Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Biol 4974/5974 Evolution Species concepts; patterns and evidence 8/22/2013 Species concepts Patterns in and evidence of Evolution Learning goals Understand: • Changing views of species through time. • Linnaeus and binomial species names and classification. • Species concepts: morphological, biological, evolutionary, and phylogenetic. • That similar structures in organisms arise through three evolutionary processes: homology, parallelism, and convergence. • Comparative embryology and fossils as evidence of relationships among organisms and evolution. Changing view of species • 4th and 5th centuries BCE, Plato and Aristotle: idealist species concept. • Each species was a product of creation and had a special purpose. • Steps from least perfect to most perfect. • Teleology What does this mean? • “Natural science became interwoven with religion.” • Manifested in the Great Chain of Being (Scale of Nature, Ladder of Nature). 1 Biol 4974/5974 Evolution Species concepts; patterns and evidence 8/22/2013 18th century view Views were growing more sophisticated: Georges Buffon (Georges-Louis Leclerc) (1707-1788): species were the biological units. Contribution? • Species were defined by reproductive isolation (were fertile or sterile offspring produced?) • Buffon accepted individual variation within species. • Ultimately, he did not believe that species change. • If species are fixed, how could new species arise? • What reasons did he give? p. 21, 24. 18th-19 century Jean-Baptiste de Lamarck (1744-1829) • Subscribed to the Great Chain of Being but thought species evolved from other species. Species did not go extinct. • Branching inheritance depicted. Clearly different routes to perfection. • Believed that organisms could evolve over time, and work up the Scale. • Lamarc provided a mechanism for change (Principle of use and disuse; Inheritance of acquired characters), which was later discredited. How did these work? Fig. 2.2 Linnaeus: modern systematics • Carl von Linnė(1697-1778) or Linnaeus’ work was a revolutionary step in our understanding of species. • Provided a basis for describing species and noting prominent features. • Binomial nomenclature. Please define. • Species relationships based on morphological features Established hierarchies of relationship: Orders, classes, etc. • He also acknowledged varieties or races, which means that he understand variation within species. 2 Biol 4974/5974 Evolution Species concepts; patterns and evidence 8/22/2013 Figure 02.F08: The nested taxonomic categories traditionally used to classify fruit flies and humans. Current species concepts (Table 2.1) Morphological species: “Unites individuals that share more characteristics (features) with one another than they do with any other organism.” These individuals would be considered a single species. • Objective, quantitative methods are used today. How? Biological species: “Based on the inability of individuals in populations to interbreed with individuals in other populations to produce viable offspring.” • Ernst Mayr proposed this concept in 1942. He defined species essentially as interbreeding or potentially interbreeding groups of populations that are isolated by other groups by absence of gene exchange. What about hybrids? • Applies to sexually-reproducing species—not clones or singlecell organisms. Current species concepts, continued Evolutionary species: Based on “evolutionary isolation” from other species. Proposed by George G. Simpson (1961), who stated, “an evolutionary species is a lineage (p. 32) evolving separately from others with its own unitary evolutionary role and tendencies.” • May be difficult to identify when speciation is complete. Phylogenetic species (phylospecies, cladospecies): “Ancestordescendant relationships define lineages of organisms.” E. O. Wiley reworked Simpson’s definition to “a single lineage of ancestral descendant populations of organisms which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate.” 3 Biol 4974/5974 Evolution Species concepts; patterns and evidence 8/22/2013 Similar adaptations: patterns of evolution Figure 03.F06: Homology, parallelism, and convergence diagrammed for two species (1, 2) that share a similar phenotypic character (phenotype a, b, c). Figure 03.F07: Skeletal structures of the forelimbs of representative terrestrial vertebrates to show the homology among bones at different levels in the limbs. Figure 03.B01_01: Vestigial (non-functioning) structures found in humans. Adapted from Romanes, G. J. Darwin, and After Darwin. Open Court, 1910. 4 Biol 4974/5974 Evolution Species concepts; patterns and evidence 8/22/2013 Figure 3.F08: Comparison of insect and bird wings to show their analogy Fig. 3.3 Parallel evolution of “wolf” phenotype. Fossil marsupial from Miocene in Patagonia. Extinct Tasmanian marsupial wolf. Placental North American wolf. Fig. 3.4. Convergent evolution between species of two different families of plants. North American Cactaceae, saguaro North African Eophorbiaceae 5 Biol 4974/5974 Evolution Species concepts; patterns and evidence 8/22/2013 Comparative embryology as evidence • Comparative embryology from Karl von Baer (1792-1876): showed similarities in embryonic development among very different vertebrates. • From this, Ernst Haeckel (1834-1919) developed his biogenetic law: In short, ontogeny recapitulates phylogeny. • We now know that only early developmental stages are repeated, using shared genes and gene networks. • Later stages differ because of developmental changes. • Regardless, embryology supports a common ancestry and common descent. Fossil record provides evidence • Discovery of fossils has been a major source of information supporting evolution. • Helps us understand the relationships among organisms as well. • Fossil record was beginning to develop in the mid-19th centrury. • Fossils with mixed traits, such as Archaeopteryx, represented transitional species. • Complete evolutionary sequences of fossils were powerful confirmation of evolution and descent with modification, e.g., the evolution of horses. Figure 03.F14: Evolutionary relationships among various lineages of horses, with emphasis on North American and Old World groups. (Adapted from MacFadden, B. J. Fossil Horses: Systematics, Paleobiology and Evolution of the Family Equidae. Cambridge University Press, 1992.) 6