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Darwin's finches are a clear and famous example of divergent evolution, in which an ancestral species radiates into a number of descendant species with both similar and different traits.

Divergent evolution or divergent selection is the accumulation of differences between closely related populations within a species, sometimes leading to speciation. Divergent evolution is typically exhibited when two populations become separated by a geographic barrier (such as in allopatric or peripatric speciation) and experience different selective pressures that cause adaptations. After many generations and continual evolution, the populations become less able to interbreed with one another.^[1] The American naturalist J. 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 the adaptive radiation of the finches of the Galápagos, changes in mobbing behavior of the kittiwake, and the evolution of the modern-day dog from the wolf.

The term can also be applied in molecular evolution, such as to proteins that derive from homologous genes. Both orthologous genes (resulting from a speciation event) and paralogous genes (resulting from gene duplication) can illustrate divergent evolution. Through gene 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]

Causes

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 or selective breeding by humans.^[6]

Distinctions

Divergent evolution is a type of evolution and is distinct from convergent evolution and parallel evolution, although it does share similarities with the other types of evolution.^[7]

Divergent versus convergent evolution

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]

Divergent versus parallel evolution

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]

Darwin's finches

One of the first recorded examples of divergent evolution is the case of Darwin's Finches. During Darwin's travels to the Galápagos 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 to geographic isolation, evolved to fill the particular niche on each of the islands.^[13] This is supported by modern day genomic sequencing.^[14]

Divergent evolution in dogs

Another example of divergent evolution is the origin of the domestic dog and the modern wolf, 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 as malamutes and huskies, who appear even more physically and behaviorally similar.^[17] There is a divergent genomic sequence of the mitochondrial 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]

Divergent evolution in kittiwakes

Another example of divergent evolution is the behavioral changes in the kittiwake as opposed to other species of gulls. Ancestorial and other modern-day species of gulls exhibit a mobbing 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]

Divergent evolution in cacti

Another example of divergent evolution is the split forming the Cactaceae family approximately dated in the late Miocene. Due to increase in arid climates, following the Eocene–Oligocene event, these ancestral plants evolved to survive in the new climates.^[21] Cacti evolved to have areoles, succulent stems, 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]

References

^ "Sympatric speciation". Retrieved 2 February 2016.
^ 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. Retrieved 26 September 2011. (subscription required)
^ Zuckerkandl, EMILE; Pauling, LINUS (1965-01-01), Bryson, Vernon; Vogel, Henry J. (eds.), "Evolutionary Divergence and Convergence in Proteins", Evolving Genes and Proteins, Academic Press, pp. 97–166, ISBN 978-1-4832-2734-4, retrieved 2024-03-24
^ ^a ^b Clark, Mary Ann; Douglas, Matthew; Choi, Jung (2018-03-28). "18.1 Understanding Evolution - Biology 2e | OpenStax". openstax.org. Retrieved 2024-03-24.
^ Johnson, Jerald B.; Belk, Mark C. (2020-10-31). "Predators as Agents of Selection and Diversification". Diversity. 12 (11): 415. doi:10.3390/d12110415. ISSN 1424-2818.
^ "Artificial selection". evolution.berkeley.edu. Retrieved 2024-03-24.
^ "18.5G: Convergent Evolution". Biology LibreTexts. 2018-07-13. Retrieved 2024-03-24.
^ Alexander, David E. (2015-09-02). On the Wing: Insects, Pterosaurs, Birds, Bats and the Evolution of Animal Flight. Oxford University Press. ISBN 978-0-19-999679-7.
^ Pearce, Trevor (2012-06-01). "Convergence and Parallelism in Evolution: A Neo-Gouldian Account". The British Journal for the Philosophy of Science. 63 (2): 429–448. doi:10.1093/bjps/axr046. ISSN 0007-0882.
^ Emerson, S.B.; M.A.R. Koehl (1990). "The interaction of behavioral and morphological change in the evolution of a novel locomotor type: 'Flying' frogs". Evolution. 44 (8): 1931–1946. doi:10.2307/2409604. JSTOR 2409604. PMID 28564439.
^ Desmond, Adrian J.; Moore, James R. (1991). Darwin (1. publ ed.). London: Joseph. ISBN 978-0-7181-3430-3.
^ Grant, Peter R. (1999). Ecology and evolution of Darwin's finches. Princeton, N.J: Princeton University Press. ISBN 978-0-691-04865-9.
^ Grant, Peter R.; Grant, B. Rosemary (2008). How and why species multiply: the radiation of Darwin's finches. Princeton series in evolutionary biology. Princeton: Princeton University Press. ISBN 978-0-691-13360-7. OCLC 82673670.
^ Lamichhaney, Sangeet; Berglund, Jonas; Almén, Markus Sällman; Maqbool, Khurram; Grabherr, Manfred; Martinez-Barrio, Alvaro; Promerová, Marta; Rubin, Carl-Johan; Wang, Chao; Zamani, Neda; Grant, B. Rosemary; Grant, Peter R.; Webster, Matthew T.; Andersson, Leif (2015-02-11). "Evolution of Darwin's finches and their beaks revealed by genome sequencing". Nature. 518 (7539): 371–375. Bibcode:2015Natur.518..371L. doi:10.1038/nature14181. ISSN 1476-4687. PMID 25686609.
^ Vila, C. (1999-01-01). "Phylogenetic relationships, evolution, and genetic diversity of the domestic dog". Journal of Heredity. 90 (1): 71–77. doi:10.1093/jhered/90.1.71. PMID 9987908.
^ Honeycutt, Rodney L (2010-03-09). "Unraveling the mysteries of dog evolution". BMC Biology. 8: 20. doi:10.1186/1741-7007-8-20. ISSN 1741-7007. PMC 2841097. PMID 20214797.
^ Freedman, Adam H.; Lohmueller, Kirk E.; Wayne, Robert K. (2016-11-01). "Evolutionary History, Selective Sweeps, and Deleterious Variation in the Dog". Annual Review of Ecology, Evolution, and Systematics. 47 (1): 73–96. doi:10.1146/annurev-ecolsys-121415-032155. ISSN 1543-592X.
^ Vilà, C.; Savolainen, P.; Maldonado, J. E.; Amorim, I. R.; Rice, J. E.; Honeycutt, R. L.; Crandall, K. A.; Lundeberg, J.; Wayne, R. K. (1997-06-13). "Multiple and ancient origins of the domestic dog". Science. 276 (5319): 1687–1689. doi:10.1126/science.276.5319.1687. ISSN 0036-8075. PMID 9180076.
^ Alcock, John (2013). Animal Behavior: An Evolutionary Approach, Tenth Edition. pp. 101–109.
^ Cullen, Esther (April 2008). "Adaptations in the kittiwake to cliff-nesting". Ibis. 99 (2): 275–302. doi:10.1111/j.1474-919x.1957.tb01950.x.
^ Hernández-Hernández, Tania; Brown, Joseph W.; Schlumpberger, Boris O.; Eguiarte, Luis E.; Magallón, Susana (June 2014). "Beyond aridification: multiple explanations for the elevated diversification of cacti in the New World Succulent Biome". New Phytologist. 202 (4): 1382–1397. doi:10.1111/nph.12752. hdl:2027.42/106989. ISSN 0028-646X. PMID 24611540.
^ https://web.archive.org/web/20120213193904/http://web.mac.com/redifiori/Russell_Di_Fiori/Phylogenetics_files/Edwards_Donoghue2006.pdf. Archived from the original (PDF) on 2012-02-13. Retrieved 2024-03-25. {{cite web}}: Missing or empty |title= (help)
^ Arakaki, Mónica; Christin, Pascal-Antoine; Nyffeler, Reto; Lendel, Anita; Eggli, Urs; Ogburn, R. Matthew; Spriggs, Elizabeth; Moore, Michael J.; Edwards, Erika J. (2011-05-17). "Contemporaneous and recent radiations of the world's major succulent plant lineages". Proceedings of the National Academy of Sciences. 108 (20): 8379–8384. Bibcode:2011PNAS..108.8379A. doi:10.1073/pnas.1100628108. ISSN 0027-8424. PMC 3100969. PMID 21536881.