Our valiant twins put their hands into a specially constructed plexiglass sealed dome where the odours either attract or repel 20 female mosquitoes without being allowed to bite. Each subject was given an attractiveness score compared to the other hand at the other end of the dome. Sure enough the identical twins, who share all their genes, had consistently more similar scores compared to fraternal twins – showing a clear genetic component. This comparison estimated that 67% of the differences between people (called heritability) was down to their genes.
Repel With Smell
Why might this be? Many years ago in another twin study we showed that underarm body odour as perceived by human sniffers had a genetic basis – with huge variability in how strong smells were perceived. This showed that we have gene variations controlling both the odours we perceive and the chemical odours we produce. In this way we are similar to mosquitoes because they also have big differences in which odours and chemicals attract and repel them.
One for Aedes Gambiae. Armpit by Shutterstock
Different mosquitoes prefer different parts of our bodies to others. The species Aedes Gambiae prefers the odours of our hands and feet to other bits like groins and armpits. Some animals use their body odour to keep insects away and companies have been trying to unravel what the best chemicals are.
The twin study authors realised that the chemicals could come from glands in our skin or from the billions of microbes on the surface. They discounted the bacteria as a cause as the dogma is that bacteria can’t be influenced genetically. It turns out they were wrong.