1. Mechanisms of Population Change
Chapter 4
Mechanisms of Population Change

2. Ch. 4 Mechanisms of Population Change
4.1 Adaptation, Variation, and Natural Selection
4.2 Developing a Theory to Explain Change
4.3 How Species Form

3. 4.1 Adoption, Variation, and Natural Selection
In this section, you will:
Describe how sexual reproduction and changes in genetic information result in variation within populations
Design an investigation to measure variation in a population
Describe how some mutations may improve an individual organism’s change for survival and reproduction
Define natural selection

4. Why is it that not all members of a species are exactly alike?

5. Adaptations and Survival An adaptation is a structural, behavioural, or physiological process that helps an organism survive and reproduce in a particular environment.

6. Adaptations are the result of a gradual change in the characteristics of members of a population over time.

7. Polar Bear Adaptations
Q#1: What are some of the adaptations that help a polar bear survive and reproduce in the Arctic?

8. Structural Adaptations
Physical features of an organism that help it survive.

9. Behavioural Adaptations
Behavioral response to stimulus (what does a cat do when threatened)

10. Physiological Adaptations
A response of an individual to a specific external stimulus in order to maintaining homeostasis
E.g., shivering

11. Variation: a visible (e. g. , color) or invisible difference (e. g
Variation: a visible (e.g., color) or invisible difference (e.g., biochemical) that helps an individual in a population survive. It is likely to be passed on from survivor to survivor.

12. Variation is an visible or invisible difference in a species as a result of genetic changes and recombinations/mutations in DNA.
A variation in an individual can be an advantage or disadvantage, or have no effect on the individuals as they live and interact in their environment.

13. Variation Within Species
Sexual reproduction allows for the genetic material from both parents to go to the offspring.
The recombination of genetic material results in great genetic variation among individuals within a population.

14. All variations are caused by mutations.
Mutations are changes in the genetic material of an organism.
Happen at the DNA level

15. Mutations Lead to Genetic Variation
Mutations can occur continuously when a cell divides, or as a result of a mutagen environmental agents that cause mutations in the DNA.
When a cell mutates it may exhibit new characteristics, result in malfunctioning, or a cluster of cells (tumor).

16. Location of Mutation:
1) Somatic cells (body cells) – disappears when the organism dies.
2) Reproductive cells (gametes-sex cell) – passed on to the next generation
– lead to variations which can lead to selective advantage

17. Results of Mutations:
Exhibition of new characteristics (ex. Sickle cell)
Cell Death
Malfunctioning Cells
Multiplication (could result in a tumor)

18. Case Study: Venom-Resistant Squirrels
In California, some ground squirrels have developed a mutation that makes them more resistant to rattlesnake venom
Which squirrel is more likely to survive?
Resistant Squirrel
Non-resistant Squirrel
If that squirrel mates with another with the same variation, what happens to the genetic makeup of the population?

19. Case Study: “Superbugs”
In 1928, Sir Alexander Fleming discovered that penicillin could be used to kill bacteria
Penicillin was first used as a medicine in 1941
By 1945, there were already reports of penicillin-resistant strains of bacteria
There are now bacterial strains that are resistant to all known antibiotics
YouTube video no longer working.

20. Mutations Can Provide a Selective Advantage
Mutations can affect the well-being of an organism and can be harmful.
In some cases, however, a mutation enables an organism to survive in its environment better, which it turn, means that the organism is more likely to reproduce and pass on its genetic material.

21. Mutations Can Provide a Selective Advantage
If an organism’s environment is changing, mutations that were no advantage (or even a disadvantage) may become favorable in the new environment.
This is an example of a mutation providing a selective advantage in the new environment.

22. Mutations Can Provide a Selective Advantage
Populations that reproduce quickly, such as bacteria, viruses, and many insects can change fairly quickly.

23. Case Study: Pesticide Resistance
In 1955, the World Health Organization initiated a widespread program to kill malaria-carrying mosquitoes using DDT (an untested pesticide)
This program was initially very successful in decreasing mosquito populations, but they quickly reappeared
Why did DDT lose its effectiveness?

24. Natural Selection
Natural Selection: a process that results when the characteristics of a population of organisms change because individuals with certain inherited traits survive specific local conditions and pass on their traits to their offspring.
For natural selection to occur there must be a variety or diversity within a species.

25. Natural Selection
Individuals do not change during their lifetime, rather, over time, the population changed in its ability to survive in particular conditions.
In other words, populations change, not individuals.

26. Natural Selection
An abiotic condition can be said to select for certain characteristics and select against different characteristics in other individuals- the environment exerts selective pressure on a population.

28. Natural Selection
Natural selection does not anticipate change in the environment; natural selection is situational.
Instead, random changes occur and influence the production of traits that may be beneficial in the future

29. Peppered Moths-Natural Selection

30. Do Now Hand-in your Invasive Species assignment into the blue bin.
Ensure you name is on it.

31. IN YOUR OWN WORDS DEFINE/DESCRIBE:
Adaptation (3 types)
Variation
Mutation (2 types)
Natural Selection

32. 4.2 Developing a Theory to Explain Change
In this section, you will:
Compare different explanations for changes in populations over time
Describe evidence to support the theory of evolution
Explain how scientific knowledge is accumulated and organized to develop theories
Analyze data to determine relatedness among organisms

33. Developing a Theory to Explain Change
How did life develop on Earth? How did scientists come up with a theory? Theories developed through observations, analysis of data, and the formulation of hypotheses. What is the difference between a hypothesis and a theory?

34. Theory of Evolution by Natural Selection
Contributors:
Plato and Aristotle believed life existed in a perfected & unchanging world (theory lasted 2000 years!)
16th C. believed that all species were created independently & that all life has remained unchanged.

35. Contributors Buffon Separate creation
Life forms were organized into a hierarchy (“chain of being”) with Man.
In the 1700’s it was generally accepted that the age of the Earth was 6000 years old.
He was one of the 1st of many scientists to challenge the idea that life forms are unchanging.

36. Contributors
Buffon
In his work he noted the similarities between humans & apes.
He thought that these 2 hominids shared a common ancestor.
He suggested the Earth was much older than 6000 years old.

37. Contributors
Cuvier
Largely credited with developing the science of palentology.
Noticed that each strata of rock is characterized by a unique group of fossil species.
The deeper (older) the stratum the more dissimilar from the modern the species became.

38. Contributors
Curvier
Found evidence that new species appeared & others disappeared over time.
This evidence showed that species could become extinct.

39. Contributors
Curvier
Proposed that Earth experienced many destructive natural events in the past.
Called these events revolutions; were violent enough to have killed numerous species each time they occurred.

40. Contributors Lyell Rejected the idea of many catastrophic events.
Suggested that geological processes operated at the same rates in the past as they do today.
If geological changes are slow & continuous rather than catastrophic the Earth must be years old.

41. Contributors
Lyell
Forces that build & erode mountains happen no differently than in the past.
If Earth is slowly changing, could slow, subtle changes also occur in populations?

42. Contributors Lamarck By comparing current species with fossil forms.
He observed what he called a “line of descent” or progression.
This series of fossils led to a modern species.
He believed that species increased in complexity over time until they achieved a level of perfection.

43. Contributors
Lamarck
Also thought that characteristics that were acquired during a lifetime could be passed on to offspring.
This theory was called the “inheritance of acquired characteristics.”
From his point of view; an organism’s adaptations to the environment could be passed on to the offspring.

44. Contributors Lamarck No knowledge of cell biology or genetics.
By the end of the 1800s, knowledge of cells, genes & hereditary caused Lamarck’s mechanism for inheritance to be rejected.

45. Contributors Darwin In 1831, Charles Darwin left on the HMS Beagle.
He had the opportunity to explore the natural history of various countries & geographical locations.
See pg. 125 Table 4.1

46. Contributors
Darwin
The flora & fauna of the different regions were distinct from those in Europe.
Extinct organisms were very similar to living animals.
The finches & other animals he saw on the Galapagos Islands closely resembled animals he observed on the West coast of South America.

47. Contributors
Darwin
Galapagos species looked identical at first, but actually varied slightly between islands.
Darwin knew from breeding animals that it was possible for traits to be passed on from parent to offspring.

48. 12 Days of Evolution

49. Thought Lab 4.3 (p. 127)
Work individually or with a partner.

50. Continuing Section 4.2

51. Contributors
Wallace
Wallace did extensive fieldwork, first in the Amazon River & then in the Malay Archipelago.
He made a number of contributions to the development of evolutionary theory.

52. Darwin, Wallace & Natural Selection
Darwin & Wallace both reached similar conclusions.
They accepted that populations change as time passed, but were unclear how populations change.
Thomas Malthus provided them with the answer in his essay on population growth.

53. Thomas Malthus
He proposed that populations produce far more than their environments can support & were eventually reduced by starvation or disease.
According to Darwin & Wallace, individuals with physical, behavioural or other traits that helped them survive in their environments were more likely to survive to pass on these traits to their offspring.

54. Darwin, Wallace & Natural Selection
Darwin & Wallace reasoned that competition among individuals of the same species would select for individuals with favorable traits.
These traits increased their chances of surviving to reproduce.
This would grow the proportion of the “advantageous traits” in the population.

55. Book: On the Origin of Species
Q #1 (p. 20 work booklet)
Darwin proposed 2 main ideas:
Present forms of life have arisen by descent & modification from an ancestral species.
The mechanism for modification is natural selection working for long periods of time.

56. Natural Selection in a Nut Shell
Organisms produce more offspring than can survive.
There is competition for limited resources within a species.
Some variations will enable an organism to survive in its environment (selective pressure)

57. Natural Selection in a Nut Shell
The organism will be more likely to survive long enough to pass the trait to offspring.
The trait occurs in higher proportions & the population as a whole would have them as time progresses.

58. How is Natural Selection Different Than Progress?
Natural selection results from an ability to survive local conditions & reproduce successfully.
This gives survivors the chance to pass on the trait that helped them survive & reproduce.

59. Further Evidence of Evolution
Fossil record
Transitional fossils
Patterns of distribution
Anatomy
Homologous & analogous structures
Embryology
Molecular biology
Genetics

60. The Fossil Record
Palentology is the study of fossils which can be defined as any sort of remains & traces of past life found in sedimentary rock.
Petrification: the tissues of the organism are exposed to minerals over a long period.

61. The Fossil Record
Imprints or Casts: soft-bodied organisms are covered very fast & has original pore spaces that may fill with minerals.
Fossilization is a process that preserves evidence of life in Earth’s rock record.

62. Burges Shale
Cambrian black shale formation in the Canadian Rockies of British Columbia
Well preserved unique fossil bed
Marella
The most abundant burges shale organism

63. The Fossil Record Fossil Record Fossils appear in chronological order.
The oldest fossils are usually found in the lower strata & the youngest in the upper strata.
Young layers of rock (close to the surface) contain fossils that are similar to species today.
Not all organisms appear at the same time
Fish are oldest vertebrates and all vertebrates evolved from fish.

64. Transitional Fossils
The original fossil record gave “scattered snapshots” of ancestral forms.
On-going discoveries of hundreds of transitional fossils show intermediary links between groups of organisms.

65. Biogeography
Biogeography: the study of past & present geographical distribution of organisms.
Darwin & Wallace hypothesized that organisms evolve in one location & then spread out to other regions.

66. Comparative Anatomy
Homologous structures: have similar structural elements & origin, but may have a different function (bat wing and human hand).

67. Analogous structures- perform similar functions, even though the organisms do not have a common evolutionary origin
Ex. Bat and insect wing (same function – different ancestor)
do not have evidence to evolution

68. Embryology
The embryonic development of many organisms shows striking similar stages.
All vertebrate embryos are particular obvious.

69. Molecular Biology
If two species have similar patterns in proteins of their DNA, this similarity indicates that these portions of their DNA were most likely inherited from a recent common ancestor.

70. Genetics
The use of modern technologies has led to many discoveries that support Darwin’s theory.
The field of genetics has lead to understanding of how species passed on their traits to their offspring & how the blueprints (genes) for these traits can change by mutation.

71. Assignment
p. 133 #3-6

72. 4.3 How Species Form In this section, you will:
Explain ways in which species can become reproductively isolated
Describe how new species form
Compare two models that explain the rate of evolution

73. Get into groups of 3-4. All you need is a pen/pencil!
Quickly!
Get into groups of 3-4. All you need is a pen/pencil!

74. Forming New Species
There are two general pathways that can lead to the creation of a new species; speciation
Transformation
New species gradually develops as a result of mutation and adaption to changing environmental conditions. Old species is gradually replaced.
Ex. Ancestral mammoth to steppe mammoth to the wooly mammoth
What does this do to biological diversity?
- Unchanged

75. Species Formation
2. Divergence- one or more species arise from a parent species
Ex. adaptive radiation
What does this do to biodiversity?
Increases- because the number of species increases
Divergence increases biological diversity because it increases the number of species

76. For speciation to occur, two populations must be prevented from interbreeding.
When populations become isolated over a large amount of time, evolution occurs and successful reproduction is no longer possible due to a change in genetics.

77. Geological Barriers- physical separation
Mountains/Rivers
Galapagos Islands
Biological Barriers- reproductive isolation
Behaviors
Pheromones

78. Adaptive radiation is the diversification of a common ancestral species into a variety of differently adapted species.

79. Why Does Adaptive Radiation Occur?
Offspring disperse- encounter new environments with slightly different selection pressures
The adaptations that allow organism to survive in new habitats result in new species

80. The Speed of Evolution
How fast is evolutionary change?
Evolutionary biologists have suggested evolution is very slow
Gradualism – steady and linear
Large differences we see between species now- sum of all of the small changes over a long period of time
However, sudden changes seen in fossil record do not support this claim

81. A New Idea
Punctuated equilibrium - evolutionary history consists of long periods of little change- broken by rapid change
When species first diverges from a parent organism, major morphological changes occur
New selection pressures select for different adaptations
Result- in the next generation being quite different

83. Gradualism vs. Punctuated Equilibrium

84. Summary – The Theory of Evolution by Natural Selection
Life forms have developed from ancestral species.
All living things are related to on another by varying degrees through common descent.
All living things on Earth share a common origin (or ancestor)

85. Summary – The Theory of Evolution by Natural Selection (Continued)
4. The mechanism by which one species evolves into another involves random heritable genetic mutations. Mutations that increase the survival advantage of an individual will most likely be passed on to offspring. Over time the successful mutation spreads throughout the population and causes a change in the population

86. Where Do We Go From Here?
There is still wide debate over evolutionary theories
Much research is being carried out to refine these hypotheses
New discoveries will further the development of these theories over time