Today’s Plan: 2/25/11

Today’s Plan: 2/25/11

Bellwork: Go over test/fly counts (30 mins)

Amino Acid Sequence and Evolution Lab (30 mins)

Begin Natural Selection Notes (the rest of class)

Pack/Wrap-up (last few mins of class)


Bellwork: Finish Flies/Compile Class Data (30 mins)

Sexual Selection Video Pack/Wrap-up (last few mins of class)


Bellwork: Go over lab/Do PTC (15 mins)

AP Lab 8: Population Genetics and Evolution-Part B Genetic Drift (20 mins)

Finish video Continue Notes-if time Pack/Wrap-up (last few mins of class)


Bellwork: Settle in/Grab cards (5 mins)

Finish Lab (30 mins) Continue notes (25 mins) Pack/Wrap-up (last few mins of class)


Finish Notes (30 mins) Restriction Mapping Exercise (the rest

of class) Pack/Wrap-up (last few mins of class)


Bellwork: Finish Restriction Mapping (20 mins)

Finish Nat. Sel Notes (20 mins) HB fun week (the rest of class)


HB Stations-the entire period!

Before Natural Selection Recall that Darwin wasn’t the 1st to think about how species have

changed over time Aristotle’s Scala Naturae grouped species with similar “affinities”

together Linnaeus came up with Binomial Nomenclature and did much

classifying based on physical similarity Cuvier noted that fossils of species differed significantly from more

modern forms (proposed the idea of Catastrophism-that changes happened b/c of catastrophic events, and not gradually)

Lamarck suggested that use/disuse and will could change an organism’s body to fit the environment (he thought that acquired traits were heritable)

Malthus also discussed population limits Darwin bred pigeons for various traits (artificial selection) Recall that besides thinking about species change, others before

Darwin worked with how the planet changed Hutton proposed that geologic features were the result of gradual

changes that are still occurring today Lyell took this a step further and proposed his principle of

Uniformitarianism-mechanisms of change are constant over time

Figure 24-1

Simple cells

Fungi

Green algae

Land plants

Invertebrates

Vertebrates

Humans

Aristotle proposed that species were organized into a sequence based on increased size and complexity, with humans at the top

Natural Selection Aka “Descent with Modification” was Darwin’s

proposal for how species change over time and was the result of careful ponderance over his Galapagos Island collections

Darwin’s main focus was on adaptations that allowed species to survive better in their environments-finches had beaks adapted to their food source

Recall that while Darwin came up with the idea first, Alfred Russel Wallace also had the same ideal later, with no knowledge of Darwin’s work

The term Natural Selection was coined by Darwin’s friend, T.H. Huxley, who was called “Darwin’s bulldog” because he staunchly defended Darwin’s hypothesis

Darwin’s Observations and Inferences Observations:

Members of a population vary greatly in their traits Traits are inherited from parents to offspring All species are capable of producing more offspring than their

environment can support Because of lack of resources, many offspring don’t survive

Inferences (Summary of Natural Selection’s Mechanism): Individuals whose inherited traits give them a higher

probability of surviving and reproducing in an environment tend to leave more offspring (have greater reproductive success)

This inequality means that favorable traits accumulate in populations over multiple generations

Remember: Populations evolve, individuals don’t Traits influenced by natural selection must be heritable Environments are moving targets, so there’s no “perfect” and

what’s good in one population isn’t necessarily good in another

Current Directly Observable Evidence for Natural Selection Predation and Coloration in Guppies

Pools of guppies w/high predation produce more drab colored males There are numerous examples of these “natural experiments” done by

scientists Drug-resistant HIV and other “superbugs”

It’s natural for some viruses or bacteria to be resistant, but when you treat, what’s all that’s left to reproduce?

The Fossil Record We can see trends in the evolution of species

Anatomical Features Similar patterns of fetal development Homology (forelimb picture) Vestigial structures

Biogeography Looking at what we think happened to the geographic features of the

planet to explain distribution of species (ex: how Pangea’s split allowed us to predict where we’d find certain types of fossils)

Molecular Similarity Studies of DNA sequence and amino acid sequence can be used to

construct “molecular clocks” that give us clues to which organisms diverged from one another, and tells us relatively how long ago the divergance occurred

Figure 24-11

M. tuberculosis

EVOLUTION OF DRUG RESISTANCE

Lung tissue

Bacteria with pointmutation in rpoB gene

1. Large population ofM. tuberculosis bacteria in patient’s lungs makes him sick.

2. Drug therapy begins killing most M. tuberculosis. Patient seems cured and drug therapy is ended. However, a few of the original bacteria had a pointmutation that made them resistant to the drug treatment.

3. The mutant cells proliferate, resulting in another major infection of the lungs. The patient becomes sick again.

4. A second round of drug therapy begins but is ineffective on the drug-resistant bacteria. The patient dies.

Figure 24-3

110 myo ammonite shell 50 myo bird tracks 20,000 y-old sloth dung

Figure 24-9

Turtle Human

Humerus

Radius and ulna

Carpals

Metacarpals

Phalanges

Horse Bird Bat Seal

Figure 24-8

Chick Human House cat

TailTailTail

Gill pouch Gill pouch Gill pouch

Figure 24-5 The human tailbone is a vestigial trait.

Humancoccyx

Capuchinmonkey tail

Goose bumps are a vestigial trait.

Erect hair on chimp (insulation, emotional display)

Human goose bumps

(used for balance, locomotion)

Figure 24-7

Aniridia (Human)

eyeless (Fruit fly)

Only six of the 60 amino acids in these sequences are different. The two sequences are 90% identical.

Amino acid sequence (single-letter abbreviations):Gene:

Figure 27-7

Tree thinking vs. Convergent evolution In many cases, evolutionary trees are

created in order to show how species evolved from common ancestors Sometimes, this happens b/c of adaptive

radiation-when organisms evolve in a variety of directions in order to exploit different aspects of the environment

Occasionally, organisms resemble each other, not because they’re related, but because some characteristics are advantageous regardless of their ancestry Ex: sugar gliders in Australia look like flying

squirrels

Figure 27-11

Hawaiian silverswords underwent adaptive radiation.

Hawaiian honeycreepers underwent adaptive radiation.

Star phylogeny (a large polytomy)

Adaptive radiations produce star phylogenies.

Rapidspeciation

Figure 24-15b

Bacteria ArchaeaGreenalgae

Landplants Invertebrates Vertebrates Fungi

Darwinian evolution produces a tree of life.

Common ancestor of all species living today

The branches on the tree represent populations through time. All of the species have evolved from a common ancestor. None is higher than any other

Sexual Selection This is a variation of natural selection where some

traits persist, not because they’re advantageous, but because they’re attractive

In some cases, the traits that evolve are disadvantageous, but continue to persist

Intersexual Selection is based on the “female choice” model-the opposite sex chooses a mate

Intrasexual Selection is based on competition within the sex for access to mates or resources that will attract mates

Causes sexual dimorphism (variation between sexes)

Figure 25-15

During the breeding season, males of the beetle Dynastes granti use their elongated horns to fight over females.

Males

Females

Scarlet tanagerBeetle Lion

Male scarlet tanagers use their brightcoloration in territorial and courtshipdisplays.

Male lions are larger than females lions andhave an elaborate ruff of fur called a mane.

Figure 25-14 Males compete to mate with females.

Variation in reproductive success is high in males.

Variation in reproductive success is relatively low in females.

The survival of the fittest. . . Remember, fitness is relative, and

“struggle” isn’t always direct conflict. Depending on which traits are favored,

there are 3 ways in which natural selection can influence phenotypic variation Directional selection-one extreme phenotype is

favored Disruptive selection-both extreme phenotypes

are favored Stabilizing selection-average is favored

Figure 25-3

Before selection

Directional selection changes the average value ofa trait.

Normal distribution

For example, directional selection caused average bodysize to increase in a cliff swallow population.

During selection

After selection

Original population(N = 2880)

Survivors(N = 1027)

Change inaveragevalue

Highfitness

Lowfitness

Change inaveragevalue

Figure 25-4

Before selection

Stabilizing selection reduces the amount of variationin a trait.

Normal distribution

For example, very small and very large babies are themost likely to die, leaving a narrower distribution of birthweights.

During selection

After selection

Mortality

Reductionin variation

High fitnessLowfitness

Heavymortalityon extremes

Lowfitness

Figure 25-5

Before selection

Disruptive selection increases the amount of variationin a trait.

Normal distribution

For example, only juvenile black-bellied seedcrackers that had very long or very short beaks survived long enough tobreed.

During selection

After selection

Increase in variation

Low fitnessHigh

fitness

Only theextremessurvived

Only theextremessurvived

Highfitness

Evolution of Populations This is fueled by genetic variation

For individuals, can be quantified using average heterozygosity (average % of genes for which an individual is heterozygous)

For populations, you can directly compare individual karyotypes or gene sequences from each population Sometimes, the difference is dramatic, and sometimes

the difference is a cline (gradual difference) This often exists b/c of geographic variation (isolation)

Genetic Variation occurs for 2 reasons Sexual Reproduction Mutation is the ultimate source for most new genetic

variations. Often these mutations are neutral, but occasionaly, you get an adaptive mutation. The rates at which mutation occurs varies between species.

Hardy-Weinberg Useful for testing whether or not a

population is evolving This is a mathematical model:

p2+2pq+q2=1 p=frequency of the dominant allele q=frequency of the recessive allele

When a population is in Hardy-Weinberg equilibrium, the equation works, but when populations are evolving, it is an inequation.

Figure 24-10 If heritable variation…

… leads to differential success…

… then evolution results.

A1A1

A1A1

A1A1

A2A2

A2A2

A2A2A1A2

A1A2

A1A2

A1A2

A1A1 A1A2

A2A2

A1A1

Color varies among individuals primarily because of differences in their genotype

Birds find and eat many more dark-winged moths than light-winged moths

Allele frequencies have changed in the surviving moths

Figure 25-1-1

A NUMERICAL EXAMPLE OF THE HARDY-WEINBERG PRINCIPLE

Allele frequencies in parental generation:

Gene pool (gametes from parent generation)

A1 A1 A1 A1A2 A2 A2 A2

Allele A1

0.7 0.7 = 0.49 0.7 0.3 = 0.21

p p = p2

0.3 0.7 = 0.21 0.3 0.3 = 0.09

= q = 0.3

= p = 0.7

q p = pq q q = q2

Allele A2

q p = pq

1. Suppose allele frequenciesin the parental generation were0.7 and 0.3.

2. 70% of gametes in the gene

pool carry allele A1, and 30%

carry allele A2.

3. Pick two gametes at randomfrom the gene pool to formoffspring. You have a 70%

chance of picking allele A1 and a

30% chance of picking allele A2.0.21 + 0.21 = 0.42

Off

spri

ng

Figure 25-1-2

A NUMERICAL EXAMPLE OF THE HARDY-WEINBERG PRINCIPLE

Off

spri

ng

Frequency ofA1A1 genotype is

p2 = 0.49


2pq = 0.42


q2 = 0.49

Allele frequencies inoffspring gene pool p = frequency of allele A1 q = frequency of allele A2

12

(0.42) + 0.09 = 0.3q =

Genotype frequencies will be given by p2 : 2 p q : q2 as long as all Hardy-Weinberg assumptions are met.

4. Three genotypes are possible.Calculate the frequencies of thesethree combinations of alleles.

5. When the offspring breed,imagine their gametes enteringa gene pool. Calculate thefrequencies of the two allelesin this gene pool.

6. The frequencies of A1 and A2

have not changed from parentalto offspring generation.Evolution has not occurred.

49% of offspring havethe A1 A1 genotype. All

will contribute A1 allelesto the new gene pool.

42% of offspring have the A1 A2Genotype. Half of their gameteswill carry the A1 allele and the

other half will carry the A2 allele.

9% of offspring havethe A2 A2 genotype. All

will contribute A2 allelesto the new gene pool.

(0.42) = 0.7p = 0.49 + 12

Conditions for Hardy-Weinberg

No mutation Random Mating No natural selection Large population size No gene flow Rarely do all of these conditions exist

at any given moment, but over time, populations tend to be in equilibrium

Altering Gene Frequencies Genetic Drift-caused by small population size or

random changes that make predicting gene frequency difficult. 2 examples: The founder effect-a small number of individuals are

isolated from the larger group and have to reestablish a gene pool

The bottleneck effect-catastrophic incidents drop population size quickly and dramatically

In either case, genetic variation is lost, and harmful alleles can persist

Gene Flow-occurs when genes transfer in and out of populations. Usually, this is negligible unless something causes any of the following factors to change dramatically: Immigration Emigration

Figure 25-6

Figure 25-8Lupines colonize sites and form populations.

Gene flow reduces genetic differences among populations.

Year 1: Seed establishes new population

Source population New population

Seed

Frequency of A1 = 0.90

Frequency of A2 = 0.10 Frequency of A2 = 0.50


A1A1


Frequency of A2 = 0.17 Frequency of A2 = 0.33


Year 2: Gene flow between source population and new population

Source population New population

A1A1A1A1 A1A1

A1A2 A1A2

A1A1A1A2

Geneflow

A1A1

A1A1 A1A1

A1A2A1A1

A1A2

A1A2

Initially, allele frequenciesare very different

Gene flow causes allelefrequencies to becomemore similar

Preserving Genetic Variation Diploidy-Since organisms get 2 copies of

each gene, recessive alleles can be preserved

Balancing Selection-occurs when natural selection maintains 2 forms of a trait in a population The heterozygote advantage-sickle cell disease

and malaria symptom resistance Frequency-Dependent selection-as a phenotype

becomes more common, it loses its advantage Neutral Variation-occurs when mutation has little

to no effect on phenotype or on reproductive success

Why isn’t there a “perfect” organism

Selection can only act on existing variations (and each intermediate step between phenotypes must be adaptive)

You can’t scrap ancestral anatomy to build something new (see above statement)

Adaptations are often compromises (multifunctionality means you have to choose a primary function. Ex: seals don’t have legs b/c they also swim)

Chance, natural selection, and the environment have to interact

Types of evolution

Microevolution-evolution of allele frequencies within gene pools

Macroevolution-patterns of evolution over long time spans (like the emergence of new species)

The Biological Species Concept

This is the classic definition of the term “species” put forth by Ernst Mayr

A species is a group of populations whose members interbreed in nature to produce fertile offspring

Species are held together by proximity and interbreeding

Making new species Requires Reproductive isolation-barriers

that prevent the production of viable offspring (remember that hybrids can exist, but are sterile: ligers, mules, etc)

Prezygotic barriers-block fertilization Blocking mating Blocking the successful completion of mating Preventing successful fertilization

Postzygotic barriers-prevent a hybrid from mating successfully

Types of Prezygotic Mechanisms

Habitat Isolation-2 species occupy different habitats

Temporal Isolation-species breed at different times

Behavioral Isolation-courtship rituals differ Mechanical Isolation-differences in

shape/form prevent mating Gametic Isolation-the gametes may not be

able to fuse

Types of postzygotic Mechanisms

Reduced Hybrid viability-parental genes prevent the hybrid’s survival

Reduced Hybrid Fertility-sterility due to inability to produce normal gametes

Hybrid Breakdown-Some hybrids can mate with one another, but their offspring are not viable

Limitations of Biological Species It’s hard to evaluate the reproductive isolation of

fossils, nor does it address species that reproduce asexually

Other species definitions Morphological species concept-characterizes species

by body shape and structure (can be applied to sexual and asexual reproducers, however this relies on subjective criteria)

Ecological species concept-characterizes a species based on its ecological niche (also can be applied to sexual and asexual reproducers, and emphasizes the role of disruptive selection in species definition)

Phylogenetic species concept-a species is defined by the smallest group of individuals that share a common ancestor (difficult to deterime the degree of difference required to separate one species from another)

Allopatric Speciation “other country” speciation-occurs when

species are geographically isolated Populations become divided and evolve

differently because of different environments, genetic drift, and different mutations

Remember that they’re not different species until they’re reproductively isolated. If the populations are put back together and can still mate, they’re not different species

Figure 26-5

DISPERSAL AND COLONIZATION CAN ISOLATE POPULATIONS.

VICARIANCE CAN ISOLATE POPULATIONS.

Island

Continent

RiverRiver ch

ang

esco

urse

1. Start with one continuouspopulation. Then, colonistsfloat to an island on a raft.

2. Island population beginsto diverge due to drift andselection.

3. Finish with two populationsisolated from one another.

1. Start with one continuouspopulation. Then a chanceevent occurs that changesthe landscape (river changescourse.)

2. Isolated populations begin to diverge due to drift andselection.

3. Finish with two populationsisolated from one another.

Sympatric Speciation “same country” speciation-occurs when organisms are

in the same area but speciate Can occur via several mechanisms:

Polyploidy-having an extra set of chromosomes Autopolyploid-more than 2 sets of chromosomes from a

single species (failure of cell division) Allopolyploid-caused by an extra set of chromosomes

via hybridization of 2 species (fertile when mating with one another only)

Habitat Differentiation-when a subpopulation exploits a resource that the rest of the population doesn’t

Sexual Selection-when different groups of females prefer different groups of males

Figure 26-7 Soapberry bugs use their beaks to reach seeds inside fruits.

Feedingon thefruit ofa nativespecies

Nonnative fruits are much smaller than native fruits.

Evidence for disruptive selection on beak length

Native plant(large fruit)

Nonnative plant(small fruit)

Feeding on the fruit ofa nonnativespecies

Short-beakedpopulationgrowing onnonnativeplants

Long-beaked populationgrowing on native plants

Figure 26-8

Tetraploid parent

Triploid zygote

Diploid gametesHaploid gametes

Diploid parent

Mating

Meiosis

Gametes

Meiosis

(Two copies ofeach chromosome)

(Four copies ofeach chromosome)

(Two copies ofeach chromosome)

(One copy ofeach chromosome)

(Three copies ofeach chromosome)

The gametes of a triploid individual rarely contain the same number ofeach type of chromosome. When gametes combine, offspring almostalways have an uneven (dysfunctional) number of chromosomes.

Hybrid Zones When allopatric species come back into

contact with one another, you get a hybrid zone

There are several possibilities for what can happen in a hybrid zone Reinforcement-occurs when hybrids are less fit

than the parent species Fusion-occurs when reproductive barriers are

weak and the species become increasingly alike Stability-occurs when the hybrids persist

Figure 26-11

Hybrids inherit species-specific mtDNA sequences from their mothers.

All individuals haveTownsend’s mtDNA

Hybrids have intermediate characteristics.

Individuals that look likeTownsend’s warblers buthave hermit mtDNA

Some individualshave Townsend’smtDNA, othershave hermitmtDNA

All individuals havehermit mtDNA

Townsend’s-hermithybrid

Townsend’s warbler

Hermit warbler

Present rangeof hermit warblers(in orange)

Pacific Ocean

Present hybridzones (where two ranges meet)

Present rangeof Townsend’swarblers(in red)

Speciation Rates Darwin originally believed that gradualism

existed (species change at a slow, steady rate over time)

From the fossil record, we now know that punctuated equilibrium exists (periods of equilibrium followed by periods of natural selection)

This can happen very rapidly, and as little as 1 gene can make a species reproductively isolated

Geologic Time

This is a time scale that uses the fossil record to trace the major events in the planet’s history

Dates are determined by dating fossils Relative Dating-accomplished via the law

of superposition Absolute Dating-accomplished via

radiometric dating

Figure 27-5

SeedsPollen Leaves

Sand and gravelBuried material from swamp

Bedrock

HOW FOSSILIZATION OCCURS1. A tree lives in aswampy habitat.The tree dropsleaves, pollen, andseeds into the mud,where decompositionis slow.

2. The tree falls.The trunk andbranches breakup as they rot.

3. Flooding bringsin sand and mud,burying the remainsof the tree.

4. Over millions ofyears, the mountainserode and the swampis filled with sediment.The habitat dries.

Earth’s History Earth is believed to have existed for 4.6

billion years Life on earth is believed to have originated

3.5 billion years ago. The first life forms were probably prokaryotes

There have been 5 mass extinctions over the history of the planet, and in each, the dominant group of organisms was replaced by another group

Figure 27-8a

The Precambrian (Hadean, Archaean, and Proterozoic Eons) included the origin of life, photosynthesis, and the oxygenatmosphere.

Format

ion o

f sola

r sys

tem

Moon fo

rms

Earth

form

atio

n com

plete

Liquid

wat

er o

n Ear

th

First o

cean

s; h

eavy

bom

bardm

ent

fr

om s

pace

ends

Orig

in o

f life

First e

viden

ce o

f photo

synth

etic

c

ells

First e

viden

ce o

f oxy

genic

p

hotosy

nthes

isFirs

t rock

s co

ntain

ing o

xygen

(i

n atm

ospher

e an

d oce

an)

First e

ukary

otic fo

ssils

First p

hotosy

nthet

ic e

ukary

otes

First r

ed a

lgae

; firs

t evi

dence

o

f sex

ual s

truct

ures

First l

ichen

-like

org

anis

m

First s

ponges; f

irst b

ilate

rally

s

ymm

etric

anim

als;

oce

an

com

plete

ly o

xygen

ated

Proterozoic Eon

Multicellularorganisms beginto diversify slowly

Most of Earth is coveredin ocean and ice.

All life is unicellular

Position of the continents unknown

Archaean EonHadean Eon

Millions of years ago (mya)

Figure 27-8b

Phanerozoic Eon: The Paleozoic Era included the origin early diversification of animals, land plants, and fungi.

First c

omb je

llies

, arth

ropods,

v

erte

brate

s, o

ther

phyl

a

Cambrian

Algae abundant,marineinvertebratesdiversify

Arthro

pods div

ersi

fy;

fi

rst e

chin

oderm

First b

ryozo

ans

(new

est

a

nimal

phyl

um)

First l

and p

lants

First m

ycorr

hizal

fungi (

Glo

mal

es)

First c

artil

agin

ous fis

h

First b

ony fis

h

First i

nsect

s

First f

ish w

ith ja

ws

First f

erns,

vas

cula

r pla

nts,

a

scom

ycet

e fu

ngi, lic

hens

on land

First t

ree-

size

d pla

nts

First w

inged

inse

cts

First t

etra

pods (a

mphib

ians)

First s

eed p

lants

First p

lants

with

leav

es

First r

eptil

es

First m

amm

al-li

ke re

ptiles

First b

asid

iom

ycet

e fu

ngi

First v

esse

ls

in

pla

nts

Ordovician Silurian DevonianCarboniferous

PermianMississippian Pennsylvanian M

ass

exti

nct

ion

Mas

sex

tin

ctio

n

Mas

sex

tin

ctio

n

Echinoderms(sea stars, seaurchins) diversify

Coralreefsexpand

First upland plantcommunities(evergreen forests),diversification of fish,emergence ofamphibians

Insects diversify,coal-forming swampsabundant, sharksabundant, radiationof amphibians

Coal-forming swampsdiminish; parts ofAntarctica forested

Supercontinent Pangeaassembles. Building ofAppalachian Mountains ends.Climate warm; little variation.

Supercontinent of Laurentiato the north and Gondwanato the south. Climate mild.

Climate cold;extensive icein Gondwana.

Supercontinent of Gondwanaforms. Oceans cover much ofNorth America. Climate notwell known.

Laurentia

Gondwana

Pangea

GondwanaGondwana

Figure 27-8c

Phanerozoic Eon: The Mesozoic Era is sometimes called the Age of Reptiles.

First n

ecta

r-drin

king in

sect

s

Triasssic

Gymnosperms become dominantland plants; extensive deserts

Mas

sex

tin

ctio

n

First d

inosa

urs

First m

amm

als

First t

yran

nosaurid

din

osaur

First a

ngiosp

erm

(flo

wer

ing p

lant)

First b

ird (A

rchae

optery

x)Firs

t cen

tric

diato

ms

First w

ater

lilie

s

First m

agnolia

-fam

ily p

lants

First b

ee; f

irst a

nt

First p

lace

ntal m

amm

als

Mas

sex

tin

ctio

n

Jurassic Mas

sex

tin

ctio

n

Cretaceous

Gymnosperms continueto dominate land

Dinosaurs diversify Flowering plants diversify

Pangea intact. Interiorof Pangea arid. Climatevery warm.

Pangea begins to break apart;interior of continent still arid.

Gondwana begins to breakapart; interior less arid.

India separated from Madagascar,moves north; Rocky Mountainsform. Climate mild, temperate.

Pan

gea

Pan

gea Gondwana

Figure 27-8d

Phanerozoic Eon: The Cenozoic Era is nicknamed the Age of Mammals.

First h

orses

Paleogene

Continents continue to drift apart.Collision of India with Eurasia begins.Australia moves north from Antarctica.Palms in Greenland and Patagonia.

First p

rimat

es

First f

ully a

quatic

whal

es

First a

pes

Old

est p

ollen fr

om

d

aisy

-fam

ily p

lants

Earlie

st h

omin

ins

Homo

s

apie

ns

Paleocene Eocene Oligocene

Neogene

Miocene Pliocene Pleistocene

Diversification of grazing mammalsDiversification of angiospermsand pollinating insects

Diversification ofmammalian orders

Strong drying trend inAfrica and other continents;grasslands form. Alps andHimalayas begin to rise.

Continents close to presentposition. Beginning ofAntarctic ice cap. Openingof Red Sea.

North and South Americajoined by land bridge.Uplift of the Sierra Nevada.Worldwide glaciation.

Figure 27-5

SeedsPollen Leaves

Sand and gravelBuried material from swamp

Bedrock

HOW FOSSILIZATION OCCURS1. A tree lives in aswampy habitat.The tree dropsleaves, pollen, andseeds into the mud,where decompositionis slow.

2. The tree falls.The trunk andbranches breakup as they rot.

3. Flooding bringsin sand and mud,burying the remainsof the tree.

4. Over millions ofyears, the mountainserode and the swampis filled with sediment.The habitat dries.

Major events in Earth’s History: The earth cools 1st life forms Accumulation of

atmospheric oxygen

1st eukaryotes Multicellular

organisms

Animals evolved Plants and fungi

colonized land Land became

colonized by other organisms

Where would life come from? Recall that Miller and Urey tested Oparin’s primordial

soup hypothesis and were able to create biochemicals Lab experiments since then have been able to form

polymers in conditions similar to early earth RNA was probably the 1st genetic material

These have been shown to be produced abiotically in the lab

Recall that Ribozymes exist as well. Protobionts can self-assemble

These are aggregates of abiotically produced molecules that form “membranes” and often can sustain chemical reactions (like a metabolism)

What about Eukaryotic cells? One current hypothesis, the

endosymbiant hypothesis tries to explain this Mitochondria have their own DNA,

resemble bacteria, and replicate themselves for cell division

This suggests that once the 1st primitive cells evolved, they “swallowed” other cells. It is believed that they could have become dependent on one another to carry out parts of their metabolism

Today’s Plan: 2/25/11

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