Download 15-3 Darwin Presents His Case

Biology
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15-3 Darwin Presents
His Case
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15-3 Darwin Presents His Case
Publication of On the Origin of
Species
After examining all of the specimens he collected
from the Galapagos Islands, Darwin realized that
each island species looked a lot like a similar species
on the South American mainland.
Yet, the island species were clearly different from the
mainland species and from one another.
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15-3 Darwin Presents His Case
Publication of On the Origin of
Species
Publication of On the Origin of Species
Darwin filled notebooks with his ideas about
species diversity and the evolution process.
These ideas challenged fundamental scientific
beliefs of his day.
Eventually, Darwin published his book, On the
Origin of Species.
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15-3 Darwin Presents His Case
Publication of On the Origin of
Species
In his book, 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.
Many considered his work brilliant, while others
strongly opposed his arguments.
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15-3 Darwin Presents His Case
Inherited Variation and Artificial
Selection
Natural Variation and Artificial Selection
Darwin argued that instead of species being
perfect and unchanging, there is natural
variation found in all types of organisms.
• Natural variation = differences among
individuals of a species
• Variation is present in species in nature, farm
crops, and livestock.
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15-3 Darwin Presents His Case
Inherited Variation and Artificial
Selection
Natural Variation
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15-3 Darwin Presents His Case
Inherited Variation and Artificial
Selection
Some cows gave more milk than others. Some plants
produced larger fruit than others.
Darwin proposed that much of this variation could be
inherited, or passed on to the next generation.
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15-3 Darwin Presents His Case
Inherited Variation and Artificial
Selection
By studying farmers and breeders, Darwin noted that
they routinely used variation to improve their crops
and livestock.
He noted that plant and animal breeders would breed
only the largest hogs, the fastest horses, or the cows
that produced the most milk.
Darwin termed this process artificial selection.
This produced a wide range of plants and animals
that looked very different from their ancestors.
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15-3 Darwin Presents His Case
Inherited Variation and Artificial
Selection
How is natural variation used in artificial
selection?
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15-3 Darwin Presents His Case
Inherited Variation and Artificial
Selection
In artificial selection, nature provided
the variation among different
organisms, and humans selected those
variations that they found useful.
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15-3 Darwin Presents His Case
Inherited Variation and Artificial
Selection
Cauliflower
In artificial selection,
humans select from
Brussels
among the naturally
Sprouts
occurring genetic
variations in a species.
This process can lead to
great differences. In
some cases, a single
ancestral species has
given rise to a variety of
modern plants.
Kohlrabi
Broccoli
Ancestral
Species
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Kale
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15-3 Darwin Presents His Case
Evolution by Natural Selection
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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15-3 Darwin Presents His Case
Evolution by Natural Selection
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.
The struggle for existence means that members
of each species compete regularly to obtain food,
living space, and other necessities of life.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
In this struggle, predators that are faster or have an
effective method of hunting catch more prey. Those
prey that are faster, better camouflaged, or better
protected avoid being caught.
The struggle for existence was central to Darwin's
theory of evolution.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
How is natural selection related to a
species' fitness?
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15-3 Darwin Presents His Case
Evolution by Natural Selection
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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15-3 Darwin Presents His Case
Evolution by Natural Selection
Successful adaptations enable organisms to become
better suited to their environment and better able to
survive and reproduce.
Adaptations can be physical characteristics, such as
a porcupine’s sharp quills, or more complex features,
such as behavior in which some animals live and
hunt in groups.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
The concept of fitness was central to the process of
evolution by natural selection.
Generation after generation, individuals compete to
survive and produce offspring. Because each
individual differs from other members of its species,
each has unique advantages and disadvantages.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
Individuals with characteristics that are not well suited
to their environment (low levels of fitness) either die
or leave few offspring.
Individuals that are better suited to their environment
(high levels of fitness) survive and reproduce most
successfully.
Darwin called this process survival of the fittest.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
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 for—
therefore increasing over time–contribute to an
organism's fitness in its environment.
*Natural selection cannot be seen directly; it is
observed as changes in a population over
many successive generations.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
Over time, natural selection results in
changes in the inherited characteristics
of a population. These changes
increase a species' fitness in its
environment.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
Descent With Modification
Natural selection produces organisms that have
different structures, establish different niches, or
occupy different habitats.
As a result, species today look different from their
ancestors.
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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15-3 Darwin Presents His Case
Evolution by Natural Selection
Descent with modification implies that all living
organisms are related to one another.
This is the principle known as common descent.
According to this principle, all species—living and
extinct—were derived from common ancestors.
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15-3 Darwin Presents His Case
Evolution by Natural Selection
Think of a single “tree of life” that links all living things
on Earth.
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15-3 Darwin Presents His Case
Evidence of Evolution
What evidence of evolution did Darwin
present?
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15-3 Darwin Presents His Case
Evidence of Evolution
Evidence of Evolution
Darwin argued that living things have
been evolving on Earth for millions of
years. Evidence for this process could
be found in the fossil record, the
geographical distribution of living
species, homologous structures of
living organisms, and similarities in
early development.
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15-3 Darwin Presents His Case
Evidence of Evolution
The Fossil Record
Before Darwin’s time, it was known that fossils
were the remains of ancient life, and that different
layers of rock had been formed at different times in
Earth’s history.
Darwin saw fossils as a record of evolution.
Darwin proposed that the Earth was millions
(rather than thousands) of years old.
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15-3 Darwin Presents His Case
Evidence of Evolution
Over this time, countless different species
appeared on Earth, lived for a time, and then
disappeared.
By comparing fossils from older rock layers with
fossils from younger layers, scientists could
document that life on Earth has changed over time.
What did these
organisms
gradually
evolve?
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15-3 Darwin Presents His Case
Evidence of Evolution
Geographic Distribution of Living Species
Darwin wondered how the organisms he observed
and collected in the Galápagos became similar, yet
distinctly different species.
Could the island finches have changed over time,
as populations in different places adapted to
different local environments?
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15-3 Darwin Presents His Case
Evidence of Evolution
Darwin decided that all Galápagos finches could
have descended with modification from a common
mainland ancestor.
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15-3 Darwin Presents His Case
Evidence of Evolution
Remember the puzzle about different species
being found in Argentina and Australia even
though they had similar grassland ecosystems?
Darwin’s theory was that species now living on
different continents had each descended from
different ancestors.
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15-3 Darwin Presents His Case
Evidence of Evolution
However, because some animals on each continent
were living under similar ecological conditions, they
were exposed to similar pressures of natural
selection.
Because of these similar selection pressures,
different animals ended up evolving certain features
in common.
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15-3 Darwin Presents His Case
Evidence of Evolution
Beaver
Similar, but unrelated
species:
Muskra
t
The existence of similar but unrelated species
was a puzzle to Darwin. Later, he realized that
similar animals in different locations were the
product of different lines of evolutionary descent.
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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15-3 Darwin Presents His Case
Evidence of Evolution
Homologous Body Structures
Further evidence of evolution could be found in
living animals. By Darwin’s time, researchers had
found striking similarities among the body parts of
vertebrates (animals with backbones).
Reptiles, birds, and mammals had similar bone
structures, but different functions—as seen in their
arms, wings, legs, or flippers.
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15-3 Darwin Presents His Case
Evidence of Evolution
Homologous Structures
Turtle
Alligator
Bird
Mammal
Ancient,
lobefinned fish
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15-3 Darwin Presents His Case
Evidence of Evolution
Each of these limbs has adapted in ways that
enable organisms to survive in different
environments.
Despite these different functions, however, these
limb bones all develop from the same clumps of
cells in growing embryos.
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15-3 Darwin Presents His Case
Evidence of Evolution
Structures that have different mature forms but
develop from the same embryonic tissues are
called homologous structures.
Homologous structures provide strong evidence
that all four-limbed animals with backbones have
descended, with modification, from common
ancestors.
Similarities and differences in homologous
structures help biologists group animals according
to how recently they last shared a common
ancestor.
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15-3 Darwin Presents His Case
Evidence of Evolution
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.
Why not get rid of them? Vestigial organs may not
affect an organism’s ability to survive and reproduce;
natural selection would not eliminate them.
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15-3 Darwin Presents His Case
Evidence of Evolution
Human vestigial organs:
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15-3 Darwin Presents His Case
Evidence of Evolution
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.
These common cells and tissues produce
homologous structures.
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15-3 Darwin Presents His Case
Evidence of Evolution
Similarities in Embryology
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15-3 Darwin Presents His Case
Summary of Darwin's Theory
Summary of Darwin's Theory
Individual organisms differ, and some of this
variation is heritable.
Organisms produce more offspring than can
survive, and many that do survive do not
reproduce.
Because more organisms are produced than can
survive, they compete for limited resources.
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15-3 Darwin Presents His Case
Summary of Darwin's Theory
Individuals best suited to their environment (highest
level of fitness) survive and reproduce most
successfully.
These organisms pass their heritable traits to their
offspring. Other individuals die or leave fewer
offspring.
This process of natural selection causes species to
change over time.
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15-3 Darwin Presents His Case
Summary of Darwin's Theory
Species alive today are descended with modification
from ancestral species that lived in the distant past.
This process, by which diverse species evolved from
common ancestors, unites all organisms on Earth
into a single tree of life.
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15-3
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The scientist who motivated Darwin to publish
On the Origin of Species was
a. Alfred Russel Wallace.
b. Charles Lyell.
c. Jean-Baptiste Lamarck.
d. Thomas Malthus.
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Differences among individuals of a single
species are referred to as
a. artificial selection.
b. genetic variation.
c. survival of the fittest.
d. environmental adaptation.
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Changes that increase a species' fitness in its
environment over time are due to
a. the principle of common descent.
b. the geographic distribution of that species.
c. natural selection.
d. habitat selection.
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An inherited characteristic that increases an
organism's chance of survival is called a(an)
a. homologous structure.
b. vestigial organ.
c. adaptation.
d. analogous structure.
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15-3
Evidence used by Darwin to support the idea of
evolution included all the following EXCEPT
a. fossils that demonstrate change over time.
b. the genetic mechanism by which useful traits
are inherited.
c. the geographic distribution of living things.
d. the presence of many homologous
structures in plants and animals.
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