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Darwin and Evolution Darwin: a reluctant rebel AP Biology 2006-2007 History of Evolutionary Thought Carolus Linnaeus (17071778) Taxonomist Binomial Nomenclature Agreed with the “fixity of species” theory AP Biology LaMarck Organisms adapted to their environments by acquiring traits change in their life time Disuse organisms lost parts because they did not use them — like the missing eyes & digestive system of the tapeworm Perfection with Use & Need the constant use of an organ leads that organ to increase in size — like the muscles of a blacksmith or the large ears of a night-flying bat AP Biology transmit acquired characteristics to next generation LaMarckian vs. Darwinian view LaMarck in reaching higher vegetation giraffes stretch their necks & transmits the acquired longer neck to offspring Darwin AP Biology giraffes born with longer necks survive better & leave more offspring who inherit their long necks AP Biology Charles Darwin 1809-1882 British naturalist Proposed the idea of evolution by natural selection Collected clear evidence to support his ideas AP Biology Voyage of the HMS Beagle Invited to travel around the world 1831-1836 (22 years old!) makes many observations of nature main mission of the Beagle was to chart South American coastline Robert Fitzroy AP Biology Voyage of the HMS Beagle Stopped in Galapagos Islands AP Biology 500 miles off coast of Ecuador Galapagos Recent volcanic origin most of animal species on the Galápagos live nowhere else in world, but they resemble species living on South American mainland. AP Biology 500 miles west of mainland Unique species AP Biology Darwin found… birds Collected many different birds on the Galapagos Islands. Finch? Thought he found very different kinds… AP Biology Sparrow? QuickTime™ and a Photo - JPEG decompressor are needed to see this picture. Woodpecker? Warbler? But Darwin found… a lot of finches Darwin was amazed to find out: All 14 species of birds were finches… But there is only one species of finch on the mainland! Finch? Large Ground Finch? Finch Sparrow? Small Ground Sparrow? Finch How did one species of finches become so many different species now? AP Biology Woodpecker? Warbler Finch Woodpecker? Warbler? Veg.Warbler? Tree Finch Tree Thinking Descendant species Ancestral species AP Biology Large-seed Large Ground eater? Finch Warbler? Warbler Finch Small-seed Small Ground eater? Finch Leaf-browser? Veg. Tree Finch Correlation of species to food source Seed eaters Flower eaters Insect eaters Rapid speciation: new species filling new niches, because they inherited successful adaptations. AP Biology radiation Adaptive More observations… AP Biology Correlation of species to food source Natural Selection gradual, non-random process by which biological traits become either more or less common in a population mechanism that drives evolution Evolution = change in a species over many gnerations (long period of time)/ accumulation of adaptations There is variation in traits. Caused by mutations in DNA Caused by inheritance of dominant/recessive alleles = different phenotypes Only organisms that are “best fit” for the AP Biology environment survive, reproduce, and pass on their traits to offspring. Natural Selection: 4 steps 1. Natural Variation exists in nature 2. Competition - Organisms struggle for 3. 4. survival: more organisms are produced than the environment can support Survival of the fittest: Only the best adapted survives. Adaptations are important Organisms change over time in response to the environment: organisms change but they have a common descent – they have common ancestors AP Biology Adaptations: inherited characteristics that allow individuals to “do better” in their environment. Adaptations increase their chance of survival and reproduction AP Biology Artificial selection This is not just a process of the past… AP Biology It is all around us today Selective breeding AP Biology Natural Selection vs. Artificial Selection Artificial Selection: nature provides variation, and humans select variations that we find useful (domestic animals and crops) Natural Selection: the environment is the selective force. Only those organisms that are well adapted will AP Biology survive in the wild. Sexual Selection AP Biology