Evidence for EvolutionEvidence for Evolution

Review (what we’ve learned so far)Review (what we’ve learned so far) Mutations provide variability within Mutations provide variability within

speciesspecies Some traits give individuals within a Some traits give individuals within a

species an advantage - those species an advantage - those organisms live longer and/or organisms live longer and/or reproduce more = natural selectionreproduce more = natural selection

Over time, the population shifts so the Over time, the population shifts so the all (or most) individuals have this trait all (or most) individuals have this trait = adaptation= adaptation

Evolution of a whole new species Evolution of a whole new species (speciation) takes long periods of time(speciation) takes long periods of time

Main evidence for evolutionMain evidence for evolution

FossilsFossils Geographic distribution of organisms Geographic distribution of organisms

around the worldaround the world Artificial selectionArtificial selection Homologous structuresHomologous structures Vestigial structuresVestigial structures EmbryologyEmbryology Comparative analysis of DNA Comparative analysis of DNA

FossilsFossils

The bulk of our The bulk of our understanding about understanding about ancient lifeancient life

Bacterial cells to Bacterial cells to complete complete T. rexT. rex skeletonsskeletons

How are fossils formed? How are fossils formed? (Short video)(Short video) http://http://

www.teachersdomain.org/www.teachersdomain.org/6-8/sci/life/div/becfossil/6-8/sci/life/div/becfossil/index.htmlindex.html

Fossil QuestionsFossil Questions1.1. How are fossils formed?How are fossils formed?

Organism covered by sediments (mud, Organism covered by sediments (mud, sand, silt, clay, ash)sand, silt, clay, ash)

Calcium replaced by minerals in the Calcium replaced by minerals in the sediments over timesediments over time

Sometimes imprints can also be preserved Sometimes imprints can also be preserved (tracks, leaf impressions, etc.)(tracks, leaf impressions, etc.)

Fossil Questions, cont.Fossil Questions, cont.2. Why do most living things 2. Why do most living things

not leave fossils behind?not leave fossils behind?

Organism was eatenOrganism was eaten Didn’t die in correct environment to be Didn’t die in correct environment to be

preserved preserved Body has no ‘hard parts’ (shell, skeleton)Body has no ‘hard parts’ (shell, skeleton) Virtually absent from fossil record: amoebae, Virtually absent from fossil record: amoebae,

flatworms, jellyfish, sea slugs, etc.)flatworms, jellyfish, sea slugs, etc.)

Fossil Questions, cont.Fossil Questions, cont.3. How are fossils uncovered?3. How are fossils uncovered?

Erosion brings fossils back to surfaceErosion brings fossils back to surface Humans dig to find fossilsHumans dig to find fossils

• Determine specific locations that are likely spots Determine specific locations that are likely spots to hold fossilsto hold fossils

Fossil Questions, cont.Fossil Questions, cont.4. How do scientists determine 4. How do scientists determine

the age of fossils?the age of fossils?

Technique known as:Technique known as:

Radiometric DatingRadiometric Dating

http://www.teachersdomain.org/6-8/sci/life/div/radiodating/index.htmlhttp://www.teachersdomain.org/6-8/sci/life/div/radiodating/index.html

Transitional Transitional FossilsFossils

A.k.a. Intermediate A.k.a. Intermediate fossilsfossils

Provide a link Provide a link between past forms of between past forms of an organisman organism

Transitional Fossils: Orca exampleTransitional Fossils: Orca example

We’ve believed for a long time that We’ve believed for a long time that whales (and seals, otters, etc) were whales (and seals, otters, etc) were mammals because they share COMMON mammals because they share COMMON FEATURES with land mammalsFEATURES with land mammals

1.1. Warm-blooded (endothermic)Warm-blooded (endothermic)2.2. Give live birth and provide milk for youngGive live birth and provide milk for young3.3. Have hairHave hair4.4. Similar respiratory, circulatory, nervous, Similar respiratory, circulatory, nervous,

and digestive systemsand digestive systems

Transitional Fossils - WhalesTransitional Fossils - Whales

Modern whaleModern whale – totally aquatic – totally aquatic Nostrils on top of head = blowholeNostrils on top of head = blowhole Tail evolved into flipperTail evolved into flipper Ears modified directional hearing underwaterEars modified directional hearing underwater

BasilosaurusBasilosaurus – clearly aquatic – clearly aquatic Sturdy flippers & long, flexible bodySturdy flippers & long, flexible body Still has small, weak hind legsStill has small, weak hind legs Nostrils on top of headNostrils on top of head

AmbulocetusAmbulocetus – amphibious (both land and water) – amphibious (both land and water) Forelimbs equipped with fingers/small hoovesForelimbs equipped with fingers/small hooves Hind feet and tail adapted for swimmingHind feet and tail adapted for swimming Nostrils on top of snoutNostrils on top of snout

Mesocynids– terrestrial Tetrapod – limbs adapted to moving on land Ears adapted to hearing in air Nostrils in front of snoutNostrils in front of snout

Gaps in Fossil RecordGaps in Fossil Record

Fossils for 350,000 species of ancient Fossils for 350,000 species of ancient organismsorganisms 0nly a tiny fraction of total!0nly a tiny fraction of total!

Fill in the ‘gaps’ using logical reasoning Fill in the ‘gaps’ using logical reasoning and other lines of evidenceand other lines of evidence

Geographic Distribution on Geographic Distribution on Organisms around the worldOrganisms around the world

Similar environments Similar environments around the world contain around the world contain organisms that are organisms that are DIFFERENT species but DIFFERENT species but have similar anatomies have similar anatomies and/or behaviorsand/or behaviors

Similar selective Similar selective pressures lead to pressures lead to common structures and or common structures and or behaviors that aid survival behaviors that aid survival and/or reproductionand/or reproduction

Example: meerkats and Example: meerkats and prairie dogsprairie dogs

Another Another example of example of Geographic Geographic DistributionDistribution

Beaver

Muskrat

Beaver and Muskrat

Coypu

Capybara

Coypu and Capabara

Geographic Distribution, cont.

• Additionally, organisms from common ancestor will change in structure and function to adapt to their specific environment

• Prime example: islands!– the more isolated the

island, the more distinct its organisms

Artificial SelectionArtificial Selection When humans breed organisms with desired When humans breed organisms with desired

trait repeatedly until desired affect is reachedtrait repeatedly until desired affect is reached Plant and animal breeders have long taken Plant and animal breeders have long taken

advantage of the heritability of traits to improve advantage of the heritability of traits to improve crops and livestock and petscrops and livestock and pets

Humans use the same mechanisms to change Humans use the same mechanisms to change organisms that nature usesorganisms that nature uses Artificial – humans ‘select’ the best traits Artificial – humans ‘select’ the best traits Natural – nature ‘selects’ most best, or ‘most fit’ traitsNatural – nature ‘selects’ most best, or ‘most fit’ traits

Artificial Selection ExamplesArtificial Selection Examples

Hundreds of varieties of peppers – all originated from an initial species

Different breeds of dogs and cats ‘created’ by man by selecting for desirable traits (fast, sociable, good smell, short fur, etc.)

Homologous StructuresHomologous Structures

Similar structures in a variety of different Similar structures in a variety of different organisms organisms

Shared trait provides evidence that the Shared trait provides evidence that the organisms had a shared common ancestor organisms had a shared common ancestor with that traitwith that trait

Homologous bone structure in forelimbs of all mammals

Vestigial StructuresVestigial Structures

As species evolve over time… some As species evolve over time… some structures become unnecessary to survival structures become unnecessary to survival of organismof organism

Over time become reduced (vestiges) Over time become reduced (vestiges) Eventually disappearEventually disappear

http://www.livescience.com/animalworld/http://www.livescience.com/animalworld/top10_vestigial_organs.htmltop10_vestigial_organs.html

EmbryologyEmbryology

Early stages of related animals are very Early stages of related animals are very similarsimilar More closely related = more similarMore closely related = more similar

Similarities in the steps of development Similarities in the steps of development are evidence of common ancestryare evidence of common ancestry

Comparative Embryology of VertebratesComparative Embryology of Vertebrates

Comparative Analysis of DNAComparative Analysis of DNA

If all organisms evolved from same original If all organisms evolved from same original ancestors (3.5 bya), then all should share ancestors (3.5 bya), then all should share come common DNAcome common DNA

YES! all life shares same general YES! all life shares same general machinery for regulation of cell division, machinery for regulation of cell division, building cell parts, etc.building cell parts, etc.

Greater similarity between 2 species = Greater similarity between 2 species = more recent common ancestormore recent common ancestor