biology unit 5 key concepts
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- Macroevolution
- Macroevolution is the origin of new species and other taxonomic groups. Two patterns of species change chronicled by the fossil record are anagenesis (phyletic evolution), the accumulation of changes associated with the transformation of one species into another, and cladogenesis, branching evolution (FIGURE 24.1).
- the biological species concept emphasizes reproductive isolation
- The biological species concept defines a species as a group of populations whose individuals have the potential to interbreed and produce fertile offspring with each other but not with members of other species.
- Prezygotic and postzygotic barriers isolate the gene pools of biological species
- Prezygotic barriers prevent mating or fertilization between species. Species that occupy the same geographic area often live in separate habitats (habitat isolation); possess unique, exclusive mating signals and courtship behaviors (behavioral isolation); breed at different times (temporal isolation); and/or have anatomically incompatible reproductive organs (mechanical isolation) or incompatible sex cells (gametic isolation). Even if two different species manage to mate, postzygotic barriers usually prevent the interspecific hybrids from developing into adults, breeding with either parent species, or producing viable, fertile offspring.
- The biological species concept has some major limitations
- For instance, it is not applicable to fossils or to organisms that reproduce only asexually.
- Evolutionary biologists have proposed several alternative concepts of species
- Alternative concepts include the ecological species concept, which explains the similarity among members of a species by their adaptation to exploit a particular set of ecological resources (or niche); the morphological species concept, which defines species by phenotypic characteristics; pluralistic species concept, suggesting that different factors operate in different creatures to explain why species exist; and a genealogical species concept, which defines a species by the close genetic relatedness among its members.
- Allopatric speciation: Geographic barriers can lead to the origin of species
- Allopatric speciation may occur when two populations of one species become geographically separated from each other. One or both populations may undergo evolutionary change and become reproductively isolated as a consequence of that change.
- Sympatric speciation: A new species can originate in the geographic midst of the parent species
- Many plant species have evolved by polyploidy (multiplications of the chromosome number). Autopolyploids are species derived this way from one ancestral species. Allopolyploids are species with multiple sets of chromosomes derived from two different species. Examples of processes that can result in sympatric speciation in animals are host-switching by parasites and nonrandom mating in polymorphic populations.
- The punctuated equilibrium model has stimulated research on the tempo of speciation
- The punctuated equilibrium model suggests that species change most as they bud from an ancestral species, after which they undergo relatively little change for the rest of their existence.
- most evolutionary novelties are modified versions of older structures
- Most novel biological structures evolve in many stages from previously existing structures. In some cases, such as the eye, the function of the organ has probably been constant during all stages of its evolution. In others, such as feathers, the function of the organ has changed.
- "Evo-devo" : Genes that control development play a major role in evolution
- Many macroevolutionary changes may have been associated with mutations in genes that regulate development. Such changes can affect the timing of developmental events (heterochrony) or the spatial organization of body parts, as in mutations of homeotic genes.
- An evolutionary trend does not mean that evolution is goal oriented
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Long-term evolutionary trends may arise because of adaptation to a changing environment. Or, according to the species selection hypothesis, trends may result when species with certain characteristics endure longer and speciate more often than those with other characteristics.