Transcript Evolution by means of Natural Selection

Evolution by means of
Natural Selection
Evoluti on by Natural Selecti on:
5 KEYS
1. VARIATION
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Variation is inherent in populations of
organisms (members of a population are not
all the same).
This Variation is Heritable – able to be
passed from generation to generation.
Elaphe obsoleta
Evoluti on by Natural Selecti on:
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2. More offspring are born than survive.
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Differential reproduction and survival.
“Survive” = Live long enough to reproduce.
Evoluti on by Natural Selecti on:
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3. Differences occur between surviving
offspring and those not surviving.
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Advantageous Varations = Certain
characteristics found in surviving offspring that
afford them a survival advantage.
Sometimes called “Adaptations” (but this implies
a goal, and Natural selection is NOT goaloriented).
Evoluti on by Natural Selecti on:
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4. More individuals with advantageous
adaptations occur in succeeding
generations of organisms.
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Their variations are beneficial, therefore they
survive & reproduce.
Individuals without beneficial variation do not
survive to reproductive age.
Individuals
Evoluti on by Natural Selecti on:
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5. Results in a population that is welladapted to its environment.
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Population as a whole is becomes fitted to
its particular environment.
NATURAL SELECTION
• This takes a long time – many generations.
– Earth is old (We now know the Earth is roughly
4.5 Billion Years Old!).
NATURAL SELECTION
• Variation is essential
– Previously viewed as imperfection…
– Now viewed as the raw material on which
evolution occurs.
– We now know that GENES (Alleles) are
responsible for variation:
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Crossing Over (Meiosis)
Independent Assortment (Meiosis)
Oogenesis
Fertilization
Mutation
NATURAL SELECTION
• “Struggle for Existence”
– Limited Resources are available for a
population, leading to Competition.
• Some survive, some don’t
• Sometimes this is random
– The “Struggle” is for the resources, not as
much direct competition between individuals.
NATURAL SELECTION
• “Survival of the Fittest”
– The most FIT organisms survive & reproduce.
– Fitness = how well an organism fits into its
environment
• Securing resources
• Avoiding predators
• Finding food
– What determines Fitness?
• Varies with organism, but ultimately….ENVIRONMENT
• This is always changing – what is most fit one month,
may not be the next.
NATURAL SELECTION
• Environment is important!
– In Artificial Selection, humans select for
survival & reproduction.
– In Natural Selection, “nature” selects for
survival & reproduction.
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Habitat
Climate
Food & Shelter Availability
Etc.
NATURAL SELECTION
• Not goal-oriented, no particular goal.
– Environmental conditions are always
changing.
– Organisms’ needs are always changing.
– Genotype is heritable, not phenotype.
NATURAL SELECTION
• Populations Evolve, NOT individuals.
– Populations: Groups of individuals belonging
to the same species and occupying the same
given area, and being similar in form,
behavior, and physiology.
– Inheritance of acquired characteristics by
Individuals (Lamarck) does NOT occur.
NATURAL SELECTION
• “Adaptation”
– Traits are sometimes referred to as either
“Adaptive” or not.
– “Adaptive” traits are those that accumulate in
each succeeding generation (due to
differential reproduction).
– This is somewhat arguable …why?
EVIDENCE for Common Descent
1. Direct observation.
Bacterial Capsules
Ev
i dence for Evoluti on
(Common Descent)
2. Fossil Record
– History of life recorded in fossils.
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Bones, plants, shells, insects, etc.
– Many fossils offer evidence for transitions.
(Transition of the Ancient Reptilian Pelvis to Early Modern Birds)
(Sequential evolution of the lower foreleg of horses)
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Special Creation predicts no historical pattern of
change -- the same organisms today as before.
Ev
i dence for Evoluti on
(Common Descent)
3. Biogeography
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Different organisms with similar adaptations found in
similar environments, but in very distant locations.
Adaptive Radiation
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Slight adaptations to slightly different environments in the
same basic geographic area.
Emu
Rhea
Ostrich
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Special Creation predicts perfectly-adapted
organisms occupying suitable habitats, despite
geography.
Evi dence for Evoluti on
(Common Descent)
4. Comparative Anatomy
– Similarities in organisms’ internal structures,
despite their functions.
– Homologous Structures
– Vestigial Structures
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Special Creation predicts no similarity in structure if
used for different functions & no such thing as a
structure with no function.
Ev
i dence for Evoluti on
(Common Descent)
5. Comparative Embryology
– Similarity of different organisms during early
(neo-natal, pre-birth) development.
Ev
i dence for Evoluti on
(Common Descent)
6. Comparative Biochemistry
– Similarities and differences in chemicals:
• Nucleotide Sequences (DNA, RNA)
• Amino Acid Sequences (Proteins)
The Theory of Evolution
• Populations of
organisms have the
capacity to change over
time, generally in
response to changes in
their supporting
environment.