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…