1. Principles of Evolution
Chapter 10

2. What is evolution?
The Simpsons Evolve

3. What is evolution?
Evolution is the process of biological change by which descendants differ from their ancestors.
A species is a group of organisms so similar to one another that they can reproduce and have fertile offspring.

4. All of these organisms are related by a common ancestor!

5. Early Ideas About Evolution
Carolus Linnaeus
Developed a classification system to group organisms based on their similarities
The system reflects evolutionary relationships

6. Early Ideas About Evolution
Georges Louis Leclerc de Buffon
Proposed that species shared ancestors instead of arising separately
Suggested that the Earth is very old

7. Early Ideas About Evolution
Erasmus Darwin
Proposed that all living things descended from a common ancestor
Proposed that more complex forms of life arose from less complex forms

8. Early Ideas About Evolution
Jean-Baptiste Lamarck
Proposed that all organisms evolve toward perfection and complexity
Proposed that changes in the environment lead to changes in an organism, which could be passed on to the offspring

9. Geologic Change
In early debates, the Earth was believed to be only about 6,000 years old

10. Geologic Change
Fossils are traces of organisms that existed in the past
It was discovered that each stratum (rock layer) had its own type of fossils
Fossils in the deepest strata were much different than the ones in the topmost strata

11. Geologic Change
Catastophism states that natural disasters shaped landforms.
These changes caused species to become extinct

12. Geologic Change
Gradualism states that landforms change very slowly over a long period of time
Species adapted to the environmental changes slowly

13. Geologic Change
Uniformitarianism states that the geologic processes that shape the Earth are uniform through time
Suggests that changes are both gradual and ongoing

14. Video Break! Theory of Evolution in 3.5 Minutes
Re-route, Put after nat sel

15. Charles Darwin In 1831, Darwin set sail from England to South America
The Galápagos Islands off the Eastern coast of South America is where Darwin began observing variations.
Variation is the difference in physical traits between individuals of the same group.

17. Darwin’s Observations
Darwin observed differences between the species on nearby islands.
Most notable were “Darwin’s Finches”

18. Darwin’s Finches
Finches with strong, thick beaks lived in areas where hard shelled nuts were available to eat

19. Darwin’s Finches
Finches with slender beaks lived in areas where insects and soft fruits were available to eat.

20. Darwin’s Finches

21. Darwin’s Finches

22. Darwin’s Finches

23. Darwin’s Observations
These observations led to the idea that species may be able to adapt to their environment
An adaptation is a feature that allows an organism to better survive in its environment
Adaptations can lead to genetic change in a population over time

24. Darwin’s Fossil Observations
He found fossils that looked similar to living organisms and thought they must be related somehow

25. Natural Selection
Darwin conducted research for over 20 years to further develop his theory of evolution
He began observing the work of farmers and animal breeders and even began breeding his own pigeons
After much research, he came up with the theory of natural selection to explain how evolution occurs

26. Natural Selection
Heritability is the ability of a trait to be passed down from one generation to the next
Artificial selection is a process by which humans change a species by breeding it for certain traits
Ex: dog breeding

27. Natural Selection

29. Natural Selection
Darwin realized that if breeders can select for desirable traits, they can also select against undesirable ones
If humans are the selective agent in artificial selection, then the environment is the selective agent in natural selection

30. Natural Selection
Natural selection is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals
Traits are passed on only if they are advantageous to the organism in the current environment
More offspring = passing on genes

31. Natural Selection
Darwin had observed in the Galápagos that some individuals in a given population had variations that were particularly advantageous in their environment
He realized that these adaptations occurred over many generations
“Descent with Modification”

32. Natural Selection
Natural selection can act only on traits that already exist.

33. Natural Selection - 4 Main Principles
Variation - Heritable differences in the population are the basis for natural selection
Overproduction - Having many offspring raises the chance that some will survive and pass on your traits

34. Natural Selection - 4 Main Principles
Adaptation - Certain traits may allow an individual to better survive in its environment. They are “naturally selected” to survive and produce more offspring and pass on those useful traits.
Descent with Modification - Over time, natural selection results in species with adaptations that are well suited for survival and reproduction in the environment

35. Natural Selection
As long as the environmental conditions continue to remain beneficial to the trait, the trait will continue to be passed from generation to generation
If the environment changes, the traits that were originally beneficial may no longer be favorable
1977 Island Drought

36. Natural Selection Example
Peppered moth is a species of moth from Europe
They are either white colored or black
Originally, the majority of peppered moths were white, which was effective camouflage against the light-colored tree bark

38. Natural Selection Example
Effective camouflage = better survival = that trait was passed on from generation to generation
The black moths stood out against the light tree bark, and were more easily spotted by predators

39. Natural Selection Example
During the Industrial Revolution, the lichens on the tree bark died, causing the trees to now have dark bark
White moths began to die off, while the black ones flourished

41. Natural Selection
Fitness - A measure of the ability to survive and produce more offspring relative to other members of the population in a given environment

42. “Survival of the fittest”
Many people think that natural selection leads to the “most complex” or “most perfect” individuals ever, and that less fit individuals are wiped out or considered more “simple”
In reality, the individuals that are most fit are only most fit for the current environmental conditions. These conditions can change at any time.
Less fit individuals are not necessarily wiped out--they have to compete more and may reproduce less offspring.
Finally, organisms do not seek to become more complex. If a certain set of adaptations is beneficial for the environment, they will continue to be passed down, no matter how “simple” they seem

43. Evidence for Evolution - Fossils
Fossils in deeper layers of rock are older than fossils in shallower layers
Fossil sequences suggested descent with modification
Transitional fossils

45. Evidence for Evolution - Fossils
Transitional fossils between whales and mammals - see pg 300

46. Evidence for Evolution - Geography
Darwin found that the finches on the Galápagos islands were similar, but had different adaptations
Local adaptations
All shared a common ancestor from the mainland

48. Evidence for Evolution - Embryology
The embryos of many vertebrates are very similar
Gill slits, tails
Suggests a common ancestor

50. Evidence for Evolution - Anatomy
Homologous structures are features that are similar in structure, but differ in function in different species
Suggests a common ancestor
Common example: forelimb of tetrapod vertebrates

53. Evidence for Evolution - Anatomy
Vestigial structures are remnants of organs or structures that had a use in an earlier ancestor, but do not anymore
Ostrich wings
Snake leg bones
Human appendix
Can suggest adaptation or a common ancestor

57. Evidence for Evolution - DNA
DNA can be analyzed and compared between organisms
The more similar the DNA, the more closely related they are

58. Evidence for Evolution - Protein Comparison
All living things have DNA and make mostly the same proteins made from the same amino acids
Unique proteins in specialized cells can be compared across species

59. Evidence for Evolution - Protein Comparison
Proteins of light-sensitive cells in the brain of this ancient marine worm are very similar to the cells in the vertebrate eye
Shows common ancestry