Download Natural Selection PPT WS

Natural Selection (Darwin’s Mechanism)
Natural Selection – the process by which organisms that are better suited to an environment survive and reproduce in
greater number than those less suited.
What causes Natural Selection? _____________________________________
Steps of Natural Selection
1.
2.
3.
4.
5.
Examples of Natural Selection
1.
2.
3.
Discussion Questions:
1. According to Natural Selection, explain why human over population exists?
2. Is the human species still evolving? Explain.
Speciation (Steps to a New Species)
Speciation – The formation of a new species by the change of allele frequency (traits) due to natural selection.
Steps of Speciation
1.
What could cause separation?
2.
3.
Divergence – the accumulation of differences between populations or species.
Species – a group of organisms that can interbreed and produce fertile offspring.
Examples of Speciation
1. Fruit fly experiment (sugar diet vs. starch diet)
2. Darwin’s Finches
3. Iguanas on Caribbean Anguilla (1995 hurricane)
Factors Contributing to Speciation
Isolating Mechanisms – Genetic differences that prevent breeding between two species (helping
to cause speciation). This can happen before or after mating.
Pre-mating Examples – mating rituals, behaviors, songs or calls, mating times (seasons)
Post-mating examples – hybrids from 2 species mating are usually sterile (genetic differences)
Genetic Drift – Loss of genetic variation (alleles) brought about by chance, not adaptation.
Usually occurs in small populations. Example: various Endangered Species
Founders Effect – Loss of genetic variation due to an isolated small founding population (could
contain some rare variations (alleles) making the gene pool different from the original).
Example: Amish (founded by small group of German immigrants; also Iguanas on Anguilla
Pace of Evolution
Gradualism - suggests that evolution occurs slowly over time and includes many transitions
Punctuated Equilibrium – suggests that evolution occurs in short bursts followed by long
periods of stasis (no evolution)