Changes Over Time
Use the fill-in notes to accompany this PPT.
Section 1:
Darwin’s Voyage
• Charles Darwin was 22 years old when he
sailed around the world for five years on a ship
named the HMS Beagle
• During his voyage, he observed plants and
animals never seen before
• He developed an important theory known as:
The Theory of Evolution by Natural Selection
Darwin’s Observations
• One of the first stops was the coast of South America
• Here, he saw insects that looked like flowers and huge
ants
• In Argentina he saw armadillos, as well as bones from
giant sloths
• Today, scientists have identified more than 1.7 million
species of organisms on Earth
• A species is a group of similar organisms that can mate
with each other and have fertile offspring
• In 1835, he reached the Galapagos Islands and found
some the greatest diversity of life forms
• He saw giant tortoises (land turtles), seals with fur, and
giant lizards
Similarities and Differences
• Darwin was surprised to see that many of
the plants and animals on the Galapagos
Islands were similar but different to those on
the mainland of South America
• From observations he made, he inferred
(guessed) that some of the plants and
animals had come to the islands from the
mainland.
• But how did they get there? He thought
maybe they had been blown over during a
storm or drifted on a log.
Adaptations
• One of the most obvious differences
among animals he noticed was the bird
beaks…many had varied sizes and
shapes
• He noticed that each species was well
suited to what it needed to do to survive
• Beak shape is an example of an
adaptation, which is a trait helps an
organisms survive
Evolution
• For the next 20 years after his
trip, Darwin continued to think
about his trip and he continued
to consult with other scientists
about his ideas
• Darwin thought the species
gradually changed over many
generations and became
better adapted to the new
conditions
• He called this gradual change
The Theory of Evolution
• He knew that people could
produce desired traits in
organisms by selective
breeding
Natural Selection
• In 1858, Darwin and Russel Wallace
proposed an explanation for evolution
• They explained that evolution occurs
by Natural Selection…“Survival of the
Fittest”
• Natural Selection is 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.
• Factors that affect this process are:
– Overpopulation: more born than
survive
– Competition: fight for resources
– Variation: difference in offspring
(helpful variations are passed down to
offspring)
The Role of
Genes in Evolution
• Without variations, all
members of a species
would have the same
traits
• We now know that
variations are passed
down on genes
(mutations)
• Because of this, only
traits that are inherited, or
controlled by genes can
be acted upon by Natural
Selection
Evolution In Action
• Since Darwin’s book, The
Origin of Species, many
scientists have observed
natural selection
• In 1977, very little rain fell,
and many plants died…so
fewer seeds were produced
for the birds to eat
• Instead, birds had to eat
bigger seeds that had
tougher pods so the birds
beaks adapted and some
birds died off
How Do New Species
Form?
• Darwin could explain how
variations occur, but how
does a whole new
species arrive?
• Isolation, or complete
separation, occurs when
some members are
completely cut off from
the rest
• This can happen from
volcanoes, rivers,
mountains, or large
waves
• A new species can form
when they have been
isolated for so long that it
evolves new traits
The Continental Drift
• Hundreds of millions of
years ago, the continents
were all together
• They were called
Pangaea
• Over millions of years,
Pangaea split apart,
creating the continents
• A great example of
isolation occurring from
this is found in Australia,
where Kangaroos live
Section 2 :
The Fossil Record
• Scientists must act like
detectives to understand
events from long ago
• Some of the most
important clues to Earth’s
past are fossils
• A fossil is the preserved
remains or traces of an
organism that lived in the
past
• Most famous? Probably
the dinosaurs!
How Do Fossils Form? • Usually only the hard
parts of an organism
body (bones or shells)
remain after death
• The parts of plants that
are left after death are
usually leaves, stems,
roots, or seeds
• Fossil formations are rare
• Most fossils form when
organisms that die
become buried in
sediments (particles of
soil and rock)
How Fossils Form
(cont’d)
• Sediments are carried by a
river flowing into a lake or
ocean and settle on the bottom
• Over millions of years, the
layers cover up the dead
organisms and harden
• Petrified Fossils: these type of
fossils actually become rock
• A mold is a hollow space in the
sediment that shells have left
behind when they dissolved.
• A cast is a copy of the shape
of the organism that made the
mold
• Preserved Remains: Entire
organisms could be preserved
in ice (like the elephant-like
mammoths) or in tarpits.
Determining A Fossil’s Age
• Relative Dating:
– Looking at the layers
of rock that have
formed over
years…the lower the
layer, the older the
fossil (does not tell the
actual age of fossils)
• Absolute Dating:
– Will determine the
actual age of a
fossil…uses
radioactivity
What do Fossils Reveal?
• Fossils help scientists piece
together info about the past
• All the fossils that have been
collected are known as the
Fossil Record
• The Fossil Record is
incomplete (because not all
animals leave fossils)
• Almost all fossils are of
organisms that are now
extinct
• The first animals are believed
to have appeared in the seas
about 540 million years ago
• The first plants are believed
to have appeared 410 million
years ago
The Geological
Time Scale
•
•
•
This is the calendar of
the Earth’s history
It is split into 4 era’s
Precambrian Era (1)
–
–
–
•
Paleozoic Era (2)
–
–
–
•
544 million years ago
First fish
Early plants
Mesozoic Era (3)
–
–
•
4.6 billion years ago
87% of Earth’s history
is here
Early bacteria: 3.6
billion years ago
Age of the reptiles
First birds
Cenozoic Era (4)
–
–
First primates
Flowering plants
How Fast Does
Evolution Occur?
• There are two
theories
• The first, Gradualism,
proposes that
evolution occurs
slowly but steadily
(what Darwin thought)
• The second,
Punctuated Equilibria,
states that species
evolve during short
periods of rapid
change
Section 3:
Other Evidence for
Evolution
• While most animals have
many of the same organs,
not all of them use them the
same way
• Humans do not really need
their appendix, but other
animals can’t live without it
• Scientists compare body
structures, development
before birth, and DNA
sequences to determine the
evolutionary relationships
among organisms
Similarities in
Body Structure
• An organism’s body
structure is its basic body
plan, such as how its
bones are arranged
• Vertebrates (fish,
amphibians, reptiles,
birds, and mammals)
have an internal skeleton
with a backbone
• Similar structures that
related species have
inherited from a common
ancestor are called
homologous structures.
Similarities in Early
Development
• During early
development, many
organisms look
similar
• A fish, a chicken, a
pig and a human all
have a tail and tiny
gill slits in their
throats when they
are developing
• When these three
animals are adults,
they look nothing
alike
Similarities in DNA
• Scientists think
animals look similar
while developing
because they may
have inherited the
same genes from a
common ancestor
• By comparing the
sequence of bases in
DNA, they can guess
how closely related
certain species are
Combining the Evidence
• By combining
evidence from
fossils, body
structures, early
development, and
DNA, scientists
have found
evolutionary
evidence.
• A branching tree is
a diagram that
shows how
scientists think
different groups of
organisms are
related.