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  • Writer's pictureKTS

It's Natural!

Today we told the true and super interesting story of the peppered moth Biston betularia.

Moths in this species come in two forms: a light-color variety and a dark variety.

Two hundred years ago, in England, most of the Biston betularia moths were light-colored. Their white wings with black speckles camouflaged them against the light-colored trees and lichens on which they rested.

Spot the light-colored moth!

But when the Industrial revolution started in England, it brought soot and widespread pollution, which killed most of the lichens and blackened the trees which peppered moths rested on. The light-colored moths were no longer camouflaged against the trees and became vulnerable to predation by birds. Most of them died out.

At the same time, the dark-colored variety, which had survived till then in very low numbers, flourished because they could hide on the darkened trees.

Years later, anti-pollution laws took effect and as the tree barks lightened again, the moth populations in formerly polluted areas returned to their previous color distributions.

Today, the kids were predatory birds, using tweezers to prey on dark and light paper "peppered moths" resting on a dark or light background (pre and post industrial revolution scenarios).

They recorded the numbers of moths of each variety and followed the trend after each bird meal.

The result? Similar to the studies done in England in the 1950s. After a few generations of pollution, a lot of the light-colored moths disappeared and the dark moths thrived.

And thus Kids Talk Science evolution detectives discovered their fifth clue!

Changes in the environment cause populations to change, not by creating new varieties, but by selecting from existing varieties those better adapted to the new conditions. And that, ladies and gentlemen, is Natural Selection!

To curious readers:

If you heard that the peppered moth evolution example has been discredited, I must tell you that that's not true.

After fair criticism suggesting that the 1950s experiments by Bernard Kettlewell, who brought the peppered moths to fame, had been poorly designed, biologist Michael Majerus, decided to repeat the experiments, doing them correctly this time.

His study lasted six years and provided solid proof that the rapid changes in the numbers of light-colored moths versus dark-colored moths were caused by bird predation and lack of camouflage. Unfortunately, Majerus didn't live to see his results vindicating Biston betularia as an excellent example of evolution by natural selection.

His results also proved that Kettlewell was not a fraud, as some had suggested, but a naturalist who wasn’t very good at designing solid experiments.

And there's more. Last year, a new study pinpointed the precise genetic mutation that led to the darker moth and determined just when this mutation occurred.

The end

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