by Richard Sidaway
理查德 希达威

What do the singer Alanis Morissette, the supermodel Gisele Bundchen and the ex-Secretary General of the United Nations Kofi Annan all have in common? The answer is, they all have a brother or sister who was born on the same day as them – a twin. And what links actresses Julia Roberts, Geena Davis and Holly Hunter? They all have twin children.

You probably either have some twins in your family or you know/knew some at school – there are more of them about these days. This is because women are older when they have their first child and because more women are having fertility treatment. Both of these things increase the probabilities of two babies developing from the same egg.

The USA seems like a particularly good place to have a similar sibling. At the University of Minnesota they have been studying 8,000 pairs of twins since they were born. In the state of Ohio, there is a festival for twins every year in a place called… Twinsburg. And in New York there is even a restaurant which employs 37 sets of identical twins!

Scientists love twins. Because they share the same genes, any differences between them must be because of environmental factors. Science now understands more about heart disease, cancer, and getting old from studying twins.

Sometimes twins are separated at birth and only meet again when they are grown up. Even so, they sometimes make choices in life which are strangely similar. One pair only met each other after 40 years apart and found that their wives had the same name. And so did their children and their pets!

Is there a difference between being physically identical and only being born on the same day? I knew a pair of non-identical twins when I was a boy. They were proud to be completely different from each other. One was very short-sighted from an early age and wore glasses. He picked up the local accent and was obsessed with trains. His brother spoke with a posh accent and was very musical. The first became a train driver and moved to Scotland. His brother went to a music college in London and became a concert pianist.

I have recently been the teacher of two pairs of identical twins - I often have difficulty telling which is which. Luckily they don’t seem to mind. One day, I gave them a list of questions to see what they felt about being so close. Each twin answered the questions in a separate room.

Both pairs said they did many everyday activities together - studying, shopping, watching TV, or just spending time together. Both pairs had similar tastes in music and food, and even thought their voices sounded the same sometimes. Both pairs also commented that they would like more time to themselves…

When I asked them what they were good at in school, one pair wrote the same five subjects almost in the same order. The other pair only had three subjects in common - one was interested in the Arts and the other more in science subjects.

I also asked them if they ever had the same thoughts as their twin. The first pair said yes –for example, one of them often started talking about what the other one was thinking. Strangely, the other pair disagreed about whether this was true. One of the twins said that her sister would take the words out of her mouth, while the other said this never happened to her.

The most interesting thing for me was studying the results of the psychological part of the test. I asked them to describe their personality using twelve different pairs of sentences. I found that each twin gave almost identical answers to her sister!