1. Evidence for Evolution
Review (what we’ve learned so far)
Mutations (and sexual reproduction/ crossing over) provide variability within species
Some traits give individuals within a species an advantage - those organisms live longer and/or reproduce more = natural selection
Over time, the population shifts so that all (or most) individuals have this trait = adaptation
Evolution of a whole new species (speciation) takes long periods of time

2. Main evidence for evolution
Fossils
Embryology
Homologous structures
Vestigial structures
Comparative analysis of DNA
Artificial selection
Geographic distribution of organisms around the world

3. Fossils The bulk of our understanding about ancient life
Bacterial cells to complete TRex skeletons
How are fossils formed? (Short video)
How are fossils formed?

4. Fossil Questions 1. How are fossils formed?
Organism covered by sediments (mud, sand, silt, clay, ash)
Calcium replaced by minerals in the sediments over time
Sometimes imprints can also be preserved (tracks, leaf impressions, etc.)

5. Fossil Questions, cont. 2. Why do most living things not leave fossils behind?
Organism was eaten
Didn’t die in correct environment to be preserved
Body has no ‘hard parts’ (shell, skeleton)
Virtually absent from fossil record: amoebae, flatworms, jellyfish, sea slugs, etc.)

6. Fossil Questions, cont. 3. How are fossils uncovered?
Erosion brings fossils back to surface
Humans dig to find fossils
Determine specific locations that are likely spots to hold fossils

7. Fossil Questions, cont. 4. How do scientists determine the age of fossils?
Technique known as:
Radiometric Dating

8. Transitional Fossils A.k.a. Intermediate fossils
Provide a link between past forms of an organism

9. Transitional Fossils: Orca example
We’ve believed for a long time that whales (and seals, otters, etc) were mammals because they share COMMON FEATURES with land mammals
Warm-blooded (endothermic)
Give live birth and provide milk for young
Have hair
Similar respiratory, circulatory, nervous, and digestive systems

10. Transitional Fossils - Whales
Modern whale – totally aquatic
Nostrils on top of head = blowhole
Tail evolved into flipper
Ears modified directional hearing underwater
Basilosaurus – clearly aquatic
Sturdy flippers & long, flexible body
Still has small, weak hind legs
Nostrils on top of head
Ambulocetus – amphibious (both land and water)
Forelimbs equipped with fingers/small hooves
Hind feet and tail adapted for swimming
Nostrils on top of snout
Mesocynids– terrestrial
Tetrapod – limbs adapted to moving on land
Ears adapted to hearing in air
Nostrils in front of snout

11. Gaps in Fossil Record Fossils for 350,000 species of ancient organisms
0nly a tiny fraction of total!
Fill in the ‘gaps’ using logical reasoning as well as other lines of evidence

12. Embryology Early stages of related animals are very similar
Similarity in the development from egg to adult form (ontogeny) is evidence of common ancestry
More similarity in ontogeny = more recent common ancestor (more closely related)

13. Comparative Embryology of Vertebrates

14. Homologous Structures
Similar structures in a variety of different organisms
Shared trait provides evidence that the organisms had a shared common ancestor with that trait
Homologous bone structure in forelimbs of all mammals

15. Vestigial Structures
As species evolve over time… some structures become unnecessary to survival of organism
Over time become reduced (vestiges)
Eventually disappear

16. Comparative Analysis of DNA
If all organisms evolved from same original ancestors (3.5 bya), then all should share come common DNA
YES! all life shares same general machinery for regulation of cell division, building cell parts, etc.
Greater similarity between 2 species = more recent common ancestor

17. Cladograms
Cladograms are “family trees” (actually, many families) that show how organisms are related.
A point at which two lines meet represents a common ancestor or the emergence of a homologous trait. The distance represents time on most cladograms.

18. Cladograms and DNA analysis
With the ability to compare DNA, cladograms have become more specific (and complicated)!

19. Artificial Selection
When humans breed organisms with desired trait repeatedly until desired characteristic is obtained
Plant and animal breeders have long taken advantage of the heritability of traits to improve crops and livestock and pets
Humans use the same mechanisms to change organisms that nature uses
Artificial – humans ‘select’ the best traits
Natural – nature ‘selects’ most best, or ‘most fit’ traits

20. Artificial Selection Examples
Different breeds of dogs and cats ‘created’ by man by selecting for desirable traits (fast, sociable, good smell, short fur, etc.)
Hundreds of varieties of peppers – all originated from an initial species

21. Geographic Distribution on Organisms around the world
Similar environments around the world contain organisms that are DIFFERENT species but have similar anatomies and/or behaviors
Similar selective pressures lead to common structures and or behaviors that aid survival and/or reproduction
Example: meerkats and prairie dogs

22. Another example of similar geography resulting in similar structure in unrelated organisms: beavers, muskrats, coypus, & capybaras
Beaver
Muskrat
Beaver and Muskrat
Coypu
Capybara
Coypu and Capabara

23. Geographic Distribution, cont.
Additionally, organisms from a common ancestor will change in structure and function to adapt to a new, specific environment
Prime example: islands!
the more isolated the island, the more distinct its organisms