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Chapter 6
Lesson 1
Darwin’s Theory
Learning objectives
• Describe how Darwin’s observations
helped him to develop his
hypothesis.
• Explain the process of natural
selection and how it contributes to
evolution.
Who Was Charles Darwin?
In 1839, Charles Darwin published his book The Voyage of the Beagle.
Charles Darwin
•
Naturalist –
studied nature
•
5 year voyage
around the world
•
Made observations
that helped him
create a theory of
how evolution
happens
•
Galapagos Islands
CREATION, The movie (2009) EXTRA
CREDIT
https://www.youtube.com/watch?v=u7X33g6eoOc
• Watch movie
• Write 20 facts you learned about Darwin
and his life
• Have your parent/guardian/grandparent,
etc., sign it
• Turn in by March 7
• ENJOY the movie
• 2 points Extra Credit in test category
Read: My Planet Diary pg 166
Darwin’s Hypothesis
In 1831, the HMS Beagle set sail from England on a 5 year
trip. Charles Darwin was on board.
5 year trip – many, many stops
Darwin’s Hypothesis
Darwin was a naturalist—someone who observes and
studies the natural world.
Diversity
•Darwin was amazed by the diversity of organisms.
•Wondered why organisms were so
different
from
those in England
• Saw insects that looked like flowers, sloths hanging
from trees
• Scientists have identified more than 1.6 million
species of organisms on Earth.
• Species – a group of similar organisms that can
mate with each other and produce fertile offspring
Darwin’s Hypothesis
Fossils
•A fossil is the preserved remains of traces of an organism
that lived in the past.
•Puzzling for Darwin – he saw fossils that resembled the
bones of living sloths but were much larger. What
happened?
Darwin’s Hypothesis
Darwin was a naturalist—someone who observes and
studies the natural world.
Giant ground sloth
Modern-day sloth
What are two
similarities that
you notice
between the
sloths? (see
figure 1)
The Galápagos Organisms
Comparisons to South American Organisms
• Discovered many similarities
• Ex: birds and plants resembled those on
mainland.
• Also noted differences between organisms
• Ex: iguanas
The Galápagos Organisms
Darwin became convinced that species do not always stay
the same.
Galápagos Island iguana
Mainland iguana
Were they related? Did they change over time? Darwin
thought so…
The Galápagos Organisms
Comparisons Among the Islands
• Discovered many differences
among organisms on the
different Galápagos islands.
• Ex: tortoises on one
island had dome-shaped
shells – on another they
were saddle shaped.
Galápagos Organisms
Adaptations
• Birds were different from one island to the next.
• Ex: finches - all related to one ancestor species
from the mainland.
• Over time they developed different beak
shapes and sizes based on the food they ate.
• Beak shape is an example of an adaptation
• ADAPTATION – a trait that increases an
organism’s ability to survive and
reproduce.
The Galápagos Finches
The structure of the Galápagos finch beaks is an adaptation to
the type of food each bird eats. What does each finch eat?
Darwin’s Hypothesis
Darwin was convinced that organisms change
over time.
•
Made observations that helped him create a
theory of how evolution happens.
•
•
Evolution – The process of change over time.
Darwin hypothesized that species change over
many generations and become better adapted
to new conditions.
Artificial Selection
Let’s read about it – pg. 171.
What animal did Darwin work with?
Pigeons, but also, not in the
book…horses, dogs, cows, monkeys, etc.
What is Natural Selection?
Natural Selection –
the process where
individuals that are
better adapted to their
environment are more
likely to survive and
reproduce more than
other members of the
same species.
Can you relate this to our Monster Lab?
Factors affecting Natural Selection
Overproduction – each species produces more
offspring that will survive
Variation – individuals within a population have
slightly different traits
Competition – since food, space, and other
resources are limited, members of a species must
compete with each other.
Selection - individuals within a population have a
particular characteristic that helps them survive and
reproduce.
Explore the Big Q
How do life forms change over time?
What are the four main points of Darwin’s theory of natural selection?
Overproduction, variation, competition, selection
What does overproduction mean?
More individuals are produced than can survive.
What is variation?
Any difference between members of the same species.
How does overproduction lead to competition?
There are more individuals in a population than there is food to consume.
There are more individuals than there are places for plants to grow or animals
to nest and hide.
Explore the Big Q
How do life forms change over time?
How does competition lead to selection?
Individuals whose variations make them better at competing for food and
shelter or better able to escape predators are more likely to survive and
reproduce.
How might natural selection have led sea turtles to develop flippers instead of
feet?
Some turtles had feet that were flatter or had more skin between the toes,
making them flipper-like. Those turtles could swim faster and dive deeper
and had a better chance of surviving and passing on their genes. Over many
generations, as the species evolved, legs became more flipper-like.
Natural Selection
Overproduction
Competition
Variation
Natural Selection
Overproduction: Turtles lay
many eggs. Not all of the
young will survive.
Competition: Turtles
compete with one
another. A faster turtle
may escape form a
shark.
Variation: Each
turtle has slightly
different traits.
Some may be
protected by
harder shells.
Explore the Big Q
How do life forms change over time?
What does overproduction not lead to overpopulation?
Because there are predators that catch and eat the turtles, especially the
baby turtles.
What are the hatchlings especially vulnerable?
They are very small and easy for predators to grab. They hatch on the beach
and have to cross the sand to get to the water. Birds and crabs can catch
then before they get to the water.
Which hatchlings are most likely to survive?
The ones that can move the fastest
As the turtles grow up , which are most likely to survive?
The ones that can swim fast and get away from predators; the ones that can
find food.
Explore the Big Q
How do life forms change over time?
How is this an example of natural selection?
The turtles that are better adapted to escape predators and get food are most
likely to survive and eventually reproduce.
In addition to survival, what else must happen for natural selection to affect
the evolution of the species?
The individuals that survive must reproduce and pass on their adaptions to
their offspring.
Darwin proposed that, over a long time,
natural selection can lead to change. Helpful
variations may accumulate in a species,
while unfavorable ones may disappear.
Environmental Change
A change in the environment can affect an organism’s ability to
survive and therefore lead to natural selection.
Read pg 174 – environmental change
Environmental Change
When copper contaminated the soil surrounding the monkey flowers, the
environment changed. Due to a genetic variation, some varieties of
monkey are now able to survive in the soil.
In the last circle, draw what you think the area will look like in ten years
time. Write a caption describing what has taken place.
Many monkey
flowers can now
grow in the soil.
Genes and Natural Selection
• Darwin could not explain what caused variations or how they were
passed on. (work in genetics came later)
• Scientists later learned, variations can result from changes in genes
and shuffling of different forms of genes.
• Only traits that are inherited (controlled by genes) can be acted upon
by natural selection.
Darwin’s Hypothesis
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Galápagos Finches
Match each finch to the type of food you think it eats.
Read: My Planet Diary pg 166
Chapter 6-1 Darwin’s Theory
Charles Darwin
Picture of Charles
Darwin
Courtesy of The
Bettmann Archive
• 1809-1882
• In 1859, following 30
years of study and
travels, Darwin published
a book called The Origin
of Species by Means of
Natural Selection
• Started a scientific
revolution: it showed
that life on Earth is
constantly changing and
only the fittest organisms
survive
Darwin’s cruise on the BEAGLE
•British ship: the HMS
Beagle
•Sailed for 5 years from
England
•Darwin was 22 years
old
•He became known as
the ship’s naturalist –
his job: learn as much
as he could about the
organisms he saw
How did birds differ among the islands
of the Galapagos?
Each
island had
its own
types of
birds that
were
clearly
different
from other
islands
• Darwin noticed wide variations – in beak
shape and size from island to island
• These differences made the finches better
adapted to get the food in their
environment
VARIATION
• Any difference between individuals
of the same species
• Example: The color of a few insects
may be different from that of most
other insects in the same species
ADAPTATION
• A trait that helps an organism survive
and reproduce
• EXAMPLE: Milkweed is poisonous and
has a nasty taste.
• ANOTHER ONE: Bright colors of flowers
attract insects which helps to pollinate it.
NEXT: Back to the finches….