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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