MECHANISMS FOR EVOLUTION

Honors Biology

REVIEW

• Evidence for Evolution and Examples• What is Natural Selection?• How did Darwin develop theory of Natural Selection?

PATTERNS OF EVOLUTION

• Coevolution:– 2 or more species evolve in association with one

another– Predators and Prey– Plants and Pollinators– Bats and Flowers

PATTERNS OF EVOLUTION

• Convergent Evolution:– Organisms that look similar but are not related– Analogous features– Similar environments– Sharks and Dolphins

PATTERNS OF EVOLUTION

• Divergent Evolution– 2 or more related populations or species become

more and more dissimilar – Usually a response to new habitat– Can result in new species– Adaptive radiation– Artificial Breeding– Humans and Chimps

POPULATION GENETICS AND EVOLUTION

• What did Darwin know?– Environment is important– Competition for Resources– Natural Selection: Individuals with traits more

suitable for a particular environment are more likely to survive AND reproduce

• What did Darwin not know?– Where does variation come from

POPULATION GENETICS

• We now know that variation comes from genetics; no variation extinction

• Population genetics: study of evolution from genetic point of view

WHAT CAUSES VARIATION

• Need to think about variation in GENOTYPE– Mutation: change in DNA/chromosomes– Recombination: during meiosis– Random fusion of gametes

OTHER MECHANISMS FOR EVOLUTION

• Things that upset genetic equilibrium• Using Hardy Weinberg you can predict

genotypes; Only in hypothetical populations

MUTATION

• Change in DNA or chromosomes• Make new alleles for a trait• Many are harmful• Can be neutral (code for same amino acid)• Some are beneficial

MIGRATION/GENE FLOW

• Call it gene flow• Populations exchange genes• Increases within group variation• Decreases between group variation• DOESN’T HAVE TO BE MIGRATION

GENETIC DRIFT

• Occurs in small populations• Allele frequencies shift as a result of RANDOM

events• Coin Toss• Founders Effect; Bottleneck

NONRANDOM MATING

• Sexual Selection• Positive assortative mating – mate with

someone similar• Negative assortative mating: redheads!

NATURAL SELECTION

• Darwin and neoDarwinians believe is the most important way evolution occurs

• Types of Selection

STABILIZING SELECTION

• Average form are selected for• Lizards:– Predators caught slow small and large visible– Select for medium size

DIRECTIONAL SELECTION

• Individuals with an extreme trait are selected for

• Anteaters with long tongues

DISRUPTIVE SELECTION

• Individuals with either extreme are selected for

• Limpet shell color; light and dark on different surfaces

SEXUAL SELECTION

• Choosing mates based on traits• Intersexual Selection• Intrasexual Selection• Bird Color

SPECIATION

• If enough changes accumulate new species• Biological concept of species: organisms can

mate and produce fertile offspring; not just morphological (what they look like)

• Isolating mechanisms speciation– Geographic isolation– Reproductive isolation

SPECIATION

• Rates of speciation– Gradualism: species evolve gradually over time– Punctuated equilibrium: species go through times of fast change and slow or no change