Evolution is weird - far weirder than Darwin ever imagined. But is it so weird that Darwinism itself should go the way of the dinosaur and the dodo? That’s the question that Jerry Fodor and Massimo Piattelli-Palmarini pose in What Darwin Got Wrong.
Darwin’s theory of evolution by natural selection rests on three elements: the existence of variation in a trait, the differential effects of such variation upon reproductive success and a mechanism by which the trait is inherited. Little was known in Darwin’s time of the principles underlying heredity and variation. It was the Austrian monk Gregor Mendel who started unravelling the story of genetic inheritance. His ideas were eventually fused with those of Darwin and Mendel to create the ‘Modern Synthesis’, the foundation stone of contemporary evolutionary theory.
Only over the past 20 years, however, have we begun to understand in greater detail what genes are, how they express themselves and how variation in the genotype relates to variation in the phenotype. Most biologists working within the Modern Synthesis had assumed that an organism was a straightforward reflection of its component genes. Specific genetic mutations, they believed, gave rise to specific changes in bodily structure or behaviour. Recent research has revealed a far more complex story of how genes make organisms.
Some genes have multiple functions while others act as ‘master genes’ helping to switch bits of DNA on and off. Master genes seem not to recognize species boundaries. The same master genes for eye development can be found in sea urchins (in which they remain unexpressed), fruit flies and humans. The implication is that major differences between species may be less about the evolution of new genes than about the same genes being regulated and expressed in new ways.
According to Fodor and Piattelli-Palmarini these discoveries reveal not just the complexity of the evolutionary process but also the wrongness of Darwinian theory. Biologists such as Richard Lewontin and the late Stephen Jay Gould have in recent years challenged what they call ‘ultra-Darwinism’, insisting that adaptation is only one of a number of evolutionary mechanisms. All, however, have accepted adaptation as important and real. Not so Fodor and Piattelli-Palmarini.
Fodor is a leading philosopher of mind. Piattelli-Palmarini is a distinguished cognitive scientist. What Darwin Got Wrong is a trenchant, entertaining assault on the very basis of contemporary evolutionary theory.
There are two halves to the argument. The first part of the book is a breezy tour through recent biological advances, particularly in the field of evolutionary developmental biology (or ‘evo devo’). The Darwinian idea that through natural selection organisms become adapted to their environment cannot be true, Fodor and Piattelli-Palmarini insist, because it is a theory that relies entirely on external factors as the drivers of evolution, whereas the new biology has shown the importance of internal organization and regulation.
Most biologists at the forefront of this research remain, however, committed Darwinians. Why? Because, suggest Fodor and Piattelli-Palmarini, they have failed to understand the fundamental conceptual flaws of Darwinism. The second part of What Darwin Got Wrong attempts to lay out these flaws.
At the heart of the argument is the critique of what Fodor and Piattelli-Palmarini call the ‘selection for’ fallacy: the belief that natural selection selects particular phenotypes because they provide the organism with an evolutionary advantage. This cannot be, they argue, because of the presence of ‘co-existent’ traits. Some bodily features that Darwinists claim have been selected for in the course of evolution possess more than one trait or property, only one of which actually increases fitness (the Darwinian term for the capacity to reproduce), but all of which may be correlated with increased fitness.
A heart is an organ that both pumps blood and makes a noise. Pumping blood efficiently increases fitness, making a noise does not. But since all hearts that pump blood also make a noise, both pumping blood and making a noise are correlated with fitness. ‘The adaptationist story’, Fodor and Piattelli-Palmarini observe, ‘was supposed to be that traits are selected-for when they are correlated with fitness, which by assumption both… are.’ So how, they ask ‘could it be that either is selected for and the other isn’t?’
Humans, they argue, can make a distinction between a trait such as an efficient heart that truly increases fitness and a trait such as a noisy heart that may be correlated with greater fitness but does not itself provide an evolutionary advantage. That’s because humans possess minds and are able to use reason and judgment and ask ‘what if’ questions – ‘What if hearts did not make a noise’?’ ‘What if hearts pumped less efficiently?’
Nature, however, is mindless. It cannot ask such questions and so cannot make such distinctions. Hence ‘the claim that selection is the mechanism of evolution cannot be true.’
Darwin, Fodor and Piattelli-Palmarini believe, was bedazzled by the idea of artificial selection. In making an analogy between the way that a horse breeder shapes an animal’s characteristics and the way that nature does, he apparently forgot that nature, unlike a horse breeder, does not possess a mind capable of distinguishing between noisy and efficient hearts.
Ironically, though, it is Fodor and Piattelli-Palmarini who confuse artificial and natural selection. Animal breeders have to decide a priori which trait to select for. Nature does not. That is because in evolution what is a ‘good’ or a ‘bad’ trait only becomes apparent in the outcome.
Natural selection describes a process whereby organisms possessing certain traits happen to leave more offspring than those with different traits. In this way the characteristics of successive generations can evolve.
Creatures whose hearts pump blood more efficiently will leave more offspring. Creatures whose hearts make more noise will, on average, leave neither fewer nor more. But creatures whose hearts pump less efficiently will leave fewer offspring, however noisy or quiet those hearts may be. The distinction between traits causally linked to increased fitness and traits that are not emerges, therefore, as the outcome of the selection process. It is true that traits that do not causally increase fitness (such as hearts that make noise) may evolve as ‘free riders’ on other traits - but only if those other traits increase fitness. The fact that natural selection is ‘blind’ to traits that do not impact on fitness should not lead to the conclusion that it is ‘blind’ to all traits.
There is, according to Fodor and Piattelli-Palmarini, one question that ‘Darwin didn’t ask… namely, why certain imaginable phenotypes simply didn’t occur.’ Why, they want to know, ‘aren’t there pigs with wings?’ The theory of natural selection cannot answer this because ‘Nobody thinks that if there aren’t any pigs with wings it’s because the winged pigs were selected against in their prehistoric days with wingless ones.’ Rather ‘pigs don’t have wings because there is no place on pigs to put them’.
This gets to the root of Fodor and Piattelli-Palmarini’s misunderstanding. Selection can only work on variation that already exists. And not all variation that can exist will exist. Variation is variation upon an existing phenotype (and hence an existing genotype). The existing genotype can only mutate in certain ways. To say that ‘there is no place on pigs to put wings’ is to say that there are constraints on porcine variation.
This is why Fodor and Piattelli-Palmarini are wrong to suggest that adaptationism relies entirely on external factors. It is through constraints on possible variation that the theory of natural selection takes internal factors into account. It is also why recent discoveries in evo devo are not an argument against Darwinism. They reveal not the impossibility of natural selection, but the complexity of controls upon possible variation.
Fodor and Piattelli-Palmarini are no Creationists, but ‘outright, card-carrying, signed-up, dyed-in-the-wool, no-holds-barred atheists’. That, however, only makes worse the incoherence of their understanding of Darwinism. There is much that Darwin got wrong, from his views of racial struggle to his occasional espousal of Lamarckism. There is nothing in this book, however, to suggest a fundamental flaw in is his central argument about evolution by natural selection.