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[18] [19] An example widely used today to study the interplay of adaptation and speciation is the evolution of cichlid fish in African lakes, where the question of reproductive isolation is complex. [20] [21] Adaptation is not always a simple matter where the ideal phenotype evolves for a given environment.
For example, the adaptation of horses' teeth to the grinding of grass. By using the term adaptation for the evolutionary process and adaptive trait for the product (the bodily part or function), the two senses of the word may be distinguished. Adaptations are produced by natural selection. [152]
Sickle cell anemia is an adaptation against malaria. Resistance to malaria is a well-known example of recent human evolution. This disease attacks humans early in life. Thus humans who are resistant enjoy a higher chance of surviving and reproducing.
An example of this is the evolution of avian flight, which was identified as a key innovation in 1963 by Ernst Mayr. [6] However, separate evolutionary changes had to occur throughout the physiology of the avian ancestor, including the enlargement of the cerebellum and the enlargement and ossification of the sternum.
The flipper forelimbs of marine mammals (cetaceans, pinnipeds, and sirenians) are a classic example of convergent evolution. There is widespread convergence at the gene level. [ 6 ] Distinct substitutions in common genes created various aquatic adaptations, most of which also constitute parallel evolution because the substitutions in question ...
Spandrels can be as prominent as primary adaptations". A main example used by Gould and Lewontin is the human brain. Many secondary processes and actions come in addition to the main functions of the human brain. These secondary processes and thoughts can eventually turn into an adaptation or provide a fitness advantage to humans.
Richard Lenski's classic E. coli long-term evolution experiment is an example of adaptation in a competitive environment, ("improvement in fitness" during "survival of the fittest"). [64] The probability of a beneficial mutation occurring on some member of the lineage to give improved fitness is slowed by the competition.
Exaptation or co-option is a shift in the function of a trait during evolution. For example, a trait can evolve because it served one particular function, but subsequently it may come to serve another. Exaptations are common in both anatomy and behaviour. Bird feathers are a classic example.