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Transcript
7th Grade
Ms. De Los Rios
11-2 Darwin’s Theory
Essential Question:
How do Life Forms Change over time?
What was Darwin’s Hypothesis?
What Natural Selection?
Darwin’s Theory
Pgs. 384-393
Vocabulary
Adaptation – An inherited behavior or physical characteristic that
helps an organism survive and reproduce in its
environment.
Scientific theory - A well-tested explanation for a wide range of
observations or experimental results.
Trait - A specific characteristic that an organism can pass to its
offspring through its genes.
Natural selection - The process by which organisms that are best
adapted to their environment are most likely to
survive and reproduce.
Variation – Any difference between individuals of the same species.
My Planet Diary pg. 384
In 1839, Charles Darwin published his book The Voyage of the Beagle. Read the
following excerpt about an animal Darwin encountered while in the Galápagos
Islands.
The inhabitants believe that these animals are absolutely
deaf; certainly they do not overhear a person walking
close behind them. I was always amused when overtaking
one of these great monsters, as it was quietly pacing along,
to see how suddenly, the instant I passed, it would draw
in its head and legs, and uttering a deep hiss fall to the
ground with a heavy sound, as if struck dead. I frequently
got on their backs, and then giving a few raps on the
hinder part of their shells, they would rise up and walk
away;—but I found it very difficult to keep my balance.
1. What kind of animal do you think Darwin was describing?
2.
Describe your reaction to an unusual animal that you may have seen at a
zoo, or at an aquarium, or in a pet store. What was your first impression of
the animal?
Charles Darwin
Darwin was a British scientist who laid the
foundations of the theory of evolution and
transformed the way we think about the natural
world.
Charles Robert Darwin was born on 12 February
1809 in Shrewsbury, Shropshire into a wealthy
and well-connected family. His maternal
grandfather was china manufacturer Josiah
Wedgwood, while his paternal grandfather was
Erasmus Darwin, one of the leading intellectuals
of 18th century England.
Darwin himself initially planned to follow a medical
career, and studied at Edinburgh University but
later switched to divinity at Cambridge. In 1831, he
joined a five year scientific expedition on the
survey ship HMS Beagle.
Online Resources
Discovery Video Evolution Theory
Brainpop Charles Darwin
Brainpop Natural Selection
Diversity and Fossils Pg. 385
In 1831, The British ship HMS Beagle set sail from England on a five year trip
around the world. Charles Darwin was on board. Darwin was a naturalist--- a
person who observes and studies the natural world.
During his five-year voyage around the world, Charles Darwin observed great
diversity among living things, often within the same species.
 Darwin also observed fossils that shared some, but not all, traits with living
animals.
A trait is a specific characteristic that an organism can pass to its
offspring.
 Darwin also observed differences in plants and animals that lived in South
America and the Galápagos Islands, which are off the coast of South America.
He attributed these differences to examples of adaptations - a trait that
increases an organism’s ability to survive and reproduce.
Darwin’s Theory
Galápagos Finches
The structure of
each bird’s beak is
an adaptation to the
type of food the bird
eats.
Match each finch
to the type of food
you think it eats.
Darwin’s Hypothesis pg. 388
Darwin thought about what he had seen during his voyage on the Beagle. By this time,
Darwin was convinced that organisms change over time. He wanted to know how
organisms change. Over the next 20 years he consulted with other scientists and
gathered more information. Based on his observations, Darwin reasoned that plants
or animals that arrived on the Galapagos Islands faces conditions that were
different from those on the nearby mainland.
The iguanas on the Galapagos Islands have large claws that allow them to grip
slippery rocks so they can feed on seaweed. The Iguanas on the mainland have
smaller claws that allow them to climb trees so they can eat leaves.
What Was Darwin’s Hypothesis?
Pg. 388
Darwin hypothesized that species gradually change
over many generations and become better adapted to new
conditions.
 Because the gradual change in a species over time is called
evolution, Darwin’s ideas are often referred to as the theory of
evolution.
What is a scientific theory?
A scientific theory is a well-tested
concept that explains a wide range of
observations.
.
Did You Know?
Galapagos Penguin
The Galápagos penguin is the northernmost penguin in the
world!
It lives on the equator and is kept cool by ocean currents. The
Galápagos penguin is the rarest penguin species and is
endangered.
Galápagos
penguin
Assess Your Understanding pg. 389
1a. Make of list of three observations that Darwin made during the
Beagle’s voyage.
b. An adaptation is a trait that increases an organism’s ability to
____________________and ___________________.
c. How does artificial selection support Darwin’s hypothesis?
I get it! Now I know that Darwin’s hypothesis was____________
___________________________________________________
What is Natural Selection? Pg. 390
In 1858, Darwin and Alfred Russel Wallace proposed the same
explanation— natural selection —for how evolution occurs.
Natural selection is the process by which
individuals that are better adapted to their environment are
more likely to survive and reproduce more than other members
of the same species.
Darwin proposed that, over a long time, natural selection can
lead to change.
Helpful variations may gradually accumulate in a species, while
unfavorable ones may disappear.
Without variations, all the members of a species would have the
same traits and equal chances of surviving and reproducing.
Overproduction pg. 390
•Darwin knew that most species
produce far more offspring than
can possibly survive.
•In many species, so many
offspring are produced that there
are not enough resources – food,
water, and living space – for all of
them.
Variation pg. 391
Members of a species differ from
one another in many of their
traits.
Variation is any difference
between Individuals of the same
species.
For Example,
sea turtles may differ in color, size,
the ability to swim quickly, and shell
hardness
.
Competition pg. 391
Since food, space, and other
resources are limited, the members
of a species must compete with
one another to survive.
Competition doesn’t always involve
physical fights between members of
a species. Instead, competition is
usually indirect.
For example,
•some turtles may not find enough to eat.
•A slower turtle may be caught by a
predator, while a faster turtle may
escape.
•Only a few turtles will survive to
reproduce.
Selection pg. 391
Darwin observed that some
variations make individuals better
adapted to environment.
Those individuals are more likely
to survive and reproduce and their
offspring may inherit the helpful
characteristic.
 The offspring, in turn, will be more
likely to survive and reproduce, and
pass the characteristic to their
offspring.
 After many generations, more
members of the species will
have the helpful characteristic.
Factors That Affect Natural Selection pgs. 130-131
•What are the factors of natural selection that affect a group of sea turtles over time?
•Examine the sequence below that shows how natural selection could affect a group
of sea turtles over time.
•Label Each Factor In The Illustration and write a brief caption explaining what is
occurring.
Darwin’s Theory
Relate Cause and Effect
Identify the factors that cause natural selection.
Environmental Change pg. 392
A change in the environment can affect an organism’s ability to survive
and therefore lead to natural selection. For example, monkey flowers
are plants that do not normally grow in soil that has a high concentration
of copper. However, because of genetic variation, some varieties of
monkey flower now grow near copper mines.
Environmental Change
When copper contaminated the soil surrounding the
monkey flowers, the environment changed. Draw what you
think the area will look like in ten years in the last circle.
Genes and Natural Selection pg. 392
Darwin could not explain what caused variations or how they were
passed on, but scientists later learned that variations can result from
changes in genes and the shuffling of different forms of genes when egg
and sperm join. Only traits that are inherited, or controlled by genes, can
be acted upon by natural selection. Other factors, such as competition
and environmental change,
can affect an organism’s
survival.
Do The Math! Pg. 392
Loggerhead Sea Turtle Data
Do you think clutch size influences the survival rate of offspring?
1.Which measure of central tendency would you use to find the average clutch size?
Calculate It! _____________________
2. Do you think clutch size influences the survival rates of the offspring?
Use the data to support your answer. ________________________________________
3. Hypothesize why Site F had the largest number of returning turtles.
______________________________________________________________________
Assess Your Understanding
pg. 393
2a. A variation is any (similarity / difference) between individuals
of the same species.
b. How do life forms change over time?
___________________________________________________
___________________________________________________
c. How does genetic variation contribute to the diversity of
organisms? _________________________________________
___________________________________________________