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Lecture 15

Biology 1001A Lecture 15.pdf

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Western University
Biology 1001A
Beth Mac Dougall- Shackleton

Biology 1001A | 2012 LECTURE NOTES Lecture 15 Why Evolution is True –––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––– What Do People Believe? - “Humans evolved from earlier species of animals” - many people do not agree with this statement - the majority of Americans (46%) believe solely in creationism, with only 15% believing in evolution alone Evolution as a Fact and a Theory - evolution is “only a theory”, but what do scientists mean by “a theory” ? - a theory is defined generally as “an assumption bases on limited knowledge...a conjecture” - but in science, a scientific theory is “a coherent set of testable hypotheses that attempt to explain facts about the natural world” - atomic theory, germ theory of infectious disease, gravitational theory, etc are not just ideas, they have been tested and found to be true - what do scientists means when we say that something is “true” ? - “an assertion for which there is so much evidence that it would be perverse to deny it” – S.J. Gould, Evolutionary Biologist, Harvard University - only willful ignorance could allow the theory to be denied - theories “graduate” to fact-hood after repeated testing fails to falsify them - assertions that cannot possibly be falsified are not scientific - a theory must be falsifiable, therefore the “flying spaghetti monster” theory is not accepted What is The Theory of Evolution ? i) Evolution Happens - change in allele frequencies in a population, between generations - evolution may happen as a result of natural selection ii) Most Evolution is Gradual - tiny incremental changes from one generation to the next - there were no “macro-mutation” that caused major phenotypic changes - there should therefore be many transitional organisms between a starting point and a final organism - the idea of gradualism is controversial, even among evolutionary biologists because fast evolution is possible in organisms such as viruses and bacteria iii) Speciation Happens - we went from LUCA because of speciation to many different species inhabiting the biosphere - if speciation had not happened, evolution would still have occurred, but only one species would exist at one time iv) All life is related through common ancestry - the ancestry of any organism can be traced back to identify MRCAs Biology 1001A | 2012 - all li
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