1. Chapter 10 Darwin's Theory of Evolution

2. Voyage of the Beagle Charles Darwin – Naturalist (1809-1882)
1831 – set sail on the H.M.S. Beagle

3. The Galápagos Islands 1000 km west of South America
Islands are close together but very different
Darwin was fascinated by the land tortoises and marine iguanas

4. Galapagos Islands
-Darwin collected animal specimens on the four islands he visited.
He noticed each island had their own varieties of animals.
The animals he saw were different than those in Europe but similar to those in South America.
He realized that there is a huge amount of diversity in animal and plant life.

5. The shape of a tortoise's shell could be used to identify which island a particular tortoise inhabited.

6. Artificial Selection
Later, Darwin thought about how pigeon breeders “selected for” traits that they wanted in the offspring.
He called this artificial selection. Can you think of some examples of how we use it today?
Darwin wondered if this could happen in nature.

7. Natural Selection 1. There is variation in species.
The Four Principles of Natural Selection
1. There is variation in species.
2. Variations can be inherited.
3. Individuals have more offspring than can survive on available resources.
4. Traits that increase survival are more likely to be passed on (remember the fast rabbit we talked about last chapter)

9. Natural Selection
Darwin thought that, given enough time, natural selection could change a population enough to create a new species.

10. Other Ideas
Lamarck thought that animals could pass on body and behavior characteristics that they acquired throughout their lives

11. Darwin realized that natural selection worked with traits that animals already had, not characteristics they had gained throughout their lives or experiences they had.

12. Evolution
When Darwin wrote a book about his findings he only used the word “evolution” on the last page.
Evolution – cumulative changes in groups of organisms through time.
Evolution is driven by natural selection.
Natural Selection explains how evolution works
Populations evolve, but individuals do not

13. Evidence of Evolution
The theory of evolution states that all life on earth descended from a common ancestor.
Fossils provide some of the best evidence for evolutionary change

14. The Fossil Record
Some ancient species have modern counterparts

15. Fossil record of the camel

16. Comparative Anatomy
These are all forelimbs. What do they have in common?

17. Homologous Structures
Homologous structures- anatomically similar structures that are inherited by a common ancestor
Example: forelimbs have very similar bones in many animals

18. Vestigial Features
Reduced forms of structures found in other organisms.
Examples: human appendix, wisdom teeth, pelvic bones in snakes, and lots more… As an embryo you even had the beginnings of gills.

19. You don’t need your appendix, but it is extremely important for some animals.

20. Human tailbone is a vestigial vertebrate tail
consists of fused
vertebrae that no
longer function
as a tail

21. Comparative Embryology
Embryos from different species have similarities.
Example: many embryos that don’t live in the water (including us) have pharyngeal slits that develop into gills in fish.

22. Similarities In Embryonic Development
Evidence for Evolution - Comparative Embryology
Similarities In Embryonic Development

23. Adaptation
A trait shaped by natural selection to increase the survival or reproductive success of an organism.

24. Camouflage
An adaptation that helps an organism blend in to the environment

25. Mimicry
A adaptation in which one species evolves to resemble another

26. Allelic Frequencies
Populations change with the frequencies of alleles change.
Genetic drift-a change in allelic frequencies in a population due to chance.

27. Hardy-Weinberg Principle
When allelic frequencies remain constant, a population is in genetic equilibrium.
The principle says that evolution won’t occur unless a population is acted on by some force.

28. Hardy-Weinberg Equation
p2+2pq+q2=1
This equation helps us understand the frequencies of alleles.
But, this equation doesn’t really describe what happens in nature (we know allelic frequencies change)

29. Why the Equation Cannot Describe Real Populations
-gene flow (new individuals come in, some leave
-nonrandom mating (mating is rarely completely random)
-Mutations (mutations change gene frequencies)
-Natural Selection (individuals aren’t equally adapted, we know natural selection changes allelic frequencies.

30. Founder Effect
Occurs when a small sample of a population gets isolated.
How would the continuing population change?
What kind of environment could cause this?
Think back to the places Darwin studied

31. Bottleneck
A bottleneck occurs when a population declines to a very low number and then rebounds.

32. Sexual selection
Change in frequency of a trait based on competition for a mate
Darwin wondered why individuals would pick mates based on traits that did not seem to enhance survival.

33. Reproductive Isolation
Speciation-the process by which some individuals change so much that they cannot produce reproductively viable offspring.

34. Even though these are both birds, they are different species
Even though these are both birds, they are different species. Some species don’t breed with one another for various reasons. Can you think of some?

35. Some species can reproduce, but some offspring cannot reproduce
Some species can reproduce, but some offspring cannot reproduce. Example: Ligers and mules

36. Zebra-donkey hybrid

37. Two Types of Speciation
Allopatric speciation-a physical barrier separates one population into two or more.
Sympatric speciation- a species evolves into a new species without a physical barrier

38. Abert Squirel
Kaibab Squirel
The grand canyon separates these two squirrel species, so they are never in contact with one another. Is this allopatric or sympatric speciation?

39. One species of apple flies only feeds one kind of apple why the other eats only another kind. However, they live side by side. Sympatric or allopatric?
There is no physical barrier between these flys

40. Coevolution
When two species live in close relationship with one another, the evolution of one species affects the evolution of another.

41. Gradualism
Remember, most of the time evolutionary changes happen in very small steps over millions of years. Scientists call this idea the theory of gradualism