Natural Selection

Species Vary Globally Similar animals (different species) , different locations in world, similar habitats Rheas Ostrich Emu South America Africa Australia

Species Vary Locally Different islands had different varieties of Finches. Their beak shape differed based on what their diet, (fruit, nuts, insects, etc).

Species Vary Over Time Some fossils of extinct animals were similar to living species. The long-extinct glyptodont, a giant armored animal similar to the armadillo.

Creates Natural Selection

1. There is variation within a. population (from inherited traits – 1. There is variation within a population (from inherited traits – mutations!)

Some variations are favorable

More young are produced than can survive (many die of disease, starvation, predation)

4. Those most likely to survive and reproduce are the individuals with the favorable variations (and their offspring are more likely to inherit those favorable variations as well)

5. Over time, changes can accumulate and populations can change.

Selection Pressures – things in an environment that make one variation favorable over another

Gene Pool – all of the genes in a population

Common Descent – all species, living and extinct, are descended from ancient common ancestors

3 Types of Natural Selection Directional Selection – population shifts towards one extreme

2. Disruptive Selection – population moves towards both extremes

3. Stabilizing selection – population narrows to center