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Chapter 15 and 16
Evolution Change through time
Theory of Evolution of Life
• Charles Darwin -A Naturalist who, in 1831,
traveled on the “HMS Beagle” for a five
year expedition to discover, collect, study,
and store biological specimens.
• Father of the Theory of Evolution
The Galapagos Islands
• Darwin observed many
islands with great
• Animals and plants
seemed to be best suited
for their own particular
• The organisms on the
islands were similar to
those on the main island
but seemed to have
adapted to the island
• After 22 years of data
analysis he formed his
Theory of Adaptation and
Natural Selection.
Adaptation: an
physiological, or
behavioral trait that
improves an
organism’s ability to
survive and
Darwin’s Theory of Natural Selection
• 1. Organisms produce
more offspring than
can survive.
• 2. Variations exist
within populations
• 3. Some variations
are more
advantageous than
others (struggle for
• 4. The “fittest”
survive and
reproduce! Thus the
species modifies itself
over time. (Natural
Darwin’s Pigeons
• Artificial Selection - By
breeding pigeons that had a
desirable trait, the offspring
would carry these same
• Natural Selection - Nature
selects or chooses which
traits in an organism will be
passed on to future
• Populations adapt as the environment changes
1) Mimicry - Structural adaptation that provides
protection by enabling it to copy another species.
(Monarch and Viceroy)
2) Camouflage - Structural adaptation that enables
the organism to blend in with its environment.
(Peppered Moths)
3) Physiological Adaptations - Bacteria
developing a resistance to penicillin.
Five Points of Evidence for
1. Fossil Record - Identifies a path a species
followed as it evolved.
Five Points of Evidence for Evolution
2.Anatomical Studies A) Homologous structures Similar in structure, but,
different in function.
B) Analogous structures
Body part similar in
function but different in
Ex. Wings of bird
and butterfly
3. Vestigial Organs - Structures
that have no function in the
organism today but may have
been used. Ex. Appendix
4. Embryological development Organisms that develop similarly
as embryos have an evolutionary
relationship. (Vertebrate
embryos- all have tails and gill
slits as they develop)
5. Genetic Similarities - DNA and
RNA sequences are similar in
related organisms.
Vestigial Features
Similarities in Embryology
Mechanisms of Evolution
• Occurs when there is a change in the genetic
makeup of a population.
• Occurs in population over many generations.
• Gene pool - All the genes in a population
• Allele frequency - Proportion of each allele in a
gene pool (SS,Ss, Ss, ss - 3:1 Spotted to black)
3 Ways Genetic Equilibrium Can
• Genetic equilibrium - Allele frequencies do not
change over time (non evolving)
• Ways equilibrium change
1) Mutations – Natural or by chance, genetic
changes in gene pool; most harmful, some
beneficial and are added to gene pool.
2) Genetic Drift - Changes due to chance events
(Small populations) Ex. Amish; short arms/legs
3) Gene flow - Movement of genes into or out of a
population; causes the gain or loss of genetic info.
3 Types of Natural Selection
• Most significant factor in gene pool changes
• 1. Stabilizing Selection - Favors the average
individuals in a population. (Grass, Spiders)
Types of Natural Selection
• 2. Directional Selection- Favors one
extreme of a trait (woodpeckers with long
Types of Natural Selection
• 3.Disruptive Selection - Individuals with
either of two extreme traits are favored.
(light, dark, and medium colored limpets)
• Formation of a new species from
an ancestral form.
• This can only occur when interbreeding or the production of fertile
offspring is somehow prevented.
• Physical barriers - New mountain
ranges, canyons, or water barriers
create Geographical Isolation.
• Reproductive Isolation -Occurs
when mutations prevent offspring
development, or seasonal mating
changes that prevent mating.
• Speciation can occur quickly or slowly.
• Gradualism- Species originate through
a gradual accumulation of adaptations.
• Punctuated Equilibrium - Occurs in
rapid bursts with long periods of
stability in between.
• Adaptive Radiation - An ancestral
species evolves into many different
species (Divergent Evolution)
• Convergent Evolution -Distantly
related organisms evolve similar
traits. Ex. Whales and Fish
Comparing Convergent and
Divergent Evolution
Divergent Evolution:
A process in which the
descendants of a single
ancestor diversifies into
species that each fit
different parts of the