Natural Selection Notes

November 10, 2014

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Charles Darwin

• British scientist in 1800's

• Traveled around the world in the Beagle

• Visited the Galapagos Islands

Galapagos Islands

• Studied finches (birds)

• Noticed lots of species and variation within species

Definitions

• Species: a group of similar organisms that can mate with each other and produce fertile offspring

• Variation: Any difference between individuals of the same species

WHY???

Darwin wondered why there are so many species and so much variation?

Darwin believed it was because of evolution

Evolution: change in a species over time

How do we know life has changed over time?

Fossil Record: The millions of fossils that scientists have collected

-There are many fossils of organisms that are no longer found on Earth (extinct)

Extinct = no longer found on Earth

Direct observations: We have observed species go extinct and as well as changing

- Examples: Dodos (birds) went extinct, fruit flies and bacteria change

Natural Selection

• Darwin did not discover evolution, he discovered HOW evolution occurs

• In 1859 Darwin wrote a book called The Origin of Species

• In this book he said that evolution occurs because of Natural Selection

Natural Selection

• Natural Selection: Organisms that are better adapted to their environment are more likely to survive and reproduce

• “Survival of the Fittest”

• Fit: bested adapted

Natural Selection

1. Genetic mutations produce variation within a population

2. The environment "selects" which organisms survive and reproduce based on fitness (matching the environment)

3. Organisms that have the variations that fit the environment reproduce and pass on those variations

4. Organisms with unfavorable variations die

Natural Selection

• Environmental pressures that can cause populations to change (evolve):

Abiotic: Biotic:Water FoodSoil CompetitionPollution CrowdingTemperature PredatorsShelter Disease

Variation and Natural Selection

• Variation: Any difference between individuals of the same species

• Some variations help organisms survive and reproduce better than others; these variations are called adaptations

• Adaptation: a genetic trait that helps an organism survive and reproduce

Giraffe's Neck

• Fossils have been found that show giraffes once had shorter necks

• Scientists asked: why did the neck length change?

Giraffe's Neck

• A French Scientist named Jean Baptiste Lamarck said that the necks grew longer because the giraffes stretched to reach leaves in trees and then they passed on their longer necks to their children

Lamarck's Hypothesis

Is a stretched neck an inherited or acquired characteristic?

Can acquired characteristics (example: tattoo, broken bone, good grades) be passed on to offspring?

NO!!!

Lamarck was WRONG!!!

How it Happened:Natural Selection

• A. There was variation in neck length due to mutations

• B. Giraffes with shorter necks couldn't reach as much food, so they died sooner

• C. Giraffes with longer necks could reach more food, live longer, and pass on their longer neck trait

• Over time this leads to longer and longer necks because of the large amount of food (leaves) in tall trees!

Artificial Selection

• Sometimes the environmental pressure that causes selection is not natural; it is human!

• Artificial Selection: Humans choose which organisms live and reproduce

• Also called Selective Breeding

• This is how we have produced different dog breeds, larger vegetables (corn), etc.