Why am I the short fat one?--The Secret Life of Twins

Twin brothers, but not quite identical

My identical twin brother Chris is 2cm taller than me.

Barely noticeable you would think. I can see what it is like to be him by standing on tip-toes just a little and frankly the world does not look much different from up there.

Nonetheless it bothers me: I could have been that tall. I have exactly the same genes as my brother.

Genes that, in the right environment, could have made me a full 185cm tall as opposed to my current 183cm.

Something, somewhere went wrong and I got stunted. Not by much but it is a reminder of what could have been.

And that is the real problem.

It is not the height, not that trousers fit him a little better or that he does not need to reach as far to change a light bulb.

It is that I wonder how many other things I am missing out on.

Ten points of IQ here, some grey hair there. Perhaps I will need glasses at age 35 instead of 40.

Most people do not have any way of knowing whether or not they are getting the most out of their genes but if you have a twin sibling then you have an exact comparison.

So how did these differences arise?

The differences between identical twins - people who should be exactly the same - are becoming increasingly useful to medical researchers interested in everything from mental illness to our ability to do maths.