Divergent evolution ordivergent selection is the accumulation of differences between closely related populations within aspecies, sometimes leading tospeciation. Divergent evolution is typically exhibited when two populations become separated by a geographic barrier (such as inallopatric orperipatric speciation) and experience differentselective pressures that causeadaptations. After many generations and continual evolution, the populations becomeless able to interbreed with one another.[1] The American naturalistJ. T. Gulick (1832–1923) was the first to use the term "divergent evolution", with its use becoming widespread in modern evolutionary literature.[2] Examples of divergence in nature are theadaptive radiation of thefinches of theGalápagos, changes inmobbing behavior of thekittiwake, and the evolution of the modern-day dog from the wolf.
The term can also be applied inmolecular evolution, such as toproteins that derive fromhomologous genes. Both orthologous genes (resulting from a speciation event) and paralogous genes (resulting fromgene duplication) can illustrate divergent evolution. Throughgene duplication, it is possible for divergent evolution to occur between two genes within a species. Similarities between species that have diverged are due to their common origin, so such similarities are homologies.[3]
Animals undergo divergent evolution for a number of reasons linked to changes in environmental or social pressures. This could include changes in the environment, such access to food and shelter.[4] It could also result from changes in predators, such as new adaptations, an increase or decrease in number of active predators, or the introduction of new predators.[5] Divergent evolution can also be a result of mating pressures such as increased competition for mates orselective breeding by humans.[6]
Divergent evolution is a type of evolution and is distinct fromconvergent evolution andparallel evolution, although it does share similarities with the other types ofevolution.[7]
Convergent evolution is the development of analogous structures that occurs in different species as a result of those two species facing similar environmental pressures and adapting in similar ways. It differs from divergent evolution as the species involved do not descend from a closely related common ancestor and the traits accumulated are similar.[4] An example of convergent evolution is the development of flight in birds, bats, and insects, all of which are not closely related but share analogous structures allowing for flight.[8]
Parallel evolution is the development of a similar trait in species descending from a common ancestor. It is comparable to divergent evolution in that the species are descend from a common ancestor, but the traits accumulated are similar due to similar environmental pressures while in divergent evolution the traits accumulated are different.[9] An example of parallel evolution is that certain arboreal frog species, 'flying' frogs, in both Old World families and New World families, have developed the ability of gliding flight. They have "enlarged hands and feet, full webbing between all fingers and toes, lateral skin flaps on the arms and legs, and reduced weight per snout-vent length".[10]
One of the first recorded examples of divergent evolution is the case ofDarwin's Finches. During Darwin's travels to theGalápagos Islands, he discovered several different species of finch, living on the different islands. Darwin observed that the finches had different beaks specialized for that species of finches' diet.[11] Some finches had short beaks for eating nuts and seeds, other finches had long thin beaks for eating insects, and others had beaks specialized for eating cacti and other plants.[12] He concluded that the finches evolved from a shared common ancestor that lived on the islands, and due togeographic isolation, evolved to fill the particular niche on each of the islands.[13] This is supported by modern daygenomic sequencing.[14]
Another example of divergent evolution is theorigin of the domestic dog and the modernwolf, who both shared a common ancestor.[15] Comparing the anatomy of dogs and wolves supports this claim as they have similar body shape, skull size, and limb formation.[16] This is even more obvious in some species of dogs, such asmalamutes andhuskies, who appear even more physically and behaviorally similar.[17] There is a divergent genomic sequence of themitochondrial DNA of wolves and dogs dated to over 100,000 years ago, which further supports the theory that dogs and wolves have diverged from shared ancestry.[18]
Another example of divergent evolution is the behavioral changes in thekittiwake as opposed to other species ofgulls. Ancestorial and other modern-day species of gulls exhibit amobbing behavior in order to protect their young due the nesting at ground-level where they are susceptible to predators.[19] As a result of migration and environmental changes, the kittiwake nest solely on cliff faces. As a result, their young are protected from predatory reptiles, mammals, and birds who struggle with the climb and cliff-face weather conditions, and they do not exhibit this mobbing behavior.[20]
Another example of divergent evolution is the split forming theCactaceae family approximately dated in the late Miocene. Due to increase in arid climates, following theEocene–Oligocene event, these ancestral plants evolved to survive in the new climates.[21] Cacti evolved to haveareoles,succulentstems, and some have light leaves, with the ability to store water for up to months.[22] The plants they diverged from either went extinct leaving little in the fossil record or migrated surviving in less arid climates.[23]
Gulick, John T. (September 1888)."Divergent Evolution through Cumulative Segregation".Journal of the Linnean Society of London, Zoology.20 (120):189–274.doi:10.1111/j.1096-3642.1888.tb01445.x. Retrieved26 September 2011.(subscription required)
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