‘The most important lesson that we’ve learnt is that you can change your genes, your destiny and that of your children and grandchildren. It really does matter what you do to your body, and importantly what your grandparents did to theirs many years ago.’

Identically Different begins with the story of two conjoint twins from Iran who sadly died in their late twenties, following an unsuccessful operation to try to separate them. What particularly interested author Tim Spector (Professor of Genetic Epidemiology at King’s College, London) is that they were genetic clones but had different personalities and interests. Ladan was a talkative extrovert, who liked animals and hoped to become a lawyer. Laleh was more introverted, preferred computer games and hoped to become a journalist.

Professor Spector has been studying twins since 1993 and this has given him fascinating insights into how far we are the product of nature or nurture. In Identically Different he explores what makes us who we are. He considers the implications across a range of areas, including susceptibility to illness, belief in God, participation in sport, sexual orientation and behaviour, criminality, obesity and longevity.

His conclusions are that:

• The nature versus nature debate is too simplistic
• We are genetically predisposed to adopt a particular character and behaviour and have a genetic predisposition to certain illnesses (which explains frequent similarities in the lives of identical twins, even if they have been separated early in life).
• However, significant events in our lives (and importantly in the lives of our parents and grandparents) can amend the way our genes are expressed (which explains why identical twins don’t always behave in the same way or die from the same illnesses at the same time).
• ‘Genes are star players in the body, but they can’t act alone and are one part of a complex team.’  
• What we do in our lives can physically affect our bodies and our brains. For instance meditation structurally alters some brain areas like the Hippocampus; and the size of the Hippocampus is enhanced in London taxi drivers due to the number of travel routes they have to memorise. These are examples of what Professor Spector sees as, ‘the amazing flexibility, adaptability and neuro-plasticity of the human brain.’
• This is explained by the developing science of epigenetics (the way our genes can be switched on and off within our cells by ‘epigenetic signals’ produced by ‘methylation (adding a methyl group), or the more complex histone modification (Chromosome folding)’.

Professor Spector suggests this is a form of ‘soft inheritance’ which complements longer term Darwinian evolution. He explains:

‘Epigenetic marks placed in one generation will influence gene expression in the next few generations. This is a short term evolutionary adaptation to major environmental challenges, such that adverse exposures in one generation (like famine, cold or toxins) act as warning signals for the next generation. Subsequent generations will then be primed to do something different from expected. They might react by getting fatter or thinner or becoming more active or sluggish. As the warning signal wanes, provided no other shocks occur, the next few generations will slowly return to responding more ‘normally,’ meaning in less extreme ways. Nature appears to have given us a parallel evolutionary survival plan allowing us to adapt quickly to adversity.’

Some advocates of epigenetics have perhaps exaggerated its importance. However Professor Spector sees this as complementing rather than replacing the longer term and more enduring Darwinian process of evolution.

Identically Different provides many interesting twin based case studies, showing both similarities and differences. These illustrate the complex interplay between nature (the genes we inherit) and nurture (our environment and experience and how these sometimes influence how our genes are expressed).

Professor Spector also provides a range of interesting other observations, for example on:

• The importance of beneficial intestinal gut flora and the potential risks of repeated exposure to antibiotics on that bacteria. He comments, ‘So if some bugs can make us lose or gain weight, give or prevent allergies or prevent ulcers or cancer, we should know how we can safely change our gut flora. As usual, Grandma’s advice may be best. Eat more greens.’
• The influence of social position on our health (echoing the work of Sir Michael Marmot, reported elsewhere on Age Watch). Joyce and Mary, identical twins with a similar childhood married husbands from different social classes who experienced different levels of success in their careers. By their mid fifties, although the twins had the same chronological age, ‘the biological difference between them now reflecting the age of their cells was around seven years.’
• ‘We have shown in large studies that lifestyle factors like stopping smoking, avoiding obesity and moderate exercise can retard biological ageing by five years.’
• ‘Our society vastly overestimates and applauds talent and ignores hard work and graft’ – providing examples from Mozart to the Beatles, from Tiger Woods to Rory McIlroy.’
• ‘Kids without a source of emotional attachment on average do very badly in life. But the extent to which the normal ranges of parenting in most families affects children has been exaggerated. It is not so much the parent who influences the child, but more the child’s genes that influence the parental response.’

Sometimes there are so many case studies and ideas in Identically Different that it can be difficult to follow where exactly the author is leading us. The book’s subtitle (Why you can change your genes) is possibly also misleading. It suggests we have more personal control over our own destinies than the examples provided always indicate – although we may have more influence over our children and grandchildren (through epigenetics rather than parenting) than we realise.

However, what Professor Spector succeeds in doing is helping us see the complex interplay between nature and nurture which makes each of us a unique individual. He provides an interesting, stimulating and largely understandable introduction to the emerging science of epigenetics. Drawing on his studies of some 11,000 twins provides both interesting case studies and an unusual opportunity to compare the effects of nature and nurture.

If Professor Spector is correct then we are not simply pre programmed by our genes. The decisions we make in our lives do matter. Adopting a healthy lifestyle can add years to our life; activities which stimulate our brains can potentially help parts of our brains grow in size; we shouldn’t underestimate the value of hard work; and what we eat matters not only for ourselves but potentially for our children and grandchildren.

Identically Different, Why you can change your genes: Tim Spector (Weidenfeld & Nicolson 2012) ISBN: 978 0 297 86631 2