darwin’s theory chapter 15 section 3. darwin presents his case the specimens darwin brought back...
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Darwin’s TheoryDarwin’s TheoryChapter 15Chapter 15
Section 3Section 3
Darwin Presents His CaseDarwin 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 BookDarwin’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 VariationNatural 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 SelectionArtificial 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 SelectionEvolution 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 Existence1. 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 Fittest2. 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 Fittest2. 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 Modification3. 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
FinchesFinches * 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 FinchesDarwin’s Finches
Evidence for EvolutionEvidence 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 EvolutionEvidence for Evolution
• 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
Beaver
NORTH AMERICA
Muskrat
Capybara SOUTH AMERICA
Beaver
Muskrat
Beaver andMuskrat
Coypu
Capybara
Coypu andCapybara
Coypu
Evidence for EvolutionEvidence for Evolution• Homologous body structures
– Limbs (arms, wings, legs, flippers) have different form and function but are constructed from the same bones
Turtle Alligator Bird Mammals
Typical primitive fish
Evidence for EvolutionEvidence 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 EvolutionEvidence for Evolution
• Embryology– Studying
embryonic development to look for similarities and differences
EmbryologyEmbryology
Summary of Darwin’s TheorySummary of Darwin’s Theory
• Evolution by 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)
Natural Selection
Evolution by Natural SelectionEvolution by Natural Selection
1.1. Over ProductionOver Production
All organisms produce more offspring than can actually survive.
Evolution by Natural SelectionEvolution by Natural Selection
2.2. Genetic Diversity (Natural Variation)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 SelectionEvolution by Natural Selection
3.3. Struggle for ExistenceStruggle 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 SelectionEvolution by Natural Selection
4.4. CompetitionCompetition
Members of each species compete for limited resources…food, water, mate, sunlight, space, shelter, etc.
Evolution by Natural SelectionEvolution by Natural Selection
5.5. Environmental ChangeEnvironmental Change
Ecosystems are constantly changing due to natural succession, changes in climate, natural disasters, man’s impact, etc.
Evolution by Natural SelectionEvolution by Natural Selection
6. Fittness6. 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 environmentwill determine its chance of surviving.
Evolution by Natural SelectionEvolution by Natural Selection
7. Adaptation7. Adaptation
Some inherited characteristics increase an organisms chance of survival in the struggle for existence in a particular environment.
Evolution by Natural SelectionEvolution by Natural Selection
8. Survival of the Fittest8. Survival of the Fittest
Organisms that are best suited to their environment, are better able to survive, reproduce, and pass their favorablecharacteristics on to their offspring.
Evolution by Natural SelectionEvolution by Natural Selection
9. Inheritance9. Inheritance
Individuals that survive pass theirtraits 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 SelectionEvolution by Natural Selection
10. Descent with Modifications10. 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 SelectionEvolution by Natural Selection
11. Common Descent11. 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?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?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?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?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 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 SelectionNatural 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 noteaten and survived
Natural SelectionNatural Selection
• What determines which mouse is better adapted to its surroundings? – Light fur evolved to help beach mice survive
on white sand dunes, while darker fur help mainland mice survive in fields.
color
Natural SelectionNatural 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