1. Evidence for Evolution

2. Evidence for Evolution
Darwin argued that living things have been evolving on Earth for millions of years. Evidence for this process could be found:
In the geographical distribution of living species
In the homologous structures of living organisms
In the similarities in early development
In the fossil record

3. Evidence of Evolution Evidence of Evolution includes The fossil record
Geographic distribution of living species
Homologous body structures
Similarities in early development
which is composed of
which indicates
which implies
which implies
Physical remains of organisms
Common ancestral species
Similar genes

4. Geographic Distribution of Living Species
Similar animals in different locations are the product of different lines of evolutionary descent
Because some animals on different continents live under similar ecological conditions, they are exposed to similar pressures of natural selection. Because of this, different animals evolve certain features in common even though each descended from different ancestors.

5. Geographic Distribution of Living Species
Beaver
Beaver
Muskrat
Beaver and Muskrat
Coypu
Capybara
Coypu and Capybara
NORTH AMERICA
Muskrat
Capybara
SOUTH AMERICA
Coypu

6. Homologous Structures of Living Species
Similarities among bones of different vertebrates, such as reptiles, birds, and mammals. Some limbs are arms, others are wings, legs, or flippers
Limbs differ greatly in form and function, yet are made from the same bones
Each of these limbs has adapted in ways that enable organisms to survive in different environments
Structures that have different mature forms, but develop from the same embryonic tissues are homologous structures

7. Homologous Body Structures
Turtle
Alligator
Bird
Mammals
Typical primitive fish

8. Homologous Structures of Living Species (continued)
Not all homologous structures serve important functions. These organs are reduced in size and are traces of homologous organs of other species = vestigial organs.
They probably served a purpose a long time ago
Ex. Whales have a pelvis (hip bone), but obviously don’t have legs = at one point, they probably walked
Ex. Humans have a tail bone, but obviously no tail = at one point, they probably had a tail
Ex. Humans have an appendix (part of the digestive tract) that doesn’t do anything = at one point, it probably did

9. Similarities in Early Development
Early stages (embryos) of many animals with backbones are so similar they can be hard to tell apart
Embryonic cells develop in similar order = homologous structures

10. Fossil Record and Evidence
Fossil – remains of ancient life
Different layers of rock form at different times in Earth’s history
Fossils that had formed in the different layers of rock were evidence of gradual change over time
Fossil record – provides evidence about the history of life on Earth. It also shows how different groups of organisms have changed over time
99% of all species that ever lived on Earth have become extinct

11. How Fossils Form Not all organisms that die become fossils
1) Organism dies and is buried in sediment
2) Soft tissues of the organism decay
3) Sediment becomes new rock
Water carries small rock particles to lakes and seas.
Dead organisms are buried by layers of sediment, which forms new rock.
The preserved remains may later be discovered and studied.

12. Interpreting Fossil Evidence
Paleontologists determine the age of fossils using two techniques
Relative dating
Radioactive dating (aka absolute dating)

13. Relative Dating
Average age of fossil is determined by comparing its placement with that of fossils in other layers of rock
Rock layers form in order by age – oldest layers on the bottom and more recent layers on top. What does this mean about the fossils found there?
Index fossils used to compare the relative ages of fossils. Index fossils are organisms that are easily recognized, existed for a short period, and had a wide geographic range
****Relative dating provides NO information about a fossil’s exact age in years****
A trilobite – an index fossil – it lived everywhere about 540 mya

14. Radioactive Dating (aka Absolute Dating)
****Used to assign exact ages to rocks and fossils****
Radioactive elements in rocks decay at a steady rate measured in a unit called half-life
Half-life – length of time required for half of the radioactive atoms in a sample to decay
In radioactive dating, scientists calculate the age of a sample based on the amount of remaining radioactive isotopes it contains
Different radioactive elements have different half-lives and therefore provide natural clocks that “tick” at different, but constant rates

15. Comparing Relative and Absolute Dating of Fossils
Can determine
Is performed by
Drawbacks
Relative Dating
Absolute Dating
Age of fossil with respect to another rock or fossil (that is, older or younger)
Age of a fossil in years
Comparing depth of a fossil’s source stratum to the position of a reference fossil or rock
Determining the relative amounts of a radioactive isotope and nonradioactive isotope in a specimen
Imprecision and limitations of age data
Difficulty of radioassay laboratory methods