Professor David Isaacs, Senior Staff Specialist, Department of Immunology and Infectious Diseases, The Children's Hospital at Westmead, Locked Bag 4001, Westmead, Sydney, New South Wales 2145, Australia. Fax: +61 2 9845 3414; email:

I am a twin. There is nothing particularly remarkable about that. My brother is a twin, too. So are four of my colleagues, whose twins are respectively a jewellery designer, an accountant, a lawyer and an Anglican minister. One in 80 pregnancies results in twins, but only one in 200 pairs is identical. Twins have their uses. They are great for elucidating the genetic component of diseases, particularly if you separate the twins at birth, which happens surprisingly often, and which increases the environmental contribution to the phenotype. It is good to have an identical twin if you need a spare kidney, too. My twin and I were often given identical toys, which we always swapped to make sure there was no favouritism, and we always knew who owned which toy. We went to different high schools and swapped school on the last day of term once (with the help of one friend each). This escapade is still talked about at the two schools years later.


Alick Isaacs, with twins, receiving an honorary degree.

Two colleagues are parents of twins, and both remark how much extra work is involved looking after twins, more than double the trouble. One said it was more restful for him to return to being on call for the Paediatric Intensive Care Unit than to help his poor wife with their newborn twins, and the twins were much easier babies than their older sibling. Talk about intensive care; pity their poor mothers. The notorious combativeness of twins is celebrated in the stories of Cain and Abel, Jacob and Esau, and Romulus and Remus. Twins can be stars, like Castor and Pollux, who were brothers of Helen of Troy, were said to have different fathers (Zeus was the father of Pollux) and who became the Gemini constellation when Zeus made them immortal. Or stars like Fred and George Weasley from the Harry Potter books.

Do twins have extrasensory perception (ESP)? When asked this question, I tell a story. I was living in London near my twin, Steve, who is a child psychiatrist. I was on a flight back from an overseas meeting and was gripped by a tragic story about twins I was reading in a wonderful book by Thornton Wilder called The Bridge of San Luis Rey. When I arrived back in London, I was feeling maudlin about the book and twins, so I tried to ring Steve from the airport. He had just been admitted to hospital with a quinsy. When he recovered, I asked him whether he thought my attempted phone call was ESP. ‘You idiot, I gave you that book to read’, he said. ‘I was doing a project on twins for work’.

It could be worse, of course. My mother tells a story of a woman with triplets. She said her triplets could count. When my mother pointed out they were only 9 months old and it was impossible that they could count yet, the triplets' mother explained that if she walked into the room with two of anything, they all burst into tears simultaneously.