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Not So Natural Selection

What Darwin Got Wrong

by Jerry Fodor and Massimo Piattelli-Palmarini
Farrar, Straus and Giroux, 264 pp., $26.00
Cary Wolinsky/Aurora Photos
A pair of peppered moths superimposed on a photograph of Sheffield, England, after the Industrial Revolution. Since the mid-nineteenth century, there has been an increase in the black-winged form of the peppered moth in England. Evolutionary biologists ha

Nothing creates more misunderstanding of the results of scientific research than scientists’ use of metaphors. It is not only the general public that they confuse, but their own understanding of nature that is led astray. The most famous and influential example is Darwin’s invention of the term “natural selection,” which, he wrote in On the Origin of Species,

is daily and hourly scrutinising, throughout the world, every variation, even the slightest; rejecting that which is bad, preserving and adding up all that is good….

Darwin, quite explicitly, derived this understanding of the motivating force underlying evolution from the actions of plant and animal breeders who consciously choose variant individuals with desirable properties to breed for future generations. “Natural” selection is human selection writ large. But of course, whatever “nature” may be, it is not a sentient creature with a will, and any attempt to understand the actual operation of evolutionary processes must be freed of its metaphorical baggage. Unfortunately, even modern evolutionary biologists, as well as theorists of human social and psychological phenomena who have used organic evolution as a model for general theories of their own subjects, are not always conscious of the dangers of the metaphor. Alfred Russel Wallace, the coinventor of our understanding of evolution, wrote to Darwin in July 1866 warning him that even “intelligent persons” were taking the metaphor literally.

The modern skeletal formulation of evolution by natural selection consists of three principles that provide a purely mechanical basis for evolutionary change, stripped of its metaphorical elements:

(1) The principle of variation: among individuals in a population there is variation in form, physiology, and behavior.

(2) The principle of heredity: offspring resemble their parents more than they resemble unrelated individuals.

(3) The principle of differential reproduction: in a given environment, some forms are more likely to survive and produce more offspring than other forms.

Evolutionary change is then the mechanical consequence of variation in heritable differences between individuals whenever those differences are accompanied by differences in survival and reproduction. The evolution that can occur is limited by the available genetic variation, so in order to explain long-term continued evolution of quite new forms we must also add a fourth principle:

(4) The principle of mutation: new heritable variation is constantly occurring.

The trouble with this outline is that it does not explain the actual forms of life that have evolved. There is an immense amount of biology that is missing. It says nothing about why organisms with the evolved characteristic were more likely to survive or reproduce than those with the original one. Why, when vertebrates evolved wings, did they have to give up their front legs to do it? After all, insects can have two pairs of wings and six legs, so there cannot be any deep general biological constraint on development. Why don’t birds that live in trees make a living by eating the leaves as countless forms of insects do instead of spending so much of their energy looking for seeds or worms? Perhaps possessing characteristic A rather than B was just a secondary consequence of a different developmental or biochemical property that was variable and heritable. Or perhaps characteristic A was the only available variation that differentiated the selected from the unselected organisms. It is these considerations that lie at the heart of Jerry Fodor and Massimo Piattelli-Palmarini’s discussion of What Darwin Got Wrong.1

Evolutionary biologists are of two sorts. A minority really do not care why one inherited characteristic confers a reproductive advantage to its possessors. They are content to show that such an advantage exists for a particular inherited difference, thus exemplifying natural selection. The dominant figure in experimental and observational evolutionary genetics in the middle of the last century, Theodosius Dobzhansky, spent most of his life showing convincingly from observations of both natural and experimental laboratory populations that natural selection was the cause of both the year-to-year stability and the repeatable seasonal changes in the proportions of certain variants in the chromosomes in natural populations of fruitflies.

Despite spending time every year on horseback, visiting localities in the Great Basin and California where he trapped fruitflies, Dobzhansky never, in fact, saw a fruitfly in its native condition. He collected living flies by putting out rotting banana traps, so the flies came to him, but from where he never knew. When flies were brought back to the laboratory and bred in large populations in which the proportions of the chromosome types were initially very different from the ones found in nature, those proportions changed in repeatable ways in a few generations. It was sufficient for him to be able to demonstrate that natural selection really worked.

In contrast, most evolutionary biologists work on natural populations of plants or animals that they have chosen because they believe they can tell a natural historical story of how selection actually operates in a particular case. The most famous example is the increase in the black form of the wings in the peppered moth that has occurred in England since the mid-nineteenth century. The explanation offered and repeatedly appearing in textbooks (although since called into question because of faulty methodology) was that the moths rested on tree trunks where they were at risk of being eaten by birds. Before the spread of heavy industry the tree trunks were covered with lichens whose speckled appearance was matched closely by the “peppered” appearance of the moth’s wings, so the camouflaged moths were only occasionally attacked. With the air pollution caused by heavy industry, the lichens were killed, so the moths were easily visible on the naked dark bark and were heavily preyed upon. A mutation to black wings appeared and was strongly favored by natural selection since the black-winged forms were now once again camouflaged.

There is little doubt that this example, widely taught in lectures and textbooks, had a powerful influence in convincing evolutionary biologists who came into the field from their prior interest in natural history that one could tell the causal story of natural selection. One unfortunate feature of this case is that the caterpillars of the dark-winged forms also have a slightly higher survival rate than those of the speckled-wing form, even though they are not black, so something more is going on, but this fact is not part of the curriculum.

The interest of modern evolutionary biologists in natural historical stories is partly a reflection of the origin of the science in the genteel nineteenth-century fascination with nature that characterized men of Darwin’s social circumstances. The country curate who is an amateur collector of butterflies is a clichĂŠ of Victorian life. The success of evolutionary biology as an explanatory scheme for its proper subject matter has led, in more recent times, to an attempt to transfer that scheme to a variety of other intellectual fields that cry out for systematic explanatory structure. As Hegel lamented in The Philosophy of History, “Instead of writing history, we are always beating our brains to discover how history ought to be written.”

One answer has been to transfer the formal elements of variation and natural selection to other aspects of human activity. It is by no means an anomaly that one of the authors of What Darwin Got Wrong comes to the subject from cognitive studies and linguistics. We have evolutionary schemes for history, psychology, culture, economics, political structures, and languages. The result has been that the telling of a plausible evolutionary story without any possibility of critical and empirical verification has become an accepted mode of intellectual work even in natural science.

The central claim of What Darwin Got Wrong is that “Darwin’s theory of selection is empty” (their italics). That is, to say that some trait was the object of natural selection and was established by the force of selection for that trait is to say nothing. If this seems a perverse claim, an example is helpful. There is a species of wild mouse that lives on both dark and light backgrounds. In the populations on light backgrounds the mice have what we think of as a “normal” mousy light brown color. The populations on dark backgrounds, however, are much darker colored. An evolutionary adaptationist argument that has been offered is that a mutation to a dark coat was favored by natural selection when it occurred in the population living on the dark surface because predators could not see the dark mice as well and so these mice survived better and eventually the gene for dark coats took over the population.

Fodor and Piattelli-Palmarini would argue that one cannot simply isolate coat color as the object of natural selection. They discuss the large body of evidence in many organisms of a number of complexities at the molecular, cellular, developmental, and physiological level that need to be taken into account as well.

First, the proteins that result from the processing of genetic information may enter into multiple metabolic and developmental pathways. From the earliest days of experimental genetics it was known that mutations that had been detected from a change in some obvious feature of an organism also affected other outcomes of the organism’s development and metabolism. For example, it is almost always the case that a mutation in fruitflies affecting any morphological character also reduces the rate of survival of the larvae, i.e., the worm-like early stages of development. So, any mutations that alter the normal dark red eye color of adult flies, making it bright red or orange or colorless, will also result in lower survival rates of larvae, even though they have no eyes.

The causes of a reduction in survival in larvae that results from mutations with obvious visible effects in adults must be as varied as the morphological character in question, and it would require a detailed examination of the process of fruitfly development to elucidate. It is precisely this phenomenon that compromises the elegant natural historical story about the industrial dark color of the peppered moth or the story about predation in the dark-colored mice. Is it the dark coat and not some other metabolic product that is changed in dark-coated mice and that is responsible for their greater success in reproduction? Perhaps the mice with dark coats are also more fertile or better able to digest their food.

It is, of course, not true that every process in a living organism interacts strongly with every other process. If interaction were both universal and effective, the organism would be so inflexible as to make life impossible and no evolutionary change could ever occur. The intensity of interaction between parts is also strongly dependent on the circumstances of life. Were I to lose the little finger of my left hand it would have little effect on my life, but if I were a cellist it would be a catastrophe. Thus it matters to the result of natural selection which of the possible multiple pathways of protein metabolism and interaction exist in each kind of organism.

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    The circulation of the proof copy of What Darwin Got Wrong, the product of a noted philosopher and a prominent student of linguistics and cognitive science, has resulted in a volume of critical comment from biologists and philosophers that has not been seen since 1859. No week has passed that a manuscript expressing bewilderment or outrage from a biologist or philosopher of science has not arrived on my desk or desktop. I have tried but not succeeded entirely in avoiding reading these before making a first draft of this review.

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