Download Theory of Evolution - Doral Academy Preparatory

Theory of Evolution
Charles Darwin
• Charles Robert Darwin
• Born February 12 1809 –
April 19 1882)
• He was an English
Naturalist
• He published his theory
of evolution with
evidence In his 1859
book “On the Origin of
Species”.
The voyage of the Beagle
• In December 1831, the British ship HMS Beagle
set sail from England on a five year trip around
the world.
• Darwin was on board as a naturalist
• His job was to learn as much as possible about
the living things he saw on the voyage.
• Darwin's observations led him to develop one of
the most important scientific theories of all time;
the theory of evolution by natural selection.
Darwin’s voyage
Darwin’s Observations
• Darwin made many observations along his stops
on the Beagle
• Darwin's observations included the diversity
of living things, the remains of ancient
organisms, and the characteristics of
organisms on the Galapagos Islands.
Darwin was amazed by the tremendous diversity
of living things. Scientists now have identified
more than 1.7 million species of organisms.
• A species is a group of similar organisms
that can mate with each other and produce
fertile offspring.
The Galapagos Islands
• In 1835 the Beagle reached
the Galapagos Islands, where
Darwin observed many
unusual life forms on these
small islands such as giant
tortoises and giant iguanas.
•
When Darwin returned to
England, he compared
organisms to organisms that
lived elsewhere. He also
compared organisms on
different islands in the
Galapagos group.
• He was surprised by some of
the similarities and differences
he saw.
• Darwin found many
similarities between
Galapagos organisms
and those in South
America. However, there
were important
differences.
• The Iguanas on the
Islands had large claws
that allowed them to grip
slippery rocks while the
iguanas on the mainland
had smaller claws to
climb trees.
• From his observations,
Darwin hypothesized that
a small number of plants
and animals had come to
the islands from the
mainland.
• Once they reached the
islands, the reproduced.
Eventually their offspring
became different from
their mainland relatives.
Adaptations
• Like the tortoises, the finches on the Galapagos
Islands were noticeably different from one island
to the next.
• The most obvious difference on the Finches was
their beak size and shape.
• Darwin proposed that each species of finch had
a different size and shaped beak to suit its
environment. This is an example of an
Adaptation.
• An Adaptation is a trait that helps an
organism survive and reproduce.
Evolution
• Darwin wanted to understand the different
adaptations of organisms on the
Galapagos Islands.
• He hypothesized that the species
gradually changed over many generations
and became better adapted to the new
conditions.
• The gradual change in species over
time is called EVOLUTION.
Natural Selection
• In 1858, Darwin and Alfred Russell Wallace,
each proposed an explanation for how evolution
could occur in nature.
• Darwin proposed that evolution could happen by
natural selection.
• 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.
• Darwin identified factors that affect Natural
Selection:
• 1. Overproduction: Most species produce
many more offspring that can possible
survive.
• 2. Variations: any difference between
individuals of the same species.
• 3. Competition: because resources are
limited, members of a species must
compete with each other to survive.
• 4. Selection: Darwin proposed that over a
long time, natural selection can lead to
change. Helpful variations may gradually
accumulate in a species while the
unfavorable ones disappear.
• 5. Environmental change: A change in the
environment can affect the organisms
ability to survive.