A question about evolution of the Butterfly?

The non-repugnant species does not know that the second tastes bad. Evolution is mainly the result of selection of the most fit individuals. In the present case, populations of the first species that have a colour pattern or shape similar to the repugnant species possess a reproductive advantage: they are less frequently eaten by birds, they live longer and have a larger posterity. That particular pattern/shape therefore tends to be more abundant that other patterns/shapes. The two species may be closely related or completely unrelated, so that evolutionary mechanisms involved may differ widely.