Chapter 22Chapter 22

Evidence for EvolutionEvidence for Evolution

Evolution occurs by Evolution occurs by natural selection…natural selection…

Darwin’s Darwin’s finchesfinches

Found on Found on GalapagosGalapagos

Descent with Descent with modificationmodification

Natural selection has 3 Natural selection has 3 conditions that must be conditions that must be met:met:

1.) variation within the population1.) variation within the population 2.) variation must lead to differences 2.) variation must lead to differences

among individuals in survival and among individuals in survival and reproductive successreproductive success

3.) variation must be genetically 3.) variation must be genetically inheritableinheritable

Found with finches:Found with finches:

variation is within the populationvariation is within the population changed from one year to the next depending changed from one year to the next depending

on the weather and plant seed productionon the weather and plant seed production drought = fewer seeds, birds with large beaks drought = fewer seeds, birds with large beaks

survived b/c could eat bigger seedssurvived b/c could eat bigger seeds wet = many more small seeds, birds with small wet = many more small seeds, birds with small

beaks survived okbeaks survived ok Traits were passed down according to those Traits were passed down according to those

who survived – fluctuated within the populationwho survived – fluctuated within the population

Peppered moths and Peppered moths and industrial melanismindustrial melanism

Industrial melanism is Industrial melanism is the darkening of a the darkening of a species due to industry species due to industry

Two main forms: Two main forms: peppered and melanicpeppered and melanic

In areas of industry, the In areas of industry, the tree bark is darker – the tree bark is darker – the dark moths do betterdark moths do better

Non-industrial areas, the Non-industrial areas, the light moths do betterlight moths do better

Kettlewell –did experiment with industrial melanismKettlewell –did experiment with industrial melanism Raised both colors of mothsRaised both colors of moths Marked their abdomens and released equal Marked their abdomens and released equal

amounts of each color into an area of industry and amounts of each color into an area of industry and a rural area.a rural area.

Waited a a few weeks and recaptured as many Waited a a few weeks and recaptured as many moths as possible in each area.moths as possible in each area.

Results:Results: light moths more in rural arealight moths more in rural area dark moths more in industrial areadark moths more in industrial area

Artificial SelectionArtificial Selection

Lab experiments:Lab experiments: Used to test if selection can produce Used to test if selection can produce

evolutionary change…evolutionary change… Used fruit fliesUsed fruit flies Chose flies with many bristles - Only bred Chose flies with many bristles - Only bred

the ones with the mostthe ones with the most Over 86 generations, increased the Over 86 generations, increased the

bristle # from 9 to over 40!!bristle # from 9 to over 40!!

In Agriculture…In Agriculture…

Only allow the Only allow the plants that plants that produce the best produce the best seeds to breedseeds to breed

Ex: corn, wheat, Ex: corn, wheat, strawberriesstrawberries

Domestication…Domestication…

Taking a once wild Taking a once wild animal and breeding animal and breeding those with desirable those with desirable traits to eventually traits to eventually spawn a desirable spawn a desirable offspringoffspring

Has been done with Has been done with wolves, foxes, cats wolves, foxes, cats and more!and more!

The fossil record…The fossil record…

Most direct evidence for evolutionMost direct evidence for evolution Can get from rock, amber, permafrost, dry Can get from rock, amber, permafrost, dry

caves or desertscaves or deserts Problem: fossilization does not occur easily!Problem: fossilization does not occur easily! Must have very specific conditionsMust have very specific conditions Usually the remains are scavenged or eroded Usually the remains are scavenged or eroded

before the process can be completedbefore the process can be completed

Must have very Must have very specific conditionsspecific conditions

Usually the remains Usually the remains are scavenged or are scavenged or eroded before the eroded before the process can be process can be completedcompleted

Here’s a bird in the Here’s a bird in the process of being process of being fossilized!fossilized!

Dating fossilsDating fossils

Date the rocks in which they are Date the rocks in which they are preserved:preserved: Absolute dating – uses UAbsolute dating – uses U238238

Relative dating – uses rock layers Relative dating – uses rock layers in respect to one anotherin respect to one another

Gaps in the recordGaps in the record

Even though gaps Even though gaps exist, links have exist, links have been found been found between:between: Reptiles and Reptiles and

birdsbirds Ex: Ex: ArchaeopteryxArchaeopteryx

Snakes and lizardsSnakes and lizards - - pelvic girdles still pelvic girdles still

visible in snakesvisible in snakes

Whales and land Whales and land mammalsmammals

- - flippers with flippers with homologous structures, homologous structures, pelvic girdlepelvic girdle

Anatomical recordAnatomical record

Homology – homologous Homology – homologous structures are structures structures are structures with different with different appearances and appearances and functions that are all functions that are all derived from the same derived from the same body part in a common body part in a common ancestorancestor

Ex: forelimbs of Ex: forelimbs of mammalsmammals

Vestigial Organs - Vestigial Organs - Rudimentary Rudimentary structures of structures of marginal, if any, use.marginal, if any, use.

Human ExampleHuman Example

Evolution ViewpointEvolution Viewpoint

Remodeling of ancestral structures Remodeling of ancestral structures as their functions or adaptations as their functions or adaptations changed.changed.

Comparative EmbryologyComparative Embryology

Problem - closely related organisms go Problem - closely related organisms go through similar stages in their embryonic through similar stages in their embryonic development.development.

Ex: Gill pouches in vertebratesEx: Gill pouches in vertebrates

Molecular BiologyMolecular Biology

Study of Evolution at the DNA or protein Study of Evolution at the DNA or protein levels.levels.

Problem - related species have similar Problem - related species have similar DNA sequences.DNA sequences.

Evolution ViewpointEvolution Viewpoint

Related species share a common Related species share a common ancestrial DNA. The closer the ancestrial DNA. The closer the relationship, the more similar the relationship, the more similar the DNA sequences should be.DNA sequences should be.

Convergent evolutionConvergent evolution

Horse evolution…Horse evolution…

For example, we can trace the evolution For example, we can trace the evolution of the modern horse through fossils.of the modern horse through fossils.

First horses:First horses: small, short legs, broad feetsmall, short legs, broad feet lived in woods and ate leaves and lived in woods and ate leaves and

berriesberriesWe will look at the changes in these We will look at the changes in these

animals…animals…

SizeSize

First horses were the size of dogs or First horses were the size of dogs or smallersmaller

Now they weigh on average about Now they weigh on average about 1000 lbs!1000 lbs!

Let’s see the fossils for this Let’s see the fossils for this change…change…

http://http://chem.tufts.edu/science/evolution/Hochem.tufts.edu/science/evolution/HorseEvolution.htmrseEvolution.htm

Toe reductionToe reduction Primitive horses had Primitive horses had

4 toes with fleshy 4 toes with fleshy pads like a dog’spads like a dog’s

Modern horses have Modern horses have one toe encased in one toe encased in bone and keratinbone and keratin

This allowed the This allowed the horse to run faster horse to run faster for longer distancesfor longer distances

First row = forefootFirst row = forefoot Bottom row = Bottom row =

hindfoothindfoot

Tooth size and shapeTooth size and shape

Primitive horses had small and simple teeth Primitive horses had small and simple teeth for the vegetation of the timefor the vegetation of the time

Modern horses now have more complex Modern horses now have more complex teeth that are longer and have ridges for teeth that are longer and have ridges for chewing grasses which evolved along with chewing grasses which evolved along with the horse the horse

The grasses are tough and the teeth need to The grasses are tough and the teeth need to tough to withstand the chewing of these tough to withstand the chewing of these materialsmaterials

Only one genus of horse still exists Only one genus of horse still exists today…today…EquusEquus

All others died out long ago – All others died out long ago – naturally selected against in the naturally selected against in the changing environmentchanging environment

SummarySummary

Know Darwin’s “facts” and “inferences”.Know Darwin’s “facts” and “inferences”. Be able to discuss the various evidences Be able to discuss the various evidences

of Darwinian evolution.of Darwinian evolution.