Beginnings of Modern Evolutionary Thought Charles Darwin hypothesized that species were modified by natural selection. Natural Selection- organisms best suited for their environment reproduce more successfully Over many generations, the proportion of organisms with favorable traits increases in a population.

How did Darwin Come up with his hypothesis? Spent 5 years on a ship called the Beagle and sailed around the world and made various stops When the ship stopped in a new place, he would collect specimens and keep careful records of his observations

Darwin’s Theories Descent with modification- newer forms of life are actually modified descendents of older species All species had descended from one or a few original types of life Based this on what he saw with the finches from the Galapagos Islands

What other scientists influenced Darwin? Thomas Malthus- studied populations -found that populations can double or grow exponentially - Darwin noticed that most populations did not grow exponentially because environmental factors limit growth

Because of Malthus….Darwin came up with the following: Fitness- how well an organism does in an environment defined by reproductive success An individual with high fitness is well adapted to its environment and reproduces more successfully (survival of the fittest)

-A population of organisms adapt to their environment as their proportion of genes for favorable traits increases -Organisms don’t select traits, environments do! -If the environment changes so fast that the organisms can’t adapt quickly enough, mass extinctions occur.

Alfred Wallace He unknowingly came up with the same theory of evolution as Darwin He asked Darwin to read his findings and once Darwin saw how similar his thoughts were to his own he know he couldn’t put off publishing his findings anymore.

Lamarck He believed that acquired traits were passed on to offspring Acquired traits aren’t determined by genes, they are something that arises during the organism’s lifetime as a result of behavior or experience

Lamarck thought that a lizard that didn’t use its tail would have offspring that would have a smaller tail. He was the first to say that organisms change over time, descending from older, similar organisms

Lamarck’s “Use/Disuse Theory”

Charles Lyell Wrote a book called “Principles of Geology” which was centered around the gradual change of the earth -ex: in Lyell’s book, he talked about how a valley could have been formed by the gradual weathering of the earth by a river Darwin applied this knowledge of the earth to organisms