Chapters 1516

1
Chapters 15-16

• Evolution

2
I. Introduction to Evolution

• Evolution change in inherited characteristics
  over time
• Theory a well supported testable explanation of
  natural phenomena

3
II. Charles Darwin

• Traveled around the world on the Beagle beginning
  in 1831

4

• Made numerous observations and collected evidence
  that led him to propose a hypothesis about the
  way life changes over time

5

• Darwins Observations
• 1. Patterns of Diversity
• a. Plants and animals were well suited
  to whatever environments they inhabited
• b. Similar ecosystems were inhabited by
  different kinds of animals

6

• 2. Living Organisms and Fossils
• a. Fossils preserved remains or
  imprints of organisms
• b. Darwin found fossils that
  resembled living organisms, others looked
  unlike any creature ever seen

7

• 3. The Galapagos Islands
• a. Each island had a different climate,
  so Darwin could observe similar species in
  different habitats
• b. Variations based upon which island a
  species inhabited
• tortoises - neck length, shell
• finches - beak shape

8
(No Transcript)
9

• c. Darwin wondered if animals living on
  different islands had once been members of the
  same species
• d. He began formulating his theory of
  evolution

10

• Influences on Darwin
• 1. Hutton and Lyell
• a. Geological processes change the earth
  over millions of years
• b. Suggested the Earth is old enough for
  evolution to have occurred

11

• 2. Jean-Baptiste Lamarck
• a. Organisms acquire or lose certain
  traits during their lifetime by
  selective use or disuse of organs
• b. These acquired traits can be passed
  on to offspring
• c. Over time, this process leads to
  change in a species

12
(No Transcript)
13

• 3. Thomas Malthus
• a. If the human population grew
  unchecked, there would be insufficient
  living space and food for everyone
• b. Darwin realized this theory of
  population control could be applied to any
  population of organisms

14

• Darwins Case
• 1. Darwin did not immediately publish his
  theory of evolutionhe was disturbed by
  his discoveries, which challenged fundamental
  scientific beliefs
• 2. Darwin was prompted to publish his theory
  when he received an essay on evolution from
  Alfred Wallace

15

• 3. Natural variation and artificial selection
• a. Natural variation differences among
  individuals of a species
• b. Artificial selection determining
  which individuals to breed based on natural
  variation (select for useful variations)

16

• 4. Evolution by Natural Selection
• a. The struggle for existence
• - members of each species compete for
  food, space, etc.
• b. Survival of the Fittest
• 1. fitness ability to survive and
  reproduce

17

• 2. fitness comes from adaptation
  (inherited characteristics that increase
  chance of survival)
• 3. the fittest (those best adapted)
  survive and reproduce
• 4. over time, this natural selection
  results in changes in the inherited
  characteristics of a population

18

• c. Descent with Modification
• 1. species descend, with changes, from
  other species over time
• 2. implies all living organisms are
  related to each other (common descent)

19

• 5. Evidence of Evolution
• a. Fossil record evidence of change
  over time
• b. Geographic distribution of living
  species different animals in similar
  environments share similar characteristics

20

• c. Homologous body structures parts
  similar in structure (ex.- flipper of a whale
  and arm of a human)
• d. Similarities in early development early
  embryos of different species look very similar

21

• Summary of Darwins Theory
• 1. Natural variation is inherited
• 2. More offspring produced than can survive
• 3. Competition for resources
• 4. Individuals with best adaptations
  survive and reproduce
• 5. Species change over time because of this
  natural selection
• Darwin did not know how traits are passed from
  parents to offspring

22
III. Evolution of Populations

• Genes and Variation
• 1. Population all members are able to
  interbreed
• 2. Gene pool combined genetic information
  of all members of a population

23

• 3. Relative frequency the number of
  times an allele occurs in a gene pool compared
  with other alleles
  relative frequency
  does not change if members of a
  population interbreed with each other

24
allele for brown fur
allele for black fur
48 heterozygous black
16 homozygous black
36 homozygous brown
25

• Sources of Genetic Variation
• 1. Mutations a change in DNA sequence
• 2. Gene shuffling responsible for most
  inheritable differences 23 pairs of
  chromosomes can produce 8.4 million
  combinations of genes to produce many
  different pheontypes!

26

• Single-Gene and Polygenic Traits
• 1. Single-gene trait controlled by 1 gene

27

• 2. Polygenic trait controlled by 2 genes
• - many phenotypes, expressed in a
  bell-shaped curve

28

• Natural Selection on Single-gene Traits
• 1. Natural selection acts on phenotypes
• 2. One phenotype is favored over the other
• 3. This could eliminate certain alleles,
  leading to evolution

29

• Natural Selection on Polygenic Traits
• 1. Directional Selection one end of the
  curve has higher fitness than others

30

• 2. Stabilizing Selection individuals near
  the center of the curve have higher fitness

31

• 3. Disruptive Selection individuals at both
  ends of the curve have higher fitness than those
  in the middle

32

• Genetic Drift
• 1. Genetic drift change due to chance
• 2. Most common in small populations

33

• Hardy-Weinberg Principle
• 1. Genetic Equilibrium allele
  frequencies remain constant (no evolution
  occurs)
• 2. Conditions required
• a. Random mating
• b. Large population
• c. No movement into/out of population
• d. No mutations
• e. No natural selection

34

• Speciation formation of a new species
• 1. Reproductive isolation separate
  populations cannot interbreed
• 2. 3 ways populations become isolated
  from each other
• a. Behavioral isolation differences in
  courtship rituals or other types of
  behavior
• b. Geographic isolation separated by
  barriers (rivers, mountains)
• c. Temporal isolation reproduce at
  different times