The Theory of Evolution
Darwin's Theory of Evolution by Natural Selection
What is evolution?
Evolution is considered the "Unifying Theory" of biology because it helps us understand the diversity of life on the planet.
For example, why are lions and tigers so similar, but live on different continents.
What is a theory? - Statements of models that have been tested and confirmed.
- Explains data and observations
- Can be used to make predictions
- Are not absolute and can be changed
Questions can be answered using established theories.
Example: Why do so many different animals have the same bone pattern in their limbs?
Homologous structures - similar body parts, but different functions
Predictions can be made using theories.
Example: Would a penguin lay eggs?
Answer: Penguins are birds, they lay eggs
Main Ideas of Evolution
- change in frequency of traits in a population over time
- organisms come from pre-existing organisms
*Frequency refers to the number of organisms that have a particular trait.
Evolution by Natural Selection
Darwin was a naturalist who
observed many species.
He is famous for his trips to the Galapagos Islands,
his observations of the finches (and other animals)
He wrote:
"The Origin of Species"
His idea of natural selection is sometimes referred to as the "survival of the fittest."
Observations from the Galapagos
- Only place where marine iguanas are found
- Blue-footed booby unique to the islands
- Several species of finches
- Galapagos penguin
- Galapagos tortoises
Darwin's
Finches:
Darwin noted that all the finches on the galapagos island looked about the same except for the shape of their beak. His observations lead to the conclusion that all the finches were descendents of the same original population. The shape of the beaks were adaptations for eating a particular type of food (Ex. long beaks were used for eating insects, short for seeds)
- Different shaped beaks
- Adapted for different food sources
- All from a common ancestor
- Process of adaptive radiation
Video on Galapagos Finch Evolution with Student Guide
Main Points from "The Origin of Species"
- Species produce more offspring than can survive
- Individuals compete for resources or mates
- Those with the best traits produce the most offspring (which will have those traits)
- All living species descended from other species - Common Descent
Use the VIDA Chart to explain evolution in model organisms
1. Variation exists among individuals
in a species.
2. Individuals of species will compete for resources (food and space)
3. Differential survival and reproduction
4. Adaptation: Individuals that had advantageous variations are more likely to survive
and reproduce.
Model Organisms
Tuskless Elephants in Africa
Lizards in the Bahamas
Anoles in the Caribbean
Artificial selection in domestic dogs
Next: What is the Evidence for Evolution?
Evolution Activities
Galapagos Finches (HHMI Video)
Evolution by Natural Selection (VIDA) Elephants
Evolution of Rabbits and Wolves (VIDA)