Evolution8 - Evolution#13 Speciation The Origin of Species...

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The Origin of Species: That “Mystery of Mysteries” speciation = origin of new species; focal point of evolutionary theory b/c appearance of new species is the source of biological diversity it is not enough to explain how adaptations evolve in a pop (microevolution) evolutionary theory must also explain … macroevolution = such evolutionary change above the species level o ex) appearance of feathers during evolution of birds from 1 grp of dinosaurs o other “evolutionary novelties” that can be used to define higher taxa o anagenesis (Grk ana, new + genos, race) = phyletic evolution = accumulation of changes that gradually transform a given species into a species w/ diff characteristics o cladogenesis (Grk klados, branch) = branching evolution = splitting of a gene pool into 2 or more separate pools, which each give rise to one or more new species o only cladogenesis can promote biodiversity by inc the # of species, thus is the basis of bioD The biological species concept emphasizes reproductive isolation species (Ltn kind/appearance) discrete (not arbitrary) units based on morphology, physiology, biochemistry, DNA sequences o biological species concept by biologist Ernst Mayr 1942 species = pop/grp of pops whose members have potential to interbreed in nature & produce viable, fertile offspring; but are unable to produce such offspring w/ members of other pops aka, unity by potential reproductive compatibility reproductive isolation [f 24.4 pp 474-475] concept of biological species hinges upon reproductive isolation the existence of biological factors/barriers that impede members of 2 species from producing viable, fertile hybrids although 1 barrier may not block all genetic exchange betwn species, a combo of several barriers can effectively isolate a species’ gene pool barriers classified according to whether they contribute to reproductive isolation before or after fertilization o prezygotic barriers (“before the zygote”) impede mating
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Evolution8 - Evolution#13 Speciation The Origin of Species...

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