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15-1 The Puzzle of Life's Diversity
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What is evolution?
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Biological evolution refers to the changes in the genetic
makeup of a population of interbreeding organisms of the same
species that occur over time.
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These genetic changes are the result of mutations in the DNA sequence
of the organism, which are passed from one generation to the next.
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Populations change over time.
The slow , gradual change in a population of organisms over
time.
Evolution
Evolution is the process by which modern organisms have
descended from ancient organisms.
A scientific theory is a testable explanation of
phenomena that have occurred in the natural world.
It can’t be proven right, only supported.
It can be proven wrong
Know the difference:
The fact of evolution.
The Theory of Natural Selection.
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Charles Darwin
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Born Feb. 12, 1809
Joined Crew of HMS Beagle,
1831
Naturalist
5 Year Voyage around world
Avid Collector of Flora &
Fauna
Astounded By Variety of Life
Voyage of the Beagle
In 1831, Darwin set sail from England aboard the H.M.S. Beagle
for a voyage around the world.
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During his travels, Darwin made numerous
observations and collected evidence that led
him to propose a hypothesis about the way life
changes over time.
That hypothesis has become the theory of
evolution (aka theory of natural selection).
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Darwin's Observations
He observed many plants and animals were well suited
to the environments they inhabited.
 He was impressed by the ways in which organisms
survived and produced offspring.
 Darwin was puzzled by where different species lived
and did not live.
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8
Living Organisms and Fossils
Darwin collected the preserved remains of ancient
organisms, called fossils.
Some of those fossils resembled organisms that were still
alive.
Others looked completely unlike any creature he had
ever seen.
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The Galápagos Islands
Darwin observed that the Galápagos Islands were close together
but had very different climates.
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The Journey Home
Darwin 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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15-3 Darwin Presents His Case
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Inherited Variation and Artificial
Selection
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Due to genes crossing-over in
the process of meiosis
(formation of gametes), all
organisms will inherit
variation. That is why no two
organisms (except for
identical twins) look exactly
alike.
However, when humans
interfere, they can decide
which individuals to breed.
They will chose to breed the
individuals with the desired
characteristics.
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Artificial selection is the
selection by humans for
breeding of useful traits from
the natural variation among
different organisms.
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Results in “breeds”
Evolution by Natural Selection
Darwin compared
processes in nature to
artificial selection.
By doing so, he
developed a scientific
hypothesis to explain
how evolution occurs.
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The Struggle for Existence
Darwin realized that high birth rates and a shortage of life's
basic needs would force organisms to compete for resources.
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Think about it…
How is natural selection
related to a species' fitness?
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Survival of the Fittest
The ability of an individual to survive and reproduce in its
specific environment is fitness.
Darwin proposed that fitness is the result of adaptations.
An adaptation is any inherited characteristic that
increases an organism's chance of survival.
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Because of its similarities to
artificial selection, Darwin
referred to the survival of
the fittest as natural
selection.
In natural selection, the traits
being selected contribute to
an organism's fitness (survival
and reproduction) in its
environment.
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Evolution by Natural Selection
The organisms that survive long enough to reproduce
because of certain traits then pass on those traits that helped
them survive. These changes increase a species' fitness in its
environment. Over time, natural selection results in changes in
the inherited characteristics of a population. This process is
known as evolution.
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Principles of Natural Selection
Descent With Modification
Natural selection produces organisms that have different
structures, establish different niches, or occupy different
habitats.
Each living species has descended, with changes, from other
species over time.
Darwin referred to this principle as descent with modification.
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Evidence of Evolution
Darwin argued that living things have been evolving
on Earth for millions of years. Evidence for evolution
include:
•the
fossil record
•geographical distribution
•homologous structures
•similarities in early development, or embryology.
•DNA Sequences
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The Fossil Record
Darwin saw fossils as a record of the history of life on
Earth.
By comparing fossils from older rock layers with fossils from
younger layers, scientists could document that life on Earth
has changed over time.
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Geographical Distribution
Similar, but unrelated species
develop similar characteristics due
to having to cope with similar
environmental pressures. Here, the
beaver and the capybara are
similar species that inhabit similar
environments of North America and
South America. The South American
coypu also shares many
characteristics with the North
American muskrat.
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Homologous Body Structures
Structures that have different mature forms but develop from
the same embryonic tissues are called homologous
structures. Examples:
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Homologous Structures
The limbs of these four modern vertebrates are homologous structures. They
provide evidence of a common ancestor whose bones may have resembled
those of the ancient fish shown here. Notice that the same colors are used to
show related structures. Homologous structures are one type of evidence for
the evolution of living things. Homologous structures are one type of
evidence for the evolution of living things.
Turtle
Alligator
Bird
Ancient, lobefinned fish
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Mammal
Structures; Comparing Anatomy
Homologous
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Physical Characteristics
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Analogous
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Found in related species
May not appear similar
at first, but they are
closely related.
Ex. Forelimbs in humans,
cats, and whale.
Physical Features
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Serve same function
Do not indicate a shared
common ancestor, but
they evolved
independently.
Ex. Wings on insects,
bats, and birds.
Homologous
Structure
Analogous
Structure
Not all homologous structures serve important functions.
There are organs in many animals that have no use and
are so reduced in size that they are just vestiges, or
traces, of homologous organs in other species.
These organs are called vestigial organs. Examples:
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Similarities in Embryology
The early stages, or embryos, of many animals with backbones
are very similar.
The same groups of embryonic cells develop in the same order
and in similar patterns to produce the tissues and organs of
all vertebrates.
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DNA Sequences