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Evolution Essential ?s
• How & why have species changed with time?
• What is the benefit & value of evolution?
• How can the theory of evolution be applied to
today?
• What evidence & thought have contributed to
the theory of evolution?
Evolution
Change in genetic make-up over
time
Process by which modern
organisms have descended from
ancient organisms
The History of the
Development of Evolutionary
Thought
st
1
Hypothesis
Use & Disuse
Jean – Baptiste
Lamark
1809
French naturalist
• Tendency Towards Perfection & Complexity
• organisms continually change to become better
adapted to their environment & improve survival
• Use & Disuse of Organs
• structure that are used frequently will become
larger and be more developed during a lifetime
• structures not used will become weaker or disappear
(vestigial organs) during
a lifetime
• Inheritance of Acquired Traits
• newly acquired traits can be passed on to offspring
Evaluation of Lamark’s Theory
• Incorrect because…..
• acquired traits (those gained during an organisms
lifetime) are NOT inherited
• acquired behaviors CANNOT develop heritable
characteristics
• Correct because….
• organisms adapt to their environment overtime to
increase survival
nd
2
Hypothesis
Natural
Selection
Charles
Darwin
1831
Voyage on the H.M.S. Beagle
The Trip around the World
• Observed many various organisms
• Researched their patterns of diversity
• Studied living organisms & fossils
• Concluded that the earth is constantly
changing
The Galapagos Islands
• Most influential location to Darwin’s
development of the theory of evolution
• 13 small islands off the
West coast of South
America by Ecuador
• Close proximity
• Extremely diverse
climates & environments
• Isolated from each other
• Organisms on each island vary greatly in
characteristics to be specialized & better
adapted to their diverse environments
Darwin’s Theory of Evolution
Published in 1931
“The Origin of Species”
Natural Selection
• Organisms varying in inheritable characteristics
(mechanics of genetics was unknown at this time!)
• Large population size causes competition for
resources & restricts survival rate
Natural
Selection
• Organisms with traits
that are better “fitted”
or adapted to their
environment survive
and reproduce more
successfully passing on
their superior genes to
the next generation
• Fitness
• resulting adaptations that
increase the survival of an
organism
• Adaptations
• any inherited
characteristic that
increases an organism’s
survival
“Survival of the Fittest”
Descents with Modification
• Over many successive generations:
• pressures of natural selection
• change traits of a population
• increase overall fitness of the population
• Species evolve:
• differences in structures & niches
• resulting in the formation of a new species
• remaining related to each other by a
common ancestor
3 Types of Natural
Selection
Stabilizing Natural Selection
• Nature eliminates both extreme traits
• Nature favors average traits
• Graph narrows
increasing the
number of
species with
the average trait
Directional Natural Selection
• Nature eliminates only 1 extreme trait
• The other extreme trait is favored
• Graph & population diversity shifts toward
favored trait
Distributive Natural Selection
• Nature eliminates the average trait & favors
the extreme traits
• Graph & population diversity shifts towards
the 2 extreme traits
• Possibly
leading to
creating
2 new
species
Finches of the Galapagos Islands
Darwin’s most famous discoveries came from his
observations on the variations of finch species on
the Galapagos Islands
which had extremely diverse and extensive gene
pools, supporting his theory of evolution
• All of the Finches from the Galapagos Island
evolved from the same founder species
• The Finches
were separated
to different islands
over several years
• On each island they
experience different
natural pressures
• Finches on each island developed variations to
make them better adapted to their different
environments of each island
• Eventually the
Finches became
specialized and
different from each
other becoming
separate & new
species on
each island
Finch’s of the Galapagos Islands