Beyond Darwin16.3 and some 17 NotesCan an individual evolve?

Is evolution the survival of the fittest?

Is evolution predictable?

Today’s theory on evolution Recognizes that GENES are responsible

for the inheritance of characteristics Recognizes that POPULATIONS, not

individuals, evolve due to natural selection & genetic drift

Recognizes that SPECIATION usually is due to the gradual accumulation of small genetic changes

Modern Theory on Evolution

Major Terms Microevolution- traits changing over time

within a population Macroevolution- patterns of change that

cause new species to develop. Speciation – formation of a new species

Speciation• A Species is a group of populations

whose individuals have the ability to breed and produce fertile offspring. 

Formation of new species One species may split into 2 or more

species A species may evolve into a new species

– speciation. Requires very long periods of time

Genetic Equilibrium and Allele Frequencies

The genetic tendencies of a population are measured by the frequency of their alleles. In other words: the ratio of homozygotes vs.

heterozygotes (AA vs. Aa vs. aa) Genetic frequencies (as percentages) should

always add up to 1.0 (.28 AA + .61 Aa + .11 aa = 1.0)

Genetic Equilibrium = genetic frequencies do not change much in stable populations Larger populations are more stable than smaller ones.

Microevolution – small changes Natural Selection

An example of the type of Natural Selection

Directional selection favors individuals at one end of the phenotypic range. Most common during times of environmental change or when moving to a new area.

Stabilizing selection favors intermediate over extreme phenotypes. - Reduces variation and maintains the current average. - Example = human birth weights.Divergent selection favors extremes over intermediate phenotypes.

 - Occurs when environmental change favors both extreme phenotype.

  -Example = Galapagos lizards when explorers introduced dogs into the ecosystem. They only ate the medium sized lizards.

Galapagos lizards

Other reasons for Microevolution Migration

to different areas For food For mating Environmental changes

Gene flow - is genetic exchange due to the migration of fertile individuals or gametes between populations.

Other reasons for Microevolution Mate Choice – different depending on type of

organism.

Other reasons for Microevolution Mutation is a change in an organism’s

DNA and is represented by changing alleles. 

Mutations can be transmitted in gametes to offspring, and immediately affect the composition of the gene pool.

The original source of variation

• Genetic drift - the alteration of the gene pool of a small population due to chance.

Macroevoluion

Convergent Evolution – organisms that evolve to become more alike because they live in similar environments and have similar pressures.

Macroevolution

Coevolution Remember symbiotic relationships where two

very different species evolve together. Goby and the shrimp Ant and catepillars

Macroevolution

Adaptive radiation

Reproductive Isolation Some “Barrier” prevents two populations of a

species from breeding. This creates two distinct gene pools and may lead to speciation. Geological or geographic (mountains and rivers, etc.) Chronological – individuals reproduce at different

times Behavioral – mating rituals are not compatible

Geographic variation between isolated populations of house mice.

Normally house mice are 2n = 40. However, chromosomes fused in the mice in the example, so that the diploid number has gone down.

Extinction When a species fails to produce more offspring.

Scientist estimate that 99% of species that have lived on Earth are now extinct. The speed of extinction has increased with Modern Man’s altering the environment.

CAUSES: Environmental change

Natural Caused by humans

Deforestation/ loss of habitat pollution

Gradualism Small changes that build up over time

Punctuated Equilibrium The idea that evolution is not always slow but

that large changes in the environment will cause quick (relatively) emergence of new species.