Transcript Artificial and Natural selection

Unit 2: Evolution
Artificial Selection
-vsNatural Selections
Artificial Selection =
Selective Breeding

Nature provides the variation or
humans select the variations that they
find useful.

Breeders often choose a characteristic
that they want passed on and only breed
those animals that have that
characteristic.
Artificial Selection
aka: Selective Breeding

Darwin’s pigeon experiment
Artificial Selection
aka: Selective Breeding

Used today in agriculture and animal
breeding.
Artificial Selection
aka: Selective Breeding
Natural Selection


Survival of the Fittest
Struggle for Existence

Members of each
species compete
regularly to obtain food,
living space, and other
necessities of life.
Natural Selection

Survival of the fittest.

Those species best
adapted to their
environment will survive
and reproduce.

Species with greater
variety have an
increased chance of
surviving environmental
changes.
Natural Selection


Fitness is the ability of
an individual to survive
and reproduce.
Adaptation is any
inherited characteristic
that increases an
organism’s chance of
survival.
Natural Selection We
Can See
The Case of the Peppered Moth
oSpecies
become endangered when the
population is decreased to the point that a
stress can affect survival.
oStresses may be natural or humanmade.
Case of the Peppered Moth
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Peppered moths are a
common moth in England.
There are variations in the
coloration of peppered moths
from silvery white with gray
speckles to dark gray/black.
The most common form
before 1850 was a mixture of
white and black called
“peppered.” About 90% of the
moths found in nature were
peppered.
Case of the Peppered Moth
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There are two alleles for the color of
silvery moths: B for black and b for
white. The black color is melanin.
In the laboratory, the moths occur in a
ratio of 1 black:2 peppered: 1 white.
BB= black, bb= white, and Bb=
peppered.
The black is the dominant allele
causing speckling when present.
Case of the Peppered Moth
B
b
B
BB
Bb
Black
Peppered
b
Bb
bb
Peppered
White
Case of the Peppered Moth
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Peppered moths lived on
trees covered by silvery
lichen.
During the Industrial
Revolution, carbon-fuel
pollution killed the silvery
lichen on urban trees.
Coal soot coated tree trunks
causing the trunks to
become darker.
Case of the Peppered Moth
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In urban industrial areas,
silvery-white peppered moths
became less common and
the dark gray/black moths
became more common.
In rural forest regions, the
silvery-white peppered moth
remained the most common
type.
Silvery lichen was still on
trees in the rural areas.
Case of the Peppered Moth
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
The next slide shows a tree with
silvery lichen.
Try to find the dark gray peppered
moth in the next slide.
Case of the Peppered Moth

Try to find the silvery-white colored
peppered moth in the next slide.
Case of the Peppered Moth
Moth
Population
Light
Colored
Dark
Colored
1850 1950 1972
95%
5%
25%
5%
95%
75%
Today, about 90% of the population is light colored. Why did the
population shift back to pre-Industrial Revolution composition?
Natural Selection

Natural selection results
in changes in the
inherited characteristics
of a population.

These changes increase a
species’ fitness in its
environment.
Natural Selection

Descent with Modification

Each living species has
descended, with
changes, from other
species over time.

The principle that all
species – living or extinct
– were derived from
common ancestors.
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.

Summary of Darwin’s Theory
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Because more organisms are
produced than can survive, they
compete for limited resources.
Each unique organism has
different advantages and
disadvantages in the struggle for
existence.
Summary of Darwin’s Theory

Species alive today are descended
with modification from ancestral
species that lived in the distant
past.