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…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?
Such talk, naturally, 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 proponents of creationism or "intelligent design", and it's true that few of the studies now coming to public prominence are all that revolutionary to the experts….
Three years ago, researchers led by a professor at the university of Linköping 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.
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.
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. 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 in future generations, if only in a short-term and reversible way.…"Today," notes David Shenk, "any high school student knows that genes are passed on unchanged from parent to child, and to the next generation and the next. Lifestyle cannot alter heredity. Except now it turns out that it can . . ."
(Oliver Burkeman, The Guardian, Friday 19 March 2010)