Natural Selection

How Changes in Organisms Can Be Explained

What did Darwin see?

What did Darwin see?

• The earth has been changing over time

• Living things have been changing over time

• Traits of organisms differed between islands

• Organisms had traits to fit environment

Finches in the Galapagos

•Finch species existed on mainland of South America

•Some relocated to Galapagos Islands 900 km away and became their own population

•Birds living in these new environments changed over time to create noticeable differences

•Colors

•Diets

•Body structures (beaks)

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What did Darwin see?

What did Darwin see?

Darwin’s Conclusions

• 1836 – 1858 (22 years)– Darwin studies observations– Writes a manuscript and puts in on a shelf.

• 1858 – Alfred Russel Wallace– Naturalist in studying in Malaysia– Reached same conclusion (evolution) as Darwin

• 1859 - Darwin finally published his ideas, The Origin of the Species

Darwin’s Conclusions• Descent with Modification

– Organisms split off from common ancestor and undergo changes (modifications) to fit their environmental conditions

• Natural Selection– The mechanism by which living things change– Individuals with traits that make them better

able to survive in their environments will leave more offspring than others

What is Evolution?• Process by which

today’s organisms have descended from ancient organisms

• Change over time

What is Natural Selection?

1. Individuals within a species vary.

2. These variations are inherited by their offspring.

3. Organisms produce more offspring than can possibly survive.

4. Offspring with the most favorable variations will survive and reproduce.  They are naturally selected.

5. Over time, offspring with the most favorable variation make up most of the population and may look entirely different from their ancestors.

Results of Natural Selection

Organisms with highest “fitness” will survive, reproduce, and pass on genes

• (remember Kerosene Karl)

– Fitness is an organism’s ability to survive and reproduce in its environment

Variation in fitness and reproduction of organisms leads to genetic and physical changes in populations

Fit and Stinky!!!

Results of Natural Selection

• Evolution by natural selection happens over millions of years

• Natural selection is not intentional!

How Many Species of Dogs Exist?

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Artificial Selection

Dog Breeding:

• Humans have been selecting for desired traits

• We hundreds of varieties of dogs!

• Only been happening for a few hundred years

Natural Selection

has been happening for billions of years!

Think of all the changes that have accumulated…