....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 amply 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 embarrassingly awkward to ask a question that seems, in the light of recent studies and several popular books, to be growing ever more pertinent. What if Darwin's theory of evolution or, at least, Darwin's theory of evolution as most of us learned it at school and believe we understand it is, in crucial respects, not entirely accurate?
.....Take, to begin with, the Swedish chickens. Three years ago, researchers led by a professor at the university of Linkφping in Sweden created a henhouse that was specially designed to make its chicken 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. Unsurprisingly, perhaps, they showed a significant decrease in their ability to learn how to find food hidden in a maze.
The surprising part is what happened next: 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 through the environment. Further research established that the inherited change had altered the chicks' "gene expression" the way certain genes are turned "on" or "off", bestowing any given animal with specific traits. 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 youthful 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 actually express themselves in a creature's traits: 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. And this doesn't, of course, apply only to chickens: some of the most striking findings come from research involving humans.
One study, again from Sweden, looked at lifespans in Norrbotten, the country's northernmost province, where harvests are usually sparse but occasionally overflowing, meaning that, historically, children sometimes grew up with wildly varying food intake from one year to the next. 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 grandchildren's lifespans, years before your grandchildren or even your children are a twinkle in anybody's eye.
It might not be immediately 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 beautiful, breathtaking, devastating simplicity. In each generation, genes undergo random mutations, making offspring subtly different from their parents; those mutations that enhance an organism's abilities to thrive and reproduce in its own particular environment will tend to spread through populations, while those that make successful breeding less likely will eventually peter out.
As years of bestselling books by Dawkins, Daniel Dennett and others have seeped into the culture, we've come to understand that the awesome power of natural selection frequently referred to as the best idea in the history of science lies in the sheer elegance of the way such simple principles have generated the unbelievable complexities of life. From two elementary notions random mutation, and the filtering power of the environment have emerged, over millennia, such marvels as eyes, the wings of birds and the human brain.
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 absolutely simple version of natural selection begins to look questionable......
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 new stuff that's introduced from elsewhere. Relatedly, there is growing evidence, at the level of microbes, of genes being transferred not just vertically, from ancestors to parents to offspring, but also horizontally, between organisms. The researchers Carl Woese and Nigel Goldenfield conclude that, on average, a bacterium may have obtained 10% of its genes from other organisms in its environment.
To an outsider, this is mind-blowing: 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 be only the latest version, applicable to the most recent, much more complex forms of life. Perhaps, before that, most evolution was based on horizontal exchange. Which gives rise to a compelling philosophical puzzle: if a genome is what defines an organism, yet those organisms can swap genes freely, what does it even mean to draw a clear line between one organism and another? "It's natural to wonder," Goldenfield told New Scientist recently, "if the very concept of an organism in isolation is still valid at this level." In natural selection, we all know, the fittest win out over their rivals. But what if you can't establish clear boundaries between rivals in the first place?
.......And now, if epigenetics and other developments are coming to suggest that environment can alter heredity, the very terms of the debate of nature versus nurture suddenly become shaky. It's not even a matter of settling on a compromise, a "mixture" of nature and nurture. Rather, the concepts of "nature" and "nurture" seem to be growing meaningless. What does "nature" even mean if you can nurture the nature of your descendants?
This is one central argument of Shenk's new book, subheaded Why Everything You've Been Told About Genetics, Talent and IQ is Wrong. All our popular notions about talent and "genetic gifts", he points out, start to collapse if the eating habits of Tiger Woods's ancestors, for example, might have played a role in Woods's golfing abilities.
(Woods always crops up in discussions on the origins of genius; more recently, he has started cropping up in evolutionary psychology discussions about whether promiscuity is inevitable.)
"What all this evidence shows is that we need a 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 . . . it's really funny how difficult it is to have this conversation, even with a lot of people who understand the science. We're stuck with a pretty limited way of viewing all this, and I think part of that comes from the terms" such as nature and nurture "that we have."
Among the arsenal of studies at Shenk's disposal is one published last year in the Journal of Neuroscience, involving mice bred to possess genetically inherited memory problems. As small recompense for having been bred to be scatterbrained, they were kept in an environment full of stimulating mouse fun: plenty of 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 never experienced the stimulating environment, even as foetuses.
"If a geneticist had suggested as recently as the 1990s 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." Not so now.