Chapter 15 Darwin modified notes.ppt - Wikispaces

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Chapter 15 Darwin modified notes.ppt - Wikispaces Powered By Docstoc
					                   The Diversity of Life
Humans share the Earth with millions of
  other kinds of organisms of every
  imaginable shape, size, and habitat.
• The process by which modern organisms
  have descended from ancient organisms is
• Evolution is the change in populations
  over time.
• Many explanations about how species
  evolve have been proposed, but the ideas
  first published by Charles Darwin are the
  basis of modern evolutionary theory.
• A theory is a well-supported testable
  explanation of phenomena that have
  occurred in the natural world.
                Darwin on HMS Beagle
• It took Darwin years to
  develop his theory of
• He began in 1831 at age
  22 when he took a job as
  a naturalist on the
  English ship HMS
  Beagle, which sailed
  around the world on a
  five-year scientific
• Darwin studied and
  collected biological and
  fossil specimens from
  several continents and
  many remote islands.
• His observations and data led Darwin to propose a revolutionary
  hypothesis about the way life changes over time.
            Darwin in the Galápagos
• On the Galápagos Islands, Darwin studied
  many species of animals and plants that
  are unique to the islands but similar to
  species elsewhere.
• The Galapagos Islands were unique in that
  although they were close together, each
  island had very different climates.
• Darwin observed that the characteristics
  of many animals and plants varied
  noticeably among the different islands of
  the Galapagos.

                                        • Many of the fossils that Darwin
                                          discovered resembles living
                                          organisms but were not identical
                                          to them.
                                        • The glyptodon, an extinct animal
                                          known only from fossil remains
                                          is an ancient relative of the
                                          armadillo of South America.
Giant Tortoises of the Galápagos Islands
• Among the tortoises, the shape of the shell corresponds to different habitats.
• The Hood Island tortoise (right) has a long neck and a shell that is curved and
  open around the neck and legs, allowing the tortoise to reach the sparse
  vegetation on Hood Island.
• The tortoise from Isabela Island (lower left) has a dome-shaped shell and a
  shorter neck. Vegetation on this island is more abundant and closer to the
• The tortoise from Pinta Island has a shell that is intermediate between these
  two forms.
• These observations
  led Darwin to
  consider the
  possibility that
  species can change
  over time.
           Influences on Darwin’s Work
• Influenced by the work of many others, Darwin worked to refine his
  explanation for how species change over time.
• Hutton and Lyell helped scientists recognize that Earth is many millions of
  years old, and the processes that changed Earth in the past are the same
  processes that operate in the present.
   – This led Darwin to think that if the Earth could change over time the
      organisms on it probably changed over time as well.
   – Also, if it took the Earth many, many years for life to change, then the
      Earth must be extremely old.
• An English economist Thomas Malthus believed that the human population
  grows faster than Earth’s food supply.
   – Applying this concept to biology, Darwin knew many species produce large
      numbers of offspring and that these species had not overrun Earth.
   – He concluded that individuals struggle to compete in changing
      environmental conditions.
   – Also, only some individuals survive the competition and produce offspring.
• Unfortunately not all scientists that influenced Darwin were completely
  accurate in their beliefs.
Acquired Characteristics and Use/Disuse
• Lamarck was one of the first
  to develop a theory about
  evolution and realize that
  organisms adapted to their
• He believed that selective use
  or disuse of a body part would                                2
  cause it to change and that this            3
  change would be passed on to

1) The male crab uses its small claws in front to attract mates and ward off
2) Lamarck believed that because it was used repeatedly it became larger.
3) According to Lamarck’s theory , the acquired characteristic, a larger claw,
   would be passed on to the crab’s offspring.
               This theory has been shown to be incorrect!
Inherited Variation and Natural Selection
 • Darwin observed that the traits of individuals vary in populations.
 • Variations are then inherited.
 • Breeding organisms with specific traits in order to produce offspring
   with identical traits is called artificial selection
 • Darwin hypothesized that there was a force in nature that worked like
   artificial selection.
 • Natural selection is a mechanism for change in populations.
     – It occurs when organisms with favorable variations survive, reproduce, and
       pass their variations to the next generation.
     – Organisms without these variations are less likely to survive and
     – As a result, each generation consists largely of offspring from parents with
       these variations that aid survival.
 • Alfred Russell Wallace, another British naturalist, reached a similar
  Darwin explains natural selection
                            • Darwin proposed the idea of
                              natural selection to explain how
                              species change over time.

• In any population,
  individuals have
  variations. Fishes, for
  example, may differ in
  color, size, and speed.
  Darwin explains natural selection
                                • Individuals with certain
                                  useful variations, such as
                                  speed, survive in their
                                  environment, passing
                                  those variations to the next

• Over time, offspring with
  certain variations make up
  most of the population and
  may look entirely different
  from their ancestors.
Adaptations: Evidence for Evolution
• Recall that an adaptation is any variation that aids an
  organism’s chances of survival in its environment.
• Darwin’s theory of evolution explains how adaptations may
  develop in species.
Structural adaptations arise over time
• According to Darwin’s theory,
  adaptations in species develop over
  many generations.
• Learning about adaptations in mole-
  rats can help you understand how
  natural selection has affected them.
• The ancestors of today’s common
  mole-rats probably resembled
  African rock rats.

• Some ancestral rats may have
  avoided predators better than
  others because of variations
  such as the size of teeth and
Structural adaptations arise over time
                                 • Ancestral rats that
                                   survived passed their
                                   variations to offspring.
                                 • After many generations,
                                   most of the population’s
                                   individuals would have
                                   these adaptations.

• Over time, natural selection
  produced modern mole-rats.
• Their blindness may have
  evolved because vision had
  no survival advantage for
Structural adaptations arise over time
 • Some other structural adaptations are subtle.
 • Mimicry is a structural adaptation that enables one species
   to resemble another species.
 • In one form of mimicry, a harmless species has adaptations
   that result in a physical resemblance to a harmful species.
 • Predators that avoid the harmful looking species also avoid
   the similar-looking harmless species.
 • In another form of mimicry, two
   or more harmful species resemble
   each other.
 • For example, yellow jacket
   hornets, honeybees, and many
   other species of wasps all have
   harmful stings and similar
   coloration and behavior.
Structural adaptations arise over time
  • Predators may
    learn quickly to
    avoid any
    organism with
    their general
• Another subtle adaptation
  is camouflage, an
  adaptation that enables
  species to blend with their
• Because well-camouflaged
  organisms are not easily
  found by predators, they
  survive to reproduce.
Physiological adaptations can develop rapidly
•   In general, most structural adaptations develop over millions of years.
•   However, there are some adaptations that evolve much more rapidly.
•   Physiological adaptations are changes in an organism’s metabolic processes.
•   For example, do you know that some of the medicines developed during the twentieth
    century to fight bacterial diseases are no longer effective?
1) The bacteria in a population vary in their ability to resist antibiotics.
2) When the population is exposed to an antibiotic, only the resistant bacteria survive.
3) The resistant bacteria live and produce more resistant bacteria.


• Today, penicillin no longer affects as many species of bacteria because some
  species have evolved physiological adaptations to prevent being killed by
• In addition to species of bacteria, scientists have observed these adaptations in
  species of insects and weeds that are pests.
          Other Evidence for Evolution
• Physiological resistance in species of bacteria, insects, and plants is direct
  evidence of evolution.
• However, most of the evidence for evolution is indirect, coming from
  sources such as fossils and studies of anatomy, embryology, and
                                              Evidence of


                              Geographic                                       Similarities
       The fossil record    distribution of                                      in early
                                                            body structures
                            living species                                    development

     which is composed of   which indicates                  which implies    which implies

           Physical           Common
          remains of          ancestral                     Similar genes     Similar genes
          organisms            species
     Fossils- Clues to the Past
• About 95 percent of the species that have
  existed are extinct—they no longer live on
• Fossils, which come in many forms such as
  leaf imprint, a worm burrow, or a bone, are
  an important source of evolutionary evidence
  because they provide a record of early life and
  evolutionary history.

• For example, fossils can help to predict whether an area had been a river
  environment, terrestrial environment, or a marine environment. They
  also provide information on ancient climate.
• Paleontologists are detectives of the past that study ancient life and
• By studying fossils, scientists learn about the diversity of life and about
  the behavior of ancient organisms.
• Although the fossil record provides evidence that evolution occurred, the
  record is incomplete.
    Camel EvolutionEvolution
               Paleocene    Eocene       Oligocene    Miocene
   Age         65 million   54 million   33 million   23 million   Present
               years ago    years ago    years ago    years ago


   Skull and


• For example, you can see how paleontologists have charted the
  evolutionary path that led to today’s camel after piecing together
  fossil skulls, teeth, and limb bones.
 Comparing Relative and Absolute Dating of Fossils Chart
               Comparing Relative and Absolute Dating of Fossils

                     Relative Dating                     Absolute Dating

Can determine        Age of fossil with respect to       Age of a fossil in years
                     another rock or fossil (that is,
                     older or younger)

Is performed by      Comparing depth of a fossil’s       Determining the relative
                     source stratum to the position      amounts of a radioactive (C,
                     of a reference fossil or rock       K) isotope and nonradioactive
                                                         isotope in a specimen

                     Imprecision and limitations of      Difficulty of radioassay
                     age data                            laboratory methods

Water carries small rock           Dead organisms are buried               The preserved remains
particles to lakes and seas.       by layers of sediment, which            may later be discovered
                                   forms new rock.                         and studied.
                      The Fossil Record
  • Earth’s history is divided into the geologic time scale, based on
    evidence in rocks and fossils.
  • The four major divisions in the geologic time scale are the
    Precambrian, Paleozoic Era, Mesozoic Era, and Cenozoic Era.
  • The eras are further divided into periods.

• By comparing
  older rock
  layers (near the
  bottom) with
  fossils from
  younger layers
  (near the top),
  scientists can
  document the
  fact that life on
  earth has
  changed over
    Movement of the Earth’s Crust


        Sedimentary rocks    When part of Earth’s       As the surface erodes     New sediment is then
        form in horizontal   crust is compressed, a     due to water, wind,       deposited above the
        layers.              bend in a rock forms,      waves, or glaciers, the   exposed older rock
                             tilting the rock layers.   older rock surface is     surface.
      Geographic Distribution of Living Species
           Beaver                   Beaver

                                                 • Darwin realized that
                                    Beaver and
                                                   similar animals in
                                    Muskrat        different locations were a
                                    Coypu          result of evolutionary
                                    Capybara       descent.
                                    Coypu and

                                    • Even though animals were on different
                                      continents, if they were living under
Capybara            SOUTH AMERICA
                                      similar ecological conditions, they were
                                      exposed to similar pressures of natural
                                    • Due to the similar selective pressures,
                                      different animals ended up evolving
                    Coypu             striking features in common.
     Homologous Body Structures

      Turtle             Alligator            Bird              Mammal

                  Ancient lobe-finned fish

• Structural features with a common evolutionary origin are called
  homologous structures.
• Homologous structures can be similar in arrangement, in function, or in
               Homologous Structures
• Although homologous
  structures show common
  ancestry, each organism’s
  limbs developed according                Crocodile
  to their environmental                   forelimb
• Structures were modified
  due to adaptations in their
  individual surroundings
  over time.
                                Whale                          Bird
                                forelimb                       wing

                                      •    Bird bones show an adaptation to
                                           flying that the bones of the
                                           flightless organisms, though
                                           homologous, do not have.
                                      •    Bird bones have evolved to be
                                           delicate, lightweight, and elongated
                                           to make flight much easier.
                Analogous Structures
• The body parts of organisms that do not have a common evolutionary
   origin but are similar in function are called analogous structures.
• Although analogous structures don’t shed light on evolutionary
   relationships, they do provide evidence of evolution.
• For example, insect and bird wings probably evolved separately when
   their different ancestors adapted independently to similar ways of life.
 • The fangs of a rattlesnake and
    the fangs of a spider are
    analogous structures. They share
    the same function in each
    organism, to deliver venom, but
    the organisms do not share a
    common evolutionary origin.
 • Analogous structures show the
    way dissimilar organisms
    adapted independently to similar
    ways of life by developing
    functionally similar structures.
                      Vestigial Structures
• Another type of body feature that suggests an evolutionary relationship is a
  vestigial structure—a body structure in a present-day organism that no longer
  serves its original purpose, but was probably useful to an ancestor.
• A structure becomes vestigial when the species no longer needs the feature for
  its original function, yet it is still inherited as part of the body plan for the
  species. Many organisms have vestigial structures.
• Vestigial structures, such as pelvic bones in the baleen whale, are evidence of
  evolution because they show structural change over time.
    – Pelvic bones are evidence that whales once possessed hind limbs. Since whales now
      have no hind limbs, their loss must be the result of an evolutionary change.
• In humans, the appendix is vestigial because
  it carries out no function in digestion.
• In some skinks legs have become vestigial.
    – They are reduced because they no longer
      function because they are no longer used in
• An embryo is the earliest
  stage of growth and
  development of both plants
  and animals.
• The embryos of a fish, a
  reptile, a bird, and a
  mammal have a tail and
  pharyngeal pouches.
• It is the shared features in
  the young embryos that
  suggest evolution from a
  distant, common ancestor.

         Pharyngeal                      Pharyngeal
         pouches                         pouches

              Tail                        Tail

     Fish               Reptile   Bird                Mammal
       Summary of Darwin’s Theory
1) Individual organism’s differ, and some of this variation is heritable.
2) Organisms produce more offspring than can survive, and many that do
    survive do not reproduce
3) Since more organisms are produced than can survive, they compete for
    limited resources.
4) Each organism has different advantages and disadvantages in the
    struggle for existence.
      – Individuals best suited for their environment will survive and
        reproduce more successfully.
      – These organisms pass their heritable traits to their offspring. Other
        individuals die or leave fewer offspring.
      – This process of natural selection causes species to change over time.
5) Species alive today are descended with modifications from ancestral
    species that lived in the distant past.
      – This process by which diverse species evolved from common
        ancestors, unites all organisms on Earth into a single tree of life.
  Evidence of Evolution Flow Chart

                                         Evidence of


                         Geographic                                       Similarities
  The fossil record    distribution of                                      in early
                                                       body structures
                       living species                                    development

which is composed of   which indicates                  which implies    which implies

      Physical           Common
     remains of          ancestral                     Similar genes     Similar genes
     organisms            species
• Biochemistry also provides strong evidence for evolution.
• Nearly all organisms share DNA, ATP, and many enzymes among
  their biochemical molecules.
• One enzyme, cytochrome c, occurs in organisms as diverse as bacteria
  and bison.
• Biologists compared the differences that exist among species in the
  amino acid sequence of cytochrome c.
• The data show the number of amino acid substitutions in the amino
  acid sequences for the different organisms.
                              Biochemical Similarities of Organisms
  • Organisms that             Comparison of Organisms
                                                            Percent Substitutions
                                                              of Amino Acids in
                                                           Cytochrome c Residues
    are biochemically
                               Two orders of mammals           5 and 10
    similar have fewer                                          8-12
                               Birds vs. mammals
    differences in             Amphibians vs. birds            14-18
    their amino acid           Fish vs. land vertebrates        18-22
    sequences.                 Insects vs. vertebrates          27-34
                               Algae vs. animals                 57
 Interpreting Evidence after Darwin
• Since Darwin’s time, scientists
  have constructed evolutionary
  diagrams that show levels of
  relationships among species.
• In the 1970s, some biologists
  began to use RNA and DNA
  nucleotide sequences to
  construct evolutionary
• Today, scientists combine data
  from fossils, comparative
  anatomy, embryology, and
  biochemistry in order to
  interpret the evolutionary
  relationships among species.

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