BUTTERFLIES AND MOTHS
Batesian mimicry. The combined advertisement was interpreted some years later by Fritz Müller and is called Müllerian mimicry.
I hope that the above paragraph makes clear the advantage that would be gained by a species whose pattern resembled that of another species which was not eaten by birds. Probably we should have an excellent opportunity of actually witnessing evolutionary progress if we could compare one imperfect mimic in such a group with what it was a hundred years ago. A century is only a drop in the ocean of time, but even in this short period some notable change might be evident. Well, we are fortunate enough to be able to make this comparison.
Between the years 1825 and 1830 the great naturalist William John Burchell was travelling in eastern Brazil, making extensive collections of animals and plants, concerning which he made the most accurate and detailed notes. I only wish that all naturalists to-day would do their work as well. His whole collection of insects is in the Oxford University Museum, and among them are many butterflies belonging to the great yellow-banded group of which I have spoken. In a certain species known as Lycorea halia, the yellow band along the hind wing is not so bright as in other species of the group, and the eight specimens in the Burchell collection show that this characteristic feature was on the average even less bright a hundred years ago. It may be suggested that the colours have become darker with age; but with age butterfly pigments generally become paler rather than darker. Besides, among the eight there is one that is fairly bright, though by no means equal to the brightest of to-day, whereas among specimens recently caught a small proportion resemble the seven that are not so bright. The evidence that the colour has changed slightly in a hundred years is, I think, unquestionable.
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