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Science - Why we're all one of a kind

Genes aren't everything - even for identical twins

Genes aren't everything - even for identical twins

Studying evolution in school, I remember the story of how the giraffe got its long neck. Jean-Baptiste Lamarck's theory of evolution was that, bit by bit, stretching to eat leaves on trees, the giraffe passed on the acquired characteristic of a longer neck until it arrived at the gangly, comical animal we see today. Charles Darwin put paid to this idea.

Neither man was aware of DNA, genes or the precise mechanisms of inheritance, but they knew that features were passed from generation to generation and modifications took place, resulting in evolution. Darwin won the day with hard evidence and Lamarck was consigned to history as the man with the "wrong" theory of evolution. But fast-forward to the early 21st century and Lamarck may have the last laugh. What our parents and grandparents ate and did can, it seems, affect us.

In Identically Different, Tim Spector, a world-renowned authority on twins, introduces us in an entertaining, eloquent and expert way to the new (yet old) science of epigenetics: the study of how the environment can influence our genes and how those influences can be passed on to future generations.

Identical twins, Spector reveals, are rarely, if ever, absolutely identical. Twins from the same egg (monozygotic twins) can have different eye colour, and can be different heights and weights. Their personalities may also differ a lot. One could be heterosexual, while the other is homosexual. Twins, it seems, can be identically different.

Drawn to the chapters on "talent" and "parenting", I wondered if I could blame my not being an Olympic gold medallist or a concert pianist on my parents' genes. But genes on their own are not enough. Interviews with Team GB medallists tell us that the dedication and hard work needed to become a champion is epic. But can athletes pass on their acquired talents to their children? Training can alter genes and, as Spector says, "some proportion of the changes to genes caused by exercising the muscles or the brain in adults could be retained as genetic marks, and passed on to our children to either use or waste".

Spector's book has moments of genuine amusement, such as his description of the "gruelling" task of researchers looking at 647 Playboy centrefolds to confirm a trend towards shaved pubic hair since 2000. It also contains disturbing facts - for example, that criminality has a strong heritable component.

His final chapter on clones, identity and the future is reassuring. Hollywood clones are far from reality. Cloned pets have failed. The owners report very different pets from the ones they loved and so badly wanted to bring back to life. Individuality, it seems, rules us more than a predestined, genetically controlled future.

Identically Different: why you can change your genes by Tim Spector is out now, published by Weidenfeld and Nicolson. James Williams is a lecturer in science education at the University of Sussex's School of Education and Social Work


Compare Darwin and Lamarck's theories of evolution using jm2450's picture slideshow.


Try rainbowhunter's PowerPoint for a guide to animal cloning.


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