EVOLUTION

1
EVOLUTION
2
(No Transcript)
3

• Jean Baptiste de Lamarck (1809)
• He developed a theory of evolution. He related
  fossils to living animals based on similar
  appearance.
• He was the first to state
• that organisms change
• over time, and new types
• are modified descendents
• of older types.

4

• Lamarck stated that acquired traits could be
  passed to offspring
• (The Theory of Acquired Inheritance)

5

• "All which has been acquired, laid down, or
  changed in the organization of individuals in the
  course of their life is conserved by generation
  and transmitted to the new individuals which
  proceed from those which have undergone those
  changes.
• This means that
  according to
• 
  Lamarck, acquired traits could
• be
  inherited by the next
• 
  generation.

6

• The Giraffe example The giraffes long neck
  could be the result of generations of giraffes
  stretching to reach leaves in high branches over
  their lifetime. Parents slightly stretch their
  necks and therefore have offspring that inherit
  this modification acquired during their parents
  life.

7

• If a giraffe stretched its neck for leaves,
  for example, a "nervous fluid" would flow into
  its neck and make it longer. Its offspring would
  inherit the longer neck, and continued stretching
  would make it longer still over several
  generations.

8
A new look at giraffe neck adaptation
9

• The Long-Legged Bird Example
• The long legs of wading birds arose when their
  ancestors responded to a need to feed on fish. As
  they waded in deeper water, they stretched their
  legs to try and keep their bodies dry. This trait
  would be passed to the next generation.

10

• Example of webbed feet

11

• "The development of organs and their force of
  action are constantly in ratio to the employment
  of these organs."
• Lamarck stated that there could be
• changes in acquired traits through use
• or disuse.

12

• Lamarck also proposed that organisms were driven
  from simple to increasingly more complex forms.
  (Darwin argued that increased complexity was
  the result of adaptation to local environments
  from one generation to the next.)
• He did not think species
  ever went extinct, they
  just changed into
  new forms.

13

• Charles Darwin (1809 1882) After college, a
  young Charles Darwin (22 yrs old), in 1831, set
  sail aboard the HMS Beagle as the ships
  naturalist. (The ship was chartered for a
  five-year mapping mission.)
• Darwin 1840

14

• Darwin was required to collect specimens and
  carefully record his observations. Darwin was
  often left at various sea ports for months at a
  time, which enabled him to collect many fossils
  and observe thousands of specimens.

15

• Darwins Voyage

16

• Darwin read Principles
• of Geology by Charles
• Lyell, who stated that
• the geological
• structure of the Earth
• resulted from cycles
• of observable
• processes that
• operate continuously
• through time.

17

• Darwin also read about
• James Huttons work
• In 1795, Hutton, a
• geologist,
• published a theory
• that the Earth is
• shaped by
• geologic forces that
• take place over
• Extremely long periods
• of time. He estimated
• the Earth to
• be millions of years old.

18

• During Darwins journey, he witnessed a
  volcanic eruption, an earthquake that lifted a
  portion of shoreline and noted that animal life
  in the water was displaced.

19

• Darwin also observed fossil shells of marine
  organism in rock beds about 4,300 meters (14,100
  ft) above sea level.
• Darwin concluded that if the Earth could
  change over time, then life could change as well.
  He also assumed that it would have taken many,
  many years.

20

• The Galapagos Islands are a group of small
• islands near the equator, about 600 miles off the
• coast of South America. The observations and
• specimens Darwin collected were especially
• important to developing his theory.

21
(No Transcript)
22
white areas over islands are clouds
23
(No Transcript)
24

• Darwins Finches Darwin collected many
• specimens of finches from the
• Galapagos Islands and found that he had
• several similar but separate species.

25

• Darwin had collected 13 different species, each
• with a different bill specialized for a
  particular
• food source.

26
(No Transcript)
27

• Since there were so many similarities, he
  believed this implied that the finches shared a
  common ancestor.
• He assumed the differences in the bills of
  offspring were adaptations to different
  environments.
• He also assumed that over many millions of years,
  many large differences could accumulate
• between species.

28

• Darwins tortoises Darwin found that the
• shapes of tortoise shells corresponded to
• different habitats.

29

• The hood Island tortoise has a long neck and a
  shell that is curved and open around the neck and
  legs, allowing the tortoise to reach sparse
  vegetation.
• The Isabela Island tortoise has a dome-shaped
  shell a shorter neck. Vegetation on this Island
  is more abundant and closer to the ground.
• Pinta Island tortoises have
• an intermediate shell
• between these two forms.

30

• Another important idea that aided Darwins
• conclusions about the change in organisms
• was proposed by Thomas Malthus in 1798.
• He stated that the human population could
• double redouble, except for
• the presence of war, disease,
• or limited food supplies.

31

• Darwins conclusions
• 1) Darwin reasoned that all organisms have
  environmental limits to their growth which
  decrease their rate of reproduction or increase
  their rate of death.
• 2) Organisms compete for limited resources.
• 3) Certain traits are beneficial to an organisms
  survival, as well as greater reproductive
  success. If the trait increases the reproductive
• success, is inherited, it is passed to many
  offspring.

32

• 4) Organisms adapt to their environment as
• their proportion of genes for favorable
  traits increases.
• 5) The resulting change in genetic makeup is
  evolution. The genetic contribution to the next
  generation termed fitness.
• 6) An individual with a high fitness is well-
• adapted to its environment and reproduces
• more successfully than an individual with
• low fitness.

33

• Natural Selection -Survival of the fittest.
• Individuals best suited
• to their environment
• survive and reproduce
• the most successfully,
• and pass their favorable
• traits to offspring. While
• those with more poorly
• -suited traits die, or
• leave fewer offspring.

34

• Species change over long periods of time.
• Natural selection causes the changes in
• species. New species arise, while others
  
• Species alive today descended, with
• modifications from species that lived in
  the
• past. All organisms on Earth are united
• in a single tree of life by common
  descent.

35
(No Transcript)
36
Darwin and Lamarck

• Darwin did not accept an arrow of complexity
  driving through the history of life. He argued
  that complexity evolved simply as a result of
  life adapting to its local conditions from one
  generation to the next.
• Darwin also argued that species could go
  extinct rather than change into new forms.
• But Darwin also relied on much the same
  evidence for evolution that Lamarck did (such as
  vestigial structures and artificial selection
  through breeding).

37

• Artificial Selection and Natural Selection
• Breeding organisms with specific traits
• in order to produce offspring with identical
• traits is called Artificial selection.
• Darwin used the term
• Natural selection to
• describe natures forces
• Selecting which traits
• are favorable and which
• organisms are better fit to survive.

38
Natural Selection, the key evolutionary mechanism
Darwin identified, is really four key
processes

• genetic variation (difference in genomes among
  organisms in a given population)
• overproduction of offspring
• struggle for existence
  (competition for food, mating resources etc.)
• differential survival and reproduction (higher
  fitness, better adaptation leads to more
  offspring).

39
Natural Selection (Modern Biology pg 300)
40

• Natural Selection and peppered moths
• As pollution darkens the trees which moth
• is favored to survive?

41

• Darwin was asked by the naturalist Alfred
  Wallace, in
• 1856 (22 years after Darwin returned to England
  on
• the Beagle) to review his paper on Natural
  Selection
• as a mechanism for Evolution.
• Darwin decided to publish his own work on
  evolution.
• Both papers were presented to the Linnaean
  Society
• of London in 1858.

42

• Darwin wrote his now famous
• book, On the Origin of
• Species by Means of
• Natural Selection, more
• commonly
• known as
• The Origin
• of Species.

43

• What causes changes in a population of organisms?
• Darwin did not know how heredity worked.
• Therefore he did not know the source of the
• variation that was
• central to his theory,
• or how these traits
• were passed to offspring.

44

• Two main sources of genetic variation
• 1) Mutations - Mutations do not always affect
• an organisms phenotype, but some may enhance
• an organisms ability to survive and reproduce.
• 2) Sexual reproduction - The Genetic
• shuffling that results from sexual reproduction
  causes variations in a population.
  
• Genes mutate from one form to another. New
  alleles are introduced into the population, and
  allele frequencies change. -------This can lead
  to evolution.

45
Populations, Not Individuals Evolve

• Within an organisms lifetime, it cannot evolve
  a new phenotype by natural selection.
• 
  
• Natural selection
  
  acts on
  
  the
  range
  
  of phenotypes
  in a
  population.

46

• All the genes of a population
  are referred to the
  gene pool.
  The percentage of any allele
  in that pool is
  the allele
  frequency.
• If there are no changes in
  the allele
  frequencies, then
  there is genetic equilibrium
  evolution does
  not occur.

47

• Environmental factors can affect the allele
  frequencies and cause evolution.
• Mutations can be causes by chemicals etc. and
  bring about useful variations and new genes in
  the gene pool.
• The gene pool can be affected by movement of
  individuals in and out of the population.

48
The change in alleles has been naturally selected.