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The Puzzle of Life's Diversity
How Populations Evolve
Warm-up: Write down everything from the
video that relates to Charles Darwin, his
voyage, and evolution. At least 10 to share
Darwin and Turner
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15-1 The Puzzle of Life's Diversity
Diversity
Evolution is the process by which modern
organisms have descended from ancient
organisms.
A scientific theory is a well-supported testable
explanation of phenomena that have occurred in
the natural world.
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Darwin’s Activity – Students will work in groups of 4.
Using the ideas from the textbook and video, write a
one page story about Darwin’s voyage. Draw a
picture to represent what you wrote (24” x 36”)
Your story should include the following information:
Who was Charles Darwin, all about his voyage, what
he found, his observations, who influenced Darwin,
the connection to evolutionary theory then and now.
You must use 10 – 12 vocabulary terms from the
book………….Show and tell Wednesday!!
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Voyage of the Beagle
Voyage of the Beagle - Charles Darwin
In 1831, Darwin set sail from England aboard the
H.M.S. Beagle for a voyage around the world. The
voyage lasted 5 years.
Purpose: to survey the waters around the
southern coast South America.
The majority of his observations were done on the
Galapagos Islands, off the west coast of Ecuador.
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Voyage of the Beagle
Darwin made observations, collected evidence,
and proposed a hypothesis about the way life
changes over time - known as the theory of
evolution.
*Evolution is the unifying theme in biology.
After he returned he wrote a book called, On the
Origin of Species. He originally referred to
Evolution as Descent with Modification
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In his book, On the Origin of Species
Darwin -
• proposed a mechanism for evolution
called natural selection.
• presented evidence that evolution has
been taking place for millions of years—
and continues in all living things.
http://phet.colorado.edu/en/simulation/natural-selection
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Darwin's Observations
EVIDENCE COLLECTED BY DARWIN
FOSSILS - preserved remains of ancient organism, organic
matter..
Fossil record- the ordered way in which fossils appear within
layers, information about past life.
The fossil record provides evidence about the history of life
on Earth. It shows how different organisms have changed
over time.
Over 99% of all species that have lived on Earth have
become extinct - have died out.
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Paleontologists (collect and study fossils) use a scale called
the geologic time scale to represent evolutionary time.
Scientists first developed the geologic time scale by
studying rock layers and index fossils worldwide.
Use of radiometric (carbon) dating – half-life timeline
DEFINE: Index fossil (pager
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Darwin's Observations
The Galápagos Islands - Darwin’s observations
• Galapagos Islands were close together but had
very different climates.
• The characteristics ( the way the organism
looked) of many animals and plants varied
noticeably
•He wondered if animals living on different islands
had once been members of the same species.
• These separate species would have evolved from
an original South American ancestor species.
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Individuals who Influenced Darwin
Charles Lyell - Principles of Geology, the Earth’s
surface is shaped mainly forces that act gradually
and continue to occur in modern times
Alfred Wallace – developed a theory of evolution
identical to Darwin’s
Buffon and Lamarck, the best explanation of the
relationship between fossils and current organisms is
that life evolves.. Although Lamarck’s ideas were not
completely accurate.
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Lamarck’s ideas: Species evolve, are descendants of other species
The characteristics an individual develops is a result
using or not using its body parts
The charateristics (traits) can be passed on to their
offspring.
Based on what we know about genetics - this is
INCORRECT
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Homologous Structures - Similarities in
different organisms; features that have different
functions, but developed from the same
embryonic tissue. Examples: wing of a bat and
flipper of a whale.
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Not all homologous structures serve important
functions.
The organs of many animals are so reduced
in size that they are just vestiges, or traces, of
homologous organs in other species.
These organs are called vestigial organs.
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Why Evolution Occurs… the evidence
Natural selection - the mechanism of evolution
•Survival of the fittest
•Struggle for existence
•Fitness: Ability of an organism (it’s population) to survive and
reproduce.
Adaptation - inherited characteristics that increase an
organism’s chance of survival; limited by the amount and kind
of genetic variation in a population. Organisms adapt to
survive – ie. our current problems with bacteria
Artificial Selection - selective breeding of domesticated
plants and animals.
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NATURAL SELECTION
–Over a long period of time, results in changes in the
inherited characteristics of a population.
–Works on the phenotype of the organism. The organism
with the most adaptive traits will have a better chance of
survival.
–These changes increase a species' fitness in its
environment.
–Affects the population - A population is the smallest unit
that can survive.
Species - a group of populations whose individuals have the
potential to interbreed and produce fertile offspring.
Population genetics studies genetic change in a population
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The Study of Evolution
Gene pool - the total collection of genes in a population at
any given time. Genetic variation is studied in populations.
A population is a group of individuals of the same
species that interbreed.
A gene pool consists of all genes, including all the
different alleles, that are present in a population.
Relative frequencies - the number of alleles in a population
(gene pool) at a given time.
Microevolution - Based on genetics. A change in the relative
frequencies of alleles in a gene pool over a few generations
(short period of time).
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Causes of Microevolution
1. Genetic Drift - change in the allele frequency of a gene
pool due to chance. SMALL POPULATIONS. In small
populations, individuals that carry a particular allele may
leave more descendants than other individuals do, just by
chance.
Over time, a series of chance occurrences of this type can
cause an allele to become common in a population.
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Two types of genetic drift
a. Bottleneck - results from an event that
drastically reduces the population (catastrophe)
b. Founder effect - colonization of a new location by
a small group of individuals (Galapagos islands)
Example: A few finches—species A,
travel from South America
to one of the Galápagos Islands.
There, they survive and reproduce.
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2. Gene flow - occurs when fertile offspring move
into or out of a population
3. Mutation - a random change in an organism’s
DNA that may create a new allele
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Variation in a Population due to Natural
Selection
Heterozygote advantage - have a greater
advantage than homozygotes, two or more alleles
can be maintained in a population
Neutral variation - a inheritable characteristic that
provides no advantage (finger prints).
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Outcomes of Natural Selection
1. Stabilizing selection - favors intermediates. A
bell-shaped curve is typical of polygenic traits.
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2. Directional Selection - acts against individuals
at one of the phenotypic extremes.
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3. Diversifying (disruptive) selection - favors
individuals at both extremes of a phenotypic
range
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Sexual Dimorphism - differences in characteristics
between male and female that may lead to natural
selection.
•Size difference
•Male adornment - mating rituals
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Chapter 14:
Speciation - the formation of new species.
A species is a group of organisms that breed with one
another and produce fertile offspring.
The gene pools of two populations must become separated
for them to become new species.
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When the members of two populations cannot
interbreed and produce fertile offspring,
reproductive isolation has occurred.
Reproductive isolation can develop in a variety of
ways: prezygotic and postzygotic
Student hand-out: page 284
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A. Behavioral isolation occurs when two populations are
capable of interbreeding but have differences in courtship
rituals or other reproductive strategies that involve behavior.
B. Geographic isolation occurs when two populations are
separated by geographic barriers such as rivers or mountains.
Some birds from species A
cross to a second island.
The two populations no
longer share a gene pool.
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C. Temporal isolation occurs when two or more
species reproduce at different times.
Allopatric speciation- speciation that occurs due
to geographic isolation
Sympatric speciation: speciation that occurs that
is NOT due to geographic isolation
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Evolutionary patterns: how fast evolution
occurs
1. Gradualist: Populations evolve differences
gradually. This model fits Darwin’s views
2. Punctuated equilibrium model: evolution
occurs in spurts
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14.1 (taxonomy) 15.10 & 15.14
Classification and Naming
Taxonomy - Branch of biology concerned with naming and
classifying living organisms- classify organisms into groups
that have biological significance.
Carolus Linneaus developed a naming system called
binomial nomenclature.
In binomial nomenclature, each species is assigned a twopart scientific name. The scientific name is italicized.
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The first part of the name is the genus to which the organism
belongs.
A genus is a group of closely related species. The genus
name is capitalized.
The second part of the name is unique to each species within
the genus.
This part of the name often describes an important trait or
where the organism lives. The species name is lowercased.
Example: Homo sapiens
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Classification
Linnaeus's seven levels of classification are—from smallest
(most complex-specific) to largest (least complex-specific):
• species
• genus
• family
• order
• class
• phylum
• kingdom
* Each level is called a taxon, or taxonomic category
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*Recently, biologists recognized that Monera were
composed of two distinct groups: Eubacteria and
Archaebacteria.
The six-kingdom system of classification includes:
Eubacteria
Archaebacteria
Protista
Fungi
Plantae
Animalia
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The Three-Domain System
Molecular analyses have given rise to a new taxonomic
category that is now recognized by many scientists.
The domain is a more inclusive category than any other—
larger than a kingdom.
1. Eukarya - protists, fungi, plants, and animals.
2. Bacteria, which corresponds to the kingdom Eubacteria.
3. Archaea, which corresponds to the kingdom
Archaebacteria.
Hand-out: Classification chart
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