Evidence for Evolution

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Evidence for Evolution
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Biogeography

• The study of geographic distribution of organisms
  based on both living species and fossils.
• Remote islands have unusual examples of animal
  behaviour. A lot of the animals are fearless
  perhaps lost their instinctive fear because they
  had no natural predators.
• All 99 lemur species live on the island of
  Madagascar, but there are fossils of lemur in
  India.

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Darwins Hypotheses
Observations Hypotheses
Many species of plants, birds, insects Only these kinds of organisms can reach remote islands by crossing open waters
No native amphibians, few land mammals They were not able to cross water.
Unique species found nowhere else on Earth Over time, ancestral species evolved into new geographically isolated species.
Unique species resemble species on nearest continental land mass Unique species are descendents of ancestral species from continental land mass
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Homologous Features

• A structure with a common evolutionary origin
  that may serve different functions in modern
  species.
• Example human arm, horses leg, cats leg, bats
  wing, whales flipper.
• Example all mammals have 28 skull bones, 7 neck
  bones.
• Why were the bones in all mammals so similar?
• Perhaps they share a common ancestor.
• Homologous developmental structures and
  processes human embryos possess a short bony
  tail and gill slits.

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Analogous Features

• Structures that perform the same function as
  another but is not similar in origin or
  anatomical structure.
• Example insect wings and bird wings.
• These structured evolved independently from one
  another.

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Vestigial Features

• Rudimentary and non-functioning structures that
  are homologous to a fully functioning structure
  in a related species.
• Examples pigs extra two toes, dogs dew claws,
  some whales and snakes have vestigial hip bones.
• Can be linked to a common ancestor
• Humans have goosebumps that are muscles which
  raise hairs in response to cold temperatures, but
  it doesnt actually make us warmer because our
  hair is too sparse!

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Competition

• Darwin wondered if nature might be able to favour
  certain individuals in a population over others.
• Darwin read a mathematics paper by Malthus called
  Essay on the Principle of Population
• All populations were limited in size by their
  environment (food supply, shelter)
• Darwin figured that there must be competition
  between organisms of different species and of the
  same species for survival.
• The organisms best suited for their environment
  will survive. Thus the term survival of the
  fittest!

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Natural Selection

• Darwin published On the Origin of Species in 1859
  after 20 years of amassing evidence.
• Waited so long because his data was very
  controversial. But he got a letter from a young
  Alfred Russell Wallace that was a match to
  Darwins theory, so Darwin knew he needed to
  publish his theory quickly.
• Natural selection the way in which nature
  favours the reproductive success of some
  individuals within a population over others.
• Evolution was the result of natural selection
  occuring over many generations.

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Darwins 5 Key Observations

• In each generation, populations produce more
  offspring than there are adults
• Populations do not continue to grow in size.
• Food and many other resources are limited
• Individuals within a population vary.
• Many variations are heritable.