UNIT FIVE – EvolutionMain Idea: How have species changed

over time? (long periods of time)

Darwin and Darwin and Mechanisms of Mechanisms of Evolution: Evolution: The theory and why it works

Click on image for Brain pop video on Darwin 4:20

Evidence of EvolutionEvidence of Evolution: : The Fossil RecordThe Fossil Record

• Indicates life began 3 byaIndicates life began 3 bya • Prokaryotes then Prokaryotes then

Eukaryotes then Eukaryotes then multicellular Eukaryotesmulticellular Eukaryotes

• Fossil record determines:Fossil record determines:• When species appearedWhen species appeared• The type of environmentThe type of environment• When/if species became When/if species became

extinctextinct

Fossils found in the rock layers are similar in some layers, but different in other layers. This shows us that the species had changed over time. [Remember that the oldest rock layers are below the youngest rock layers]

YOUNG

OLDER

What does the theory of evolution What does the theory of evolution say?say?• Theory b/c lots of evidence Theory b/c lots of evidence

• Tested and re-tested by many Tested and re-tested by many scientistsscientists

• States that:States that:

• Variations in individuals can lead Variations in individuals can lead to changes in whole speciesto changes in whole species

1. Trunk = an ancestor common to all organisms represented on the tree.

2. Branches = ancestors common to species at the ends of the branches.

3. Buds of the tree = species that are alive today.

4.Branches without buds at the ends = species that have died out (or have gone extinct).

It is believed that evolution does not necessarily produce any long-term progress in any one direction. Instead, evolutionary changes appear to be more like the growth of a bush. Turn to pg 81 of your RB

Evolution Video (21:22min)

Natural Selection: The Idea Natural Selection: The Idea Behind the Theory Behind the Theory http://www.brainpop.com/science/ecologyandbehavior/naturalselectionhttp://www.brainpop.com/science/ecologyandbehavior/naturalselection

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• Evolution controlled by NATURAL Evolution controlled by NATURAL processesprocesses

• THE PROCESS IS:THE PROCESS IS:

LIVELIVE + + BREEDBREED + PASS ON GENETIC INFO + PASS ON GENETIC INFO = = SURVIVAL OF SPECIESSURVIVAL OF SPECIES

• ““Survival of Fittest”Survival of Fittest”• Those Those best ADAPTEDbest ADAPTED will be able to will be able to DO DO

THE PROCESSTHE PROCESS

Results of Natural SelectionResults of Natural Selection

• Short term result:Short term result:• Best fit (adapted) will pass on Best fit (adapted) will pass on GOODGOOD genes genes

to offspringto offspring

• Long term result:Long term result:• Change in Change in frequencyfrequency (number) of certain (number) of certain

traitstraits

Which do you think will increase in frequency Which do you think will increase in frequency GOOD OR BAD?GOOD OR BAD?

GOOD OF COURSE!GOOD OF COURSE!• As more individuals have good trait, As more individuals have good trait,

species is evolvingspecies is evolving

What drives evolution?What drives evolution?

Interactions between individuals and Interactions between individuals and the environment:the environment:

1.1. OVERPRODUCTIONOVERPRODUCTION

2.2. STRUGGLE FOR SURVIVALSTRUGGLE FOR SURVIVAL

3.3. GENETIC VARIATIONGENETIC VARIATION

4.4. SELECTION BY THE SELECTION BY THE ENVIRONMENTENVIRONMENT

Evolution Cause #1: Evolution Cause #1: OVERPRODUCTIONOVERPRODUCTION

• POTENTIAL TO PRODUCE MORE OFFSPRING THAN WILL SURVIVE

• This means the best “fit” individuals will survive, grow and reproduce.

• EX: DEER, FISH

Evolution Cause #2: Evolution Cause #2: STRUGGLE FOR SURVIVALSTRUGGLE FOR SURVIVAL

• Overproduction leads to STRUGGLE Overproduction leads to STRUGGLE within species:within species:

1.1. Only some live to reproduceOnly some live to reproduce

2.2. Competition for resourcesCompetition for resources

3.3. Best competitors will live and breedBest competitors will live and breed

• Must STRUGGLE with environment also Must STRUGGLE with environment also (disease, predators, temp changes etc)(disease, predators, temp changes etc)

• Those that withstand will survive!Those that withstand will survive!

Competition: • Not all offspring live

long enough to reproduce.

• All the offspring will have to cope with environmental conditions such as temperature, disease, parasites, and predators.

• If they are to survive, they must compete for limited resources.

• Those that are best suited for the environment are more likely to survive and pass on their genes.

Evolution Cause #3: Evolution Cause #3: GENETIC VARIATIONGENETIC VARIATION

• Variation must exist within survivors• Ex: Longer legs, bigger claws, diff. fur

color

• Favored traits will stay in population and lead to evolution

• Adaptive Value:• Describes a trait that helps an individual

survive in a particular environment• EX: polar bears have black skin; the black

skin has adaptive value b/c it helps them value b/c it helps them survivesurvive

• The differences among offspring are due to genetic variation, the unique combination of traits that each organism inherits from its parents.

• Organisms that reproduce sexually have more variation, than those who reproduce asexually!

Evolution Cause #4: Evolution Cause #4: SELECTION BY ENVIRONMENTSELECTION BY ENVIRONMENT

• Traits w/ adaptive value benefit those Traits w/ adaptive value benefit those individualsindividuals

• If reproduce, offspring have traits tooIf reproduce, offspring have traits too

• Eventually, # of individuals with trait Eventually, # of individuals with trait increases, and most all will have it!increases, and most all will have it!

• Therefore, adapting to environment Therefore, adapting to environment DRIVES EVOLUTION!DRIVES EVOLUTION!

Evolutionary (Phylogenic) Trees: AnimalsEvolutionary (Phylogenic) Trees: Animals= COMMON ANCESTOR= COMMON ANCESTOR

Comparison of Human and Comparison of Human and Chimp ChromosomesChimp Chromosomes

Variation and Evolution

Why differences among a pop’n are good!

A. Review of VariationA. Review of Variation

• Order of DNA bases determines Order of DNA bases determines traitstraits

• Changes can occur that can change Changes can occur that can change individualindividual

• Two possible ways changes occur:Two possible ways changes occur:

1.1. MutationsMutations

2.2. Genetic Shuffling (Recombination)Genetic Shuffling (Recombination)

B. MutationsB. Mutations• Are random (cannot be predicted)Are random (cannot be predicted)• Caused by radiation and Caused by radiation and

chemicalschemicals• To be passed on:To be passed on:

• Single celled organisms Single celled organisms (mitosis)(mitosis)

• Sex cells of multicellular Sex cells of multicellular organismsorganisms

Mutations con’t…Mutations con’t…

• Most mutations harmfulMost mutations harmful• Some are beneficial (have adaptive Some are beneficial (have adaptive

value)value)• These get passed on These get passed on • Ex:Ex: polar bears probably didn’t polar bears probably didn’t

always have black skin; mutation always have black skin; mutation caused it and it was beneficialcaused it and it was beneficial

• THIS IS MAIN SOURCE OF THIS IS MAIN SOURCE OF NEWNEW VARIATIONVARIATION

C. Genetic ShufflingC. Genetic Shuffling

• Sorting and recombination of genes = Sorting and recombination of genes = new combos of genesnew combos of genes

• Think deck of cardsThink deck of cards: : deck always the deck always the same but each hand is differentsame but each hand is different

• Sexual reproduction uses 2 decks so Sexual reproduction uses 2 decks so even more variationeven more variation

• THIS IS MAIN SOURCE OF VARIATION THIS IS MAIN SOURCE OF VARIATION WITHIN A SPECIESWITHIN A SPECIES

Results of Genetic VariationResults of Genetic VariationTypes: Types: •Structural changesStructural changes•Functional changes Functional changes •Behavioral changesBehavioral changes

Evidence of Evolution Homolgous features:.

A. Structural ChangesA. Structural Changes• Result of organisms entire Result of organisms entire

historyhistory• Ex:Ex: polar bears vs other polar bears vs other

bearsbears• Homologous StructuresHomologous Structures• Evolution helps explain Evolution helps explain

structural similaritiesstructural similarities• Ex:Ex: (Arm structure) Humans, (Arm structure) Humans,

whales, birds and bats whales, birds and bats (see RB (see RB p88)p88)

• All have 1 long bone, 2 All have 1 long bone, 2 shorter ones, and 5 digitsshorter ones, and 5 digits

• Tells us they all had a Tells us they all had a common ancestorcommon ancestor

• These are homologous These are homologous structures!structures!

EmbryologyEmbryology

Structural Changes con’tStructural Changes con’t

2. 2. Vestigial StructuresVestigial Structures

• Structures that are present but Structures that are present but no longer in useno longer in use

• EX:EX: Snakes contain tiny, non- Snakes contain tiny, non-functional leg bones which functional leg bones which suggest it evolved from 4-suggest it evolved from 4-legged lizardslegged lizards

Vestigial StructuresVestigial Structures(click link)(click link)

Hind leg Hind leg limbs in limbs in whaleswhales

Pelvic Pelvic bone in bone in humanshumans

Appendix Appendix in humansin humans

B. Functional ChangesB. Functional Changes• Molecular changeMolecular change

• EX:EX:

• All muscles produce tiny electric All muscles produce tiny electric currentcurrent

• Eels have developed stronger current Eels have developed stronger current to help them find food and kill preyto help them find food and kill prey

Evidence of Evolution Similarities in Macromolecules:

C. Behavioral ChangesC. Behavioral Changes

• Adaptive changes that increase Adaptive changes that increase reproductive successreproductive success

• EXEX::

• Fighting among males to “win” Fighting among males to “win” femalefemale

• Rhythms of bird callsRhythms of bird calls

• Rates blinking in lightning bugsRates blinking in lightning bugs

Importance of VariationImportance of Variation1.1. Environment changes, organisms Environment changes, organisms

have to adapthave to adapt

2.2. Without variation, species likely to Without variation, species likely to become extinctbecome extinct

3.3. If diversity lost, difficult to recoverIf diversity lost, difficult to recover

1.1. Endangered species have small Endangered species have small populations with little variationpopulations with little variation

2.2. If environment changes, they If environment changes, they cannot adaptcannot adapt

The Rate of Evolution and The Rate of Evolution and ExtinctionExtinction

What affects how fast organisms evolve?

What leads to extinction?

Change is Everything!Change is Everything!

• Change in environment = Change in species!

• Failure to adapt to changes = possible extinction

Rate of EvolutionRate of EvolutionWhat affects how fast a species What affects how fast a species evolves?evolves?

1.1. Rate of Rate of environmentaenvironmental changel change

2.2. Rate of Rate of reproductionreproduction

A. Rate of Environmental A. Rate of Environmental ChangeChange

• Rapid environmental Rapid environmental change = rapid change in change = rapid change in speciesspecies• Rapid changeRapid change

• ExEx. Modern horse: . Modern horse: many changes over past many changes over past million yearsmillion years

• Slow changeSlow change• Ex.Ex. Horseshoe crab: Horseshoe crab:

nearly identical to nearly identical to ancestors from 300 myaancestors from 300 mya

Environmental Change con’t:Creation of new species can occur if species are separated by geography such as water or land features.

Harris's antelope squirrel inhabits the canyon's south rim (left). Just a few miles away on the north rim (right) lives the closely related white–tailed antelope squirrel .

Geographic isolation of squirrels on opposite rims of the Grand Canyon.

B. Rate of ReproductionB. Rate of Reproduction• The # of offspring produced The # of offspring produced

can tell us how quickly a can tell us how quickly a species can evolvespecies can evolve

• Few offspring = longer life = Few offspring = longer life = slowslow evolution evolution

• Ex.Ex. Humans, elephants Humans, elephants

• Many offspring = shorter life Many offspring = shorter life = = quickerquicker evolution evolution

• Ex.Ex. Bacteria, single celled Bacteria, single celled orgs, fishorgs, fish

Let’s look at bacteriaLet’s look at bacteria• Reproduce very quickly

• See page 90 figure 5-6

• Millions exposed to antibiotic• Very good chance a few will have resistant

gene due to random mutation• These will live, THEN pass on resistance• Pretty soon, large population that have this

resistance• If same antibiotic used again, will increase

resistance• Soon, a SUPER STRAIN of this bacteria has

evolved

http://www.sumanasinc.com/scienceinfocus/sif_antibiotics.html

Refer to RB page 90 figure 5-6

Brain Pop linkBrain Pop link

Lesson learned:Lesson learned:

• Only use antibiotics when necessaryOnly use antibiotics when necessary• Many strains are resistant to penicillin, the first Many strains are resistant to penicillin, the first

antibiotic usedantibiotic used• Humans are creating Super Strains with Humans are creating Super Strains with

continued misuse of antibioticscontinued misuse of antibiotics• Similar occurrences with insects and Similar occurrences with insects and

insecticidesinsecticides

What causes extinction?What causes extinction?1.1. Death rate higher than birth rateDeath rate higher than birth rate

• Usually due to rapid env. changesUsually due to rapid env. changes2.2. These env. changes cause major drop in These env. changes cause major drop in

pop’n size if species cannot adaptpop’n size if species cannot adapt• Variation drops!Variation drops!

• Less variation to pass onLess variation to pass on• Offspring essentially inbreeding, Offspring essentially inbreeding,

variation drops even morevariation drops even moreNO VARIATION = NO VARIATION =

NO ADAPTIVE VALUE = NO ADAPTIVE VALUE = EXTINCTIONEXTINCTION