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Darwin and the Theory of
Evolution-Changes over Time
Evolution
What’s the
Standard?
S7L5. Students will examine the evolution of living
organisms through inherited characteristics that promote
survival of organisms and the survival of successive
generations of their offspring.
a. Explain that physical characteristics of organisms have changed
over successive generations (e.g. Darwin’s finches and peppered
moths of Manchester).
Darwin &
Evolution by
Natural Selection
Cactus
eater
Insect eaters
Seed eaters
2006-2007
Bud eater
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
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
Robert Fitzroy
Voyage of the HMS Beagle
• Stopped in Galapagos Islands
– 500 miles off coast of Ecuador
Galapagos
Recently 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
Darwin found…many unique species
Many of Darwin’s observations made
him wonder… Why?
Darwin asked:
Why were these creatures found only
on the Galapagos Islands?
Darwin found…clues in the fossils
Darwin found:
Evidence that creatures
have changed over time
present day Armadillos
Darwin asked:
ancient Armadillo
Why should extinct
armadillos & modern
armadillos be found on
same continent?
Darwin found… more fossils
Darwin found:
Evidence that creatures
have changed over time
present day Sloth
(extinct) Giant ground sloth
Darwin found:
Different shells on tortoises on different islands
Darwin asked:
Is there a relationship
between the environment
& what an animal
looks like?
Darwin found… birds
Darwin found:
Many different birds on
the Galapagos Islands.
He thought he found
very different kinds…
Finch?
Woodpecker?
Sparrow?
Warbler?
But Darwin found… a lot of finches
Darwin was amazed to
find out:
All 14 species of birds
were finches…
But there is only one
Large ground
species of finch on the Finch?
finch
mainland!
Darwin asked:
Small ground
Sparrow?
finch
If the Galapagos finches
came from the
mainland, why are they
so different now?
Warbler finch
Woodpecker?
Tree finch
Warbler?
The finches
cinched
it!are
 different
beaks
Darwin found:
The differences between

species of finches were
associated with the
different food they ate.
inherited variations
serve as adaptations
that
help birds
Darwin
said: compete
for food
Ahaaaa!
 these birds survive &
Aground
flock
Large
Big seed
eater of South
Small seed
ground
eater
reproduce
finchAmerican finches
finch
 pass on the genes for
were stranded on the
those more fit beaks
Galapagos…
 over time nature selected
for different species with
different beaks
Warbler
Insect
eater
finch
Tree &
Leaf
finch
bud eater
Relationship between species (beaks) & food
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
From 1 species to 14 species…
Warbler finch
Cactus finch
Woodpecker finch
Sharp-beaked finch
Small
insectivorous
tree finch
Large
insectivorous
tree finch
Small
ground
finch
Cactus
eater
Insect eaters
Seed eaters
Vegetarian
tree finch
variation
Bud eater
Medium
ground
finch
Large
ground
finch
natural selection for best
survival & reproduction
Earlier ideas on Evolution
• LaMarck
– evolution by acquired traits
• creatures developed traits
during their lifetime
• give those traits to their
offspring
– example
• in reaching higher
leaves giraffes stretch their
necks & give the acquired
longer neck to offspring
– not accepted as valid
Darwin’s view of Evolution
• Darwin
– giraffes that already
have long necks
survive better
– leave more offspring who
inherit their long necks
• variation
• selection & survival
• reproduction &
inheritance of more
fit traits
What did Darwin’s
Travels reveal
• The diversity of living
species was far greater
than anyone had
previously known!!
• These observations led him
to develop the theory of
evolution!!
Natural Selection: Examples
Are these two butterflies the same species?
These are the Monarch and Viceroy butterflies.
The Monarch on the left is poisonous and the Viceroy is not.
Question: Why would it be beneficial for the Viceroy to look like the
Monarch?
Natural Selection: Examples
Checkpoint: A species of hare
(rabbit) that is found in a cold
tundra environment. How are
oversized feet an advantage to
the Arctic Hare?
Natural Selection: Examples
How many moths do you see?
Darwin’s Theory: REVIEW….
1. Organisms differ; variation is inherited
2. Organisms produce more offspring than survive
3. Organisms compete for resources
4. Organisms with advantages survive to pass those
advantages to their children
5. Species alive today are descended with
modifications from common ancestors
Evolution is a Theory – Just like
Gravity!
• Evolution is a well supported
explanation of phenomena that have
occurred in the natural world
• A theory in science is a well tested
hypothesis, not just a guess
Differences among Organisms
• Adaptation-a different characteristic that
helps an individual survive
• Species-a group of organisms that can mate
and produce fertile offspring
• Within any population there are variations
among members
• Some variations are helpful and some are not
Evolution
• Those variations that are helpful accumulate
in the population
• Eventually a new species forms with the new
variations
• This is Evolution
– Defined as the process in which populations
change over time to form new species.
Do species change over time?
• Evidence suggests that species have changed
over time.
• Many organisms have appeared and died out.
• As populations change over time new species
arose and other species became extinct.
Extinction
• Several periods of mass extinction have
occured
Evidence for evolution
• the fossil record show change from earlier species to
present day species
• There are chemical and anatomical similarities
between related life forms
• the recorded genetic changes in living organisms
over many generations-DNA evidence
• the geographic distribution of related species
Evidence-Fossil record
• Show estimated age and physical similarities
of organisms
• Show changes from earlier life forms
Fossil record
Fossil Record
Evidence-Common Ancestry
Common ancestors in canines
Cladogram showing common ancestry among
some lizards
Evidence from Whales
Horse Evolution
Evidence of Evolution
Turtle
Homologous Body
–
Structures
Structures that have
different mature forms
but develop from the
same embryonic
tissues
Alligator
Bird
e.g. Wing of bat, human
arm, leg of turtle
Homologous structures
Homologous structures in Embryos
Embryological development
DNA evidence
• Many organisms share common DNA
• The more DNA that is shared, the more closely
related the two organisms are
Pangea and the fossil record
Pangea and the fossil record
Evolution took a long time
Evidence for Evolution
The Fossil Record: These imprints allow scientists to
see an entire evolutionary history, including “in
between” fossils.
Homologous Body Structures: Why else use the same
skeletal plan for very different appendages? And
Similarities in Embroylogy: During the very early
stages of life (in the womb), many organisms go
through similar stages of development.
DNA evidence-shows close relationship between
different species