When the theory of mimicry was first proposed by H W Bates in 1862, it was immediately recognised as a beautiful example of Darwin’s theory of Natural Selection. At that time, the mechanism of how traits are inherited (what we know as genetics) was unknown, and the details of how mimicry evolved, indeed whether it existed at all, were debated.
Following the discovery of the mechanism of inheritance by Gregor Mendel, mimetic butterflies were at the forefront of attempts to reconcile the theory of natural selection with the new discoveries from genetics.
The central issue in these discussions, in the early years of the 20th Century, was whether evolutionary novelty (new characteristics, traits or species) arose as the result of many small changes across many millions of years, or whether they arose more or less instantly as the result of major changes in the underlying genes. The answer to this question would have a profound impact on the understanding of evolution – whether evolution was mostly a fast or a slow process, and the relative role of directional selection relative to random mutation.
Experiments breeding mimetic butterflies had revealed that in many cases, the spectacular polymorphisms were determined by inheritance of a single factor (gene); the differences between alternative female forms behaved as though they were determined by a single factor and that the different forms were inherited complete and without intermediates. Biologists offered differing explanations of this startling fact (that although the wing patterns of the various forms differ in many respects, the genetics behave as a single gene), depending on whether they believed that large-effect mutations were more important, or if they favoured Darwin’s theory of evolution by gradual accumulation of changes. Eventually, the competing explanations were brough togther in the Modern Synthesis, the incorporation of genetics into the study of evolution.