Claire Ainsworth, contributor
In Identically Different, genetic epidemiologist Tim Spector reveals what twin studies tell us about nature versus nurture
"AN APPLE, cleft in two, is not more twin than these two creatures." This line, from Shakespeare's Twelfth Night, plays on the similarities between (supposedly) identical twins for comic effect.
But for all their uncanny similarities, identical twins are not simply two uniform halves of a single whole. As Tim Spector explains in this fascinating and provocative book, despite sharing the same sets of genes, such twins differ in many important ways. These differences are giving new insights into how our genes and environments interact - and raise the question of whether we have more control over our genetic destinies than we might think.
Spector is a genetic epidemiologist who heads the Department of Twin Research at King's College London. He draws on his extensive experience to explore epigenetics: the study of chemical marks on or around DNA that can respond to changes in a cell's environment. Alterations to these marks can increase or decrease the activity of genes. Unlike genes themselves, which are largely fixed, epigenetic marks are plastic and can change in response to factors such as diet and stress. What's more, some studies suggest that epigenetic changes can be passed down from one generation to the next.
This blurring of nature and nurture is central to Spector's thesis. He aims to demolish the popular view of genes as the chief architects of a person's characteristics. This involves delving into some fairly hardcore genetics, molecular biology and epidemiology, but he does so in a lively and accessible style.
Spector is a talented storyteller, weaving real-life accounts of identical twins into each chapter. These highlight how, even when they are brought up together, subtle differences in identical twins' experiences might explain dramatic differences in their characteristics. These range from the risk of developing cancer or diabetes to, more controversially, traits such as propensity for religious belief, mood, sexual orientation and sociopathy.
Behavioural epigenetics is a hotly debated field, with critics claiming that many of the animal and human studies cited in its support are overinterpreted and lack a plausible mechanism linking a person's experiences with changes to the chemical marks on their DNA. Spector doesn't really address these criticisms, which is a pity because it would have made his argument more convincing.
Nonetheless, this is an informative and thought-provoking tour of some of the most exciting areas in biology right now. Spector concludes by inviting us to imagine a future in which we see our genes as malleable, rather than as masters of our biological destiny - just one part of the endlessly complex and fascinating story of what makes each of us unique.
Book Information
Identically Different
by Tim Spector
Published by: Weidenfeld & Nicholson
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