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Evolution
History of Evolution
The historical context of Darwin′s life and ideas. The
dark blue bars above the timeline represent the lives of
some individuals whose ideas have contributed to our
modern understanding of evolution.
Darwin
• Naturalist (biology and geography)
• 5 year mapping expedition of southern
hemisphere.
– Encountered organisms with different
forms, yet similar to others in different parts
of world.
– Observed that the Earth changes.
Galapagos Islands
• Tortoises: Shell form
and neck length varied
from island to island.
– These giant tortoises are
found nowhere else in
world. Yet three varieties
exist that are locally
adapted.
Galapagos Islands
• Finches: Beaks varied from island to
island.
– Realized that these variations were
adapted for different food sources.
– Suggested that 1 ancestral species could
give rise to many different species
Darwin’s Idea
While rewriting his notes, came up with a
process for how these changes could
develop.
Natural Selection
1. Members of a population have
heritable variations
Natural Selection
2. Individuals w/in a
population will overproduce
their offspring.
3. Certain individual’s
variations will be better
suited for that environment,
and therefore be more
likely to survive &
reproduce better than
those without.
Natural Selection
4. Increased portion of population will
have those variations after many
generations with that particular
environmental pressure.
5. This results in population that are
adapted to local environment.
Natural Selection
Struggle for existence:
• Limiting resources; not enough for all
members of a population to survive.
– Therefore organisms differ in their fitness =
how many offspring an organism produces
that survive to reproduce themselves.
– “survival of the fittest”
– Fitness is directionally proportional to the
organisms adaptations
Natural selection results
in Adaptations
Any heritable trait that aids in the survival
and reproductive success of an
organism.
Types
• Structural
• Behavioral
• Physiological: biochemical
Structural
Behavioral
Physiological
Artificial Selection
When humans (not envt.)
select desired traits.
• Domesticated animals,
crops, pets, ourselves.
Evidence for Evolution
Earth is 4.6 billion years old and the
oldest evidence of life found is 3.6
billion years old. If this process has
been shaping the organisms on this
planet, then there should be evidence of
it occurring.
Evidence for Evolution
Fossil Record: Skeletons, bones, impressions,
etc. of organisms no longer found living on
the planet.
• Radiometric dating (carbon, potassium)
suggests life billions of years old.
• Activity
• The older the fossils the more simple and
the greater the differences between existing
organisms.
• Incomplete and includes inferences
Evidence for Evolution
Biogeographical: The study of the geographic
distribution of organisms.
• Islands of the world have species found no
place else. (13 different species of finch on
Galapagos, aquatic iguanas, Hawaiian
honeycreepers, etc.)
• Marsupials found in both Australia and S.
America. Few placental mammals in Aus;
many in S. America. Results in a wide
diversity of marsupials in Australia and low
diversity of marsupials in S. America.
• Organisms that are similar on different
continents are that way b/c adapted to similar
ecosystems.
Evidence for Evolution
Anatomical: Outside
appearance of body
parts of similar
categories of
organisms may look
and function
differently.
• If internal structures
are examined lots of
similarities exist.
• Ex. Forelimbs in
vertebrates
Anatomical Evidence Con
• Homologous Structures: Structures in
different species that are similar in makeup,
and may have different functions.
• Wings of bat, forelimbs of dog.
• Analogous Structures: Structures in different
species that have different makeup but have
same function.
• Wings of bat and wings of bee
• Vestigial Structures: Any structure that is
reduced in function.
• Results in reduction of size. (ex. Appendix, whale pelvic
bones, ostrich wings.)
Evidence for Evolution
Genetic Comparisons: Comparing the base
pairs, and amino acid sequences of
different organisms.
• The more similarities the closer related.
• 60% of human genes are fundamentally the
same as a fruit fly.
• 90% same as mice
• 96% similar to chimpanzees
• All humans are 99.9% the same genetically