Key concept :Evolution occurs in patterns • Evolution through natural selection is not random. • Natural selection can have direction. • The effects of natural selection add up over time.
Convergent Evolution • Defined: Describes evolution toward similar traits in unrelated species. • Survival advantage to a particular environment. • Ex: Tuna (fish) and dolphins (mammals). They are an unrelated species living in a similar environment, the ocean. • Faced similar evolutionary pressures.
Divergent Evolution red fox kit fox ancestor Kaibab Squirrel (Grand Canyon) • Defined: Describes evolution toward different traits in closely related species. • Cause: Different environments
Coevolution • Defined: Two or more species evolve in response to changes in each other • Evolutionary paths become connected • Both species receive benefits from the other as a result of adaptations. • Ex: Plants and Insects • Plants: provide insects with nectar • Insect: transfers pollen from one plant to another
Coevolution Continued… • Coevolution can occur in competitive relationships, sometimes called an evolutionary arms race. • Example: Crab vs. Snail & Bacteria vs. Humans
Evolutionary Arms Race Continued… Antibiotic Resistance Bad Good • Antibiotics: chemicals designed to kill bacteria • Produced by other microorganisms to fight bacteria • Antibiotic Resistance: Bacteria are adapting to the use of antibiotics • Overuse & misuse speeds up the process • Importance: Bacteria infections are becoming harder to treat
Most bacteria killed Strong Survive Bacterial Resistance Strong Reproduce
Species Can Become Extinct • Defined: The elimination of a species from Earth. • Mass Extinctions: • Cause: Catastrophic events • Ice Age, Meteorites • Very severe • Destroys many species at global level • Rare but much more intense • At least 5 mass extinctions in last 600 million years • Background Extinctions: • Cause:Local changes in environment • Forest fires, habitat destruction. • Less severe. • Affects a few species in a small area • Occur at roughly the same rate as speciation
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
How Fast Does Evolution Occur? To radiate = to s-p-r-e-a-d out • Adaptive radiation: A process of evolution where one species can split into a number of different species. • Ancestral species diversifies into many descendent species • Descendent speciesusually adapted todifferent (wide range of)environments