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Charles Darwin and Natural Selection

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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?
  • Due to 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

29
Archaeopteryx links reptiles and birds
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Hind leg bones in whales
32
Diarthognathus, an animal with reptile and mammal
characteristics
33
An amphibious reptile found in Texas, 2005
34
Early mammals may have looked like this
35
Evolution of the horse
36
B. Biological Molecules
  • Differences in amino acid sequences and DNA are
    greater between species that are distantly
    related than between species that are closely
    related
  • phylogenetic trees show how organisms are related
    through evolution
  • Homeobox genes

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C. Homologous structures similar in structure,
with different functions
39
D. 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

40
The cassowary, a flightless bird with wings
41
Wisdom teeth in human
42
Human appendix
43
E. Vertebrate Embryos
  • 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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Examples of Evolution
  • A. Tuskless elephants becoming more common in
    Africa

46
B. Antibiotic resistance in bacteria such as
those that cause pneumonia and tuberculosis
47
C. Pesticide resistance in insects
  • Tobacco plants are sprayed with pesticides
  • The pesticides kill many insects, but not all.
  • Survivors lay eggs
  • Future generations are resistant

48
D. Industrial Melanism
  • Example is the peppered moth.
  • Explained by the concealment hypothesis.
  • Peppered Moth Simulation

49
E. Beaks of finches

50
Adaptation
  • the changing of a species that results in its
    being better suited to its environment.
  • Examples camouflage, mimicry, echolocation,
    migration, dormancy

51
Camouflage
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53
Mimicry one species resembles another
54
Snake mimicry which is harmful?
55
Eastern Coral snake Highly venomous
King snake Non-venomous
56
Echolocation in bats.
57
Hibernation
58
Migration
59
Dormancy cacti embryos coming out of dormancy
60
Patterns of Evolution
  • Divergence Darwins finches.
  • Dogs evolving from wolves. Can lead to
    formation of new species (speciation)

61
B. Convergent evolution
  • distantly related organisms evolve similar
    traits.
  • Example is seen in the streamlined, finned bodies
    of dolphins and sharks.
  • The fins would be an example of analogous
    structures.

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  • Analogous structures are not evidence of a common
    ancestor.
  • Analogous structures have a similar function.

64
Fitness
  • the genetic contribution of an individual to
    the next generation's gene pool relative to the
    average for the population, usually measured by
    the number of offspring that survive to
    reproductive age

65

66
Microevolution
  • a change in gene frequency in a population
    such as all the individuals of one beetle species
    living on a particular mountaintop.

67
Macroevolution
  • generally refers to evolution above the species
    level

68
Evolution of whales from land-dwelling mammals
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70
Evidence
  • transitional fossils between land mammals and
    whales
  • vestigial structures such as pelvic and leg
    bones, and external ear muscles
  • nostrils at end of snout in embryos nostrils
    travel to top of head before birth
  • DNA for milk protein very similar in hippos and
    whales
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