- What if Darwin's theory of natural selection is inaccurate? Oliver Burkeman explores research suggesting it's only part of the story of how life develops
- The story, still sometimes repeated in creationist circles, goes like this: it is the 1960s, at Nasa's Goddard Space Flight Centre in Maryland, and a team of astronomers is using cutting-edge computers to recreate the orbits of the planets, thousands of years in the past. An error message flashes up. There's a problem: way back in history, one whole day appears to be missing.
The scientists are baffled, until a Christian member of the team fetches a Bible. He thumbs through it until he reaches the Book of Joshua, chapter 10, in which Joshua asks God to stop the world for ... “about a full day!" Uproar. The astronomers have happened upon proof that God controls the universe on a day-to-day basis, that the Bible is literally true, and that by extension the "myth" of creation is a reality. Darwin was wrong - according to another creationist rumour, he'd recanted on his deathbed, anyway - and here is scientific evidence!
- Inevitably, those of us who aren't professional scientists have to take a lot of science on trust. And one of the things that makes it so easy to trust the standard view of evolution, in particular, is illustrated by the legend of the Nasa astronomers: the doubters are so deluded or dishonest that one needn't waste time with them. Unfortunately, that also makes it awkward to ask a question that seems, in the light of recent studies and several books, to be growing more pertinent. What if Darwin's theory of evolution - or, at least, Darwin's theory of evolution as most of us believe we understand it - is not entirely accurate?
- Such talk is liable to drive evolutionary biologists into a rage, or, in the case of Richard Dawkins, into even more of a rage than usual. They have a point: nobody wants to provide ammunition to the creationists or adherents of "intelligent design", and it's true that few of the studies now coming to public prominence are that revolutionary to the experts. But in the culture at large, we may be on the brink of a major shift in perspective. As David Shenk puts it in his new book, The Genius in All of Us, "This is big, big stuff - perhaps the most important [discovery] in the science of heredity since the gene."
- Take the Swedish chickens. Three years ago, researchers at the university of Linkoping in Sweden created a henhouse designed to make its occupants feel stressed. The lighting was manipulated to make the rhythms of night and day unpredictable, so the chickens lost track of when to eat or roost. Not surprisingly, they showed a significant decrease in their ability to learn how to find food hidden in a maze.
- Then the chickens were moved back to a non-stressful environment, where they conceived and hatched chicks who were raised without stress – and yet these chicks, too, demonstrated unexpectedly poor skills at finding food in a maze. They appeared to have inherited a problem that had been induced in their mothers. Further research established that the inherited change had altered the chicks' "gene expression" - the way certain genes are turned "on" or "off". The stress had affected the mother hens on a genetic level and they had passed it on to their offspring.
- The Swedish chicken study was one of several recent breakthroughs in the field of epigenetics, which primarily studies the epigenome, the protective package of proteins around which genetic material - strands of DNA- is wrapped. The epigenome plays a crucial role in determining which genes express themselves: in effect, it switches certain genes on or off, or turns them up or down in intensity. It isn't news that the environment can alter the epigenome; what's news is that those changes can be inherited.
- Another study, again from Sweden, looked at lifespans in Norrbotten, the country's northernmost province, where harvests are usually sparse but occasionally abundant, meaning that, historically, children sometimes grew up with wildly varying food intake. A single period of extreme overeating in the midst of the usual short supply, researchers found, could cause a man's grandsons to die an average of 32 years earlier than if his childhood food intake had been steadier. Your own eating patterns, this implies, may affect your grand-children's lifespans.
- It might not be obvious why this has such profound implications for evolution. In the way it's generally understood, the whole point of natural selection - the so- called modern synthesis of Darwin's theories with subsequent discoveries about genes - is its simplicity. In each generation, genes cause random mutations, making offspring subtly different from their parents; those mutations that enhance an organism's abilities to thrive and reproduce in its particular environment will tend to spread through populations, while those that make successful breeding less likely will eventually peter out.
- Yet epigenetics suggests this isn't the whole story. If what happens to you during your lifetime - living in a stress- inducing henhouse, say, or overeating in northern Sweden - can affect how your genes express themselves in future generations, the simple version of natural selection begins to look questionable. Rather than genes simply "offering up" a random smorgasbord of traits-in each new generation, which then either prove suited or unsuited to the environment, it seems that the environment plays a role in creating those traits, if only in a short-term and reversible way. You begin to feel sorry for the much-mocked pre-Darwinian zoologist Jean-Baptiste Lamarck, whose own version of evolution held, most famously, that giraffes have long necks because their ancestors were "obliged to browse on the leaves of trees and to make constant efforts to reach them". As a matter of natural history, he probably wasn't right about how giraffes' necks came to be so long. But Lamarck was scorned for a much more general idea: that lifestyle might influence heredity.
- Epigenetics is the most vivid reason why the popular understanding of evolution might need revising, but it's not the only one. We've learned that huge proportions of the human genome consist of viruses, or virus-like materials, raising the notion that they got there through infection - meaning that natural selection acts not just on random mutations, but on stuff that's introduced from elsewhere. There is growing evidence, at the level of microbes, of genes being transferred not just vertically, from parents to offspring, but also horizontally, between organisms. Carl Woese and Nigel, Goldenfield conclude that, on average, a bacterium may have obtained 10% of. its genes from other organisms.
- Since most of the history of life on earth has been the history of micro-organisms, the evidence for horizontal transfer suggests that a mainly Darwinian account of evolution may only be applicable to the most recent, much more complex forms of life. Perhaps, before that, most evolution was based on horizontal exchange.
- It is a decade since the biologist Randy Thornhill and the anthropologist Craig Palmer published The Natural History of Rape. In the book, they made an argument that - however obnoxious at first glance - seemed, to many, to follow strait-forwardly from the logic of natural selection. Evolution tells us. that the traits that flourish are ones that help organisms reproduce. Evolution psychology argues for the inclusion of psychological traits. And since rape is a trait in human society, it follows that a desire to commit rape must be adaptive. There must be a genetic basis, for it - a "rape gene", in the words of some media stories following the book's publication - because, in prehistoric times, those men who possessed the tendency would reproduce more successfully. Therefore, authors concluded, rape was "natural".
- Understandably the book was hugely controversial. But there was nothing that radical about idea that natural selection might be able to illuminate any aspect of human behaviour. Evolutionary psychology, in the hands of various practitioners sought to explain why militarism is so prevalent or why men tend to dominate women in so many hierarchical organisations. If the field seems politically charged these days, that is because it has become less questioned.
- For much of the past decade, a week never seems to pass without a book or news story attributing some facet of modern-day life to the evolution past. It explained music and art and why we reward senior executives with top-floor corner offices (because we evolved to want a clear view of our enemies approaching across the savannah). Lefty and feminist critics frequently misinterpreted evolutionary psychology, imagining that when some trait was described as adaptive, that meant it morally justifiable. But that was how many findings - often better described as speculations – came be believed. "We're not exactly saying it's right for, say, men to sleep around," evolutionary psychologists would observe. "But ... well, good luck trying to change millennia of evolved behaviour."
- Far more than biologists, evolutionary psychologists bought into the ultra-simple version of natural selection, and so they stand to lose far more from advances in our understanding of what's really going on. They were always prone to telling "just-so stories" - plausible tales about why a trait might be adaptive, instead of demonstrating that it was- and recent studies have begun to chip away at what evidence there was. And now if epigenetics and other developments are suggesting that environment can alter heredity, the terms of the debate - nature versus nurture - become shaky, It's not even a matter of settling on a "mixture" of nature and nurture. Rather, the concepts of "nature" and "nurture" seem to be growing meaningless. What does "nature" mean if you can nurture the nature of your descendants?
- This is a central argument of Shenk's book, sub-headed Why Everything You've Been Told About Genetics, Talent and IQ is Wrong. Popular notions about talented "genetic gifts”, he points out, collapse if the eating habits of Tiger Woods's ancestors, for example, might have contributed to Woods's golfing abilities.
- "What all this evidence shows is that we need much more subtle and nuanced understanding of Darwinism and natural selection," Shenk says. “I think that's inevitably, going to happen among scientists. The question is how much nuance will carry over into the public sphere."
- Among the studies at Shenk's disposal is one published last year in the Journal of Neuroscience, involving mice with genetically inherited memory problems. As recompense for having been bred to be scatterbrained, they were kept in an environment full of stimulating toys, exercise and attention. Key aspects of their memory skills were shown to improve, and crucially so did those of their offspring, even though the offspring had not experienced the stimulating environment, even as foetuses
- "If a geneticist had suggested as recently as the1990s that a 12-year-old kid could improve the intellectual nimbleness of his or her future children by studying harder now," writes Shenk, "that scientist would have been laughed right out of the hall."
- And then there is Jerry Fodor, the American philosopher. I started reading What Darwin Got wrong, the book he has co-authored with the cognitive scientist Massimo Piattelli-Palmarini, one morning, with that day's first coffee. A few pages later I grasped with astonishment at what Fodor had done. He hadn't just identified evidence that natural selection was more complicated than previously thought - he'd uncovered a glaring flaw in the whole notion! Natural selection, he explains, “simply cannot be the primary engine of evolution". I got up and refilled my cup. But by the time I returned, his argument had slipped from my grasp.
- I called Fodor and asked him to explain his point in language an infant school pupil could understand. "Can't be done," he shot back. "These issues really are complicated. If we're right that Darwin and Darwinists have missed the point we've been making for 150 years, that's not because it's a simple point and Darwin was stupid. It's a really complicated issue."
- As far as I can make out, it can be summarised in three steps. Step one: Fodor notes – undeniably correctly - that not every trait a creature possesses is necessarily adaptive. Some just come along for the ride: for example, genes that express as tameness in domesticated foxes and dogs also seem to express as floppy ears, for no evident reason. Other traits are coextensive: a polar bear, for example, has the trait of "whiteness" and also the trait of "being the same colour as its environment". (Yes, that's a brain-stretching statement. Take a deep breath.) Step two: natural selection, according to its theorists, is a force that "selects for" certain traits. (Floppy ears appear to serve no purpose, so while they may have been "selected", they weren't "selected for". And polar bears, we'd surely all agree, were "selected for" being the same colour as their environment, not for being white per se: being white is no use as camouflage if snow is say, orange.)
- Step three is Fodor's coup de grace: how, he says, can that be? The whole point of Darwinian evolution is that it has no mind, no intelligence. But to "select for" certain traits - as opposed to just "selecting" them by not having them die out - wouldn't natural selection have to have some kind of mind? It might be obvious to you that being the same colour as your environment is more important than being white, if you're a polar bear, but that's because you ran a thought-experiment1 about a hypothetical situation involving orange snow. Evolution can't run thought experiments2, because it can't think. "Darwin has a theory that centrally turns on the notion of ‘selection-for'," says Fodor. "And yet he can't give an account - nobody could give an account - of how natural selection could distinguish between correlated traits. He waffles."
- The response to Fodor among evolutionary thinkers has been derision and awkwardness. Philosopher Daniel Dennett said via email: "Jerry Fodor's book is a stunning demonstration of how abhorrence of an idea (Jerry's visceral dislike of evolutionary thinking) can derange an otherwise clever thinker ... a responsible academic is supposed to be able to control irrational impulses, [but] Fodor has simply collapsed in the face of his dread and composed some dreadfully bad arguments." What Darwin Got Wrong, Dennett concludes, is "a book that so transparently misconstrues its target that it would be laughable were it not such dangerous mischief".
- It would be surprising, to say the least, were Fodor to be right. A safer conclusion to draw is that his work acts as an important warning to those of us who think we understand natural selection. It's probably not a bankrupt concept, as Fodor claims. But nor should lay people assume that it's self-evidently simple and exhaustively true.
- The irony in all this is that Darwin never claimed that it was. He went to his deathbed protesting that he'd been misinterpreted: there was no reason, he said, to assume that natural selection was the only imaginable mechanism of evolution. Darwin, writing before the discovery of DNA, knew that his work heralded the beginning of a journey to understand the origins and development of life. All we may be discovering now is that we remain closer to the beginning of that journey than we've come to think.
See "McKie (Robin) - Out of Africa: The Sequel"
Text Colour Conventions (see disclaimer)
- Blue: Text by me; © Theo Todman, 2018
- Mauve: Text by correspondent(s) or other author(s); © the author(s)