1. Evidence for Evolution
Biology 9

2. EVIDENCE FOR EVOLUTION
What is the evidence that all species on earth are related to each other and share common ancestors?
Overview:
4 Major Types of Evidence:
Homologous Structures
Embryos
Gene Sequences
Fossils

3. 1. HOMOLOGOUS STRUCTURES –
Similar body parts or bone structures due to sharing a common ancestor that had those structures
Don’t necessarily have the same function now, but did in the common ancestor
Ex: human arm, cat leg, whale flipper, bat wing all have same bones

4. Homologous Structures, continued:
Vestigial Traits -
Don’t have a function now, but suggest that they descended from an ancestor that did use them.
Examples:
human tailbone, human goose bumps, ostrich wings Ex: human tail bone, human goose
animal.nationalgeographic.com

5. Don’t confuse Homologous Structures with Analogous Structures
structures that have the same function but NOT the same skeletal structure
This suggests these organisms did NOT descend from a common ancestor with that trait
Ex: insect wing and bird wing
Bird wing
Insect wing
bio.miami.edu

6. 2. Embryos
Similar characteristics appearing during specific embryonic/ developmental stages of development
Example: Fish, reptile, bird, and human embryos all have gill slits and a tail (but some lose these features before birth)

7. 3. Gene Sequences
Similarities between DNA or amino acid sequences for different organisms
Closer the similarities = Closer relationships

8. 4. FOSSILS Fossils show… show species that are now extinct
show transitions to new body forms
Example: Tiktaalik (lived 375 million years ago)
fish with legs and (maybe) primitive lungs…
earliest amphibian?
Artist Rendering
Fossil
Objectives for Class:
Describe how fossils are used as evidence for evolution and give one example that illustrates this.

9. FOSSILS, cont. Example: Archaeopteryx (lived 150 million years ago)
earliest bird… but has many dinosaur features
Objectives for Class:
Describe how fossils are used as evidence for evolution and give one example that illustrates this.