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Darwin Presents His Case Section 15.3 – Darwin Presents His Case 1. A species is a group of organisms that can: • successfully reproduce • produce offspring that are fertile 2. Variation = differences between organisms of a population. 2 sources: • sexual reproduction and gene shuffling during Meiosis (sperm + egg) • mutation 3. Adaptations: • • • a variation that increases an organism’s chances of survival “all adaptations are variations” “not all variations are adaptations” 4. A niche is: • • not something you scratch the job an animal does in its environment Decomposer Predator (heterotroph) (heterotroph) Consumer Producer(heterotroph) (autotroph) 5. Fossils: • • • preserved remains or imprints of ancient organisms usually requires organisms to become buried in sediment organism and sediment are compressed into rock Evolution is: • a change in a population of organisms over time • it NEVER states that humans came from monkeys Ideas That Influenced Darwin Geology Scientists were discovering that the world was a lot older than people thought (Hutton, Lyell) Artificial Selection Farmers were changing the characteristics of their animals and crops by breeding the ones with the best features Population Control Evidence was pointing to the fact that humans may soon outgrow the food supply (Malthus) One of the First Ideas About Evolution • The Inheritance of Acquired Characteristics (Lamarck) The Inheritance of Acquired Characteristics (Lamarck) 1) 2) 3) 4) Organisms try to “improve” themselves The most used parts develop The least use parts waste away Developed parts can be passed on to children Section 15.3 – Darwin Presents His Case: Evolution by Natural Selection • Darwin’s idea revolved around VARIATION (new or different features) • Variations come from: • Mutations (usually , sometimes good) • Different combinations of features from sexual reproduction / meiosis Adaptations: • • • a variation that increases an organism’s chances of survival “all adaptations are variations” “not all variations are adaptations” Artificial Selection • One of Darwin’s best insights was that not only is there variation in nature, but that farmers had been taking advantage of this for centuries • Humans take advantage of these variations to create organisms with the features we like best • Darwin figured the same thing happens in the wild, but with NATURE SELECTING which organisms live and die Main Points of Natural Selection 1) Populations Have Variations (Everyone is Different) 2) Some Variations Are Favorable (called Adaptations) 3) More Babies Are Produced Than Can Survive (Competition / Struggle for Existence) 4) Those With Favorable Variations Survive And Reproduce Most (Descent with Modification) Evolution by Natural Selection (Darwin) Evidence of Evolution How to Determine the Relatedness of Organisms 1) Homologous Structures • have same anatomy, may not do the same job • indicate common ancestor • good measure of relatedness 2) Analogous Structures • Do not have same anatomy, but do the same job • Give no evidence of a recent common ancestor • Not a good measure of relatedness 3) Vestigial Structures • • • structures inherited from ancestors reduced in size may no longer be used Section 10.4 – Origin of Species 1) Speciation: a) is the evolution of one species from another b) usually occurs when species get separated from one another for long periods of time (They DIVERGE) c) members can no longer breed together = they have now become separate species d) process can also be called DIVERGENT EVOLUTION Two Speeds of Evolution c) Example: polar bears are related to brown bears, but are adapted for living on ice floes, not land Brown Bear Color Variations Brown Bear Color Variations Brown Bear Color Variations Brown Bear Color Variation Brown Bear Color Variation 3. Adaptive Radiation a) a type of divergent evolution b) MANY species come from a single ancestor c) for example, Darwin’s finches All came from a common ancestor on mainland South America Each island now has its own finch, each with a beak adapted for doing a certain job = divergent evolution