Transcript Ch 15 *Darwin*s Theory of Evolution*

Ch 15 “Darwin’s Theory of Evolution”
• Evolution, or change over
time, is the process by
which modern organisms
have descended from
ancient organisms
• The theory can explain
Earth’s biodiversity
• A scientific theory is an
explanation of natural
events that is supported
by evidence
Charles Darwin
• In the 1830s, Charles
Darwin sailed around the
world
• He made many
observations and collected
evidence
• He noticed that many plants
and animals were very well
suited to their environment
• He collected fossils, some of
which were unlike any
creatures he had ever seen
• He wondered why the
species in the fossils had
disappeared
Darwin’s Observations on the
Galapagos Islands
• The Galapagos Islands are
near each other but have
different climates
• Darwin noted that the
characteristics of many
animals and plants varied
noticeably among the
different islands
• He wondered whether
animals on different
islands had once
belonged to the same
species
Ideas That Shaped Darwin’s Thinking
• In Darwin’s day, most
Europeans thought that
the Earth and all of its life
forms had existed for only
a few thousand years
• They also thought that
species did not change
• Some scientists of
Darwin’s time began
challenging these ideas
and helped to develop
Darwin’s Theory of
Evolution
Contributing Scientists to Darwin’s
Theory of Evolution
• Hutton and Lyell helped
scientists recognize that
Earth is many millions of
years old, and that it had
changed over time
• These ideas helped
Darwin realize that life
might change as well.
• Knowing that Earth was
very old convinced
Darwin that there had
been enough time for life
to evolve.
• Jean-Baptiste Lamarck was one of
the first scientists to see that
evolution occurred.
• He also recognized that organisms
adapt to their environments
• He proposed that by selective use
or disuse of organs, organisms
acquired or lost certain traits
during their lifetimes.
• These traits, could then be passed
on to their offspring which, over
time, led to a change in the species
• Scientists now know that was
incorrect, but his general ideas
about adaptation was correct and
influenced Darwin.
• Economist Thomas
Malthus thought that if
the human population
kept growing, sooner or
later there would be
insufficient living space
and food for everyone
Darwin’s On the Origin of Species
• In his book, he supplied
evidence that evolution has
occurred and explained how
evolution occurs
• His theory is based on
artificial selection where
nature provides the
variation, and humans select
those variations they found
useful
• He thought that a similar
process occurs in nature and
called it natural selection
Natural Selection
• Individuals differ, and some of
the differences can be passed
on to their offspring
• Individuals best suited to
their environment survive and
reproduce most successfully
(survival of the fittest)
• Fitness results from
adaptations that are inherited
and increase an organism’s
chance of survival
• Only the fittest organisms
pass on their traits which
leads to a change in species
over time
The tortoises eat plants. On one island, plants grow
very close to the ground. Which island is this most likely to be?
Why?
Which island most likely has sparse vegetation that is hard to reach?
Struggle for Existence
• There is competition
for limited
resources, or a
struggle for
existence
Evidence for Evolution
Reasons for an incomplete
fossil record:
• Many species have lived
in environments where
fossils do not form.
• Their bodies are eaten
and/or scattered by
scavengers.
• It is difficult to form a
fossil from a soft bodied
animal as opposed to a
hard bodied animal.
Evidence for Evolution
• Homologous structures
of living organisms.
• Similarities in bone
structures suggest that
vertebrates share a
common ancestor
Evidence for Evolution
• Similarities in early
development.
• Scientific advances have
upheld most of
Darwin’s hypotheses
• However, evolutionary
theory continues to
change as new data are
gathered & new ways of
thinking arise