1. Artificial Selection -vs- Natural Selections
Unit 2: Evolution
Artificial Selection
-vs-
Natural Selections

2. 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.

3. Artificial Selection aka: Selective Breeding
Darwin’s pigeon experiment

4. Artificial Selection aka: Selective Breeding
Used today in agriculture and animal breeding.

5. Artificial Selection aka: Selective Breeding

6. 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.

7. 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.

8. 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.

9. Natural Selection We Can See
The Case of the Peppered Moth
Species become endangered when the population is decreased to the point that a stress can affect survival.
Stresses may be natural or human-made.

10. 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.

11. 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.

12. Case of the Peppered MothB b BB
Black Bb
Peppered bb
White

13. 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.

14. 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.

15. 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.

18. Case of the Peppered Moth
Try to find the silvery-white colored peppered moth in the next slide.

21. Case of the Peppered Moth
Moth Population
1850
1950
1972
Light Colored
95% 5%
25%
Dark Colored
75%
Today, about 90% of the population is light colored. Why did the population shift back to pre-Industrial Revolution composition?

22. Natural Selection
Natural selection results in changes in the inherited characteristics of a population.
These changes increase a species’ fitness in its environment.

23. 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.

24. 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.

25. 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.

26. Summary of Darwin’s Theory
Species alive today are descended with modification from ancestral species that lived in the distant past.