Transcript lecture 2: darwinian evolution

LECTURE 2:
DARWINIAN EVOLUTION
What is
Evolution?
• Evolution is
the slow ,
gradual
change in a
population of
organisms
over time
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What was the Voyage of the
Beagle?
Charles Darwin
• Joined Crew of HMS Beagle,
1831
• Naturalist
• 5 Year Voyage around world
• Collected specimens of South
American plants and animals
• Observed adaptations of plants
and animals that inhabited
many diverse environments
• Main focus of geographic
distribution of species =
Galápagos Islands near the
equator west of South America
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Darwin Left England in 1831
Darwin returned 5 years later in 1836
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• Both Living
Organisms &
Fossils collected
• Fossils included:
•Trilobites
•Giant Ground
Sloth of South
America
This species NO longer existed.
What had happened to them?
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• Noted flora and fauna on islands off of
South America were more like continental
species than those of other islands with
similar climate and habitats
• Contributions of Lyell and Malthus along
with his observations lead him to his
mechanism for evolution
• He spent the next 28 years researching
more evidence.
What are The Galapagos
Islands?
• Small Group of Volcanic Islands 1000
km West of South America
• Very Different Climates
• Animals On Islands Unique
• Tortoises
• Iguanas
• Finches
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What are The Galapagos
Islands?
• Island species varied
from mainland
species & from
island-to-island
species
• Each island had long
or short neck
tortoises
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What are Characteristics of
Finches?
• Finches on the islands resembled a
mainland finch
• More types of finches appeared on the
islands where the available food was
different (seeds, nuts, berries, insects…)
• Finches had different types of beaks
adapted to their type of food gathering
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What were Darwin’s
Observations?
• Left unchecked, the number of
organisms of each species will
increase exponentially,
generation to generation
• In nature, populations tend to
remain stable in size
• Environmental resources are
limited
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What were Darwin’s
Observations?
• Individuals of a
population vary
extensively in their
characteristics with no
two individuals being
exactly alike
• Much of this variation
between individuals is
inheritable
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What were Darwin’s
Conclusions?
• Production of more
individuals than can be
supported by the
environment leads to a
struggle for existence
among individuals
• Only a fraction of offspring
survive each generation
• Survival of the Fittest
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What were Darwin’s
Conclusions?
• Individuals who
inherit
characteristics most
fit for their
environment are
likely to leave more
offspring than less fit
individuals
• Called Natural
Selection
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What is
Darwin’s
Theory of
Evolution?
•The unequal ability of individuals to
survive and reproduce leads to a gradual
change in a population, with favorable
characteristics accumulating over
generations (natural selection)
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• Eventually, New species evolve
What are Natural Selection
Concepts?
• The Struggle for Existence
– compete for food, mates, space, water, etc.
• Survival of the Fittest
– better adapted able to survive and
reproduce
• Descent with Modification
– new species arise from common ancestor
replacing less fit species
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What is Fitness?
• Ability of an Individual To Survive & Reproduce
• An individual’s contribution of genes to the
next generation (i.e. number of offspring)
– Fitness Is Central To The Process Of Evolution
– Individuals With Low Fitness
• Die
• Produce Few Offspring
Survival of the Fittest
AKA Natural Selection
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What are Adaptations?
Inherited Characteristic That Increases
an Organisms Chance for Survival
• Adaptations Can Be:
–Physical
• Speed, Camouflage, Claws, Quills,
etc.
–Behavioral
• Solitary, Herds, Packs, Activity, etc.
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What is Survival of the Fittest?
Key Concept
Over Time, Natural Selection
Results In Changes In The
Inherited Characteristics Of A
Population (adaptations). These
Changes Increase A Species
Fitness In Its Environment
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Natural Selection
• Cannot Be Seen Directly
• It Can Only Be Observed As
Changes In A Population Over
Many Successive Generations
– Radiation
– Fossil Record
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What is Common Descent with
Modification?
• Darwin proposed
that organisms
descended from
common ancestors
• Idea that
organisms change
with time,
diverging from a
common form
• Caused evolution
of new species
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What is Descent With
Modification?
• Takes Place Over Long Periods of
Time
• Species Today Look Different From
Their Ancestors
– Each Living Species Has
• Descended With Changes From Other
Species Over Time
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Descent With Modification
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What is Descent With
Modification?
• Implies
– All Living Organisms Are Related
– Single Tree of Life
• DNA, Body Structures, Energy
Sources
• Common Descent
– All Species, Living & Extinct, Were
Derived From Common Ancestors
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What are the 5 main points of
Darwin’s Theory of Evolution by
Natural Selection?
Variation is the raw
material for natural
selection.
• #2 Some Variations are
better than others
• #1:
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 22.8


#3: Living things face a constant struggle for existence.
“Survival of the fittest”
 Organisms produce more offspring than can survive.
#4: Only some individuals survive and reproduce.
 Some individuals survive the challenges of life better
than others. They have favorable traits
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
#5: Natural Selection causes
genetic change
• The ones with the
favorable trait
survive, reproduce
and pass on this
favorable trait to
their offspring.
• Over time the
favorable trait
increases in the
population.
What are the 5 main points of
Darwin’s Theory of Evolution by
Natural Selection?
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•
•
•
•
Population has variations.
Some variations are favorable.
More offspring are produced than survive
Those that survive have favorable traits.
A population will change over time.
Natural Selection and
Adaptation
• Evolutionary biologist
Ernst Mayr has
dissected the logic of
Darwin’s theory into 3
inferences based on five
observations
• Observation #1
• For any species, population sizes would
increase exponentially if all individuals that
are born reproduced successfully
• Observation #2
• Populations tend to be stable in size, except
for seasonal fluctuations
• Observation #3
• Resources are limited
• Inference #1:
• Production of more individuals than the
environment can support leads to a struggle
for existence among individuals of a
population, with only a fraction of their
offspring surviving
• Observation #4
• Members of a population vary in their
characteristics; no two are exactly alike
• Observation #5
• Much of this variation is heritable
• Inference #2
• Survival depends in part on inherited
traits; individuals whose inherited traits
give them a high probability of surviving
and reproducing are likely to leave more
offspring than other individuals
• Inference #3
• This unequal ability of
individuals to survive and
reproduce will lead to a
gradual change in a
population, with favorable
characteristics accumulating
over generations
A flower mantid
in Malaysia
A stick mantid
in Africa
Species adapt to their
environment
• Natural Selection tends to make a
population better suited to its
environment.
• The environment determines the
direction of genetic change.
• -ADD DIRECTIONAL SELECTION