unit 2: evolution learning goal 2: describe the effects of environmental factors on artificial and...
TRANSCRIPT
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Unit 2: Evolution
Learning Goal 2: Describe the effects of environmental factors on artificial and natural selection.
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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.
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Artificial Selectionaka: Selective Breeding
Darwin’s pigeon experiment
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Artificial Selectionaka: Selective Breeding
Used today in agriculture and animal breeding.
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Artificial Selectionaka: Selective Breeding
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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.
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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.
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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.
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Natural Selection We Can SeeThe 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 human-made.
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Case of the Peppered Moth 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.
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Case of the Peppered Moth 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.
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Case of the Peppered Moth
B bB BB
Black
Bb
Pepperedb Bb
Peppered
bb
White
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Case of the Peppered Moth 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.
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Case of the Peppered Moth
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.
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Case of the Peppered Moth
The next slide shows a tree with silvery lichen.
Try to find the dark gray peppered moth in the next slide.
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Case of the Peppered Moth
Try to find the silvery-white colored peppered moth in the next slide.
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Case of the Peppered MothMoth Population
1850 1950 1972
Light Colored
95% 5% 25%
Dark Colored
5% 95% 75%
Today, about 90% of the population is light colored. Why did the population shift back to pre-Industrial Revolution composition?
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Natural Selection
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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Natural Selection
Descent with Modification Each living species has
descended, with changes, from other species over time.
Common descent is the principle that all species – living or extinct – were derived from common ancestors.
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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.
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Summary of Darwin’s Theory
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.
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Summary of Darwin’s Theory
Species alive today are descended with modification from ancestral species that lived in the distant past.