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Darwin, Evolution, and Natural Selection Scientific Theory A. Social use of the word “theory” 1. Not the same as in science 2. Implies a hunch or a casual guess B. Scientific Theory 1. Highly probable explanation based on vast collections of scientific data 2. There are relatively few scientific theories C. Examples of Scientific Theories 1. 2. 3. 4. Cell Theory Atomic Theory Plate Tectonic Theory Big Bang Theory Theories of Evolution Contributing Ideas…. Theories of Evolution Hutton and Lyell (late 1700/early 1800’s) - Fundamentalists said that the Earth was around 6000 years old. - Hutton and Lyell argued that the Earth is many millions of years and because - Layers of rocks take time to form - Processes such as volcanoes and earthquakes shaped the Earth and still occur today. Theories of Evolution Malthus (1766-1834) • Reasoned that if the human population continued to grow unchecked, sooner or later there would be insufficient living space and food for everyone Theories of Evolution A. Lamarck (1800) 1. Similar species descended from a common ancestor – related to fossil record 2. Species change by ACQUIRING traits in their lifetime by using their bodies in new ways 3. Acquired traits are NOT genes; they are things that are learned Theories of Evolution Theories of Evolution C. Charles Darwin (late 1800’s) 1. Background a. medical and clergy student naturalist b. HMS Beagle –goal was to survey the coast of S. America (1831-1836) –Darwin collected biological & geological specimens c. Read Lyell’s Principles of Geology which influenced his thinking as he observed fossils—book proposed the earth was millions of years old Theories of Evolution Darwin sailed on the Beagle from 1831-1836 Theories of Evolution On the Galapagos Islands a. Different islands seemed to have their own slightly different varieties of animals b. Finches had distinctive bills – 13 different species c. Very similar – must have descended from a common ancestor d. Related this to artificial selection Theories of Evolution Theories of Evolution Galapagos Turtles Theories of Evolution DARWIN ideas ~ Framework for Natural Selection (1840) a. Individuals in a population show differences b. Variations are inherited c. Organisms have more offspring than can survive on available resources d. Variations that increase reproductive success will have a greater chance of being passed on than those that do not increase reproductive success Theories of Evolution DARWIN~ Wrote a book – Origin of Species (1859) a. Compiled evidence for evolution and explained how natural selection might provide a mechanism for the origin of species B. b. 1858: another naturalist (Alfred Wallace) proposed a theory almost identical to Darwin’s (saying species were modified by natural selection)—Darwin published his book a year later; evolution is only used once: on the last page! “Natural selection and species fitness” fitness” • Overtime, natural selection results in changes in the inherited characteristics of a population. • These changes increase a species fitness (survival rate) Summary of Darwin’s Theory 1. Organisms differ; variation is inherited 2. Organisms produce more offspring than survive 3. Organisms compete for resources 4. Organisms with advantages survive to pass those advantages to their children 5. Species alive today are descended with modifications from common ancestors