1. Last Time…

2. Biston betularia

3. Distribution Map Biston betularia f. typica
1700
1800
1900
2000
1600

4. Discovery Biston betularia f. carbonaria
Manchester, UK
1700
1800
1900
2000
1600

5. James W. Tutt
( )
Manchester in 1843
1700
1800
1900
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1600

6. 1950 Frequency of dark form Centers of pollution 1700 1800 1900 2000
Glasgow
Manchester
London
1700
1800
1900
2000
1600

7. Mystery Phenomenon Part 2

8. Unpolluted vs. Polluted Forest

9. Unpolluted Woods & Moths

10. Polluted Woods & Moths

11. Three Theories 1. Physiological Response to Changed Environment
2. Natural Selection
3. Mutation

12. Three Theories 1’ . Lamarck’s Theory of Acquired Inheritance
2’. Darwin’s Theory of Natural Selection
3’. De Vries’ Mutation Theory

13. Lamarckian Inheritance
All creatures have a natural tendency to become more complex.
Changes in behavior can result in morphological changes inherited by offspring
Jean Baptiste Lamarck
( )

14. Lamarckian Inheritance Applied to the Mystery Phenomenon
This trend is the result of the moths adapting to environmental conditions that have led to a general darkening of their resting sites, such as pollution and increased humidity.
Individuals adapt to local circumstances and these changes are passed to their offspring.
Nicholas Cooke
( )
1700
1800
1900
2000
1600

15. Natural Selection
There are small heritable variations within populations.
Some variations give their possessors a better chance at surviving and reproducing.
Over time the favored variation will become more common.
Charles Darwin
( )

16. Natural Selection & the Mystery Phenomenon
Increase of the dark form is due to crypsis or the protective advantage of dark color in soot- darkened environments.
J.W. Tutt )
1700
1800
1900
2000
1600

17. Natural Selection & the Mystery Phenomenon
The spread of the dark form is due to its physiological superiority over the pale form.
The spread is limited to areas darkened by pollution owing to the handicap of dark coloration in unpolluted environments.
E.B. Ford
( )
1700
1800
1900
2000
1600

18. Mutation Theory
Speciation is the result of large discontinuous changes caused by mutations that produce offspring radically different than their parents.
Hugo De Vries
( )

19. Mutation Theory & the Mystery Phenomenon
Lead salts in the pollutants covering the foliage of trees have mutagenic properties.
Exposure to these salts has led to this mutation.
Heslop Harrison
( )
1700
1800
1900
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1600

20. To Sum it Up…

21. Cooke’s Theory
Increasing
Pollution

22. Tutt & Ford’s Theory
Increasing
Pollution

23. Heslop Harrison’s Theory
Increasing
Pollution

24. What is a theory?

25. How do scientists choose between competing theories?