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Chapters 22, 23, and 24 (Descent with Modification: A Darwinian View of…

- - - - Carolus Linnaeus developed a binomial format for naming species (genus species); and adopted a nested classification system, grouping similar species into increasingly general categories (genus into family)
    - - gradualism: evolution proceeds chiefly by the accumulation of gradual changes
        
        uniformitarianism: changes in the earth's crust during geological history have resulted from the action of continuous and uniform processes
    - - Charles Darwin: descent with modification (Earth's many species are descendants of ancestral species that were different from the present-day species)
      - Jean Baptiste Lamarck: use and disuse (giraffe stretching its neck to reach leaves on high branches) , inheritance of acquired characteristics (an organism could pass these modifications to its offspring)
  - - - artificial selection: the intentional reproduction of individuals in a population that have desirable traits
- - - - founder effect: when a few individuals become isolated from a large population, the smaller group may establish a new population whose gene pool differs from the source population ; some of population splits from the rest due to an event
- - - - sympatric speciation: reproductive isolation in a single population that shares a geographic location
  - - - if hybrids are less fit than their parent species, natural selection should strengthen prezygotic barriers to reproduction, reducing the formation of unfit hybrids; the process involves reinforcing reproductive barriers -> reinforcement
    - - gene flow may occur that weakens reproductive barriers further than they were when the two species met in the hybrid zone and the gene pools of the two species become increasingly alike, causing the two hybridizing species to fuse into a single species
    - - some hybrid zones are stable because hybrids continue to be produced because the hybrids survive or reproduce better than members of the parent species, though in some the hybrids are selected against
  - - - reduced hybrid viability: the genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment (ex: some salamander subspecies in hybrid zone produce hybrids that do not complete development)
      - reduced hybrid fertility: if the chromosomes of the two parent species differ in number or structure, meiosis in the hybrids may fail to produce normal gametes; infertile hybrids can't produce offspring when they ate with either parent species, genes can't flow between the species (ex: mule = male donkey = female horse)
      - hybrid breakdown: some 1st gen hybrids are viable and fertile , but when they mate with one another or with either parent species, offspring of the next generation are feeble or sterile (ex: strains of cultivated rice have accumulated different mutant recessive alleles at two loci, but plants that carry too many are small and sterile)