The Theory of Evolution

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The Theory of Evolution
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What exactly is a theory?

• A theory is a well tested concept that explains a
  wide variety of observations.
• A theory should be able to make predictions about
  future observations.

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What is Biological Evolution?

• Biological evolution is the change that species
  undergo over time. More precisely, it is the
  change in the gene pools of living populations of
  species which occurs over time.

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What exactly does theory of evolution state?

• All life forms (species) have developed from
  other species.
• All living things are related to one another to
  varying degrees through common decent (shared
  common ancestors).
• All life on Earth has a common origin. In other
  words, that in the distant past, there once
  existed an original life form that gave rise to
  all subsequent life forms.
• The process by which one species evolves into
  another involves heritable genetic mutations.

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How does Natural selection Work?

• Any Species of animals produces more offspring
  then the environment can handle.

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• There are individual differences among the
  offspring (mutations).
• Because too many offspring are in the environment
  only some will survive.

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• Those that possess traits to survive best in the
  environment will survive.
• Those that do not die pass on their genetic code
  to their offspring.

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• In this way only the fittest of the species will
  survive and through this process of Natural
  Selection evolution or changes occur in the
  species.

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What is the Evidence for Evolution?

• Fossil Record
• Biogeography
• Comparative Anatomy
• Comparative Embryology
• Comparative Biochemistry

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Fossil Record

• Organisms have changed over time.
• Some present species are not present in the
  fossil record
• Some current species are similar, but not
  identical, to some previous species.

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Biogeography

• Organisms evolve to adapt to their particular
  environment, then spread to other locales.
• Evidence comes from the distribution of similar
  species found around the world

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Biogeography
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Comparative Anatomy

• Related organisms share a unity of body plan.
• The same body structures can perform adaptive
  functions.
• Among vertebrates, forelimbs have the same set of
  bones.

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Homologous Structures
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Comparative Embryology

• Related organisms develop similarly.
• Early embryos of all vertebrates are very similar
• Early development reflects evolutionary origins
• - Ontogeny recapitulates phylogeny

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Do these look Similar?
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Comparative Biochemistry

• All living things use the same basic biological
  molecules for similar functions.
• - The nitrogen bases in all organism are the
  same A T G C.
• Metabolic systems are similar among species.
• - Photosynthesis, respiration, fermentation,
  etc.
• Basic cell structure is almost universal.

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Vestigial Organs

• Hunan appendix is useless yet in other mammals,
  including primates, it is necessary to aid in
  digestion of high cellulose diet.
• Human external ear muscles still present but
  useless.
• Humans have tailbones and some babies are
  occasionally born with tails.
• Some snakes have skeletal limbs.

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Misconceptions about Evolution

• Evolution only progresses forward
• Reality There are several species including the
  crocodile and the shark that have remained
  virtually unchanged for millions of years

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• Man evolved from monkeys
• Reality is that man is on different branch of the
  evolutionary tree than monkeys.

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• Evolution occurs in individuals
• Reality is that evolution occurs in populations.

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There are no modern intermediate species

• Consider the platypus! It is a mammal that lays
  eggs.

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Different Model of Evolution

• Evolution always occurs very slowly
• Reality Punctuated evolution can occur over a
  relatively short time.