Natural Selection

Natural Selection
Today’s Objectives: SOL BIO.8b-d
TSW investigate and understand how
populations change through time,
– How variation of traits, reproductive
strategies, and environmental pressures
impact on the survival of populations
– Recognizing how adaptations lead to
natural selection
– How new species emerge
Charles Darwin
On the Origin of Species
 Sailed with the HMS Beagle
 Observations made in the Galapogos
 These observations helped him form the
theory of how species change over time
called natural selection
What is Natural Selection?
Natural selection is governed by the
principles of genetics.
Types of Adaptations
Protective Coloring
– Camouflage
– Mimicry
Physiological Adaptations
– Reproductive Changes
– Other changes
Behavioral Adaptations
Evidence for Evolution
Fossil record
 Anatomy
– Homologous structures
– Analagous structures
Vestigial structures
 Embryology
 Molecular biology (DNA differences)
What is a Population?
Populations evolve over many
generations, individuals don’t
 Populations are groups of interbreeding
individuals that live in the same place at
the same time
 Individuals in a population compete for
resources with each other
How Does Evolution Work?
Populations produce more offspring
than the environment can support
 The unequal ability of individuals to
survive and reproduc leads to the
gradual change in a population over
many generations
Mechanism for change in a
population of organisms
Animals who have greater fitness
survive in environment and live to
 Random changes (mutations) can lead
to greater or less fitness
 Adaptations allow an organism to
survive better in their environment
Mutations & Variety Produced by
Sexual Reproduction Allow for
Diversity within a Population
Genetic drift (caused by chance)
– Bottleneck
– Founder effect
Genetic equilibrium
– Hardy-Weinberg law
– In H-W equilibrium, does not occur
Can arise in response to environmental
– Temperature
– Antibiotic resistance in bacteria
– Pesticide resistance
– Morphological changes in peppered moths
Types of Selection
– Extreme form favored by natural selection
– Middle form most successful
– Two extreme forms successful in separate
How are new species created?
Geographic isolation
 Reproductive barriers
 Change in chromosome numbers
 Adaptive radiation
Types of Evolution
Convergent evolution
– Dolphins & fishes
– Wings of bees & bats
Divergent evolution
– Darwin’s finches
– Adaptive radiation
How fast does evolution occur?
– Darwin
– Species change slowly over time
Punctuated Equilibrium
– Gould & Lewontin
– Species can make rapid “leaps” in
Modern Synthesis
– Parts of both are correct