Shaping Evolutionary TheoryChapter 15

Section 3

Hardy-Weinberg principleThis principle suggest when allelic

frequencies remain constant, a population is in genetic equilibrium.

Shows mathematically that evolution will not occur in a population unless allelic frequencies are acted upon by forces that cause change

Genetic Drift any change in the allelic frequencies in a population that is due to chance

Founder effectThe founder effect can occur when a small sample of a population settles in a location separated from the rest of the population

BottleneckBottleneck occurs when a population

declines to a very low number and the rebounds

Researchers think that cheetahs in Africa experienced a bottleneck 10,000 years ago and then another one about 100 years ago

Directional SelectionIf an extreme version of a trait makes an

organism more fit, directional selection might occur

The peppered moth exists in two forms light colored and dark colored

Industrial pollution favored the dark colored moths. The darker moth matched the sooty background of its tree habitat, therefore it was harder for predators to see

Disruptive selectionIs a process that splits a population into two

groups

Snakes living on the mainland shores inhibit grasslands and have mottled brown skin. Snakes inhabiting rocky island shores have gray skin

Each is adapted to its particular environment

Snake with intermediate coloring would be disadvantaged because it would be more visible to predators

Sexual SelectionThis type of selection often operates in

populations where males and females differ significantly in appearance

Males are usually the largest and most colorful of the populationDarwin wondered why some qualities

of sexual attractiveness appeared to be the opposite of qualities that might enhance survival

SpeciationAllopathic speciation a physical barrier

divides one population into two or more populations

Geographic barriers can include: mountain ranges, channels between islands, wide rivers, lava flows

Grand Canyon

Sympatric speciation a species evolves into a new species without a physical barrier

Several insect species have evolved via sympatric speciation

Patterns of EvolutionAdaptive radiation is also called divergent evolution, can occur in a relatively short time when one species give rise to many species in response to the creation of new habitat or another ecological opportunity

Co-evolution many species evolve in close relationship with other species. The relationship might be so close that the evolution of one species affects the evolution of other species

Convergent evolution unrelated species evolve similar traits eve though they live in different parts of the world

Convergent evolution occurs in environments that are geographically far apart but have similar ecology and climate

Class WORK…Answer these questions and turn them in!

1. How can you observe how species have changed over time?

2. What are the four principles of natural selection?

3. Why is understanding natural selection key to understanding evolution?

4. What similarities and differences exist between homologous structures and analogous structures?

5. Compare mimicry and camouflage