EVOLUTIONDarwin’s theory of evolution by natural selection – On

the Origin of Species – 18591. Organisms produce more offspring than can

survive (Malthus)2. Resources are limited3. Individuals must compete for these resources4. Variation exists in populations5. Natural selection – individuals with beneficial traits

(adaptations), more likely to survive, leave more offspring

“Fitness” - # of fertile offspring produced is the measure

6. Adaptations passed onto next generation

Mechanisms of EvolutionMacroevolution – large scale, major change

-new trends, new speciesMicroevolution – changes of gene

frequencies within a population

Genetic variation–raw material for evolutionGene pool – sum of all alleles of all genes of

all individuals in a population*A change in gene pool evolution

Allele FrequenciesWhat can change them?

1. Mutation2. Migration – immigration or emigration3. Genetic drift – in small populations

- random loss of alleles4. Non random mating –if only certain individuals mate5. Selection - artificial (people choose) OR

- natural (environment selects)

*Natural selection is the most powerful –the only one that adaptive change

Hardy-Weinberg Principle-If none of above occurs, allele frequencies will not

changeresult is genetic equilibrium

p2 + 2pq + q2 = 1

p – frequency of one alleleq – frequency of the other

p + q = 1

(example on board)

Evidence for EvolutionMicroevolution examples:

-peppered moths-sickle cell anemia + malaria-the lethal sickle cell allele remains in high frequency where malaria occurs-recent changes in finch beaks-guppies (see graphic)

Macroevolution examples:-paleontology (fossils)-comparative anatomy :homologies, vestigial structures-embryology-biogeography – convergent evolution-biochemistry – similarities in proteins - nucleotide sequences

Sources of variation in populationsNatural selection acts on variation1. Mutation – only sources of new variation (new alleles)

2. Genetic recombination (sexual reproduction)-crossing over

-independent assortment

-random gamete joining (fertilization)

3. Diploidy – 2 copies of each gene-can have 2 different forms (alleles)

-maintains diversity

4. Symbiosis-endosymbiosis, lichen, etc.

The Origin of SpeciesSpeciation, Macroevolution

Species – definition?

Isolation:

-populations become separated (one way or another)

-gene pools now isolated

-each gene pool changes over time

-each population becomes distinct species

Isolating MechanismsPrezygotic (Pre-mating):

1. Geographical – physical separation

2. Ecological – distinct habitat or niches within region

3. Behavioral

4. Temporal – reproduction occurs at different times

5. Mechanical – mating is physically impossible

6. Prevention of gamete fusion

-sperm and egg incompatible

Postzygotic:

1. Embryo dies

2. Hybrid weakness

3. Hybrid sterility

Divergent Evolution

1 species 2 or more species

Adaptive radiation: -1 common ancestor cluster of closelyrelated species eg. Darwin’s finches Placental mammals

Hybridization and Polyploidy – can create new species in plants

Types of Selection

Sexual Selection

-when one gender (usually males) competes to mate with the other gender

-often females choose mates

-selection is for (examples):

-large body

-horns, antlers

-colorful plumage

-certain behaviors

Primate EvolutionProsimians (40 million years ago):

-grasping fingers and toes-binocular vision-lemurs are modern prosimians

Apes, monkeys-monkeys – even better vision

-opposable thumb-complex social behavior -learning (extended parental care) -large brains

-apes – hominoids (15 million years ago)Hominids -humans and extinct ancestors - bipedal, larger brains (extensive use of tools, language)

-Australopithecus

-Homo habilis

-Homo erectus

-Homo sapiens (500,000 years ago)