Ch. 15 – Theory of Evolution 15-1: History of Evolutionary Thought

What is Evolution?  An orderly succession of changes  Biological evolution The development of new types of organisms from preexisting types of organisms over time  Passing down hereditary traits “A process at work”

Idea of Darwin’s Time  In Europe in the 18 th century, most scientists thought that all species were permanent and unchanging  Furthermore, they thought that the Earth was only thousands – not billions – of years old  New evidence was introduced to prove these scientists wrong

Ideas About Geology  By the 1800s, scientist began studying strata (rock layers) to study fossils

Ideas About Geology  Georges Cuvier Presented evidence that some organisms in the past differed greatly from any living species and that some organisms become extinct Also found sudden changes in the kinds of organisms found in one rock stratum compared to the next Catastrophism  Idea that sudden geologic catastrophes caused the extinction of large groups of organisms at certain points in the past

Ideas About Geology  Charles Lyell Shared common ideas with Cuvier  Uniformitarianism  Geological processes that have changed the shape of Earth’s surface in the past continue to work in the same way  What does this mean?  If it took millions of years for the environment to change, so to would it take for organisms to change  Fits Darwin’s idea of evolution

Lamarck’s Explanation  Jean Baptiste de Lamarck ( ) Proposed a unifying theme of species modification  Populations of organisms change over time To explain how species changed, he hypothesized that acquired traits were passed on to offspring  One that is not determined by genes – acquired during the life of the parents from behavior or experience

Lamarck’s Explanation(cont.)  His hypothesis was easily disproved  The good news? Was the first to state that types of organisms change over time and that new types of organisms are modified descendants of older types  50 years later….Charles Darwin presented this same idea more convincingly

Darwin’s Ideas  Mid 1800s, Charles Darwin + Alfred Wallace independently proposed theories to explain how evolution takes place  Darwin’s name became more associated with evolutionary theory after he published his book, On the Origin of Species by Means of Natural Selection, in 1858  Two goals of book: Present evidence that evolution has occurred Explain that the variety + distribution of organisms are observable

Darwin’s Ideas  Descent with modification Every species – living or extinct – must have descended by reproduction from preexisting species and that species must be able to change over time Example:  Galapagos Island  Found 13 similar species of finches  The only difference between the 13 finches was their beaks  This implied that the finches shared a recent common ancestor

Darwin’s Ideas  Natural Selection Mechanism for descent w/ modification Four main parts of reasoning:  Overproduction  Each species produces more individuals than can survive to maturity  *Based on Thomas Malthus’ essay on human population*  Genetic Variation  The individuals of a population may differ in traits  Struggle to Survive  Individuals must compete for limited resources  Some adaptations may increase change of survival and reproduction

Darwin’s Ideas  Differential Reproduction  Organisms with the best adaptations are more likely to survive and reproduce  Over time, these adaptations become more frequent in the populations

Darwin’s Ideas  Nat. selection proposes that nature changes species by selecting traits The environment selects the favorable traits  Example: Peppered MothsPeppered Moths AKA “Survival of the Fittest” fitness An organism that can adapt to their environment or changes in the environment, will have a higher fitness  The ability to produce more offspring