Evolution

3/27/12

• Objective: Introduce origins theories

• Do Now: Hand in popular science questions

• Do Later: Read sections 13.1-3

Diversity of life

• Estimated 10 million species on earth– Phylogenetic trees show relationships

Origins Theories

• Lamarck– Spontaneous generation• Simple organisms are more recent• Complex organisms are older, gained complexity over

time

– Theory of Acquired Characteristics• Characteristics acquired by parents get

passed on to offspring

Origins Theories

Origins Theories

• Catastrophism– Rapid, catastrophic events shape

geology and extinction

• Gradualism– Slow change of geologic features

and life forms over time

Georges Cuvier

Charles Lyell

Origins Theories

• “Descent with modification”– Species have natural variation– Certain characteristics are favored over time

Natural Selection

• Condition 1: Variation– Populations must have variation in traits for

selection to occur

Natural Selection

• Condition 2: Competition– “Survival of the fittest”• Scarce resources, avoiding predators, etc.

– Only the best adapted species survive

Natural Selection

• Condition 3: Inheritance– Favorable traits are passed on to offspring– Genetic inheritance

Natural Selection

• Theory of Natural Selection– Heritable traits that confer an advantage in

survival and reproduction will increase in frequency in a population.

– Gradually a population will change as a result of natural selection.

Artificial Selection

• Selection performed by a conscious agent. – Dog breeding– Crop selection

4/2/12

• Objective: To examine speciation and evidence for natural selection

• Do now: – Discuss with a partner – What is a species? – Come up with a definition in pairs

• Do later: Read 13.5-6 in text– On separate paper: Pg. 275 #1, 3-7, 12

Species

• A species is a group of organisms that are able to interbreed and produce fertile offspring.

Mules are the offspring of a male donkey and a female

horse. They are sterile.

Hybrid Species

Zebra + horse zebroid (sterile)

Tiglons can occasionally reproduce with difficulty.

Speciation

• How do new species come to be (speciation)?– 1) Population is separated– 2) Each population changes due to natural

selection– 3) Differences accumulate to make interbreeding

impossible

Evidence for Natural Selection

• Biogeography– Geographic distribution of species

Why do all marsupials live in Australia?


• Homologous Structures– Anatomically similar structures in groups of

related organisms– May serve different functions


• Molecular Biology– DNA sequencing can confirm the relationship

between two species• Few genetic differences = closely related• Many genetic differences = distantly related

98.5% similar

4/3/12

• Objective:• Do Now: – Pick two evidences for evolution and explain (in

writing) how they show “descent with modification”. (3 minutes)

• Do Later:


• Vestigial Structures– Structure that is no longer used in an organism– Artifact of a useful structure in an ancestor

Vestigial Structures

• Whale pelvis

Vestigial Structures

• Human Coccyx

Vestigial Genes

• Vestigial genes – organisms have genes in their DNA that are no longer active

• Chicken teeth– Genes for teeth can be

turned back on in chickens

Transitional forms

• Fossil evidence of an intermediate form between a present day species and an ancestor.

Transitional Forms

• Archaeopteryx – transitional form between dinosaurs and modern birds

Archaeopteryx – between dinosaurs and aves (birds)

Transitional forms

• Tiktaalik– Transitional form between aquatic and land

animals– “lobe finned fish”

Transitional Forms

Basilosaurus – intermediate between land mammals and whales

whale

Comparative Embryology

• Early stages of development are similar across the animal kingdom

4/6

• Objective: To discuss pesticide and antibiotic resistance

• Do later: Popular Science – Pesticide and antibiotic resistance

Pesticide Resistance

• Application of pesticides selects for pesticide resistance

Red = pesticide resistant

White = wild type (‘normal’)


• Colorado Potato Beetle– Agricultural pest – Resistant to all major classes of insecticides


• Can you think of any ways to combat pesticide resistance? – Pesticide rotation

– Natural predators

– Diversifying crops

The fungus Beauveria bassiana is toxic to many beetles but non-toxic to humans

Diversifying crops can limit the spread of pests

Antibiotic Resistance

• Use of antibiotics selects for antibiotic resistant bacteria.

– Drug resistance evolves over time.


• Methicillin-Resistant Staph Aureus (MRSA)– “Staph infection”– Resistant to many classes of anti-staphylococcus

drugs


• Extensively Drug Resistant Tuberculosis (XDR-TB)– Lung disease

– Resistant to three or more major anti-TB drug classes

– High mortality (50% +)


• Solutions? – Limit prescription of antibiotics

– Limit use of antibiotics in agriculture

– Use full prescriptions

– Vary prescriptions

4/17/12

• Objective: To examine varieties of selection

• Do Now: – With a partner, describe the differences between

natural selection, artificial selection, and sexual selection. Provide an example of each.

• Do later: – Read 13.13 and 13.17 in text

Stabilizing Selection

• Selection that favors intermediate phenotypes

Stabilizing selection regulates birth weight

Directional Selection

• Selection that favors extreme phenotypes in one direction

Peppered moths

Disruptive Selection

• Selection that favors extreme phenotypes in both directions

Galapagos iguanas

Practice time!

• With a partner, come up with an example of stabilizing and directional selection.

• Challenge: Can you think of an example of disruptive selection?

Popular Misconceptions

• Natural Selection does not create any traits. – It only selects on existing traits.

Where do new traits come from?


• Natural Selection is not goal oriented– Simpler organisms are older, but not less fit.


• Natural Selection is subject to constraints– Advantageous traits often come with trade-offs

4/20/12

• Objective: To learn about hypotheses for the origin of cells

• Do Now: In your notes, make a T chart to compare the conditions of early and modern Earth

• Do Later: Read Ch. 15.1-3 in text

Early Earth Modern Earth

Evidence for Early Life

• Stromatolites – 3.5 billion years old– Oldest fossils– Single celled organisms– Grow in mats that harden into rock

Cell Theory

• Cell theory– All living things are composed

of cells and their products– New cells arise from the

division of older cells– Cells are the basic building

blocks of life

– Where did the first cells come from?

Miller’s Experiment

• Stanley Miller (1953)– Hydrogen gas (H2)– Ammonia (NH3)– Methane (CH4)– Water vapor– Spark

• Product? Amino acids.

Synthesis of Nucleic Acids

• Clay minerals catalyze the synthesis of DNA and RNA polymers

Montmorillonite

Meteorite Delivery

• Murchison meteorite (1969)– Found in Victoria, Australia– Over 100 amino acids• L-amino acids

– Nitrogenous bases (DNA/RNA)

– Potential for extraterrestrial life

Formation of Protocells

• Lipids in water spontaneously arrange into vesicles– Hydrophobic effects– Can also be catalyzed by clay

Chicken-Egg Problem

• DNA is needed to make proteins, and proteins are needed to make DNA– Which came first?

RNA World

• 1989 – Discovery of catalytic RNA– RNA has a sequence of bases like DNA– RNA can catalyze reactions like proteins

Ribosomes contain RNA to help catalyze protein synthesis

Prokaryotic Life

• Oldest species on earth are prokaryotes– No membrane bound organelles

Eukaryotic Life

• Eukaryotic cells have membrane bound organelles

Mitochondria and Chloroplasts• Mitochondria and chloroplasts have unusual

properties– Double phospholipid membrane– Mitochondrial/Chloroplast DNA

Endosymbiont Theory

• Primitive prokaryotes became eukaryotic organelles

Evolution

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