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Chapter 15 Evolution
What You’ll Learn
You will analyze the theory of evolution.
You will compare and contrast the processes of evolution.
• Section Objectives:
Summarize Darwin’s theory of natural selection.
Explain the 4 principles of natural selection
Show how natural selection could change a population
Darwin’s Theory of Natural Selection
What is Evolution?• Evolution ~process of change through time– explains how modern organisms have descended
from ancient organisms
Evolution!
Evolution!Evolution!Why do we accept this as a
Scientific Principle? Why do we accept this as aScientific Principle?
Evolution: process of change through time
• The change in characteristics of populations through generations. Thus, existing life forms have evolved from earlier life forms
• A unifying principle for biology.• Provides an explanation for the difference in
structure, function, and behavior among organisms
What do we know?• There are many different creatures on Earth• How do we know this?
Diversity of Life on EarthDiversity of Life on Earth
OBSERVATIONOBSERVATION
How did all these creatures come about?How did all these creatures come about?What accounts for all this biological diversity?What accounts for all this biological diversity?
Biodiversity of Life on EarthBiodiversity of Life on Earth
What do we know?• All creatures have common characteristics• How do we know this?
DNAcells
Unity of Life on EarthUnity of Life on Earth
How could all of life have the same basic features?How could all of life have the same basic features?
OBSERVATIONOBSERVATION
What do we know?• Creatures have changed over time• How do we know this?
Fossil RecordFossil Record
OBSERVATIONOBSERVATION
DNA
Evolution explains Unity & Diversity• Only evolution explains both – unity of life• similarities between all living things
– diversity of life• wide variety of different creatures on Earth
2006-2007
Insect eaters
Bud eater
Seed eaters
Cactuseater
Warbler
finch
Tree
finc
hes Ground finches
Darwin & Evolution by
Natural Selection
Charles Darwin• Proposed a way how
evolution works– How did creatures
change over time?– by natural selection
• Collected a lot of evidence to support his ideas – 1809-1882– British naturalist
Robert FitzroyRobert Fitzroy
Voyage of the HMS Beagle• Invited to travel around the world– 1831-1836 (22 years old!)– makes many observations of nature
• main mission of the Beagle was to chart South American coastline
Voyage of the HMS Beagle• Stopped in Galapagos Islands– 500 miles off coast of Ecuador
GalapagosRecently formed volcanic islands. Most of animals on the Galápagos live nowhere else in world, but they look like species living on South American mainland.
800 km west of Ecuador
Many of Darwin’s observations made him wonder… Why?Many of Darwin’s observations made him wonder… Why?
Darwin asked:
Why were these creatures found only on the Galapagos Islands?
Darwin found…many unique species
present day Armadillos
Darwin found:Darwin found:
Evidence that creatures that creatures have changed over timehave changed over time
ancient Armadillo
Darwin asked:Darwin asked:
Why should extinct Why should extinct armadillos & modern armadillos & modern armadillos be found on armadillos be found on same continent?same continent?
Darwin found…clues in the fossils
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Finch? Sparrow?
Woodpecker? Warbler?
Darwin found… birds
Finch? Sparrow?
Woodpecker? Warbler?
Darwin found:Darwin found:Many different birds on Many different birds on the Galapagos Islands. the Galapagos Islands.
He thought he found very He thought he found very different kinds…different kinds…
Darwin was amazed to find out: All 14 species of birds were finches…
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Finch? Sparrow?
Woodpecker? Warbler?
Finch? Sparrow?
Woodpecker? Warbler?
But Darwin found… a lot of finches
Large ground finch
Small ground finch
Warbler finch Tree finch
But there is only one species of finch on the mainland! Darwin asked:Darwin asked:
If the Galapagos finches If the Galapagos finches came from the mainland, came from the mainland, why are they so different why are they so different now?now?
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Finch? Sparrow?
Woodpecker? Warbler?
The finches cinched it!
Large ground finch
Small ground finch
Warbler finch Tree finch
Big seed eater Small seed eater
Insect eater Leaf & bud eater
Darwin said:Darwin said:
Ahaaaa! Ahaaaa! A flock of South A flock of South American finches were American finches were stranded on the stranded on the Galapagos…Galapagos…
Darwin found: The differences between species of finches were associated with the different food they ate.
different beaks are inherited variations
serve as adaptationsthat help birds compete for food
these birds survive & reproduce
pass on the genes for those more fit beaks
over time nature selected for different species with different beaks
Relationship between species (beaks) & food
DARWIN’S THEORY AND THE MODERN SYNTHESIS
• Darwin also saw that humans choose organisms with specific characteristics Breeding organisms with specific traits in order to produce offspring with identical traits is called artificial selection.
• Darwin hypothesized that there was a force in nature that worked like artificial selection.
Darwin proposed natural selection as the mechanism of evolution
• Darwin hypothesized that there was a force in nature that worked like artificial selection.
• Darwin saw natural selection as the basic mechanism of evolution
• Darwin concluded that individuals best suited for a particular environment are more likely to survive and reproduce than those less well adapted
– As a result, the proportion of individuals with favorable characteristics increases
– Populations gradually change in response to the environment
• Organisms without these variations are less likely to survive and reproduce.
Darwin’s finches• Darwin’s conclusions – variations in beaks • differences in beaks in the original flock• adaptations to foods available on islands
– natural selection for most fit• over many generations, the finches were selected for
specific beaks & behaviors
– offspring inherit successful traits• accumulation of winning traits:
both beaks & behaviors
– separate into different species
Warbler finch
Woodpecker finch
Small insectivorous
tree finchLarge
insectivoroustree finch
Vegetariantree finch
Cactus finch
Sharp-beaked finch
Small groundfinch
Mediumground finch
Large groundfinch
Insect eaters
Bud eater
Seed eaters
Cactuseater
Warbler
finch
Tree
finc
hes Ground finches
variation natural selection for best survival & reproduction
From 1 species to 14 species…
What do we know?• Populations are a mix of different individuals• How do we know this? OBSERVATIONOBSERVATION
VariationVariation
How does that work?
VariationVariation
Over-Production & CompetitionOver-Production & Competition
Natural SelectionNatural Selection
Nature selects the ones that “fit” the environment better … survive & reproduceNature selects the ones that “fit” the environment better … survive & reproduce
AdaptationAdaptation
What determines survival?• Natural Selection– traits that help individuals survive• survive predators• survive disease• compete for food• compete for territory
– traits that help individuals reproduce• attracting a mate• compete for nesting sites• successfully raise young
Survival & Reproduction of the FittestSurvival & Reproduction of the Fittest
Adaptations Adaptations
Survival & Reproduction of the fittest
not the strongest…not the strongest…not the bravest…not the bravest…not the fastest…not the fastest…not the biggest…not the biggest……the fittest!…the fittest!
the traits that help an organism fit the environment better tosurvive & reproduce
the traits that help an organism fit the environment better tosurvive & reproduce
AdaptationsAdaptations
Survival & reproduction of the fittest bug…