ABSTRACT
Adaptation Selection, which acts on variation, results in the appearance of new and stable features in a population that are seen as adaptations, a word that reects the success of those new features in particular environments. More subtle changes to the phenotype that cannot be linked in any obvious way to pressures from the environment (for example, the human liver has four lobes, whereas the mouse liver has ve) are just viewed as minor species differences, perhaps deriving from genetic drift. Adaptation is, however, an umbrella term that covers any stable novelty; examples at dierent levels include a minor change in a bacterium’s biochemistry that allows it to survive on a new food source, the various heritable respiratory adaptions that allow humans to live at high altitude (Beall, 2013), the replacement in dipteran ies of the pair of rear wings seen in early winged insects with haltere-balancing organs that increase ight control (Fox et al., 2010), and the recent changes in pigmentation in Biston betularia, the peppered moth, to survive when its tree habitat changed due to carbon deposition (Figure 14.1A, B).
