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Download The Theory of Evolution
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The Theory of Evolution Chapter 15 Charles Darwin Proposed a Mechanism for Evolution • English naturalist. Born 1809 and died in 1882 • Darwin found evidence of evolution during his voyage on the Beagle (419) • he studied fossils, plants, and animals and concluded that they changed over time Jean Babtiste Lamarck also proposed a mechanism for evolution • French scientist • proposed a mechanism for evolution BEFORE Darwin in 1809 Jean Babtiste Lamarck also proposed a mechanism for evolution • According to Lamarck, evolution happened to organisms through use and disuse • happens within the organisms lifetime • if used a lot a physical feature will become bigger is not used smaller • the traits are then passed on the to next generation • ex. giraffe necks Darwin’s Theory of Natural Selection • Natural Selection (420) • “survival of the fittest” (not Darwin’s words but Herbert Spencer’s) • organisms with a particular trait are better suited for their environment and survive, reproduce, and pass that trait on to the next generation • Natural Selection has four main principles: Darwin’s Theory of Natural Selection 1. Individuals in a population of the same species show variation 2. Variations are inherited 3. Organisms have more young than can survive on available resources 4. Variations that increase reproductive success will be more common in the next generation Darwin’s Theory of Natural Selection • Darwin wrote the famous book On the Origins of Species by Means of Natural Selection about his work • He continued to collect evidence to support his theory for many years Darwin’s theory of Natural Selection • The heart of Darwin’s theory lies in the concept of adaptation • Adaptation - changing of a species that results in it having a better chance to survive in it’s environment and reproduce Choose an organism: Describe 3 adaptations Darwin’s Ideas Have Been Updated • Scientists now know that DNA and genes are involved • Isolation – when two populations can not breed – over time leads to different species • ex. Grand Canyon squirrels (438) Darwin’s Ideas Have Been Updated • Extinction – species disappear completely due to some environmental change Evidence for Evolution • Fossils – show a gradual changes of organisms over time • older fossils were near the bottom layers, newer near the top • organisms started out simple and gradually got more complex Evidence for Evolution • Vestigial Structures – any body structure that is reduced in function in a living organism but was used by an ancestor • wings in flightless birds (ostriches, emus, penguins) • hind limb bones in whales (285) • appendix in humans Evidence for Evolution • Homologous Structures – structures that share common ancestry • forelimbs of humans, alligator, bird wing (287) • Analogous Structures – Different structures evolved for the same function • wing of a bird and a wing of a butterfly Evidence for Evolution • Embryological Evidence – Similarity of the structure of embryos of different species • all vertebrate embryos have a tail and gill slits during development (288) Evidence for Evolution • Comparative biochemistry – Scientists can compare the number of DNA, RNA, and amino acid sequences species have in common – The more they have in common the more closely they are related How Does Evolution Occur? • Gradualism – gradual change over a long period of time • Punctuated Equilibrium – proposed by American biologists Gould and Eldredge, suggests long periods of no change and short bursts of rapid change Domesticated Fox Video How Does Evolution Occur? • Convergent Evolution – Distantly related organisms evolve similar traits because of similar environments • Ex. Dolphins and sharks • Divergent Evolution – Species evolve from same ancestor and develop different characteristics Examples of Evolution • Kettlewell’s study of peppered moths • most were light to match the tree trunks covered with lichens, few were dark • after industrial revolution most were black • soot had turned the tree trunks black making the dark moth better suited for the environment – natural selection • What if there were no dark moths? Examples of Evolution • Galapagos Finches • beak size was related to how wet or dry the season was • dry years large tough seeds needed to be eaten, in wet yeasr smaller seeds were eaten