Sexy Symmetry

Have you ever spotted someone you can't seem to take your eyes off? The reason could be that person is more symmetrical than most. It's been known for a while the more symmetrical a person is, the more attractive we tend to find them. Dr William Brown who's at Brunel University has been using 3 dimensional scanning technology to look into the area a little bit more closely and to see just how finely tuned our sense for symmetry are. We sent Meera Senthillingham down to Brunel to find out more about the research and also to find out about her own symmetry...

William - There's several things - looking at the association between symmetry and bodily attractiveness and also trying to improve the ability to measure the subtle asymmetries between the left and right side of the body. These symmetries, I need to point out, are subtle. They're so subtle that we need to measure them with very precise equipment.

Meera - What have you been doing here at Brunel to look into this?

William - I met up with some people from engineering design who had purchased a 3D scanner that is used in the medical and textiles industries to get 3-dimensional images quite quickly: about 5-6 seconds for a scan. 24 cameras around the individual, flashes optical light and puts together a surface scan of that person's body. I'm using it for the first time to measure the subtle difference between the left and right side of the body.

米拉-我们的扫描仪。这是我的你rn to actually go inside and have my body scanned. You've already taken my height and my weight so now I guess I just have to go inside...

Scanner voice - Welcome to the NX-12, [TC]²'s new 3D body scanner. Place your feet as shown by the footprints on the floor and grip the handle. When you are ready to start your scan...

Meera - I've finished my scan now which was quite a surreal experience, actually. We've got my profile on the computer. What can you see so far, Will?

William - Because it's 3-dimensional information it's called a point cloud display. There's thousands of little points on the body.

Meera - The actual image is quite amazing. It is an entire person made purely of lots of dots. There's a measurement at each of these dots.

William - Exactly. At some traits there's sub-millimetre accuracy in measurements. What it's done is measure everything in girths to lengths. It tells me the waist circumference to waist circumference.

Meera - What's my leg length?

William - We can do leg measurement, we can do something like get your ankle girth. Your right ankle girth is 269.9mm. I cannot just eyeball this and say you're more symmetrical or you're more asymmetrical than average because we need to put this into statistical software comparing you to the rest of the sample.

Meera - It's very strange seeing myself made up of many, many dots. You had people analysing and rating these samples you had.

William - Yes, they were simply rating these 360 degree videos for attractiveness.

Meera - What did you find?

William - What we found was, if you're a male with more masculine body proportions, broad shoulders, they are rated as more attractive. Females though, with more curvy figures are rated as more attractive. That's not the interesting part, because we already knew and expected that finding. The interesting finding is that individuals with a higher degree of sex-typical features (what I means is guys with more masculine bodies) are in fact more symmetrical in the left and right side. Women with more feminised bodies and physiques are more symmetrical. Both symmetry and your degree of masculinity are associated with attractiveness ratings.

Meera - What do you think that it is about someone being symmetrical that's reflected for them to be more attractive?

William - A lot of people in general, it may not be clear to them that it's not the asymmetries themselves that we're detecting. The asymmetries themselves are tapping into something very difficult to measure: how difficult your development is. If you are having poor development which could be cause by all sorts of things: bad genes, bad environments, stress, pathogens or infection starting off from the womb throughout development. I can give you a quick example, some of the work that was first done on asymmetry was done by fish biologists and modelling biologists. What they found was in polluted lakes and streams the fishes there would have more asymmetries. The exact same species in the fresh lake that's not polluted were more symmetrical. It's used as an indicator for maybe population stress. What the subtle asymmetries we're tapping into is probably poor development. Individuals that are better able to be better developers would be ideal mates. Not just are you passing the genetic resources by giving individuals parents who aren't so ill but some of those environmental things can actually be passed onto your offspring to the individual during copulation.

Meera - So I'm assuming that someone's symmetry can change throughout their lives. Is it fair to say it would probably be at its peak when they're at their mating peak?

William - Exactly. That is the hypothesis. There is some cross-sectional data which means different people across different ages supporting that hypothesis. I think a lot of people fail to realise it's not like you're born symmetrical and you stay with the exact same symmetry through your entire lifespan. There's very few longitudinal studies done tracking youngsters all the way through to when they're older. Development is not just about a one gene for symmetry. Development's a very dynamic process. It's going to be difficult given your conditions to develop a symmetrical human. What they seem to find is, early on in development when you're going through that kind of growth spurt and putting on weight. The faster that rate is the more asymmetrical you are because that's stressful to develop. When you start to get beyond that growth spurt and reach a peak breeding period you'd be more symmetrical. After that period there may be some decline. You may expect individuals to become more asymmetrical. The rate of decline may be your health and other factors.