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Charles Darwin and Natural Selection

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Charles Darwin and Natural Selection Draw a visual for divergent evolution and one for convergent evolution. Give an example of each. (convergent and divergent) Which ... – PowerPoint PPT presentation

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Title: Charles Darwin and Natural Selection


1
Charles Darwin and Natural Selection
2
Darwin journeyed on the HMS Beagle as a
naturalist
  • 5 year journey
  • studied and collected many biological specimens
  • on Galapagos Islands, off coast of Ecuador,
    observed animals such as finches, tortoises, and
    iguanas
  • Thirteen different but similar species of
    finches, each with a distinctive bill that is
    specialized for a particular food source.
  • Suggested that these birds migrated from Ecuador
  • and changed after they arrived.

3
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Darwins ideas were influenced by
  • Jean Baptiste Lamarck, who hypothesized that
    acquired traits were passed onto offspring

5
  • Charles Lyell, a geologist, who suggested that
    the Earth was much older than 6000 yrs
  • Thomas Malthus, who wrote that human populations
    grow much faster than their food supply
  • Alfred Wallace, who suggested natural selection
    after studying wildlife in the Malay Archipelago.

6
Darwin observed differences among island species.
7
Marine iguana
8
Land iguana
9
Thirteen different but similar species of
finches, each with a distinctive bill that is
specialized for a particular food.
10
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Suggested that these birds migrated from South
America and changed after they arrived
12
Key insights led to Darwins idea for natural
selection.
  • Darwin noticed a lot of variation in domesticated
    plants and animals.
  • Artificial selection is the process by which
    humans select traits through breeding.

13
  • Heritability is the ability of a trait to be
    passed down.
  • There is a struggle for survival due to
    overpopulation and limited resources.
  • Darwin proposed that adaptations arose over many
    generations.
  • Natural selection is a mechanism by which
    individuals that have inherited beneficial
    adaptations produce more offspring on average
    than do other individuals.

14
Principles of Natural Selection
  • Variation. What can cause variation in a
    population?
  • Genetic differences and mutation
  • Overproduction. What are pros and cons of
    overproduction?
  • Having many offspring increases the chance for
    survival, but also results in competition for
    resources.

15
  • Adaptation. What determines whether an
    adaptation is beneficial or not?
  • A certain variation that allows an individual to
    survive better than other individuals it competes
    against.
  • Descent with Modification. How does natural
    selection change a population over time?
  • Over time, more members of the species will have
    adaptations that are well suited for survival and
    reproduction in an environment.

16
Elephants in Queen Elizabeth National Park,
Uganda, Africa
17
  • Normally, nearly all African elephants, male
    and female, have tusks. In 1930, only one
    percent of the elephant population in Queen
    Elizabeth Park was tuskless because of a rare
    genetic mutation. Food was plentiful, and by
    1963 there were 3,500 elephants in the park.

18
  • In the 1970s, a civil war began in Uganda.
    Much of the wildlife was killed for food, and
    poachers killed elephants for their ivory tusks.
    By 1992, the elephant population had dropped to
    about 200. But by 1998, the population had
    increased to 1,200. A survey revealed that as
    many as 30 percent of the adult elephants did not
    have tusks. Ugandan wildlife officials also
    noted a decline in poaching.

19
Natural selection acts on distributions of
traits.
  • A normal distribution graphs as a bell-shaped
    curve.
  • Populations have a normal distribution when they
    are not undergoing natural selection

20
  • Microevolution is evolution within a population.
  • observable change in the allele frequencies
  • can result from natural selection

21
Directional selection favors one of the extreme
variations
22
  • Woodpeckers with long beaks capture the most
    insects, as they can reach the insects deep in
    the tree trunk.

23
  • Stabilizing selection favors the average

24
  • Small spiders have a hard time capturing prey
  • Large spiders easily spotted by birds
  • Medium sized spiders are best suited to survive
    in their environment, reproduce more often, leave
    more offspring.

25
Disruptive selection - favors both extremes
26
  • On light colored rocks, the light limpets are
    camouflaged and survive the best
  • On dark rocks, the dark limpets are most
    successful
  • Tan (intermediate) limpets are visible on both
    the light rocks and dark rocks, and their numbers
    decline due to predation

27
Evidence of Evolution
  • Fossils
  • Fossil links found between
  • fish and amphibians
  • reptiles and birds
  • reptiles and mammals
  • Whales from land mammals

28
Fossil linking fish and amphibians
  • 365 million years old
  • arm bone with fish fin characteristics
  • found in Pennsylvania
  • thought to be from a lobed-finned fish

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Archaeopteryx links reptiles and birds
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An amphibious reptile found in Texas, 2005
34
Hind leg bones in whales
35
Diarthognathus, an animal with reptile and mammal
characteristics
36
Early mammals may have looked like this
37
Evolution of the horse
38
  • B. Geography
  • island species most closely resemble nearest
    mainland species
  • populations can show variation from one island to
    another

39
C. Embryology
  • Crabs and barnacles with similar larvae,
    different adult body forms

40
  • Early in development, vertebrate embryos have
    similar characteristics such as a tail, buds that
    become limbs, and pharyngeal pouches that hold
    the gills of fish and amphibians.
  • Vertebrate embryos

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D. Anatomy
  • Homologous structures similar in structure,
    with different functions

43
Vestigial Structures
  • Structures that are reduced in size and either
    have no use or a less important use than they do
    in other, related organisms.
  • Examples wings on flightless birds, Human ear
    muscles, human wisdom teeth human appendix , hind
    leg bones in whales, human tailbone (coccyx)

44
The cassowary, a flightless bird with wings
45
Wisdom teeth in human
46
Human appendix
47
  • Analogous structures are not evidence of a common
    ancestor.
  • Analogous structures have a similar function.

48
Evolutionary Biology Today
  • DNA sequence analysis two closely-related
    organisms will have similar DNA

49
  • Homeobox genes indicate a very distant common
    ancestor.
  • control the development of specific structures
  • found in many organisms

Homeobox genes
50
Mechanisms of Evolution
1. Natural Selection certain traits might be
an advantage for survival 2. Mutation creates
new genetic variation 3. Sexual selection
certain traits may improve mating success
alleles for these traits increase in frequency
51
Sexual selection occurs when certain traits
increase mating success.
  • Sexual selection occurs due to higher cost of
    reproduction for females.
  • males produce many sperm continuously
  • females are more limited in potential offspring
    each cycle

52
Alternative reproductive tactics
Rememberthere may not be a best way to be a
male (or female)
53
  • The Red Queen

Evolutionary arms-races The Red Queen It takes
all the running you can do, to keep in the same
place.--Lewis Carroll, Through the Looking
Glass The Red Queen Hypothesis For an
evolutionary system, continuing development is
needed just in order to maintain its fitness
relative to the systems it is co-evolving with.
--Leigh Van Valen (1973)
54
  • Gene flow movement of individuals to or from a
    population (also known as migration). Immigrants
    add alleles, emigrants take alleles away.
  • Example troops of baboons in eastern Africa.
    Females remain with the troop, but younger or
    less dominant males leave their birth troop,
    eventually joining another troop. This ensures
    gene flow.

55
5. Genetic drift is a change in allele
frequencies due to chance.
  • Genetic drift causes a loss of genetic diversity.
  • It is most common in small populations.
  • A) A population bottleneck can lead to genetic
    drift.
  • It occurs when an eventdrastically
    reducespopulation size.
  • The bottleneck effect isgenetic drift that
    occursafter a bottleneck event.

56
  • Example In the 1800s, northern elephant seals
    were overhunted. The population was reduced to
    about 20 individuals. Hunting has ended, and
    there are now about 100,000 seals. However, the
    population has little genetic variation.

57
B) The founder effect is genetic drift that
occurs after start of new population
  • It occurs when a few individuals start a new
    population.

58
What is speciation?
  • The rise of two or more species from one
    existing species

59
What causes speciation?
60
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61
Types of reproductive isolation
  • Geographic isolation

62
  • 2. Temporal isolation
  • timing of reproductive periods prevents mating

63
  • 3. Behavioral isolation
  • includes differences in courtship or mating
    behaviors
  • Example female fireflies only respond to light
    patterns of males of their own species

64
  • Satin bowerbird
  • and McGregors
  • bowerbird ?

65
  • What process keeps the number of total species on
    Earth from growing exponentially through
    speciation?

66
Draw a visual for divergent evolution and one for
convergent evolution.
67
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68
Give an example of each. (convergent and
divergent)
  • Which type leads to analogous structures?

69
Convergent or divergent?
70
Convergent or divergent?
71
Polar bears and grizzly bears?
72
  • Convergent or divergent?
  • (Adaptive radiation)

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74
What is coevolution?
  • Evolutionary Arms Race

75
True or false
  • When sexual selection is acting in a species, all
    males tend to look alike.

76
  • There are two groups of pine trees that appear to
    be very similar phenotypically and genotypically.
    However, one releases pollen in January, when the
    female structures of that group are receptive,
    and one in March. What kind of reproductive
    barrier is this?

77
Microevolution
  • a change in gene frequency in a population
    such as all the individuals of one beetle species
    living on a particular mountaintop.

78
Industrial Melanism
  • Example is the peppered moth.
  • Peppered Moth Simulation

79
Macroevolution
  • generally refers to evolution above the species
    level
  • Macroevolution
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