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Adaptive Change via Sophie’s World
Saturday 6th May 2017 @ 2:25 pm

 The following is s great example of what it means to adapt … it is taken from ‘Sophie’s World, and hits several nails on it’s head.


“In Britain there is a certain species of butterfly called the peppered moth, which lives on the trunks of silver birches. Back in the eighteenth century, most peppered moths were silvery gray. Can you guess why, Sophie?’

‘So they weren’t so easy for hungry birds to spot.’

‘But from time to time, due to quite chance mutations, some darker ones were born. How do you think these darker variants fared?’

‘They were easier to see, so they were more easily snapped up by hungry birds.’

‘Yes, because in that environment –where the birch trunks were silver –the darker hue was an unfavorable characteristic. So it was always the paler peppered moths that increased in number. But then something happened in that environment.

In several places, the silvery trunks became blackened by industrial soot. What do you think happened to the peppered moths then?’

‘The darker ones survived best.’

‘Yes, so now it wasn’t long before they increased in number. From 1848 to 1948, the proportion of dark peppered moths increased from 1 to 99 percent in certain places. The environment had changed, and it was no longer an advantage to be light. On the contrary. The white “losers” were weeded out with the help of the birds as soon as they appeared on the birch trunks.

But then something significant happened again. A decrease in the use of coal and better filtering equipment in the factories has recently produced a cleaner environment.’

‘So now the birches are silver again?’

‘And therefore the peppered moth is in the process of returning to its silvery color. This is what we call adaptation.’ “


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