The Theory of Evolution

What is a theory? A scientist’s explanation or interpretation of factual information gathered through observation & experimentation Supported by repeated testing & evidence, it becomes the accept explanation for a given phenomenon It is important to remember that when we use the word “theory” very differently in everyday speech. In a non-scientific context, it means something that is unproven or speculative, which can get confusing and cause people to doubt the truth of various scientific theories. Facts are things which are measurable and observable. The facts do not change, but theories may change or be modified based on a reinterpretation of the facts or as new information comes to light. We must keep this definition of “theory” in mind when learning about Darwin’s theory of evolution

Read pp. 1-3 in your textbook & answer the following: What discoveries first created doubts about the Biblical creation story? Describe Darwin’s theory of evolution? On what evidence was it based? Why did he hesitate to publish his findings? What is natural selection? Once students have had time to read the selection and answer the questions, go over the answers as a class. Be sure students include an explanation for WHY evolution takes place (changing environment to which species must adapt or become extinct).

The Evolution of a Theory 1865: Gregory Mendel’s theory of genetics suggests organisms inherit traits through their genes 1953: James Watson & Francis Crick discover DNA DNA=how traits are inherited Chance mutation: random mutations in DNA lead to evolution with positive traits being passed on & negative traits dying out 1972: Stephen Jay Gould & Niles Eldredge develop theory of punctuated equilibrium Explains gaps in fossil evidence Sudden geographic isolation of a group from its main population forces it to evolve quickly without leaving evidence of its transition New characteristics give it an advantage & it eventually wipes out the main population that didn’t evolve If we look at more recent scientific discoveries we can see how theories evolve as new information comes to light. As long as the new information is consistent with the findings of the original theory, the theory remains the accepted scientific truth Chance mutation: Explanation of HOW natural selection takes place Punctuated equilibrium: Gaps in fossil evidence caused some to doubt the theory of evolution If a portion of a species was suddenly isolated, it could evolve quickly while the rest of the population remained unchanged Must evolve quickly in order to adapt to new surroundings Main population would not evolve and would be at a disadvantage causing its eventual extinction TRANSITION Remind students that prior to the development of this theory most cultures developed their own creation stories to explain the origins of humanity and the world. As their reading today states, some viewed these stories as being 100% true while others saw them as symbolic. What is truly interesting is how many common threads can be found in these stories even though they come from vastly different cultures. Our activity today will help us draw these connections.