1. 16.3 Evolution by Natural Selection 16.4 Evidence of Evolution
PICTURES/FIGURES IN BOOK ARE VERY HELPFUL IN UNDERSTANDING THESE TWO SECTIONS – USE THEM!

2. Evolution by Natural Selection
Natural selection only occurs under certain conditions:
Organisms struggle for existence
Ex: More are born than can survive
2. Organisms inherit variable traits
Ex: Varied traits give organism’s different fitness
3. Survival of the fittest
Ex: Most adapted to environment survive AND REPRODUCE

3. Evolution by Natural Selection
Adaptations – any heritable characteristic that increases an organism’s ability to survive and reproduce
Involve body parts/structures, physiological functions, or different behavior patterns
Examples? Write your own

4. Survival of the Fittest
What’s “fitness”?
How well an organism can survive and reproduce in its environment
Low fitness – means individuals are less adapted to surviving/reproducing
High fitness – means individuals are more adapted to surviving/reproducing
Survival is MORE than staying alive
Survival of the species!

5. What is Natural Selection?
Natural selection - the process by which organisms with variations MOST suited to their local environment survive and leave more offspring
More individuals are born than can survive
What selects who lives or dies?
Example – Page 462

6. Fitness can vary --- Who is most fit?

7. Fitness can vary --- Who is most fit?

8. Natural Selection Natural selection occurs in any situation when:
More individuals are born than can survive
There is natural heritable adaptation
There is variable fitness among individuals
Natural selection does NOT make “better” organisms – they are just good enough to survive and reproduce

9. Darwin’s Most Dangerous Idea
Descent with modification:
Offspring changed/modified to better survive
Darwin proposed that adaptations could produce new species over many generations
Common descent:
All living and extinct species are descended from ancient common ancestors
Darwin's Tree
of Life

10. 16.4 Other Evidence for Evolution
Today, we are able to use new fields of science to provide further evidence for evolution
Includes:
Biogeography
Age of Earth and Fossils
Comparing Anatomy
Comparing Embryology
Genetics and Molecular Biology

11. 1. Biogeography Fossils help us study biogeography –
The study of where organisms live now and where they and their ancestors lived in the past
Many organisms on the Galapagos Islands are ONLY found on the Galapagos Islands…
How did they get there?

12. 2. Age of Earth and Fossils
Radioactive dating gives accurate age of Earth – 4.5 billion years old!
Proves that evolution has had time to occur
Fossil record is incomplete, but does show enough to indicate evidence for evolution

13. 3. Comparing Anatomical Structures (Important section of book!)
Homologous structures – body parts that are structurally similar in different species
Look at cladogram below: Which organisms are most similar? What does this tell you?
Birds and reptiles most recent common ancestor
This is a cladogram 

14. Analogous Structures
Analogous structures – body parts that share a common function, but not structure
DOES NOT indicate common descent just because parts are used for same function
Ex: wings of…

15. Vestigial Structures
Vestigial structure – structure inherited from ancestors but has lost much or all of its original function
Ex: hipbones of bottlenose dolphins are vestigial structures. In their ancestors, hipbones played a role in terrestrial locomotion. However, as the dolphin lineage adapted to life at sea, this function was lost
Others?

16. 4. Embryology
Vertebrates (animals with backbones) have similar embryological development patterns
Develop in the same order and in similar patterns to produce many homologous tissues and organs
Provide further evidence that organisms have descended from a common ancestor

17. 5. Genetics and Molecular Biology
The universal genetic code and homologous molecules provide evidence of common descent
Genetic code is nearly identical in almost all organisms, including bacteria, yeasts, plants, fungi, and animals
Remember – amino acid sequence lab!