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Western University
Biology 1201A
Jennifer Waugh

What is a Theory? How did cheetahs evolve to run fast? – they had to chase after their prey – faster cheetahs survived and produced more offspring – they moved from a high density forest to flat lands and had to run faster – they had to compete with bigger and stronger animals for their prey Common vernacular: an untested idea or opinion; speculation Scientific Definition: an explanation of a set of natural phenomena, based upon proven or testable hypotheses and observations; theory tries to explain what we observe in nature based on testable concepts Examples: • Theory of Continental Drift – Pangaea • Kinetic Molecular Theory • Theory of Relativity • The Big Bang Theory  • Theory of Panspermia Verifiability – true verification would require a positive result in every instance; has to be good, testable, and tests must be able to prove theory wrong (theory you can’t prove wrong isn’t as strongly supported by evidence) Fallibility – “only when a theory could be wrong is it impressive that it survives testing and criticism” Karl Popper Is the following statement (i) verifiable and (ii) falsifiable? All swans are white. i. Not Verifiable – you’d have to gather ALL swans to check ii. Is Falsifiable – find ONE instance where the statement is false Historical Development of Evolutionary Thought Early Evolutionary Thought • Static classification and characterization ○ All creatures on Earth created once (by Earth of divine being) and remain the same; unchanging ○ Aristotle – the Scala natura (384-322BCE)  Argued that all species were fixed; once placed on ladder they didn’t change/move  Argued that you could rank all organisms on a ladder of intellect (increasing complexity) ○ Natural Theology (1700s)  Tried to understand God’s purpose for humans by studying classification of objects (merged Aristotle with story of how life was created in Genesis) ○ Carl von Linne- the Linnean system (1707-78)  Tried to classify species on Scale of Natura to understand God’s purpose  Recognized as father of taxonomy  “Deus creavit, Linnean dispousit” – God creates, Linne arranges • It’s time for a change ○ Le Comte du Buffon (1707-88)  Discovered vestigial traits –things that don’t have any apparent function for the organism based on its environment  Suggested that populations of species change over time, not actual species (stuck to static classification) ○ Erasmus Darwin (1731-1802)  Suggested same as le Comte du Buffon  Thought all organisms were created by one cause and then because of sensations, volitions, irritations, they were able to change, acquire new parts, and pass those on  No mechanism for evolution • Lamarckian evolution 11-10-19 ○ Jean-Baptiste Lamarck (1744-1829)  Species evolve to better fit their environment ○ HOW?  Orthogenesis – “perfecting principle” all organisms are trying to be best suited to environment (primitive  more complex) directional, decided, gradual change in organism to become more complex, perfect  Principle of use and disuse  Inheritance of acquired characteristics • Transformational theory of evolution ○ ○ As organism interacts with environment, they use or disuse something which changes characteristics and then those acquired characteristics are passed on when they reproduce ○ RA= reproductive age ○ Why do we still see simple forms? – Lamarck says they are spontaneously regenerated Many cave-dwelling organisms are blind and/or lack developing eyes. ○ Payne (1910) raised 49 generations of fruit flies in the dark. What do you think happened in this experiment? Why?  the
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