Download Evolution

Evolution
&
Natural
Selection
First thoughts on the idea…
• “Acquired Traits”
• Once a structure
is modified it is
passed onto
offspring
Lamark
Charles Darwin Thoughts
(Galapagos Islands)
• Evolution occurs
– Change over time
• Evolution is due to
Natural Selection
Darwin’s Finches
• Finches had different beaks that were
specialized for what they ate
– Each had their own NICHE
• All of these finches were descendents
of the same finch
What is Evolution?
• Gradual change
over time
• Descent with
modifications
Cladogram
– Newer forms (in
fossils) are the
modified
descendants of
older species
Natural Selection
• Organisms with
favorable traits
reproduce more
than those with out
these traits
• Traits = Variation =
MUTATIONS
Variation / Diversity
• Slight differences in
the appearance of
organisms
(phenotypes)
– Sexual reproduction
– Gene recombination
• IMPORTANT: if
environment
changes SOME
organisms will survive
What determines Natural Selection?
• ENVIRONMENT
• In order to be
beneficial the
trait must help the
organism live in its
environment
• Based on
phenotypes
Adaptation & Fitness
• Adaptation –
increasing # of
favorable traits
• Fitness – An
organisms genetic
contribution to
offspring
• High fitness = well
adapted
Natural Selection & Genetic Change
• Natural selection can
not occur without
genetic variation
• Organisms that have
beneficial traits will
pass those traits to
their offspring
Fitness & Genes
• Each generation
has more
individuals with
the genes that
make them “fit”
• The frequency of
these alleles
increases over
time
Competition
• Because
resources (food,
space…) are
limited, organisms
compete for them
• Only the most fit
will compete
successfully and
reproduce
Lethal Genes
• Genes that cause
death
• How can these
genes exist?
• Heterozygous
individuals keep
these genes in the
gene pool
– Total genetic info in
population