And now for something completely different... This is a repost with a difference - it's an edited interview I did with London scientist Chris McManus way back in September 2007. This has a fond place in my heart, for it was the first proper freelance writing assigment that I did after winning the Telegraph's Science Writer award. This is where all the cool freelancing began. It was originally published on Nature Network, but I note that their news archives have disappeared. As such, here it is again.
McManus, a Professor of Psychology and Medical Education at UCL, is an expert on asymmetry and left-handedness. He won the Aventis Prize for Science Books in 2002 with his first book - Right Hand, Left Hand. Now, he's turned his attention to the rise and fall of left-handedness during British history.
About 11% of the British population is currently left-handed. But that wasn't always the case. Among people born in 1900, the proportion of lefties was just 3%. McManus and Alex Hartigan from University College London worked this out with the help of old films made at the turn of the 19th century and recently restored.
What made you want to study historical rates of left-handedness?
People have always assumed that the rate of left-handedness has been constant throughout history but it's never been properly explored. Recent data showed us that left-handedness was less common in people born at the beginning of the twentieth century than those born later, by a factor of four.
We wanted to find out what happened before that and why things changed. But of course, there's very little data. People have talked about left-handers in the literature since the time of Aristotle but they never say how many there were.
How did you find out?
It was a stroke of luck. We came across these wonderful films by Mitchell and Kenyon, made between 1900 and 1906, where they filmed people coming in and out of factories. They're wonderfully evocative films. You really get a sense of that late Victorian era.
We noticed that the people in the films waved whenever they saw the camera. My student, Alex Hartigan, went through this footage and recorded every time someone waved and which hand they used.
How long did that take?
Many, many hours. Alex watched an hour and a half of footage, frame-by-frame. He worked very hard and I don't think he realised how long it was going to take, so it was typical of any undergraduate project. The only differences was that all of his subjects had been dead for years!
We also needed a modern control group, and Alex had the brilliant idea of doing a Google image search for 'waving' He found tens of thousands of pictures and chose all the colour ones to make sure they were modern.
What did you find?
It was very clear that the rate of left arm-waving in the Mitchell and Kenyon films was much lower than in the modern data. And the older people were more likely to use their left arms than the younger ones, which is the exact opposite of modern findings.
We think this is evidence that the rate of left-handedness was already declining during the nineteenth century and was lowest for people born between 1870 and 1900.
What caused the decline?
It's not the standard explanations. Usually, people say that left-handers pretend to be right-handed because of social stigmas against left-handedness. But that's unlikely to apply to a natural spontaneous behaviour like arm-waving. And it's not because left-handers don't live as long as right-handers since the older people were more likely to be left-handed.
It might be because this period was the beginning of universal literacy and education. Left-handers wouldn't have been able to write as well with old-fashioned dip pens. In the regimented Victorian classroom, they would have stuck out and faced large social pressures or even physical punishment.
It could also be to do with the Industrial Revolution. Again, left-handers had visible trouble with operating large and heavy machinery that were almost certainly designed for right-handers. And in most societies, when you have a visible minority group, there's the possibility of stigmatisation.
Left-handers today still say that people have names for them or say they do things in strange ways, which makes them embarrassed. We have unpublished data to suggest that this could lead to left-handers having fewer children because they are less likely to marry or marry later. If there are genes involved, the rates of these would go down.
Have you considered non-social environmental factors?
It's possible, but people have looked for something like that for years and it never works. The strongest evidence against that idea is that in Britain, there's no social class variation in left-handedness. Most deleterious environmental factors vary across the social spectrum.
You used Google Image Search in your study - what do you think of the potential of the web as a research tool?
It's vast. On my book's website, 6,000 people have answered immensely detailed questionnaires on handedness and we've used them as control groups for other studies.
You can get lovely modern data sets. Recently, the BBC did a survey of 250,000 people who were asked, among other things, about their handedness. It showed that the rate of left-handedness varies across Europe and is highest in Belgium and Holland. You can only find out that sort of thing if you have a quarter of a million people filling in your survey.
Do you need to take special care to guard against bias?
In general, if you do a survey explicitly on handedness, you get more left-handers responding than usual, and that was true even in 1900. Left-handers seem three times more interested in handedness than right-handers!
But that's good - you get a larger left-handed sample and you can do more powerful statistics. Bias isn't a problem if you're aware of it and design it into your study.
Do you read any science blogs?
The only one I read is Improbable Research by Marc Abrahams, because I won an IgNobel prize a few years back. One or two of the anonymous things there are actually from me. I send them to Marc and say "What do you make of this? It's ridiculous!"
Do you have a favourite of London's science museums?
The Royal College of Surgeons. My art student friends and I sometimes go down there and draw these beautifully dissected human specimens. It's like a death-drawing class. The place really typifies London for me - it's a little corner of a quiet square with all this quality stuff lurking inside.
Do you have any new books coming out?
I'm been working on one about my first academic love - the psychology of art. It'll probably be out in two years. I do a lot of painting and drawing myself and I'm trying to make sense of the vast range of art from a scientific angle. I find the attitudes that some of my scientific colleagues have on art a bit embarrassing. It's rubbish to say that it's all evolutionary psychology and sexual selection.
And finally, are you right-handed or left-handed?
I'm right-handed and I can guess that you are too. Left-handers mostly notice the handedness of other people whereas right-handers don't.
Reference: McManus & Hartigan. 2007. Declining left-handedness in Victorian England seen in the films of Mitchell and Kenyon. Curr Biol 17: R793-R794.
More on asymmetry: