Download Darwin and Natural Selection

Darwin and Natural Selection
Evolution
• The change in a species over time.
• Proposed by Charles Darwin
• Natural selection is the process by which
organisms that are best suited to their
environment survive and pass their
genetic traits on to their offspring.
• “Survival of the Fittest” (fitness determined
by number of offspring produced)
Some Ideas That Had to be
Changed
• Belief that the Earth was young
– Most Europeans in Darwin’s day believed that
Earth and all its forms of life had been created
only a few thousand years ago
– Too little time for evolution
• Wrong Ideas
– Lamark’s Theory of Evolution
• Use and Disuse
• Inheritance of Acquired Traits
How Did Giraffes Get Long Necks?
Stabilizing Selection
Directional Selection
Disruptive Solution
Summary of Darwin’s Theory
• Individual organisms in nature differ from
another. Some of this variation is inherited.
• Organisms in nature produce more
offspring than can survive, and many of
those that survive do not reproduce.
• More organisms are produced than can
survive, members of each species must
compete for limited resources.
• Because each organism is unique, each
has different advantages and
disadvantages in the struggle for
existence.
• Individuals best suited to their environment
survive and reproduce most successfully.
The characteristics that make them best
suited to their environment are passed on
to offspring. Individuals whose
characteristics are not as well suited to
their environment die or leave fewer
offspring.
• Species change over time. Over long
periods, natural selection causes changes
in the characteristics of a species, such as
in size and form. New species arise, and
other species disappear.
• Species alive today have descended with
modifications from species that lived in the
past.
• All organisms on Earth are united into a
single tree of life by common descent.
Evidence For Evolution
• Adaptations – evolution of a structure,
behavior, or internal process that enables
an organism to respond to stimuli and
better survive in an environment
• (e.g. mole-rats on pp. 404-405)
• Can you name some examples?
Fossil Record
Homologous Body Structures
Analogous Structures
Vestigial Organs
Similarities in Early Development
Geographic Distribution of Living
Species
Evidence For Evolution
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The Fossil Record
Homologous Body Structures
Analogous Body Structures
Vestigial Organs
Similarities in Early Development
Geographic Distribution of Living Species
Biochemistry
Evolution on Different Scales
• Evolution that occurs within the species
level is called microevolution. It results
from genetic variation and natural
selection within a population of organisms.
• Macroevolution is evolution that occurs
between different species. It focuses on
how groups of organisms change (i.e., the
splitting of a species into two species).
Summary of Darwin’s Theory
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Individual organisms in
nature differ from one
another. Some of this
variation is inherited.
Organisms in nature
produce more offspring
than can survive, and many
of those that survive do not
reproduce.
Because more organisms
are produced than can
survive, members of each
species must compete for
limited resources.
Because each organism is
unique, each has different
advantages and
disadvantages in the
struggle for existence.
All organisms on Earth are
united into a single tree of
life by common descent.
• Individuals best suited to their
environment survive and
reproduce most successfully.
The characteristics that make
them best suited to their
environment are passed on
to offspring. Individuals
whose characteristics are not
as well suited to their
environment die or leave
fewer offspring.
• Species change over time.
Over long periods, natural
selection causes changes in
the characteristics of a
species, such as in size and
form. New species arise, and
other species disappear.
• Species alive today have
descended with modifications
from species that lived in the
past.