Evolution
Study Guide
Learning Target #1
Describe important observations Darwin made on his voyage
a) Explain the hypothesis Darwin made to explain differences between similar
species
What did Charles Darwin do in his life that led him to create his hypothesis about evolution?
In 1831, he traveled on the British ship, HMS Beagle, for a 5 year trip around the world.
What observations did Charles Darwin record during his trip around the world?
1. Diversity of living things
2. The remains of ancient organisms
3. The characteristics of organisms on the Galapagos Islands
What did he mean by “diversity of living things?”
Today, scientists have identified more than 1.7 million species of organisms on Earth.
a) In Brazil, he saw insects that looked like flowers and ants that marched across the forest floor
like huge armies
b) In Argentina, he saw sloths, animals that moved very slowly and spent much of their time
hanging in trees
What is a species?
a group of similar organisms that can mate with each other and produce fertile offspring
What did he mean by “the remains of ancient organisms?”
Darwin was puzzled by some of his observations – he saw fossil bones that resembled the bones of living
sloths that were much larger than those sloths that were actually alive at that time.
What is a fossil?
preserved remains or traces of an organism that lived in the past
What is adaptation?
a trait that helps an organism survive, thrive, and reproduce (maintain stable conditions)
What were some of the characteristics of organisms found in the Galapagos Islands?
He observed giant tortoises (land turtles). Some of these tortoises were so large that they could look
him in the eye.
As a result, he compared these organisms to those that he had seen on other islands. He was surprised
by the similarities and by the differences
What similarities did he note?
Many of the birds on the islands such as hawks, mockingbirds, and finches resembled those on the
mainland. Many of the plants were similar to those on the mainland as well.
What differences did he note?
The iguanas on the island had large claws, but those on the mainland had much smaller ones. The larger
claws allowed them to grip slippery rocks where they fed on seaweed. The smaller claws allowed them
to climb tree where they ate leaves.
What do the differences in the size of beaks of birds mean in regards to adaptations?
The size of the beak is determined by the adaptations the birds have to make for survival primarily
based on what type of food is available and the difficulty in obtaining it.
 A pointy more narrow beak is used by those who hunt insects
 A larger more broad beak is used by those who hunt for seeds
What did he hypothesize based on the similarities and the differences he observed?
A small number of different plant and animal species had come to the Galapagos Islands from the
mainland. While there they reproduced, and eventually the offspring became different from their
original relatives.
Learning Target #2
Explain how natural selection leads to evolution
a) State evidence that supports the theory of evolution
b) Explain how scientists infer evolutionary relationships among organisms
c) Explain how new species form through evolution
d) Identify some unanswered questions about evolution
After returning to England, WHAT CONCLUSIONS did Darwin make about the similarities and
differences of organisms?
1. Plants and animals that arrived at Galapagos Islands faced conditions that were different from
those on the mainland.
2. The species gradually changed over many generations and became better adapted to the new
conditions.
What is evolution?
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 scientific theory ?
a well-tested concept that explains a wide range of observations.
What is The Origin of Species
A Book by Darwin that proposed that evolution occurs by means of natural selection.
What is natural selection ?
the process by which individuals that are better adapted to their environment are more likely to survive
and reproduce than other members of the same species.
 It causes a species to change gradually
What factors affect natural selection?
a) Overproduction – produce more offspring than can possibly survive
b) Competition – compete for food/other resources for survival
c) Variations – any difference between individuals of the same species
Over a long period of time, natural selection can lead to change.
Helpful variations may gradually accumulate in a species, while unfavorable ones may disappear.
Does natural selection occur today? yes
For example - Pesticides are used to kill harmful insects.
The first time it is used, it will kill most of them. But a few will survive because they have traits that
protect them. They will reproduce and pass those traits to their new offspring. Eventually, the pesticide
will not work anymore against these insects.
What evidence supports evolution?
a) fossils
b) patterns of early development
c) DNA
d) Protein Structure
e) similar body structures
What is a homologous structure?
Similar structures that related species have inherited from a common ancestor
Example:
Scientists have found fossils of ancient whale-like creatures. The fossils show that the ancestors of
today’s whales had legs and walked on land. This evidence supports other evidence that whales and
humans share a common ancestor.
What evidence do scientists use to infer species’ relationships?
a) Evidence from DNA
d) Early development
b) Protein structure
e) Body structure
c) Fossils
What is a branching tree?
a diagram that shows how scientists think different groups of organisms are related
 Scientists use the combined evidence of species relationships to draw branching trees.
How can isolation lead to the formation of a new species?
When a group of individuals remains isolated from the rest of its species long enough to evolve different
traits
How do new species form?
When a group of individuals remain isolated from the rest of its species long enough to evolve different
traits
Example: A population of rabbits become separated on two islands and don’t have any contact for a
significant period of time --- They eventually evolve into 2 different species
When scientists try to determine how closely related species are, what evidence do they examine?
Evidence from DNA, protein structure, fossils, early development, and body structure
Which types of evidence would be most reliable?
DNA and protein structure because they show distinct patterns that can be easily compared
Learning Target #3
Describe how most fossils form
a) Explain how scientists can determine a fossil’s age
What fossil was discovered in 1990 in South Dakota?
In 1990, a dinosaur nicknamed “Sue” was discovered in South Dakota.
 It is now located in a museum in Chicago.
 She is 67 million years old and classified as a “Tyrannosaurus Rex.”
How do fossils form?
Most fossils form when an organism that dies becomes buried in sediments.
 The formation of a fossil is a rare event.
 Usually, only the hard parts of the organism, such as the bones or shells, form the fossil.
What are different types of fossils?
Petrified fossils, molds and casts, and preserved remains
What are petrified fossils?
Gradually, minerals replace the remains, changing them into rock
 Some remains change into rock
What is a fossil mold?
A hollow space in sediment in the shape of an organism or part of an organism
 Sometimes shells or hard parts buried by sediments are gradually dissolved.
What is a fossil cast?
A mold may become filled with hardened minerals, forming a cast.
 A cast is a copy of the shape of the organism that made the mold.
What are preserved remains?
Organisms can be preserved in substances other than sediment----Such as ICE.
What are sediments?
Particles of soil and rock that are broken down and transported through weathering and erosion.
These particles eventually get placed (deposited) through deposition
Through the process of lithification the sediment eventually becomes sedimentary rock
How are sediments involved in the formation of fossils?
fossils form when organisms that die become buried in sediments.
 Particles of soil and rock
 Layers of sediments cover the dead organism and after millions of years the layers harden to
become sedimentary rock
How do scientists determine a fossil’s age?
Two ways
1. Relative dating
2. Radioactive dating
What is relative dating?
Used to determine which of two fossils is older
 In a sequence of rock layers, the top layers are usually younger than the lower layers, therefore
fossils found in top layers are usually younger than fossils found in bottom layers
What is radioactive dating?
The half-life of a radioactive element is the time it takes for half of the atoms in a sample to decay. This
information can be used to calculate the age.
 The rocks contain radioactive elements, which are unstable elements that decay or break down
into different elements
 Allows scientists to determine the actual age of fossils.
What is a fossil record?
The millions of fossils that scientists have collected
 Despite gaps in the fossil record, it has given scientists a lot of important information about past
life on Earth.
What are extinct organisms?
Almost all of the species preserved as fossils are now extinct
A species is extinct if no members of that species are still alive.
What are 2 unanswered questions about evolution?
1. Causes of mass extinctions
2. Rate at which evolution occurs
What are the two theories about the rate of evolution?
Theory of gradualism
Theory of punctuated equilibria
What is the theory of gradualism?
evolution occurs slowly, but steadily
 tiny changes in a species gradually add up to major changes over very long periods of time
What is the theory of punctuated equilibria?
A theory that accounts for the gaps in the fossil record
Species evolve quickly during relatively short time periods: These periods of rapid change are separated
by long periods of little or no change.
How are the theories of gradualism and punctuated equilibria different and similar?
Different: gradualism states that evolution occurs slowly and steadily, but punctuated equilibria states
that evolution occurs rapidly during short periods separated by long periods of no change.
Similar: both theories propose that organisms evolve; both attempt to explain the fossil record