IV. The Process of EvolutionA. Two types of evolution

1. Macroevolution – any change of a species over time into another. Any changes or “long-term” trends at higher taxonomic levels (i.e. new genera, families, phyla)

2. Microevolution – A change in gene frequencies (i.e. alleles) within a pop. or species over time.

Ex. Overuse of antibiotics has selected for resistant microbes

Example (microevolution): light v. dark colored moths frequency due to change in env’t (i.e. color of tree trunk) industrial melanism

B. Causes of microevolution

1.Natural selection

a. gradualism – species evolve at a slow and constant pace

b. punctuated equilibrium – species evolve rapidly over short time then remain the same for long periods

2. Mutations – a change in an allele the origin of genetic variation

3. Gene Flow – the mov’t of alleles b/n populations due to migration of breeding indiv. Results in interbreeding

4. Genetic Drift – allele freq. change due to chance causes alleles to be lost from pop. small populations suffer (i.e. greater chance that rare alleles won’t contribute to make-up of next generation) ex. Coin toss:

toss 100x: probability is 50/50 of getting heads/tails toss 10x: better chance of getting 8 heads/2 tails

Genetic drift can be due to: a. bottleneck effect – dramatic decrease in alleles b/c of major disaster ex. Hunting in 1890’s reduced one elephant seal pop. to ~20 indiv. very little genetic variation 24 exact same proteins

b. Founder’s effect – 1. when a new pop. is started, the pioneers contain only a fraction of the total genetic diversity of original gene pool 2. also not likely to have all representations

5. Nonrandom mating Examples:

a. assortative mating – mate with someone w/ same phenotype (e.g. tall people)

b. sexual selection – mates are chosen on basis of particular appearance

C. Genetics of evolution (population genetics)

1. Gene pool – all the various alleles at every locus of every indiv. in a pop. the gene pool is defined by allele frequencies

2. Calculating gene pool frequencies the Hardy-Weinburg Principle

Hardy- Weinburg Principle states that the frequencies of alleles and genotypes in a population’s gene pool will remain constant (i.e. unchanging) over generations as long as there is:

1. no selection2. no mutations3. no gene flow4. no genetic drift5. random mating

If these conditions are met, the pop. is @ equilibrium

V. Speciation – the formation of a new species

So, what is the final result of changes in gene pool allele and genotypic frequencies?

A. Due to Isolation – any geographical, reproductive, or behavioral event preventing gene flow b/n populations

B. Modes of speciation

1. Allopatric – geographic separation prevents gene flow

Example of allopatric speciationDarwin’s finches (Galapagos Islands)

Adaptive Radiation – different species evolved from one common ancestral species

2. Sympatric – reproductive isolation w/o any geographic barrier results in polyploidy indiv. common in

flowering plants (e.g. sunflowers) rare in animal (but, orcas)

VI. Patterns of Evolution

1.Divergent – two species gradually become increasingly different

occurs when related species diversify to new habitats

Example: humans and apes

2. Convergent – When diff. species begin to share traits b/c of shared env’t example: whales (mammals), sharks (fish), penguins (birds)

3. Parallel – when two species evolve independently while maintaining the same level of similarity occurs b/n unrelated species that don’t occupy the same habitat example: marsupial v. placental mammals (give birth to live young)

4. Coevolution – Species that interact closely often adapt to one another. Ex. Hawk moth and Orchids