1. Chapters 15, 16, and 17
Evolution

2. The Theory of Evolution
Theory – well-tested explanation that unifies a broad range of observations
Evolution – change in a kind of organism over time; process by which modern organisms have descended from ancient organisms
Can theories change over time?
Are theories supported scientifically?

3. Charles Darwin – 1831 Voyage of the Beagle

4. Darwin studied: Fossils – he was curious as to why some were extinct
Diversity – he found a wide range of living things well adapted to their environment
Fossils – he was curious as to why some were extinct
Ground Sloth Fossil

5. Galapagos Islands Volcanic islands off the west coast of South America
Unique species found nowhere else in the world
How did this
happen?

6. Galapagos

7. Galapagos

8. Darwin Returns Home
After Darwin returned home, he studied his notes and specimens
He struggled with his observations and how they conflicted with his religion
He finally published On the Origin of Species, a book which outlined his theories of natural selection and evolution over time

9. Darwin’s Influences:
James Hutton and Charles Lyell – Geologists whose theories suggested that Earth was extremely old and was always changing slowly over time.
Darwin proposed that living things were not fixed in one form, but also changed slowly over time.

10. Darwin’s Influences:
Jean-Baptiste Lamark – proposed the theory of acquired characteristics
Use or disuse…some traits were passed down to help survival of offspring
False theory

11. Darwin’s Influences
Thomas Malthus – an English economist who studied human population growth
He believed that if humans became overpopulated, they would struggle to survive without sufficient resources
Darwin applied this to animals and plants and believed it was the driving force for evolution.

12. Darwin studied variation
Darwin did not know about genes, but did observe traits being passed on
Artificial selection – when humans choose which traits are to be passed on in animals and plants by selective breeding
Examples: Breeds of dogs, pidgeons, cows, corn, Brassica oleraceae

13. Darwin proposed Natural Selection
The idea that there is a struggle for survival…need to find food, mates, run away, hide, or protect themselves
Darwin proposed that some individuals were better adapted for their environment
Adaptation - any inherited characteristic that increases an organism’s chance of survival
“SURVIVAL of the FITTEST”

14. Adaptations:

15. Descent with Modification
Darwin proposed Descent with Modification
Living things changed over long periods of time due to natural selection
He believed that living things evolved from a “common ancestor”
“Tree of life” links all living things

16. Darwin’s early drawing of a tree of life…

17. Evidence of Evolution:
The fossil record

18. Evidence of Evolution
Geographic distribution of living things – different animals on different continents looking similar (marsupial wolf and grey wolf)
Animals that are not closely related have similar adaptations

19. Evidence of Evolution
Homologous Structures – structures that have different mature forms but develop from the same embryonic tissues.
Vestigial organs
remnants of
legs in skinks,
appendix in
humans…

20. Evidence of Evolution
Similarities in Embryology

21. Pattern of Evolution
Coevolution: the change in two or more species in close association with each other
Ex: Plants and their pollinators

22. Patterns of Evolution Cont’d
Convergent Evolution
Organisms appear similar, but are not related
The environment selects similar phenotypes
Ex: streamlined body of dolphins and sharks

23. Patterns of Evolution Cont’d
Divergent Evolution
Two or more related species become more and more dissimilar
Can result in new species
Response to differing habitats
Adaptive radiation: many related species evolve from a single ancestral species

24. Chapter 16 – Evolution of Populations
Evolution in genetic terms – any change in the relative frequency of alleles in a population.
Gene pool – all genes (T, t) present in a population
Relative frequency – number of times one allele appears compared to all alleles in the gene pool. (Example: B = 40%, b = 60%)
The population is evolving if the frequency changes

25. Gene Pool
allele for
brown fur
allele for
black fur

26. Sources of Genetic Variation:
Mutations – a change in the sequence of DNA. Caused by chemicals, radiation, or just randomly. Can be harmful, helpful, or have no effect.
Gene shuffling – genes are recombined during the formation of gametes for sexual reproduction. Does not change gene frequencies on its own.
How many genes control one trait?

27. Single Gene and Polygenic Traits
If a trait is controlled by one gene it is called a single-gene trait.
Single-gene traits result in only two phenotypes. Example: Tall or Short
Polygenic traits result in a range of phenotypes. Example: height of a human being.

28. Which graph represents a polygenic trait?

29. Polygenic traits continued…
Directional Selection

30. Polygenic traits continued…
Stabilizing selection
(Example: Birth weight)

31. Polygenic traits continued…
Disruptive selection
Example: Beak Size

32. Genetic Drift Genetic drift is a random change in gene frequency.
Common in small populations
Founder effect – a small group migrates away from the original group and has a unique gene pool
Examples: Galapagos, Hawaii..

33. Hardy-Weinberg principle
If a population does not evolve, it is in genetic equilibrium. It must:
1. Have random mating
2. Consist of a large population
3. No members move in or out of the group
4. Have no mutations
5. No natural selection occurs
Example? Coelacanth?

34. Speciation
Species – a group of organisms that can breed with one another and have fertile offspring
Speciation – formation of a new species due to natural selection or chance events

35. Isolating Mechanisms
In order for new species to evolve, groups of organisms must be separated or isolated.
If the two groups change enough, and can no longer breed and create fertile offspring, then new species were formed.

36. Causes of reproductive isolation -
Geographical isolation – Groups are physically separated.
Ecological isolation- Groups occupy different habitats.
Temporal isolation- reproduce at different times of the day.
Behavioral isolation- no attraction.
Mechanical isolation- structural differences.
Reproductive failure- no fertile offspring.

37. Speciation in Darwin’s Finches:

38. 17-2 Earth’s Early History and 17-4 Patterns of Evolution
Earth is about 4.6 billion years old
Earth’s early atmosphere probably contained:
Hydrogen cyanide
Carbon dioxide
Carbon monoxide
Nitrogen
Hydrogen sulfide
Water

39. Where did organic compounds come from?
1950s – Stanley Miller and Harold Urey designed experiments that showed organic compounds could be formed from elements in Earth’s early atmosphere if an electric current was introduced
Lightning could provide the electric current
Amino acids, cytosine, and uracil could be formed in these experiments.

40. Miller/Urey’s experiment
Mixture of gases simulating atmospheres of early Earth
Spark simulating lightning storms
Cold water cools chamber, causing droplets to form
Liquid containing amino acids and other organic compounds

41. Organic molecules to cells?
Organic molecules can form tiny bubbles called proteinoid microspheres, almost like oil in water
RNA may have been the first hereditary material, as it can self-replicate and act as catalysts.
These components may have been the first primitive cells…but the exact origin of life is a MYSTERY!

42. Early Bacteria created Oxygen
Cyanobacteria (blue green algae) were probably the first living things to manufacture oxygen
Oxygen changed the atmosphere, turned the sky blue, and allowed organisms to respire aerobically (more efficient)

43. Endosymbiotic Theory
Eukaryotic cells may have formed when larger cells engulfed smaller prokaryotes
Mitochondria and chloroplasts may have been free-floating bacteria
Evidence: They have DNA and ribosomes similar to bacteria and reproduce by binary fission
The ability to respire aerobically and the ability to reproduce sexually increased diversity and influenced evolution

44. Endosymbiotic Theory

45. Other Topics: Fossils and ancient life Index fossils
Radioactive dating
Geologic time scale
Evolution of
multicellular life
Mass extinctions

46. Patterns of Evolution
Macroevolution – large scale evolutionary patterns and processes over long periods of time
Extinction
Adaptive Radiation
Convergent Evolution
Coevolution
Punctuated Equilibrium
Changes in developmental genes

47. Extinction When a species no longer exists on earth
Most extinctions were natural until recent times
Can be gradual for individuals or can be catastrophic mass extinctions that affect multiple life forms
Scientists believe an asteroid impact caused a mass extinction event in the Cretaceous

48. Adaptive Radiation
When a single species or small group of species evolve into many diverse forms over time.
Examples: Mammals evolved, finches evolved

49. Convergent evolution
When unrelated organisms that live in similar environments develop similar adaptations to survive

50. Coevolution
The process by which two species evolve in response to changes in each other over time

51. Punctuated Equilibrium
Long, stable periods with little change in species interrupted by brief periods of rapid change
Results from small populations, isolated populations, following mass extinctions…

52. Developmental Genes and Body Plans
In some cases, small changes in just a few genes can cause major changes in an organism
Hox genes are “master control” genes for animal body plans
One change in a gene can lead to wingless, one pair, or two pairs