File:Fisher Population Genetics and Microevolutionary Theory 7. 8 book.png

English: The caption in the book is: "Fisher’s adaptive target. The point in the center of the circle corresponds to a population that is adapted to the environment in the optimal fashion. The point on the circle corresponds to the level of adaptation of the current population, with increasing distance from the optimal point corresponding to decreased levels of adaptation. The circle encloses the area within which a population would be better adapted than the current population. Fixation for a mutation is indicated by an arrow starting at the current population and ending at a new point in space that is random in direction and magnitude from the current population. On the right is an expanded section of the circle in the vicinity of the current population to illustrate the increased chances of mutations with small phenotypic effect being selectively advantageous." (Templeton)