1. KEY CONCEPT Evolution occurs in patterns.

2. Evolution through natural selection is not random.
Natural selection can have direction.
The effects of natural selection add up over time.

3. Convergent evolution describes evolution toward similar traits in unrelated species.
- Example: Dolphins, which are mammals, and sharks, which are fish, have evolved similar tail fins, as each has adapted to similar environmental conditions.

4. Divergent evolution describes evolution toward different traits in closely related species.
Analyze: How do convergent and divergent evolution illustrate the directional nature of natural selection?
Infer: Are the shells of turtles and snails examples of convergent or divergent evolution? Explain.
ancestor
red fox
kit fox
Fig. The kit fox and the red fox evolved from a common ancestor while adapting to different environments.

5. Species can shape each other over time.
Two or more species can evolve together through coevolution.
evolutionary paths become connected
species evolve in response to changes in each other
Example: the hawk moth and the orchid

6. Coevolution can occur in beneficial relationships.
Fig. The relationship between this ant and the acacia plant has developed through coevolution. The ant lives inside the hollow thorn and protects the acacia by stinging any potential predators.

7. Coevolution can occur in competitive relationships, sometimes called evolutionary.
Predict: What do you think will happen in future generations of crabs and snails?

8. Species can become extinct.
Extinction is the elimination of a species from Earth.
Background extinctions occur continuously at a very low rate.
occur at roughly the same rate as speciation
usually affects a few species in a small area
caused by local changes in environment
Fig. Native to Portugal and Spain, the Iberian lynx is the world’s most endangered feline. The World Wildlife Federation estimates that there may be fewer than 200 individuals remaining in the wild.

9. Mass extinctions are rare but much more intense.
destroy many species at global level
thought to be caused by catastrophic events
at least five mass extinctions in last 600 million years
Compare and Contrast: What are the differences and similarities between background and mass extinction?

10. Speciation often occurs in patterns.
A pattern of punctuated equilibrium exists in the fossil record.
theory proposed by Eldredge and Gould in 1972
episodes of speciation occur suddenly in geologic time (bursts of evolutionary activity)
followed by long periods of little evolutionary change (stability)
revised Darwin’s idea that species arose through gradual transformations

11. Many species evolve from one species during adaptive radiation.
ancestral species diversifies into many descendent species
descendent species usually adapted to wide range of environments
Synthesize: The adaptive radiation of mammals followed the extinction of the dinosaurs. How do these events support the theory of punctuated equilibrium?