Patterns in Evolution Divergent Evolution Defined closely related

Patterns in Evolution

Divergent Evolution • Defined: closely related species become increasingly different • Cause: Different environments • Ex: Red fox (forest) vs. Kit fox (desert)

Convergent Evolution • Defined: different species evolve similar traits due to similar habitats • Survival advantage to a particular environment • Ex: Tuna (fish) and dolphins (mammals) – Unrelated species with a similar environment (ocean) – Faced similar evolutionary pressures

Dragonfly Convergent Evolution

Coevolution • Defined: 2 or more species evolve in response to changes in each other • Ex: Plants and Insects – Plants: provide insects with nectar – Insect: transfers pollen from one plant to another

Hummingbirds: Beak shape depends on flower shape

Extinction • Background Extinctions: – Less severe; local level – Forest fires, habitat detruction • Mass Extinctions: – Very severe; global level – 5 identified in earth’s history (volcanic activity, meteor strikes)

How Fast Does Evolution Occur? • No exact time frame • Gradualism: slow & steady change of 1 species into another – Small changes continually build • Punctuated Equilibrium: Rapid periods of evolution – Due to sudden environment change – Ex: Mammal diversity exploded after dinosaur extinction • Examples of both models exist

Gradualism of the Horse