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Transcript
What is a species? Development of Evolution Theory History of Evolutionary Thought • Early biological thought didn’t include evolution • Creationism – Organisms remain fixed and unchanged • 427-347 B.C. – Plato • 384-322 B.C. – Aristotle – Scala Naturae (ladder of Nature) – categorized organisms into a linear hierarchy • Until 1700’s creationism was unchallenged • We need to define what a species is to understand evolution, the mechanisms, and diversity • Species – basic unit of taxonomic classification; population of closely related and similar. In sexually reproducing organisms, the similar organisms must be able to breed and produce viable, fertile offspring New Evidence Eroded View of Creationism • New lands – revealed diversity of life – Africa, Asia, Americas – Many different species; some closely resembled each other • Fossil Discoveries – Fossils – remains of dead organisms (in rock, petrified bones and wood, shells, impressions of body forms – showed life changed over time 1 2. skin impression 3. bones 1. eggs in nest (a) (b) (c) 4. fossilized feces (coprolites) 5. footprint Nonevolutionary explanations for fossils • Catastrophism – Georges Cuvier (1769-1832) • Proposed a vast # of species was created and successive catastrophes produced layers of rock and destroyed many species, fossilizing them – Problem: some organisms that survived should have shown up in fossils because some would have died; the majority of fossils are extinct species – Louis Agassiz (1807-1873) • Proposed there were new creations after each catastrophe Speculations Life Did Evolve • Original creation produced a small # of founding species and later species evolved through natural processes – Georges Louis LeClerc (Comte de Buffon) (1707-1788) – Problem: couldn’t prove a mechanism and also no one thought the earth was old enough to allow time for producing a new species 2 Geological Evidence – Earth is Old • Uniformitarianism – View of geologists Thomas Hutton and Charles Lyell – Earth developed gradually through natural processes that occur over long periods of time • Examples – river flooding, volcanoes, geologic shift Darwin and natural selection PrePre-Darwin Biologists Proposed Mechanisms for Evolution • Jean Baptiste Lamarck (1744-1829) • Hypothesized that organisms evolved through the inheritance of acquired characteristics – Proposed that all organisms have an innate drive for perfection – Example: Giraffes – Problem: Acquired characteristics cannot be inherited • Though he was wrong, Lamarck’s evolution ideas influenced later biologists The Voyage of the Beagle 1831 - 1836 3 Darwin’s Voyage Galapagos islands • Volcanic archipelago- geologically young. • Several groups of closely related species found nowhere else. • Mockingbirds, Finches, giant tortoisesdistinct types on the different islands • Diversification (adaptive radiation) from mainland ancestors 14 Varieties of finches 4 Darwin and Wallace Proposed a Mechanism of Evolution • 1858 – Charles Darwin and Alfred Russel Wallace came up with the mechanism for evolution • Worked separately • 1859 – Darwin published On the Origin of Species by Means of Natural Selection How Does Natural Selection Work? • • • • • Overproduction Struggle for existence Variation Survival of fittest Origin of a new species Important Points Underlying Evolutionary Change • Variations that natural selection works on are produced by chance mutations – Mutations that produce traits occur spontaneously and are made common or rare by natural selection • Natural selection selects organisms that are best adapted to a particular environment – Conditions change in environments so the best at one point may not survive at another time 5