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Evolution
Chapter 15
Voyage of the Beagle
Darwin’s Adventures
• Observations
– Darwin saw plants/animals and took notes
– Noted how well they were suited to their
specific environment
– Had visited similar environments but did
not see same species
– Why no kangaroos in England?
– Many fossils he discovered resembled living
organisms but not identical
Galapagos Islands
• Close together, but different islands
– Smallest were hot dry and barren
– Largest greater rainfall
Shape of Shells
• Tortoises
– Shell shape could determine which island
the tortoises inhabited
Birds of Galapagos
• Finches
– Collected finches and studied their
beaks
An Ancient Changing Earth
• Hutton
– Earth much older than a couple thousand
years
– Mountains, valleys took thousands of years
to form
• Lyell
– Explain past events with observations
– Caused Darwin to ask….if earth can change
over time then is it possible that organisms
could as well
Jean Baptiste Lamarck
• Noticed that blacksmiths were usually
muscular
• Noticed that their children would usually
become muscular
• Hypothesized that being muscular was
passed down from parent to offspring
• Used no scientific evidence
Jean Baptiste Lamarck
• Use and Disuse of Organs
– Organisms constantly strive
to improve themselves to
become more
advanced/perfected
– The effort to improve
causes the most used body
structure to develop and the
most unused structure to
waste away
• Principle of Acquired
Traits
– The modified structure can
be passed down from
parent to offspring
Jean Baptiste Lamarck
• Lamarck was disproved by August Weismann
– Weismann cut off tails of over a 100 mice
– mated the mice for 50 generations
– all of the mice were born with tails
Malthus
• 1798…observed more babies born than
people dying
• Reasoned population continue to grow
unchecked sooner or later not enough
resources to support all life
• Darwin related this to plants/animals
• All offspring could not have survived
because continents would be filled
Charles Darwin
• RECALL
• Sailed on the Beagle as the ship’s
naturalist
• Visited the Galapagos Islands
• Then publishes “Origin of Species”
**Abandoned Lamark’s idea that
species “perfected” themselves
Natural Variation and
Artificial Selection
• Natural Variation- differences among
individuals of a species
– Some cows give more milk
– Some plants bigger fruits
– Some plants produce more peas
• Artificial Selection- picking which
individuals can reproduce
Artificial Selection with Dogs
Charles Darwin
• Darwin’s Theory:
– All organisms compete for limited space
(Struggle for existence)
– Organisms produce more offspring than can
survive (survival based on fitness)
– Natural selection (survival of the fittest)states
that organisms best suited to the environment
survive while those not suited may eventually
die
Charles Darwin
Big Picture
Over time natural selection results in
changes in the inherited
characteristics of a population ****
Descent with Modifications………... As a
result species look different from
their ancestors
Types of Evolution
• Divergent – related species become dissimilar
• Extinction – disappearance of a species
– Ex dinosaurs
• Adaptive Radiation – 1 species evolves into more species
adapted to surrounding
– Ex Darwin’s finches
• Convergent evolution – unrelated species come to look alike due
to evolving similar adaptations to similar environments
– Ex penguins and dolphins
• Coevolution – 2 species evolve in response to change in each
other
– Ex plants evolved poison to protect themselves from insects
and insects evolved ways to protect themselves
• Punctuated equilibrium – long periods of no change are
interrupted by short periods of rapid change
Types of Evolution
• Divergent
– Related organisms become more distant
• ex: Grizzly Bears & Polar Bears
Types of Evolution
• Convergent
– Distantly related organisms develop similar
characteristics
• ex: Dolphins & Penguins
Evidence of Evolution
•
•
•
•
Fossil Record
Geographic distribution of living species
Homologous structures
Similarities of early development
Fossil Evidence
• By examining fossils from, sequential
layers of rock one could view how a
species had changed over time
Geographic Evidence
• Little brown birds that all looked
different were in reality all finches
• THIS IS DIFFERENT FROM:
Evolution of shared traits in unrelated
species because of similar environments
is called convergent evolution
Anatomical Evidence
• Analogous Structures
– Body parts of different organisms that have
the same function but different structures
– ex: Bird’s Wing & Butterfly’s Wing
• Vestigial Structures
– Body parts with no apparent functions
– ex: human appendix, tiny hip bones in some
snakes
Homologous Structures
• Notice similarities of similar structures
• Each limb adapted in way to best fit the
organism in their environment
• Strong evidence that 4 limbed animals
with back bone all
descended, with
modifications from
common ancestor
Anatomical Evidence
• Homologous
Structures
– Body parts of
different organisms
that have the same
basic structure
• Example: Human
Arm, Bird Wing,
Whale Fin, Bat Wing
Similar Early Development
• Early stages are so similar that it is
difficult to tell them apart
Embryological Evidence
• Study of early growth
stages & development
of embryos
• The embryos of
different organisms look
very similar
– similar genes at work
• The DNA sequences
which control early
development remain
unchanged because of
little or no mutations
Summary of Charles Darwin
• Darwin’s Evolution:
– Variation exists within a species
– Some variations are favorable
– Survival of the fittest
• The strongest will survive and reproduce
• The weak will die out
• Organisms better adapted to the environment will
survive
– Adaptations will happen gradually
• Gradualism
Chapter 16
• Evolution of Populations
Remember Evolution
• Gradual change in characteristics over time
• A theory that explains how organisms
change over a period of time
• Results in:
– New organisms
– Some organisms becoming extinct
Evolution
• Variations - differences in traits
• Adaptation - gradual changes to an
organisms to help it survive
• Gradualism - the belief that evolutionary
changes in organisms take several years to
occur
Charles Darwin
• Natural Selection
Charles Darwin
• Natural Selection:
– Disruptive Selection
• Selection can act against the middle of a normal distribution
after an environmental change, this is selection against the
most common variation (ex. African Swallowtale Butterfly
– Directional Selection
• After several generations, the normal distribution shifts in the
direction of change (ex. DDT and insects)
– Stabilizing Selection
• Environments may go through long periods of stability, when
conditions remain about the same. Organisms that are best
adapted to the existing environment will be favored, and
there is selection against the extremes
Speciation
• Speciation
– When one or more new organisms evolve
from a single ancestral species
• Divergent Isolation
– When an isolated population evolves into
different populations that cannot interbreed
Synthesis of Organic Molecules
• Miller & Urey
– Mixed water vapor, methane, ammonia, &
hydrogen gas (all inorganic) together with
electrodes (lightning)
– After a week they produced Organic Molecules
Prokaryotic to Eukaryotic
• Origin of an inner membrane - Cell
membrane infolded to create
compartments
• Endosymbiosis
– Mitochondria and Chloroplast (free living
Prokaryotes) were consumed by a larger
Prokaryote
– They were not digested and formed a
permanent partnership - Symbiosis
Chapter 17
• The History of Life
Evidence of Evolution
• Fossil
• Anatomical
• Embryological
• Biochemical
Fossil Evidence
• Organisms became increasingly complex
over time
• Types of fossils
– Preserved Tissue
– Preserved Trace
• Youngest fossils are on top, Oldest are on
the bottom
How old are fossils?
• In sedimentary rock
layers, the oldest
fossils are in the
bottom layers, the
youngest fossils are
in the top layers
• Radioactive dating &
Carbon-14 dating
Population Genetics
• Population
– Group of organisms that live in the same are &
interbreed
• Evolution can only occur when there is a
change in the kinds or % of genes in the
gene pool of a population (allele
frequencies)
Hardy-Weinberg Principle
• Describes the conditions that must be met
in order for the allele frequencies to
remain constant
• It describes genetic equilibrium
• Five conditions
Hardy-Weinberg Principle
• 1. No Mutations
• 2. Random Mating
• 3. No Genetic Drift
• 4. No Natural Selection
• 5. No Gene Flow