Reconstructed Skeleton                   Evolution                                 Reconstructed Skeleton of Lucy Lucy stood some 3.5 feet tall and lived 3.0 to 3.5 million years ago  

Darwin’s Theory of Evolution Evolution is the progressive change in organisms over time. It is the process by which modern organisms have descended from ancient organisms. A scientific theory is a well-supported testable explanation of phenomena that have occurred in the natural world. Like all theories, it is based on evidence, subject to inferences, and can change depending on new evidence.

Darwin Darwin video – PBS What Darwin Never Knew

How did Darwin come up with his theory?

Voyage of Beagle Dates: February 12th, 1831 Ship: H.M.S. Beagle Destination: Voyage around the world. Findings: evidence to propose a revolutionary hypothesis about how life changes over time

Voyage of the Beagle

Patterns of Diversity Darwin visited Argentina and Australia which had similar grassland ecosystems. those grasslands were inhabited by very different animals. neither Argentina nor Australia was home to the sorts of animals that lived in European grasslands.

Living Organisms and Fossils Darwin collected the preserved remains of ancient organisms, called fossils. Some of those fossils resembled organisms that were still alive today. Glyptodon Armadillo

Living Organisms and Fossils   Others looked completely unlike any creature he had ever seen. As Darwin studied fossils, new questions arose. Why had so many of these species disappeared? How were they related to living species?

The Galapagos Islands The smallest, lowest islands were hot, dry, and nearly barren Hood Island-sparse vegetation The higher islands had greater rainfall and a different assortment of plants and animals Isabela- Island had rich vegetation.

The Galapagos Island Darwin was fascinated in particular by the land tortoises and marine iguanas in the Galápagos. Giant tortoises varied in predictable ways from one island to another. The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

Animals found in the Galapagos Land Tortoises Darwin Finches Blue-Footed Booby Marine Iguanas Finches

The Journey Home Darwin observed that characteristics of many plants and animals vary greatly among the islands Hypothesis: Separate species may have arose from an original ancestor

Mutations lead to genetic Variation Mutations are changes in DNA Mutations are the raw material of evolution. Mutations provide new alleles in a species.

Mutations are Random Mutations are random. Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not “try” to supply what the organism “needs.” In this respect, mutations are random—whether a particular mutation happens or not is unrelated to how useful that mutation would be.

Not all mutations matter to evolution. Since all cells in our body contain DNA, there are lots of places for mutations to occur; however, not all mutations matter for evolution. Somatic mutations occur in non-reproductive cells and won’t be passed onto offspring. If a mutation alters the DNA in a gamete, it can be passed on. In order for a mutation to be subject to natural selection, it must be expressed in the phenotypes of individuals. 

Evolution by Natural Selection Darwin’s main points: Variation - Individuals of a species vary in physical characteristics, these characteristics can be passed from generation to generation. The Struggle for Existence - members of each species have to compete for food, shelter, and other life necessities

Evolution by Natural Selection Survival of the Fittest - Some individuals are better suited for their environment, they are better able to survive and reproduce Adaptation - Natural selection causes a population of organisms and a species to become adapted (exhibit characteristics that increase survival) to the environment. The process is slow, but each subsequent generation includes more individuals that are better adapted to the environment.