Transcript Chapter 15 The Theory of Evolution1

Darwin’s Theory
Chapter 15
Section 3
Darwin Presents His Case
• The specimens Darwin brought back had
the scientific community in a buzz
• Observed that Galapagos species are
found nowhere else in the world
• They looked similar to South American
mainland species but were clearly
different
Darwin’s Book
• Published his ideas about
species diversity and
evolution in The Origin of
Species
• Proposed a mechanism for
evolution called natural
selection
• Many agreed with Darwin
while others strongly
opposed him
Natural Variation
• Scientists used to believe species were
perfect and unchanging
• Darwin argued natural variation
(differences among species) is found in all
types of organisms
– Some cows give more milk
– Some plants give larger fruit
Artificial Selection
• Darwin also studied English
farmers and breeders
• Used selective breeding to breed
the “best” individuals
– Largest hogs, fastest horses
• Darwin called this
artificial selection
• Still used today!
Evolution by Natural Selection
• Darwin believed that evolution occurred
through natural selection
• Natural selection = the process by which
only the organisms best adapted to their
environment will survive and reproduce
• 3 main parts to natural selection
1. The Struggle for Existence
• There are more living
things than resources
• Results in competition
• Competition = the
struggle among living
things to get their
needs for life
2. Survival of the Fittest
• Individuals that are better suited to their
environments survive (high fitness)
• Individuals not suited to their environment
will die (low fitness)
• Fitness – the ability of an individual to
survive and
reproduce in
its environment
– Is a result of
adaptations
2. Survival of the Fittest
• Adaptation – any inherited characteristic
that increases an organism’s chance for
survival
– Long necks in giraffes
– Long toes / webbed feet
in birds
– Coloring / Camouflage
3. Descent with Modification
• Each living species has descended, with
changes, from other
species over time
• Implies all organisms
are related to one
another
– Known as common
descent
Finches
* Darwin studied different
types of finches found
on different Islands
* Each finch seemed
perfectly fitted for it’s
island environment
* Especially with its beak
Darwin’s Finches
Evidence for Evolution
• Fossil Evidence
– When living things from the past are
compared to living things today, we can see
that change has occurred
Evidence for Evolution
Beaver
Beaver
NORTH
AMERICA
Muskrat
Muskrat
Beaver and
Muskrat
Coypu
Capybara
Capybara
SOUTH
AMERICA
Coypu
Coypu and
Capybara
• Geographic distribution
of living things
– Species are located in
different parts of the
world but share
similarities
– Beavers and capybara
are similar
– Muskrat and coypu are
similar
Evidence for Evolution
• Homologous body structures
– Limbs (arms, wings, legs, flippers) have
different form and function but are
constructed from the same bones
Turtle
Alligator
Typical primitive fish
Bird
Mammals
Evidence for Evolution
• Vestigial structures
– Body parts that no longer have
functions
– i.e. Pink lump in corner of eye
• Remnant of a third eyelid
• Frogs and turtles have third eyelid
to see underwater
– Appendix
• In many mammals the appendix is
used to help digest food
Evidence for Evolution
• Embryology
– Studying
embryonic
development to
look for similarities
and differences
Embryology
Summary of Darwin’s Theory
• Evolution by Natural Selection
Natural Selection - The process by which
_______________
organisms with favorable variations produce at
higher rates because they are better adapted than
those lacking increased fitness. Species change
over time as new
species arise and
others disappear.
(Survival of Fittest)
Evolution by Natural Selection
1. Over Production
All organisms produce more offspring
than can actually survive.
Evolution by Natural Selection
2. Genetic Diversity (Natural Variation)
All species have genetic variation. No
two organisms are exactly alike. Some
of this variation is inherited.
If variation is limited, the
species is less able to adapt.
Evolution by Natural Selection
3. Struggle for Existence
Every organism faces a constant
struggle to survive. Not all organisms
survive, many that do, don’t reproduce.
Living things face many challenges.
Without challenges all alleles are equal.
Evolution by Natural Selection
4. Competition
Members of each species compete for
limited resources…
food, water,
mate, sunlight,
space, shelter,
etc.
Evolution by Natural Selection
5. Environmental Change
Ecosystems are constantly changing
due to natural succession, changes in
climate, natural
disasters, man’s
impact, etc.
Evolution by Natural Selection
6. Fittness
Because each organism is unique, each
has different advantages and
disadvantages in the struggle for
existence. How well suited an organism
is to its environment
will determine its
chance of surviving.
Evolution by Natural Selection
7. Adaptation
Some inherited characteristics increase
an organisms chance of survival in
the struggle for existence in a
particular environment.
Evolution by Natural Selection
8. Survival of the Fittest
Organisms that are best suited to their
environment, are better able to survive,
reproduce, and pass their favorable
characteristics on to their offspring.
Evolution by Natural Selection
9. Inheritance
Individuals that
survive pass their
traits on to their offspring.
The characteristics of the individuals
best suited to a particular
environment are inherited and tend
to increase in a population over time.
Evolution by Natural Selection
10. Descent with Modifications
Species alive today are modifications of
species that lived in the past. They
have descended, with changes, from
other
species
over time.
Evolution by Natural Selection
11. Common Descent
All organisms on Earth
(living and extinct) are
related to one another.
They have a common
ancestor and are united
into a single tree of life.
How does color affect survival?
• A group of mice lives in an area that has
dark soil.
• Owls eat mice in the area but because
dark mice blend well with the soil, owls
cannot see them easily
How does color affect survival?
• Dark mice are better protected because
they blend in
• Color is an adaptation because it helps
them survive
How does color affect survival?
• Dark mice sometimes have light colored
offspring which are easy to spot
• Light colored mice are usually eaten first
thus remain low in number
How does color affect survival?
• What do you think would happen if a
chemical change took place and the soil
changed to a light color?
• Owls will spot dark mice easier and as a
result will eat more dark than light mice
• Dark mice are no longer adapted to the
new surroundings
• Light mice are now better adapted
How does color affect survival?
• How will this change affect the balance of
light and dark mice?
• More light mice will survive, reproduce,
and grow
• Dark mice will get
eaten more and will
reduce in number
Natural Selection
• What determined which mouse was better
adapted to its surroundings?
• Soil color and the owls
– When soil was dark,
dark mice were not
eaten and survived
– When soil was light,
light mice were not
eaten and survived
Natural Selection
• What determines which mouse is better
adapted to its surroundings? color
– Light fur evolved to help beach mice survive
on white sand dunes, while darker fur help
mainland mice survive in fields.
Natural Selection
• Natural selection is the process by which
only the organisms best adapted to their
environment will survive and reproduce
• Something in nature does the selecting
(i.e. owls chose light or dark mice)
• The change in mouse color was
a result of natural selection