How the Zebra Got Its Stripes - and How Humans Stole the Trick
How the Zebra Got Its Stripes - and How Humans Stole the Trick
Harnessing the wisdom of natural selection
Here’s a fun pair of papers from a few years ago.
The first explored a novel idea about how to keep biting flies away from cows and other livestock. The inspiration came from an unlikely source: the evolutionary biology of zebras’ stripes.
A long-standing question in evolutionary biology is why zebras evolved their famous stripy pelt. What’s its function? What are the stripes for?
According to one prominent theory, the function is to ward off biting flies, perhaps by confusing the flies’ motion-detection mechanisms.
If this is true, reasoned a team of Japanese researchers, then perhaps painting black-and-white stripes onto livestock would give them zebra-like powers to repel biting flies.
So, that’s what they did: They painted zebra stripes onto Black cows, then tallied how many flies the cows attracted compared to their non-stripy compatriots.
Sure enough, as expected, the stripes reduced the number of biting flies on the cows by more than 50%.
Were the flies just repelled by the paint? Apparently not. When control cows were painted with black stripes only, there was little reduction in the number of flies, as shown in the following graph.
The authors summed up their findings as follows:
painting black-and-white stripes on livestock such as cattle can prevent biting fly attacks and provide an alternative method of defending livestock against biting flies without using pesticides in animal production, thereby proposing a solution for the problem of pesticide resistance in the environment.
So, that’s the first study. The second used the zebra-stripes-ward-off-flies theory to a very different end: shedding light on one of the possible functions of body art in traditional cultures.
The authors of the study reasoned that if black-and-white stripes ward off flies for zebras, they should also do the same for people painted with zebra stripes.
They tested this hypothesis in much the same way that the Japanese cow team did: They painted stripes on participants’ bodies, then monitored how often their stripy participants were pestered by the local flies.
Consistent with expectations, stripes on humans deterred flies to almost exactly the same degree that they did on cows.
Based on these findings, the researchers proposed that “white-striped bodypaintings, such as those used by African and Australian people, may serve to deter horseflies, which is an advantageous byproduct of these bodypaintings that could lead to reduced irritation and disease transmission by these blood-sucking insects.”
If so, then body-painting traditions like those depicted below are a fascinating example of a general human trend: that much of what other animals achieve through biological evolution, humans achieve through culture.
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