An adaptation is a trait of an organism that is maintained or spread by either natural selection or indirect selection. Such a characteristic does so by confering a higher inclusive fitness than other available analogous characteristics in other individuals in a population  The process of adaptation is the evolutionary modification of a character for efficient or advantageous (fitness-enhancing) functioning. Consistent with these definitions, adaptations can be physiological, behavioral or morphological features of organisms that enable them to survive and reproduce effectively.
Adaptation in action
A famous example of adaptation is the case of the "industrial melanism" of the peppered moth (Biston betularia). Found in northern England, the most common form of the peppered moth prior to the industrial revolution was a light-colored speckled form called typica. Around the middle of the nineteenth century, a darker form called carbonaria began to be found more often, particularly in the vicinity of industrialized cities such as Manchester where the darker moths had become predominant by the end of the century.
Ecologists explain the rise of the carbonaria form by making reference to changes that took place in the moths' habitat. As English cities industrialized in the late 18th and early 19th centuries, factories began to spew forth enormous quantities of soot, which settled over the surrounding countryside and darkened the moths' habitat. The lighter moths were thus less able to blend into their environment and became easier prey for birds. Darker moths, on the other hand, were now able to better avoid detection by predators. Interestingly, an early researcher, H. B. D. Kettlewell, "found that in unpolluted areas, more of his light-colored moths had survived. In soot-blacked areas, more of the dark-colored moths had survived. Thus Kettlewell showed that in each environment the moths that were better camouflaged had the higher survival rate."
More recently, the carbonaria form has been on the decline and the lighter form has again become more common. Ecologists attribute this shift to the creation of Clean Air laws and the cleaner countryside that has resulted.
- Alcock, John. 2005. Animal Behavior. Sinauer Associates. ISBN:0-87893-005-1
- Miller, K. R., & J. S. Levine (1998) Biology. 4th Edition. Prentice Hall Co.