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Outline. History of Evolutionary Thought Darwin’s Theory of Evolution Earth very old Descend with change from a common ancestor Adaptation to a changing environment The Evidence of Evolution Fossil Biogeographical Anatomical Biochemical. Voyage of the HMS Beagle. Charles Darwin at 31.
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Outline • History of Evolutionary Thought • Darwin’s Theory of Evolution • Earth very old • Descend with change from a common ancestor • Adaptation to a changing environment • The Evidence of Evolution • Fossil • Biogeographical • Anatomical • Biochemical
History of Evolutionary Thought • Prior to Darwin • View of nature determined by deep-seated beliefs • Held to be intractable truths • Biology thought had slowly begun to accept • Various ideas of evolution • Similarities between living things reflect recent common ancestry • Dissimilarities between living things reflect ancient common ancestry
Mid-Eighteenth Century • Taxonomy matured during mid-eighteenth century • Linnaeus believed in: • The fixity of species • That each species had: • An ideal structure and function, and • A place in the scala naturae (scale of complexity) • Count Buffon: • Wrote 44-volume catalog of all known plants and animals • Suggested descent with modification
Late Eighteenth Century • Cuvier: • First to use comparative anatomy to develop a system of classification • Founded Paleontology • Proposed Catastrophism • Local catastrophes in past had caused later strata to have a new mix of fossils • After each catastrophe, the region was repopulated by species from surrounding areas
Late Eighteenth Century • Lamarck: • First biologist to: • Propose evolution • Link diversity with environmental adaptation • Concluded more complex organisms are descended from less complex organisms • Proposed inheritance of acquired characteristics – Lamarckianism • Charles Lyell: • Earth is subject to slow but continuous cycles of erosion and uplift • Proposed uniformitarianism, rates and processes of change are constant
Darwin’s Theory of Evolution • Geological observations consistent with those of Hutton & Lyell • Biogeographical observations: • The study of the geographic distribution of life forms on earth • Darwin saw similar species in similar habitats; • Reasoned related species could be modified according to the environment
Galápagos Islands • Tortoises • Darwin observed tortoise neck length varied from island to island • Proposed that speciation on islands correlated with a difference in vegetation • Finches • Darwin observed many different species of finches on various islands • Speculated they could have descended from a single pair of mainland finch
Natural Selection and Adaptation • Individuals have heritable variations • More individuals produced each generation than environment can support • Some individuals have adaptive characteristics • Enables increased survival and reproduction • Increasing proportion of succeeding generations will have these characteristics • Populations become adapted to their local environment through change in individuals
Organisms Have Variations • Darwin emphasized that individuals from a population vary in their: • Functional characteristics • Physical characteristics • Behavioral characteristics • Proposed that these variations: • Are essential • Allow adaptation to the environment over time
Organisms Struggle to Exist • Malthus • Each generation has the same reproductive potential as the previous generation • Reproductive potential is greater than environment can support • Death, disease, and famine were inevitable if population were to have stability • Individuals experience a constant struggle for survival
Organisms Differ in Fitness • Fitness is the relative reproductive success of an individual • The most-fit individuals in a population capture a disproportionate share of goodies • Interactions with the environment determine which individuals reproduce the most • Adaptation • Changes that help a species become more suited to its environment • Product of natural selection
The Evidence of Evolution:Anatomical • Vertebrate forelimbs: • Homologous - All contain the same sets of bones in similar ways • Yet they are modified extensively to meet various adaptive needs • Darwin interpreted this as support for a hypothesis of common descent • Embryological development • All vertebrate embryos have: • A postanal tail and • Paired pharyngeal (gill) pouches
The Evidence of Evolution:Anatomical • Homologous Structures: • Anatomically similar because they are inherited from a common ancestor • May be functionally similar or not • Analogous Structures: • Serve the same function • Not constructed similarly • Do not share a common ancestor • Vestigal Structures: • Fully-developed anatomical structures • Reduced or obsolete function
The Evidence of Evolution:Fossil & Biogeographical • Fossil Evidence • Fossils record the history of life from the past • Document a succession of life forms from the simple to the more complex • Sometimes the fossil record is complete enough to show descent from an ancestor • Biogeographical • Distributions of plants and animals across earth • Consistent with origin in one locale and then spread to accessible regions
Biochemical Evidence • Almost all living organisms: • Use the same basic biochemical molecules • Utilize same DNA triplet code • Utilize same 20 amino acids in their proteins • DNA base-sequence differences: • When very similar, suggest recent common descent • When more different, suggest more ancient common descent
Review • History of Evolutionary Thought • Darwin’s Theory of Evolution • Earth very old • Descend with change from a common ancestor • Adaptation to a changing environment • The Evidence of Evolution • Fossil • Biogeographical • Anatomical • Biochemical
