Darwin’s Theory of Evolution Chapter 16 Darwin’s Theory of Evolution

Darwin’s Voyage HMS Beagle – around world Studied various specimens Saw 3 patterns of diversity

1. Species vary globally Saw that different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe. Ex. Flightless birds – rheas (SA), ostriches (Africa), emu (Australia)

2. Species vary locally Saw that different, yet related, animal species often occupied different habitats within a local area. Ex. Tortoises, finches

3. Species vary over time Saw that some fossils of extinct animals were similar to living species. Ex. Glyptodont & armadillo

Darwin’s Theory of Evolution Evolution = genetic change in a species over time Modern organisms evolved over long periods of time through descent from common ancestors. all species—living and extinct—are descended from ancient common ancestors.

Darwin influenced by other’s info Lyell and Hutton – - said Earth is very old, and geologic processes that changed Earth in the past are the same as now

Lamarck – - similar species descended from a common ancestor - “use it or lose it” - to explain changes, said acquired traits were passed on to offspring Acquired traits = traits that arose during lifetime, not determined by genes

Malthus – - humans produce too many offspring to sustain them all - other factors (war, disease, etc.) helped out

Artificial selection = process in which nature provides the variations, and humans select those they find useful.

Evolution by Natural Selection The Struggle for Existence Variation and Adaptation Survival of the Fittest Fitness = how well an organism can survive and reproduce in its environment.

2 Variation and Adaptation There is variation in nature, and certain heritable variations—called adaptations—increase an individual’s chance of surviving and reproducing. In this population of grasshoppers, heritable variation includes yellow and green body color. Green coloration is an adaptation: Green grasshoppers blend into their environment and so are less visible to predators. 1 The Struggle for Existence Organisms produce more offspring than can survive. Grasshoppers can lay over 200 eggs at a time. Only a small fraction of these offspring survive to reproduce.

3 Survival of the Fittest Because their green color serves to camouflage them from predators, green grasshoppers have a higher fitness than yellow grasshoppers. This means that green grasshoppers survive and reproduce more often than do yellow grasshoppers in this environment. 4 Natural Selection Green grasshoppers become more common than yellow grasshoppers in this population over time because: (1) more grasshoppers are born than can survive, (2) individuals vary in color and color is a heritable trait, and (3) green individuals have a higher fitness in their current environment.

Natural Selection = the process by which organisms with variations most suited to their local environment survive and leave more offspring.