Objective:Understand how the mechanism of natural

selection causes evolution.

Bible: Earth is only a few thousand years old.

Aristotle: organisms don’t change◦ Scala naturae: ladder of

increasing complexity Linnaeus: taxonomy

(naming/classifying organisms) using genus and species

Cuvier: paleontologist discovered the deeper (older) the rock, the less like modern organisms fossils look.◦ Also found extinctions and

speciations.

Gradualism (slow, continuous change) Hutton: geologic features explained by graddual

erosion and deposition. Lyell: uniformitarianism – same geologic

processes are operating today as in the past, at the same rate.◦ Darwin proposed this also happened with organisms.

Lamarck (INCORRECT) Use and disuse: body parts used got

bigger/stronger; not used got small/disappeared.

These body parts could be passed on to offspring (inheritance of acquired characteristics).

Darwin’s Research From 1831-6 Charles Darwin traveled the

world on the HMS Beagle. Earthquakes moved rocks up Andes

mountains exposing sea creature fossils. Finches were unique to islands but also

were found on 2 or more.◦ They came from S. America and diversified

according to food found on the island they were on.

Published in 1859 stating:1. All organisms come from ancestors2. Mechanism for evolution is natural selection Populations change over generations passing beneficial

heritable traits to offspring.

Modifications (adaptations) that helped organisms survive and have more offspring with these modifications (descent).

Evolutionary trees could be made showing where fossils fit in with living organisms.

Hyracoidea(Hyraxes)

Sirenia(Manatees

and relatives)

Yea

rs a

goM

illio

ns

of y

ea

rs a

go Deinotherium

Mammut

Stegodon

Mammuthus

Platybelodon

Barytherium

Moeritherium

Elephasmaximus

(Asia)

Loxodontaafricana(Africa)

Loxodontacyclotis(Africa)

How natural selection works: Struggle for existence. Individuals survive due to heritable

phenotypic differences. These lead to changes in characteristics of

a population over generations.

Artificial Selection Humans change organisms by choosing

traits and breeding. Led Darwin to believe that natural selection

could work the same over longer periods of time thus produces drastic changes.

Terminalbud

Lateralbuds

Brussels sproutsCabbage

Flowercluster

Leaves

Cauliflower

Flowerandstems

Broccoli Wild mustard Kohlrabi

Stem

Kale

Summary of Natural Selection Individuals do not change. Only works on heritable traits. The same trait is not always favorable.

Guppies Size and age differences between

populations Different predators

◦ Killifish: preys on juveniles◦ Pike-cichlid: preys on mature

Result: sexual maturity in pops with killifish decreased.

Drug Resistant Bacteria◦ Staphylococcus aureus is commonly found on

people◦ Became resistant to:

penicillin in 1945 (2 years after it was 1st widely used) methicillin in 1961 (2years after it was 1st widely used)

◦ Methicillin inhibits a protein in bacteria’s cell walls MRSA uses a different protein and is now pathogenic.

◦ MRSAs are now resistant to many antibiotics12,750,000

2,500,000

2,250,000

2,000,000

1,750,000

1,500,0001,250,000

1,000,000

750,000

500,000

250,000 base pairs

Chromosome map of S. aureus clone USA300

Key to adaptations

Methicillin resistanceAbility to colonize hosts

Increased disease severityIncreased gene exchange(within species) andtoxin production

Evidence for Evolution• Homology: similarities resulting from common ancestry

– Comparative Anatomy– Homologous: same structure different function– Vestigial: remains of structures that have no current

function– Molecular: same DNA/RNA/amino acids

Human Cat Whale Bat

Homologies◦ Comparative embryology reveals anatomical

homologies not visible in adult organisms

◦ Homologies form nested patterns in evolutionary trees

◦ Evolutionary trees can be made using different types of data, for example, anatomical and DNA sequence data

Pharyngealpouches

Post-analtail

Chick embryo (LM) Human embryo

Convergent Evolution◦ The evolution of similar (analogous) features in

distantly related groups Analogous traits arise when groups independently

adapt to similar environments in similar ways◦ Convergent evolution does not provide

information about ancestry

Sugarglider

Flyingsquirrel

NORTHAMERICA

AUSTRALIA

The Fossil Record◦ The fossil record provides evidence of the extinction

of species, the origin of new groups, and changes within groups over time

◦ Fossils can document important transitions◦ EX: the transition from land to sea in the ancestors of

cetaceans

Other even-toedungulatesHippopotamuses

†Pakicetus

†Rodhocetus

†Dorudon

Livingcetaceans

Commonancestorof cetaceans

Millions of years ago70 Key60 50 40 30 20 10 0 Pelvis Tibia

Femur Foot

Biogeography: closely related species are geographically close.◦ Earth’s continents were formerly united in a

single large continent called Pangaea, but have since separated by continental drift

Study of molecular basis of genes and gene expression

Universality of genetic code

Conservation of amino acid sequences in proteins such as hemoglobin