Darwinism Evolution extinction Intelligent Design Natural selection

Stripes confuse people but they do not cool zebras

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barrels used in the experiment

From ScienceDaily:

Susanne Åkesson, a biologist at Lund University in Sweden, refutes the theory that zebras have striped fur to stay cool in the hot sun. That hypothesis is wrong, she and her colleagues show in a study recently published in Scientific Reports.

There has been an ongoing discussion among researchers, dating back to Darwin, on why zebras have their signature black and white stripes.

One of several theories is that it keeps them cool in the sunshine. The black stripes get warmer than the white areas, and the theory states that this creates small vortexes when the hotter air above the dark fur meets the cooler air above the white fur. According to the theory these vortexes works as a fan to cool the body.

To test this theory, the researchers filled big metal barrels with water and covered them with skin imitations in different colours: black and white stripes, black, white, brown and grey. They then placed the barrels in the sun and later measured the temperature in each barrel. Not surprisingly, the black one was the hottest and the white one the coolest. The striped and grey barrels were similar, and in these the temperature did not go down.

“The stripes didn’t lower the temperature. It turns out stripes don’t actually cool zebras,” says Susanne Åkesson. Paper. (open access) – Gábor Horváth, Ádám Pereszlényi, Dénes Száz, András Barta, Imre M. Jánosi, Balázs Gerics, Susanne Åkesson. Experimental evidence that stripes do not cool zebras. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-27637-1 More.

This experiment probably won’t settle the matter but it does point up a curious fact about Darwinian thinking: the assumption that a striking trait evolved as a result of conferring a survival benefit. If that is not the case, Darwinian thinking is getting in the way. It’s the same problem as when a Darwinian explanation is sought for the low immune resistance in in some migratory birds: Maybe it isn’t a benefit to the birds but they are stuck with it. Haven’t tens of thousands of species that we know about gone extinct? Extinctions don’t usually happen right away; it may take a very long time before the fact that something isn’t really a benefit becomes a problem. Meanwhile, we may be confusing the matter by telling just-so stories about the benefit.

And, as for zebras, see also: Study: Zebra stripes neither hide nor flaunt

Stripes offer no advantage to zebra?

How the zebra got its stripes, this time really

How the zebra got its stripes, maybe

How the zebra did NOT get its stripes?

3 Replies to “Stripes confuse people but they do not cool zebras

  1. 1
    vmahuna says:

    As I’ve mentioned before, simply watch “Big Cat Diary”.

    The herbivores come in all shapes and sizes, including solid black wildebeest and lots of variation on tan. I find the white bellies more odd than stripes. Fish and birds have white bellies allegedly because it’s good camouflage when viewed from below against a bright sky. Why would a giraffe have a white belly? Among other things, it has no natural predators. Adult male giraffes kill lions, no problem.

    So I figure somebody in the Exterior Design Branch got bored doing yet another solid tan color scheme and started throwing in stripes and spots and white bellies.

  2. 2
    polistra says:

    Always good to see a real PHYSICAL experiment instead of the usual false theories accepted without question, or the usual computer simulation based on false theories.

    Reality doesn’t lie.

  3. 3
    Jon Garvey says:

    This experiment probably won’t settle the matter but it does point up a curious fact about Darwinian thinking: the assumption that a striking trait evolved as a result of conferring a survival benefit. If that is not the case, Darwinian thinking is getting in the way. It’s the same problem as when a Darwinian explanation is sought for the low immune resistance in in some migratory birds: Maybe it isn’t a benefit to the birds but they are stuck with it.

    Ask a neutral theorist (and they seem to have won the “adaptationist wars”, so they’re the in-crowd to ask), and she will tell you that most characters are fortuitous and confer no benefit.

    On the face of it that might seem to throw out the baby of design with the bathwater of function. But it doesn’t – it’s only because of being so wedded to Darwinian adaptation that “utility to the organism” is seen as the be all and end all of things.

    Include teleology in the mix, and there could be any number of other good reasons for stripes, from decreasing survival to control numbers for the balance of the whole ecology, to sheer aesthetics. Beauty doesn’t have a role in evolution, but it sure does in the world.

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