Tuesday, 25 June 2013

Light and shade

Here's an interesting pair from the trap last night: two Peppered Moths, one the standard salt-and-pepper version and the other melanic, or black. The story of the different varieties is famous outside the world of entomology; you can spend hours reading arguments and counter-arguments from creationists and mainstream scientists on the net.

The reasons is the moth's role in the story of change and survive which Charles Darwin (and his less well-known contemporaries especially Alfred Russel Wallace) standardised as the Theory of Evolution. Normally the process of adaption to circumstances is long drawn-out as the less fit are eliminated by predation or disease; but the Peppered Moth's population in the UK has changed in my lifetime, in terms of the balance between the ordinary and melanic types.

In particular, the melanics have declined in remarkably similar proportion to the disappearance of the filthy conditions created by industrial pollution in which their colouring was perfect camouflage. In a famous study, the eminent doctor Sir Cyril Clarke who was also a great enthusiast for butterflies and moths, showed that the decline also paralleled the rise of centenarians in the UK - another indicator of our improving environment. He used the traditional telegrams to 100-year-olds from Buckingham Palace in his data.

It is increasingly unusual to find a melanic version; they were rare in Leeds in my time, even though the pollution had been pretty considerable there into my boyhood in the 1950s.  While we're on the subject of black, here's a pretty red and black Cinnabar to finish up with. It interrupted my efforts yesterday to keep the lawn under control.

No comments: