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Peppered Moths
Chapter 15
What is Evolution?
• Evolution is…..
– Change in a species over time
– The process by which modern
organisms have descended
from ancient organisms
– A theory
• Well-supported testable
explanation (hypothesis) of
phenomena that have occurred in
the natural world
• Used to be called
“transmutationism”
Charles Darwin
• The major contributor to the theory
• Born Feb. 12, 1809
– Same day as Abe Lincoln!
• Theology major in college
– Religion
• Competitor
– Alfred Wallace
– Published work on natural selection
before Darwin
• Very Controversial character
Darwin’s Expedition
• H.M.S. Beagle
– Darwin took a trip around the
world on a ship
• Like a vacation
– Went ashore when the ship
ported
– Gathered animals and other
evidence for his ideas
– Galapagos Islands
• Main area of collection and
influence on his work
• 1000 km west of South America
What did he find?
• Patterns of diversity
– Looked at why certain organisms were
found in only certain spots
– Why did they survive there when
others didn’t?
• He looked at Galapagos turtles and
finches in particular
Influences on Darwin’s Work
• James Hutton
– Hypothesized that the earth was shaped
slowly
– This went against the church btw
• Charles Lyell
– Principles of Geology
– Explained how the earth could be changed
so drastically over time
– Volcanoes, earthquakes, etc.
– So… if the earth changes over time, can
animals?
Influences on Darwin’s Work
• Jean-Baptiste Lamarck
– French naturalist studied animals’ ability to adapt
– Tendency Toward Perfection
• Changing to acquire adaptations to reach a perfect state
– Use and Disuse
• If an organism doesn’t use a trait, then it’s lost over time
• Ie our appendix and coccyx (tail bone)
– Inheritance of Acquired Traits
• Traits gained can be passed on
• Ie if I lift weights my whole life, then my children will
look like Arnold
Natural Selection
“It is not the strongest of the species that survives,
nor the most intelligent that survives. It is the one
that is the most adaptable to change.” -Charles
Darwin
• Survival of the fittest
– Fitness: the ability of an individual to survive and
reproduce in its specific environment
• Those individuals that possess
adaptations that help them survive
the best, will be the ones that
reproduce and pass on their genes.
Evolution of Populations
Occurs when there is a change in relative
frequency of alleles
Natural Selection and Species Fitness
• Overtime, natural selection results in
changes in the inherited characteristics of a
population.
• These changes increase a species fitness
(survival rate)
Descent with Modification
• Each living species has
descended with changes
from other species over
time
• Darwin’s idea
Endosymbiosis Theory
• Theory that during the
evolution of the cell, one
large bacteria cell
engulfed another one that
became the mitochondria
– This is also how they
thought the chloroplast
evolved as well
– They have their own DNA
and a double membrane
Darwin’s Postulates
1. Organisms differ; variation is
inherited
2. Organisms produce more offspring
than survive
3. Organisms compete for resources
4. Organisms with advantages survive
to pass those advantages to their
children
5. Species alive today are descended
with modifications from common
ancestors
Evidence of Evolution
1. Fossil Record
2. Geographic
Distribution of Living
Species
3. Homologous Body
structures
4. Similarities in
Embryology
Fossil Record
Fossil Record provides
evidence that living
things have evolved
Fossils show the history of
life on earth and how
different groups of
organisms have changed
over time
Relative Dating
• Can determine a fossil’s
relative age
• Performed by estimating
fossil age compared with
that of other fossils
• Drawbacks – provides no
info about age in years
– Index fossil: compares time
periods best over a short
period of time and a wide
geographic range
Absolute dating
• Can determine the absolute
age in numbers
• Is performed by radioactive
dating – based on the amount
of remaining radioactive
isotopes remain
• Drawbacks - part of the
Trilobites:
to
fossil is destroyed during the related
snowshoe
crab
test
Carbon Dating
Geographic Distribution of Living
Species
• How can animals be similar, but
distinctly different?
– The ones Darwin saw on the
Galapagos islands must have
descended from a common
ancestor
• Animals on different continents
in similar environments have
similar anatomies (body
structures) and behaviors
Convergent Evolution
• When species who are
not related evolve
similarly due to a
similar environmental
pressures
– Sugar glider and the
flying squirrel
More Evidence
Homologous Body
Structures
– Structures that have
different mature
forms but develop
from the same
embryonic tissues
e.g. Wing of bat,
human arm, leg of
turtle
Analogous Body Structures
• There appear to be many
structures that are similar
because of the function they
carry out and in their external
appearance. However, these
structures differ internally.
These species are NOT
descended from a common
ancestor. For example, wings
of bat and butterfly are similar
in appearance.
Vestigial Structures
– traces of homologous organs in other species
– Organ that serves no useful function
e.g. Appendix
Evidence Continued
Similarities in
Embryology
– In their early stages of
development,
chickens, turtles and
rats look similar,
providing evidence
that they shared a
common ancestry.
Speciation
– Adaptive Radiation
• The process in which multiple species adapt and change
(evolve) due to different environmental pressures from
one common ancestor
How Does Speciation Occur?
• Geographic Isolation
– Physical barrier separates a population
• Behavioral Isolation
– Capable of breeding, but are separated by
courtship rituals or reproductive strategies
• Temporal Isolation
– Reproduce at different times
Coevolution
• When organisms that are
ecologically close -- for example,
predators and prey, or hosts and
parasites -- influence each other's
evolution, we say that coevolution
is occurring
– One species’ evolution is in response
to the other
– One example is the bacteria living in
our stomachs. They have evolved
along with us.
Human Skulls
Australopithecus
Homo erectus
Homo sapien
Liger
Result of male lion and female tiger mating
in captivity. Offspring are infertile.
Tigon
Result of male tiger and female lion
mating in captivity. Offspring are
infertile.
Extinction
• 99% of all species that have ever lived are now
extinct