Download The Theory of Evolution

Evolution
change over time
The Theory of Evolution
• What is a theory?
– A well supported, testable explanation of
phenomena of the natural world
What is the Theory of Evolution?
The Theory of Evolution
• Evolution is change in a
population over time. As
the environment changes,
species either adapt or go
extinct.
• Adaptation: an inherited
characteristic that increases
an organisms chance of
survival.
Common Beliefs during Darwin’s
Time
• Many believed that Earth was only a
few thousand years old. In addition,
most people believed that neither the
planet nor the species that inhabited it
had changed since the beginning of
time.
Challenges to Common Beliefs
• During Darwin’s time, many fossils
were being discovered which
challenged the notion that plants and
animals had not changed since Earth
was formed.
Hutton and Lyell
• Proposals from James Hutton and
Charles Lyell helped scientists
recognize that Earth is many millions of
years old and the processes that
changed the Earth in the past are the
same ones that change the Earth today.
Jean-Baptiste Lamarck
• Argued that
organisms acquire or
lose certain traits
during their lifetime
by use or disuse.
He thought that these
traits could then be
passed on to
offspring. Over time
this would cause
change in a species.
Charles Darwin
• Darwin was influenced by the
work of Thomas Malthus.
Malthus argued that if the
human population continued to
grow at high rates, sooner or
later there wouldn’t be enough
space and food for everyone.
• Darwin reasoned that this
should apply to all organisms.
He began to consider why
some survive and others do
not.
Charles Darwin
• Traveled around the world on the HMS Beagle,
collecting fossils and specimens of organisms that
he found living in different environments. He was
astonished at the amount of diversity he found
among organisms in different environments.
Charles Darwin
• He made many important observations
on the Galapagos Islands.
The Galapagos
• Darwin noticed that the shape of turtle shells
was different for each island.
The Galapagos
• The finches on each
island had different
types of beaks.
Darwin reasoned
that the finches had
adapted beaks that
were well suited to
eat the type of food
available on their
island.
• Darwin hypothesized that these finches
had started as one species, but had
adapted to the environments of each
island over large periods of time.
• He developed the
theory of natural
selection.
Natural Selection
• Species change over time because of
changes in the environment (selection
pressures)
• Natural Selection: Those adapted to the
environment are more likely to survive and
pass their genes to the next generation,
while those not well suited do not survive or
leave fewer offspring.
Natural Selection
• Struggle for existence: members of a
species compete for food, space, and
other necessities
• Survival of the Fittest: adaptations that
make an organism better suited for its
environment help them survive and
reproduce.
• Over time, natural selection causes a
change in the characteristics of a
population (adaptations)
Populations Evolve,
Individuals Do Not!!!!
• Darwin suspected that
all species present on
earth had begun as one
species, and through a
series of adaptations
over millions of years,
had diverged into all the
species present today.
• Descent with
Modification: through a
series of adaptations,
each new species
arises from another.
The Origin of Species
• He published his
theory of natural
selection in 1859,
many many years
after he had come
up with the
theory.
The Peppered Moth
There must be genetic variation in order for
natural selection to occur. There are two
forms of the peppered moth prevalent in
England.
typica
carbonaria
Peppered Moths
• The lighter colored moth is more difficult to
spot against typical tree bark, while the
darker moth stands out and makes easier
prey.
Peppered Moths
• At the beginning of the industrial
revolution in England, coal burning
produced soot that covered the
countryside of some areas.
Peppered Moths
• Now the white moths stand out, while the black moths
are hard to see. The black moths are more likely to
survive and pass on the genes for dark color to
offspring. Over time, the black moths became more
common than the white moths.
Populations Evolve,
Individuals Do Not!!!!