1. Darwin’s Theory of Evolution
Chapter 16

2. Section 16.1 Darwin’s Voyage
Objectives:
State Darwin’s contribution to science
Describe the biodiversity Darwin observed
Video clip

3. Evolution: Evolution: change in species over time Charles Darwin
Born in England on Feb. 12, 1809
Naturalist who studied diversity of life
Took 5 year trip on HMS Beagle ( )
HMS Beagle (captain and crew) would be mapping the coastline of S. America
Evolution not just something that happened in the past
Darwin’s ideas help to explain modern phenomenon like drug-resistant bacteria and newly emerging diseases like the avian or swine flues

4. Darwin’s Observations
Species vary globally
Different but ecologically similar animal species inhabited separated, but ecologically similar, habitats around the globe
Also, noticed that kangaroos lived only in grasslands of Australia (not in similar grasslands of Europe) and rabbits that lived in grasslands of Europe were not found in grasslands of Australia – WHY??
Rhea
S. America
Ostrich
Africa
Emu
Australia

5. Darwin’s Observations
Species vary locally
Hood Island Tortoise
Different yet related species often occupied different habitats within a local area
Tortoises of the Islands differed based on Island they were found on
- Hood Island: tortoise has curved shell that is open near neck and legs to allow animal to reach the sparce, high vegetation
- Isabela Island: tortoise has the dome shaped shell and short neck; vegetation is plentiful on this island
Also observed several types of small brown birds on the islands with beaks of different shapes – thought they were wrens, warblers and blackbirds – all turned out to be finches found no where else (although related to species found in S. America)
Isabela Island Tortoise

6. Darwin’s Observations
Species vary over time
Fossil: preserved remains or traces of ancient organisms
Related??
Darwin also collected fossils on his journeys.
He found a fossil of an organism called a glyptodont (long-extinct) in an area where armadillos currently live
He wondered if the two might be related
Looking at pictures – how are they the same? How are they different?
On his way home, Darwin thought about what he had seen. He sent plant and animal species he collected out to experts for identification and discovered that many of the species he collected were related (several types of birds that he had observed turned out to be finches found no where else, although they resembled a S. American finch species)
Began to wonder if different Galapagos species might have evolved from S. American ancestors

7. Check-in What is evolution?
Contrast the pattern Darwin observed among the large, flightless birds and the pattern he observed among the tortoises.
Change in species over time
For the second question, have students write for 1 minute in response – then call on several students to share their responses
Similar environments seem to result in similarities among organisms. Different environments result in differences among organisms.

8. Section 16.3 Darwin’s Ideas
Objectives:
Describe conditions under which natural selection occurs.
Explain common descent.

9. Evolution by Natural Selection
Struggle for Existence
Not all young survive
Some killed by disease, predators
Only some reproduce
Grasshoppers can lay over 200 eggs at a time. Only a small fraction of these offspring will survive to reproduce.

10. Evolution by Natural Selection
Variation and Adaptation
Natural differences among same species
Adaptation: heritable variation that increases change of surviving and reproducing
Variation in nature – green and yellow grasshoppers (color is a heritable trait)
In this case, green is an adaptation because it allows the grasshoppers to blend into their environment and reduces the risk that they will be caught by predators.

11. Evolution by Natural Selection
Survival of the fittest
Fitness: how well an organism can survive and reproduce
Organisms with favorable traits survive and reproduce
Offspring inherit
those traits/genes
Green grasshoppers have a higher fitness than yellow grasshoppers because their green color allows them to hide better from predators. This means that green grasshoppers survive and reproduce more than yellow grasshoppers in this environment.

12. Evolution by Natural Selection
Natural Selection occurs when
More individuals are born than can survive
There is natural heritable variation
There is variable fitness among individuals
More grasshoppers are born than can survive
Individuals vary in color and color is a heritable trait
Green individuals have a higher fitness in their current environment

13. Principle of Common Descent
Descent with modification
“All species – living and extinct – descended from ancient common ancestors”
Darwin drew the first tree of life to describe how descent with modification could produce the diversity of life seen today.
If you look back in time, you can find common ancestors shared by tigers, panthers, and cheetahs.
Further back, you find ancestors that these felines (cats) shared with dogs.
Further back, is the common ancestors of all mammals with birds, reptiles and fish.
Further back still, are the common ancestors of all living things.

14. Check-in
Describe the expected evolutionary change of these rabbits over time. Include the conditions under which natural selection occurs.
Given two variations in rabbit fur color and the new environment (it is getting colder and so there is snow for a greater period of the year), what do you expect to occur. Be sure to describe HOW natural selection will work in this situation.

15. Section 16.4 Evidence of Evolution
Objectives:
Describe various types of evidence to support evolution.

16. Evidence of Evolution Biogeography Closely related but different
Distantly related but similar
Biogeography – study of where organisms live now and where they and their ancestors lived in the past
Finches – populations on the islands evolved from mainland species (environments on the islands selected for closely related species)
Similar habitats can produce species that have similar adaptations (environment selects for similar adaptations) even though they are distantly related (eg. similar ground dwelling birds inhabit similar grasslands in several different continents)

17. Evidence of Evolution Age of Earth Fossils
Radioactive dating indicates Earth is about 4.5 billion years old
Fossils
Trace evolution of
modern species from
extinct ancestors
In order for evolution to have occurred, the Earth must be very old.

18. Evidence of Evolution Anatomical Structures
Homologous: similar structures inherited from common ancestor
EX. Similar arm and hand bones in human, cat, whale, bat

19. Evidence of Evolution Anatomical Structures
Analogous: similar function, but different structure (and different ancestor)
EX. Wings of bird vs. wings of butterfly

20. Evidence of Evolution Anatomical Structures
Vestigal: reduced in size and function
EX. Pelvic bones in whale; appendix in humans

21. Evidence of Evolution Embryology Similarities in fetal development
Early development of vertebrates is very similar which suggests that they have a common ancestor

22. Evidence of Evolution Biochemistry / DNA Similar DNA patterns
98% similarity between humans and chimps
90% similarity between human and mouse
Similarities in the chemical compounds that make up organisms
Ex. Cytochrome C used in cellular respiration is similar in almost all living cells

23. Check-in
List some things that provide evidence to support the theory of evolution.
Give an example of biogeography in which species are closely related but different.
Biogeography, age of Earth, fossils, anatomical structures, embryology, biochemistry/DNA
Finches, tortoises

24. Check-in
What type of structure is each of the following an example of:
Wings of bird and wings of bee
Human appendix
Wing of chicken and foreleg of alligator
Analogous structure
Vestigal structure
Homologous structure

25. References
DNA similarity: