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Chapter 4
Life Changes Over Time
4-1What is Evolution?
Key Terms
• Species- group of organisms that look alike
and can reproduce among themselves.
• Evolution- process by which species change
over time
• Adaptation- trait that helps an organism
survive in its environment
• Mutation- change in a gene
Evolution
• Evidence shows that the earliest life forms
on this planet were very simple and very
small.
• In the approximately 4 billion years since
this planet was formed, organisms have
developed, and become more and more
complex.
• They have developed into species, which
is a group of organisms that look alike and
can reproduce among themselves.
• Some species have become extinct.
• Most scientists believe that new species
come from older species through a
process of known as evolution.
• This process takes many years to
complete and is very slow.
Adaptations
• Organisms are found all over the planet, in
all kinds of conditions.
• There are organisms that live on mountain
tops, and then in the deepest parts of
oceans.
• They have developed adaptations, which
are a feature or trait that help an organism
to live in a certain environment.
Examples
Mutation
• As species change over time, generally these
changes are caused by genetics.
• In time, a generation will develop new genes
from it’s ancestors.
• These changes take place over a VERY long
time, and are in response to new
environments.
• Sometimes, mutations, will occur very
suddenly. If the mutation is helpful it will be
passed on to other generations. If it is not, or
is harmful, then the individual will probably
die, before they can reproduce.
Earth’s Evolution
• Fossil evidence shows that
plant Earth’s contents have
been changing as well as
the life that is present here.
• Fossils of tropical plants
have been found at the
North and South poles.
Fossils of marine life have
been found in desserts.
• Earth scientists believe that
the contents that we know
of today, formed 220million
years ago from one large
continent called Pangaea.
4-2 What are Fossils?
Key Terms
• Extinct- no longer found as a living species
• Fossil – remains or traces of a once-living
organism
• Amber- hardened tree sap
Fossils
• There are many
organisms that are
extinct, or no longer
found as a living
species, however
they have left behind
clues that they did
exist.
• These clues are
called fossils.
Fossils are the
remains or traces of
once-living
organisms.
Types of Fossils
• There are more than
1 kind of fossil.
• Some fossils are
imprints left by
organisms in mud
that is later changed
to rock.
• For example: in
March of 1990, a
whole mammoth
was found in
Siberia.
• Insects have been
trapped and
persevered in
amber.
• Amber is harden
tree sap that has
been preserved in
the earth for
millions of years.
Fossils in Rocks
• Sedimentary rock is
the most common
place for fossils to
be found.
• Sedimentary rock is
made of layers of
sediment, which is
bits of clay, sand,
soil and other earth
materials.
• Molds are formed when an organism is
buried by sediment and the sediments
change into rock.
• The organism decays and leaves a cavity
or opening in the rock. The cavity is now a
mold.
• Sometimes that mold fills with sand or
mud, which will harden, creating a cast.
4-3 What evidence supports
evolution?
Key Terms
• Homologous structures- body parts that
have the same basic structure
• Vestigial structure- body parts that seem to
have no function.
The fossil record
• The fossil record clearly shows that changes
have taken place throughout Earth’s history.
• There is also evidence that Earth’s climate
has changed many times.
• Fossils of ferns have been found on
Antarctica, which implies that the now frozen
continent was once warmer.
• There are also fossils of many extinct
organisms.
– The best known group is the dinosaurs.
– Fossils of more than 400 different species of
dinosaurs have been found.
The changing Horse
• Fossils provide
scientists with clues
about how species
have evolved.
• The most compete
fossil record,
showing
evolutionary change
is that of a horse.
• This record goes
back almost 60
million years!
Similar Body Structures
• Scientists also study living organisms for
clues about evolution.
• For example: a lion’s foreleg, a dolphins
flipper and a bat’s wing all look very
similar.
• These similar structures are called
homologous structures.
Homologous Structures
Similar Body Structures
• As well as homologous structures, there are
also body structures that seem to have no
function.
– For example- our appendix and tail bone.
• These structures are called vestigial
structures.
• Scientists believe that at one time vestigial
structures did have a function in the
ancestors of the organisms that now have
them.
DNA Evidence
• Scientists also study an organism’s DNA
to learn more about evolution.
• For example, dogs and bears have similar
DNA, which means that they are closely
related and could have evolved from a
common ancestor.
• They have also been able to extract DNA
from fossils, which allows them to
compare the DNA of extinct species to
those that are still alive.
4-4 What is natural Selection?
Key Terms
• Natural selection- survival of offspring that
have favorable traits.
• Variation- differences in traits among
individuals of a species.
Explaining Evolution
• The fossil record shows that living things
have evolved throughout Earth’s history.
• But that does not explain HOW the
changes happened.
• Offspring are supposed to be the same
species as their parents.
• So…how does a new species develop
from an old one?
Lamarck’s Theory
• Jean Baptiste de Lamarck was one of the
first scientists to develop a theory of
evolution.
• According to Lamarck:
– All organisms develop new characteristics to
help them adapt to their new surroundings.
– Then they pass these adaptations onto their
offspring.
• Lamarck used giraffe’s to
model his theory.
• According to Lamarck:
– 1st giraffes had short necks
and ate grass.
– 2nd giraffes had to find a
new food source, so they
had to grow longer necks to
reach tree leaves. The
parents passed this on to
their offspring.
• There was no evidence to
support his theory and it
was proven wrong.
The Voyage of the Beagle
• Over 150 years ago, Charles Darwin
suggested a theory of evolution that is
accepted by most scientists today.
• In 1831 Charles Darwin set sail on the
HMS Beagle on a 5 year expedition to the
South Pacific and South America.
• The original purpose of the voyage was to
make maps and observe and collect
specimens of various plants and animals.
• One of the places
that the Beagle
stopped was the
Galapagos Islands.
• Here, Darwin
observed tortoises,
and noted that every
island had a
different species of
tortoise.
• He also discovered
13 species of
finches.
• Darwin observed that each species of
finch had a different shaped beak.
• Each beak was adapted for eating a
certain type of food, and most of the
finches other traits were similar.
• Darwin inferred that all finches had
evolved from a common ancestor.
• These observations lead Darwin to his
ideas about natural selection.
Natural Selection
• Darwin used the term natural selection to
describe his theory of evolution.
• Nature favors the survival of organisms
that are best suited for their environment.
• The theory has 5 parts:
– 1. Overproduction- each species produces
more offspring than can survive. Not all can
survive because there is not enough food or
living space for all.
– 2. struggle for existence- the offspring of each
generation compete for things they need to
survive. Only a few will live long enough to
reproduce. The others will die.
– 3. variation- the offspring of each generation
are not exactly alike. Differences in traits
amount individuals of a species are called
variations.
– 4. Survival of the most fit- some variations
make organisms better suited for survival in
their environments. These organisms are
more likely to survive and reproduce than are
others.
– 5. Evolution of new species – individuals with
favorable variations survive to reproduce.
They pass their favorable traits to their
offspring. Therefore their offspring are more
likely to survive and reproduce to the next
generation.
• Over many generations, these changes can result
in the appearance of a new species
4-5 How does the environment affect
natural selection?
Key Terms
• Extinction- disappearance of all members
of a species
Factors in living space
• All organisms must have a place to live that
supplies them with food, water, and shelter.
• Members of the same species will compete
for resources in their living space.
• This competition results in not all of the
offspring surviving .
– Ex.) In Asia, Tigers and deer live in the same
space. Tigers eat the deer, so tigers will compete
with each other for food. Those that are stronger
and faster are more likely to catch deer and
survive.
Human Activities
• Human activities can produce great
changes in the living spaces of other
organisms.
• Some species have become extinct
because people have hunted them or built
roads and buildings that took away their
living space.
• Ex.) black bears forage for food, but
because of garbage dumps, they now eat
our garbage instead of searching for it in
Pollution
• Pollution will change an organisms home.
Harmful materials are produced from
factories, and cars. These pollute the air,
water and land.
• Ex.) In the 1800’s during the industrial
revolution a moth in England were a light
color. The pollution covered tree trunks with
black soot. Making the lighter colored moth’s
easy for the birds to pick out. Black moths
now had an adaptation that allowed them to
survive.
Extinction
• Extinction is the disappearance of all members of
a species.
• Organisms that are unable to adapt to changes in
their environment will become extinct.
• Thousands of organisms have become extinct,
and most occurred because of slow changes in
the environment.
• However, in recent years, due to human
involvement, the rate of extinction has increased
and the number of animals facing extinction has
also increased.
• There are many laws that help protect endangered
species.
4-6 How have humans changed over
time?
Key Terms
• Anthropology- science that deals with the
study of human beings
Early Humanlike species
• The fossil record for humans is incomplete,
and is still being pieced together by
scientists.
• Anthropology is the study of human beings.
People who study anthropology are known as
anthropologists.
• A noteworthy anthropologist is Donald
Johanson. He discovered one of the oldest
fossils of humanlike ancestors in 1974. They
determined that the fossil was female, and
named her Lucy.
• Lucy is about 3.5 million years old. Her
skeleton indicates that she was about 1
meter tall (3 feet) and walked upright
• Lots of other fossils have been found, and
range in age from 500,000 years ago, to 6
million years old.
Modern Humans
• All modern humans belong to the species
homo sapiens. Which means “wise
human”.
• Fossils of two types of homo sapiens have
been found which are called Neanderthals
and CroMagnons.
• Neanderthals lived from 130,000 to
35,000 years ago. They were shorter than
modern humans, and are characterized by
their sloping foreheads and heavy brow
• Cro-Magnons looked like modern
humans. They living from 35,000 to 10,000
years ago. They were tall and had large
brain cases with rounded skulls.
– Fossil records show that Cro-Magnons lived
together, they also hunted and made tools.