Unit 5 Evolution

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Unit 5 Evolution

• Ch. 15 Darwins Theory of Evolution

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The Puzzle of Lifes Diversity

• Evolution - modern organisms have descended from
  ancient organisms (change over time)
• Theory - a well-supported, testable explanation
  of phenomena that have occurred in the natural
  world

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Voyage of the Beagle

• Charles Darwin contributed most to our
  understanding of evolution
• He made observations collected evidence that
  led him to propose a hypothesis about the way
  life changes over time

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Voyage of the Beagle

• That hypothesis, now supported by a large amount
  of evidence, has become the theory of evolution

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Darwins Observations

• Darwin collected the preserved remains of ancient
  organisms - Fossils
• Some of these fossils resembled organisms that
  were still alive
• Others looked unlike any creature ever seen

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Darwins Observations

• The Galapagos Islands influenced Darwin the most
• He observed that the characteristics of animals
  plants varied among the different
  Islands

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An Ancient, Changing Earth

• Hutton Lyell helped scientists recognize that
  Earth is millions of years old
• They also noted that the processes that changed
  Earth in the past are the same processes
  that are changing Earth now

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Lamarcks Evolution Hypothesis

• The year that Darwin was born, Lamarck published
  his hypothesis
• He proposed that by selective use or disuse of
  organs, organisms acquired or lost certain traits
  during their lifetime
• Over time, this process led to change in a species

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Lamarcks Explanation
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Population Growth

• English economist, Malthus, published a book,
  noting that babies were being born faster than
  people were dying
• He stated that if the human population continued
  to grow unchecked, sooner or later there would be
  insufficient living space food for everyone

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Darwin Presents His Case

• Darwin published the results of his work in a
  book, On the Origin of Species
• In his book, he proposed a mechanism for
  evolution called natural selection
• He stated that evolution has been taking place
  for millions of years, continues in all living
  things

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Inherited Variation Artificial Selection

• Artificial selection - nature provided the
  variation, humans selected those variations
  that they found useful
• It has produced diverse plants animals by
  selectively breeding for different traits

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Evolution by Natural Selection

• Struggle for existence - the members of each
  species compete regularly to obtain food, living
  space, other necessities of life
• Predators that are faster better at catching
  prey are more likely to survive

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Evolution by Natural Selection

• Fitness - the ability of the organism to survive
  reproduce in its specific environ.
• Fitness is the result of adaptations

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Evolution by Natural Selection

• Adaptation - any inherited characteristic that
  increases an organisms chance of survival
• Successful adaptations allow organisms to
  become better suited to their environ. thus
  better able to survive

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Evolution by Natural Selection

• Individuals that are better suited to their
  environ., with adaptations that enable fitness,
  survive reproduce most successfully - Survival
  of the Fittest

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Evolution by Natural Selection

• Since it is similar to artificial selection,
  Darwin referred to survival of the fittest as -
  Natural Selection
• In both AS NS, only certain individuals of a
  population produce new individuals

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Evolution by Natural Selection

• However, in NS, the traits being selected,
  therefore, increasing over time, contribute to an
  organisms fitness
• NS takes place without human control or direction
  

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Evolution by Natural Selection

• NS results in changes in the inherited
  characteristics of a population, that increase a
  species fitness in its environ.
• Over time, NS produces organisms that have
  different structures, occupy different habitats

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Evolution by Natural Selection

• As a result, species today look different from
  their ancestors
• Each living species has descended, with changes,
  from other species over time - Descent with
  Modification

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Evolution by Natural Selection

• Descent with modification also implies that all
  living organisms are related to each other
• Common descent - all species (living extinct)
  were derived from common ancestors

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Evidence of Evolution

• Darwin argued that living things have been
  evolving on Earth for millions of years
• Evidence of this could be found in the fossil
  record, the geographical distribution of living
  species, homologous structures of living
  organisms, similarities in early development

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Evidence of Evolution

• The Fossil Record
• Darwin noticed that the sizes, shapes,
  varieties of related organisms preserved in the
  fossil record, changed over time

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Evidence of Evolution

• Geographic Distribution of Living Species
• Darwin realized that similar animals in different
  locations were the product of different lines of
  evolutionary descent

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Evidence of Evolution

• Homologous Body Structures
• Homologous structures - structures that have
  different mature forms but develop from the same
  embryonic tissues
• Not all homologous structures serve important
  functions
• Organs of many animals are so reduced in size
  that they are just vestiges, or traces, of
  homologous organs

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Homologous Structures
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Evidence of Evolution

• Homologous Body Structures
• Vestigial organs - may resemble miniature legs,
  tails, or other structures, a trace of a
  homologous structure

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Evidence of Evolution

• Similarities in Early Development
• The early stages or embryos, of many animals with
  backbones are very similar

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Summary of Darwins Theory

• Individual organisms differ, some of this
  variation is heritable
• Organisms produce more offspring than can
  survive, many that do survive do not reproduce

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Summary of Darwins Theory

• Because more organisms are produced than can
  survive, they compete for limited resources
• Individuals best suited to their environ.,
  survive reproduce most successfully

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Summary of Darwins Theory

• These organisms pass their heritable traits to
  their offspring
• This process of NS causes species to change over
  time

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Summary of Darwins Theory

• Species alive today are descended with
  modification from ancestral species that lived in
  the distant past
• This process, where diverse species evolved from
  common ancestors, unites all organisms on Earth
  into a single tree of life