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Evolution
Evolution:
 The process by which modern organisms have
descended from ancient organisms
Change in a type of organism over time
Favorable traits become more frequent in a population,
while less favorable traits become less frequent
Puzzle of Life’s Diversity
 Voyage of the Beagle ( 1831 - 1836 )
 Charles Darwin
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Traveled to the Galapagos Islands and around the world from
England
Made numerous observations and collected evidence leading
to his Theory of Natural Selection
Darwin’s Observations
 Collected 68 different beetle species in one day in the
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Brazilian rainforest
Observed different but similar species on different
continents that had similar biomes
Collected Fossils from different continents ( some
resembled living organisms, some were like nothing he
had ever seen before )
Shapes of tortoise shells varied from one Island to the
next
Beaks of finches varied on each Island
Ideas that Shaped Darwin’s
Thinking
 Most people believed that the Earth and its
inhabitants were only a few thousand years old, and
that they had not changed over that time
 Fossil evidence was being collected, and interpreted as
the demise of creatures from some great catastophe
 Catastrophism
Ancient and Changing Earth
 James Hutton (1795)
 Published a detailed hypothesis about the geological
forces that shaped the Earth ( over millions of years )
-Charles Lyell (1830)
- published “Principles of Geology”
- proposed that the observable forces seen today are
the same that acted in the past (uniformitarianism )
Jean-Baptiste Lamark (1809)
- organisms acquired or lost certain traits during their
lifetime, these traits could be passed to offspring, over
time this could lead to new species
Thomas Malthus ( 1798 )
 Published that if the human population continued to
grow unchecked, sooner or later there would be
insufficient living space and food for everyone
 - War, famine and disease work against this growth
Darwin reasoned that this would be true of all species
- but not all offspring survive, and not all survivors
reproduce - Why???
Darwin Presents His Case
 Began filling notebooks with his ideas about species
diversity and the process that would later be called
evolution.
 1858 – he receives a short essay by Alfred Russel
Wallace, summarizing thoughts on evolutionary
change
 1859 – publishes “On the Origin of Species”
 Proposed Natural Selection as the mechanism for
evolution (descent with modification )
Inherited Variation and Artificial
Selection
 Noted that members of each species vary from each
other in important ways, and they could be inherited
 Current thought was that the variations were not
important
 Artificial Selection
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Nature provides the variation, and humans selected the
variations they found useful
Evolution by natural Selection
 1. the Struggle for existence
 Members of a species compete for survival
 2. Survival of the Fittest ( natural selection )
 Fitness : ability of an individual to survive and reproduce
in its specific environment
 Adaptation: any inherited characteristic that increases an
organism’s chance of survival
 Changes increase the specie’s fitness in its environment
 3. Descent with Modification
 Common Descent: all species were derived from common
ancestors ( single “tree of life” links all living things )
Evidence for Evolution
 1. Fossil Record
 2. Geographic Distribution of living species
 3. homologous body structures
 4. similarities in embryology
 5. Analogous structures
 6. Vestigial Structures
 7. DNA evidence
Fossil Record
Geographic Distribution
Homologous structures
Analogous Structures
Vestigial Structures
DNA evidence
Summary of Darwin’s Theory
 1. individual organisms differ, and some of this
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variation is inheritable
2. organisms produce more offspring than survive, and
some survivors do not reproduce
3. organisms compete for limited resources
4. successful organisms survive to reproduce and pass
on characteristics to their offspring, this process causes
speciation over time
5. Modern species are descendents from a common
ancestor
 Microevolution
 Changes within individuals that lead to new species
 Macroevolution
 Changes in populations that lead to changes in species
Biogeography
How does the geographic distribution of species today
relate to their evolutionary history?
 Patterns in the distribution of living and fossil
species tell us how modern organisms evolved from
their ancestors.
 Closely Related but Different
 Distantly Related but Similar
Genetics and Molecular Biology
How can molecular biology be used to trace the process
of evolution?
At the molecular level, the universal genetic
code and homologous molecules provide evidence of common
descent. Also, we now understand how mutation and the reshuffling
of genes during sexual reproduction produce the heritable variation
on which natural selection operates
All living cells use information coded in DNA and RNA to carry information from one
generation to the next and to direct protein synthesis. This genetic code is nearly
identical in almost all organisms, including bacteria, yeasts, plants,
fungi, and animals. This is powerful evidence that all organisms evolved from
common ancestors that shared this code.
Peter and Rosemary Grant of
Princeton University
 spent more than 35 years studying Galápagos finches.
They realized that Darwin’s hypothesis rested on two
testable assumptions.
 First, for beak size and shape to evolve, there must be
enough heritable variation in those traits to provide
raw material for natural selection.
 Second, differences in beak size and shape must
produce differences in fitness.
 The Grants have documented that natural
selection takes place in wild finch populations
frequently, and sometimes rapidly.
Changes in food supply created selection pressure that
caused finch populations to evolve within decades.
This evolutionary change occurred much faster than
many researchers thought possible.
 The Grants’ work shows that variation within a
species increases the likelihood of the species’
adapting to and surviving environmental change
Chapter Review
 P.476 # 1 – 13
 P. 476-77 # 16 – 20, # 25 - 29