Identically Different: Why You Can Change Your Genes by Tim Spector – Review
Epigenetics is one of the keys to explaining the mystery of life, writes Peter Forbes
The Olympic Isle on opening night was “full of noises, / Sounds, and sweet airs that give delight and hurt not”. The lion of the industrial revolution could lie down with the lamb. But beneath the fantasy a sewer ran, diverted but untamed: the spectre of doping. And not just doping, because this is the age of genomics: gene doping.
The man who came to warn of this prospect is himself a Spector: Tim Spector, professor of genetic epidemiology at King’s College London and the author of this book. The means by which gene doping might be achieved (no one is sure whether it has yet been, or in practice can be, done) is Spector’s field of expertise: epigenetics. So he has become a media pundit during the Olympics, but his real subject is twins and what they tell us about genes. Identical twins are a unique test of genes in action because, having come from a single fertilised egg, they have identical genomes, all 3bn letters of them. They are clones.
The point about twins and identical genes is that genes in action do some strange things that we are only just beginning to understand – identical genes can diverge in their expression during the course of a lifetime. This is epigenetics. It is now generally accepted that personal experience can change our genes. If you practise music for six hours a day and become a great musician, your brain will show recognisable changes both in large-scale anatomy and genetically. London cabbies have “knowledge” – enhanced regions of the brain that start to recede when they retire. The chemical processes that alter the genes in epigenesis – methylation and deacetylation of the packaging proteins of the genes, the histones – are fairly well understood.
But the puzzle is that some of these changes can be passed on to offspring, and the effect – although it eventually disappears after three to four generations – can have profound consequences. One hundred and fifty years of biological orthodoxy claimed that these phenomena were impossible. What is supposed to happen at reproduction – and mostly does – is that all the epigenetic marks acquired during life are erased and every birth is a fresh start. But the case of Dolly the sheep and other animals cloned since then show that where adult cells have been reprogrammed to wipe out the epigenetic marks, the process is inefficient. So Dolly, whose parent cell was six years old, was not really a fresh start. She died prematurely as a result. But even in normal reproduction, it seems that some epigenetic marks can persist for a few generations.
Spector explains these facts clearly and does not overdo the deep biology. Most of the book consists of case histories and studies of the crucial traits that matter to all of us: intelligence, athletic and artistic skill, disease, obesity, sexual orientation. What the genomic revolution has done is to reopen the old nature/nurture debate. How wildly this has lurched, protagonists on both sides blithely ignoring what little evidence there was. Spector recalls that in the 1960s and 70s it was almost possible to obtain funding for research on twins because of the prevailing blank slate, nurture-is-all ideology. This was preceded by the appalling eugenics period when, despite the evidence that hereditary genius dissipated over the generations, far too many serious biologists endorsed the idea of breeding the best and brightest and preventing this in the unfit. Today there are fewer excuses because the solid evidence is piling up. But the evidence is often puzzling. To the embarrassment of the Human Genome Project, researchers have come to the conclusion that the genetic component of some multi-factorial diseases is exceptionally low. Many genes have been found to be implicated in such conditions but their overall contribution might be as low as 2%.
Like most writers on genetics these days, Spector has to reiterate, yet again, a health warning: genes are not “for” bodily attributes: only about 2% of the genome is literally “for” anything at all: the target is proteins not traits, and what the proteins do next depends on concerted action with other proteins. They nudge and tweak one another (up and down – regulating, according to the jargon). Yes, there are cases in which a single mutation in one of the 3bn bases in DNA causes disease. These are single-gene disorders such as muscular dystrophy, cystic fibrosis, sickle-cell disease and Tay-Sachs syndrome but they are the exception. In these cases, the gene codes for a vital metabolic protein – and to harm it is to throw a huge spanner in the works. For decades, the 98% of the genome that doesn’t make protein was dismissed as junk DNA. Some of it is now known to regulate the expression of protein-making genes; much of it is still dark matter.
Nevertheless, Spector is able to attach some fairly reliable figures to the heritability of many traits. Where there is autism in an identical twin, there is a 60% chance the other will have it. More surprisingly, Spector reports “a 40%-50% genetic component to belief in God”. But you don’t live your life by percentages: your life is 100% yours – genes, good and bad luck, roads not taken, all included. Spector has done a good job in revealing how human variability works. On the one hand, there are twins separated at birth who meet decades later wearing the same clothes, with wives bearing the same forename. On the other hand, there are twins who grew up together who diverge in sexual orientation, wealth and health. Genetic determinism is still prevalent in our culture and Identically Different is a necessary corrective.
Epigenetics will revolutionise medicine and it is one of the keys to explaining the mystery of life. But, as Saul Bellow wrote: “In our world it appears that as soon as a clear need appears, it is met falsely. It becomes a new occasion for exploitation.” The idea of gene doping is to shortcut the epigenetic changes wrought by the 10,000 hours of practice that lie behind every artistic and sporting genius simply by adding or subtracting epigenetic marks to or from certain key genes. Spector said on BBC2’s Newsnight that many people in sports genetics believe they have a list of more than 100 possible candidate genes for epigenetic enhancement (although in the book he appears to be sceptical). One must hope that this shortcut to glory will prove as illusory as the dream of cloning pets. Cloned cats are not true to the original in coat colour because that trait is an unpredictable epigenetic phenomenon.