A Study in the Evolution of Birds
The head of the guillemot is either all black or bridled, i. e., decorated with markings resembling spectacles. This phenomenon, known as polymorphism, is a clue to the operation of evolution
The head of the guillemot is either all black or bridled, i. e., decorated with markings resembling spectacles. This phenomenon, known as polymorphism, is a clue to the operation of evolution