problem solving; there is only the gradual accommodation of a creature's behaviours and behavioural dispositions to regularities in its environment. In neither learning nor evolution is the claim for gradualism self-evidently true. Apparent discontinuities in the fossil record were a cause of considerable worry to Darwin himself, and there continues to be a tug-of-war about how they ought to be interpreted: evolutionary biologists may see fortuitous geological artefacts where palaeontologists see bona fide evidence that evolution sometimes proceeds in jumps (Eldredge, 1996). Likewise, a still robust tradition in developmental psychology postulates a more-or-less fixed sequence of cognitive 'stages', each with its distinctive modes of conceptualization and correspondingly distinctive capacities for problem solving. Piagetian psychology is the paradigm; for decades Piaget and Skinner seemed to be exclusive and exhaustive approaches to the psychology of learning.14 It is thus possible to wonder why gradualism has seemed, and continues to seem, so attractive to both evolutionary theorists and learning theorists. Some of the answer will become apparent whe...
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