NATURAL SELECTION

Sun (Auckland), Volume IV, Issue 1061, 27 August 1930, Page 14

NATURAL SELECTION

We have all heard the scientific phrase natural selection. It is hard sometimes just to explain what we mean by this, but the following story gives a splendid illustration. Many years ago a large wood in Yorkshire was divided by a stretch of heath. A few years later birches replaced the pines growing in one part and in the other part pines began to oust the birches. A moth which lived in both woods and was often dark and often pale, found itself in two environments. In the birch wood it was soon found that only 15 per cent, of the moths were of a dark variety, in the pine wood over 96 per cent, were dark. This was not due to the direct effect of the surroundings, as the dark pine wood race did not become any lighter after feeding the caterpillars on bii'ch trees for three generations in captivity; nor could the light sort be made darker by placing this variety on pines. But the reason for the difference was discovered when somebody collected moths' wings found scattered in the pine wood, wings of moths that had been eaten by bats and owls. Most of the wings found were light-coloured a. 3 the whiter moths showed up more distinctly against the dark pines, while their darker and more numerous neighbours escaped destruction by not being so easily seen. Thus, the whiter kind of moths were being gradually exterminated. It is a case of natural selection.