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6.2 Charles Darwin & His Theory of Natural Selection Image from: Biology by Miller and Levine; Prentice Hall Publishing©2006 Slide by Kim Foglia@ http://www.explorebiology.com/ Who Was Charles Darwin? In 1831, 22-year old Charles Darwin left England as naturalist aboard the HMS Beagle for 5 year voyage around the world. Mission: Chart the South American coastline Darwin noticed plants and animals were different from those he knew in Europe Wrote thousands of pages of observations and collected vast number of specimens http://www.solarnavigator.net/history/explorers_history/HMS_Beagle.jpg Who Was Charles Darwin? Darwin spent a month observing life on the Galapagos Islands Each island has different rainfall and vegetation and its own unique assortment of plant and animal species. Biology by Miller and Levine; Prentice Hall Publishing©2006 http://mikebaird.com/ecuador/images/galapagos_off_ecuador_ng_map.jpg Who Was Charles Darwin? Although animals on Galapagos resemble species on the South American mainland, many species were found no where else in the world = ENDEMIC http://www.darwinadventure.com/pictures/galapagos_giantortoise.jpg http://www.destination360.com/south-america/ecuador/galapagos-animals.php http://www.photoseek.com/galapago.html DARWIN’S FINCHES Darwin collected 14 species of finches and hypothesized that the Galapagos had be colonized by organisms from the mainland that had then diversified on the various Who Was Charles Darwin? After Darwin returned to England in 1836, he spent years examining specimens he brought back from voyage and filling notebooks with his ideas. He did not rush to publish his ideas because they disagreed with the fundamental scientific views of his day. In 1844 he wrote an essay describing his ideas and asked his wife to publish it if he died. http://www.elsie.brandeis.edu/images/journals.gif In 1858 Alfred Russel Wallace, another Naturalist working in the West Indies, wrote an essay describing his work that summarized the same ideas Darwin had been thinking about for 25 years! http://www.thesecondevolution.com/wallace&darwin.jpg Suddenly Darwin had incentive to publish the results of his work! In 1859 On the Origin of Species by Means of Natural Selection presented evidence and proposed a mechanism for evolution that he called NATURAL SELECTION http://www.loc.gov/exhibits/world/images/s125.jpg Darwin’s Theory of Evolution Darwin Presents his Case Image from: Biology by Miller and Levine; Prentice Hall Publishing©2006 Isn’t evolution “just a theory”? In every day usage “theory” often refers to a hunch or a speculation. When people say, “I have a theory about what happened,” they are often drawing a conclusion based on fragmentary or inconclusive evidence. The formal scientific definition of “theory” is quite different from the every day meaning. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence. http://evolution.berkeley.edu/evosite/evohome.htm Isn’t evolution just a theory? In Science a theory is a well supported, testable explanation of phenomena that have occurred in the natural world. Example: Cell theory Atomic theory Gravitational theory http://www.avgoe.de/StarChild/DOCS/STARCH00/questions/apple_falling.gif http://sixthsense.osfc.ac.uk/chemistry/atomic_structure2/atom.gif VOCAB ADAPTATION- Any inherited characteristic that increases an organism’s chance of survival http://www.wildlife-traps.com/skunks.html http://www.atomtigerzoo.com/photos/images/20060421233733_duckfeet.jpg http://www.3kitty.org/travelrama/Photos/123-21-4x6.jpg WHAT IS DARWIN’S THEORY? OVERPRODUCTION of OFFSPRING Capacity to over-reproduce seems characteristic of all species. http://www.biospheres.com/photogallery2ag/images/ladybugs_jpg.jpg http://atthecreation.com/DEER/too.many.deer.jpg WHAT IS DARWIN’S THEORY? STRUGGLE FOR EXISTANCE means that members of each species must compete for food, space, and other resources. http://www.wasatchcomputers.net/gallery/elk_fight.jpg WHAT IS DARWIN’S THEORY? GENETIC VARIATION is found naturally in all populations Image from www.biologyzone.com http://www3.nationalgeographic.com/animals/images/primary/zebra-herd.jpg WHAT IS DARWIN’S THEORY? Some organisms in a population are less likely to survive. http://www.cartoonstock.com/newscartoons/cartoonists/rrs/lowres/rrsn69l.jpg VOCAB Ability of an individual to survive and reproduce in its specific environment = FITNESS http://www.cartoonstock.com/newscartoons/cartoonists/cga/lowres/cgan170l.jpg WHAT IS DARWIN’S THEORY? SURVIVAL OF THE FITTEST = Organisms which are better adapted to their environment tend to produce more offspring than organisms without those traits. Competition for limited resources results in differential survival. WHAT IS DARWIN’S THEORY? Over time, NATURAL SELECTION results in changes in the inherited characteristics of a population. These changes increase a species’ fitness in its environment. How Does Evolution Really Work? IMPORTANT TO REMEMBER ! •POPULATIONS evolve NOT INDIVIDUALS. •NATURAL SELECTION only works on heritable traits. •A trait that is favorable in one environment may be useless or detrimental in another. WHAT IS DARWIN’S THEORY? DESCENT WITH MODIFICATION suggests that each species has descended with changes from other species over time. This idea suggests that all living species are related to each other and that all species, living and extinct, share a common ancestor.