Last Time…

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Biston betularia

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Distribution Map Biston betularia f. typica

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1840 Distribution Map

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DiscoveryBiston betularia f. carbonaria

1848 - Manchester, UK

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James W. Tutt

(1858-1911) Manchester in 1843

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Frequency of dark form Centers of pollution

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London

Manchester

Glasgow

Mystery PhenomenonPart 2

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Unpolluted vs. Polluted Forest

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Unpolluted Woods & Moths

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Polluted Woods & Moths

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Three Theories 1. Physiological Response to Changed Environment

2. Natural Selection

3. Mutation

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Three Theories 1’ . Lamarck’s Theory of Acquired Inheritance

2’. Darwin’s Theory of Natural Selection

3’. De Vries’ Mutation Theory

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Lamarckian Inheritance

Jean Baptiste Lamarck(1744-1829)

• All creatures have a natural tendency to become more complex.

• Changes in behavior can result in morphological changes inherited by offspring

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Lamarckian InheritanceApplied to the Mystery Phenomenon

Nicholas Cooke(1818-1886)

• 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.

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Natural Selection

Charles Darwin(1809-1882)

• 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.

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• Increase of the dark form is due to crypsis or the protective advantage of dark color in soot- darkened environments.

J.W. Tutt1858-1911)

Natural Selection& the Mystery Phenomenon

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Natural Selection& the Mystery Phenomenon

E.B. Ford(1901-1988)

• 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.

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Mutation Theory

Hugo De Vries(1848-1935)

• Speciation is the result of large discontinuous changes caused by mutations that produce offspring radically different than their parents.

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Mutation Theory& the Mystery Phenomenon

Heslop Harrison(1881-1967)

• Lead salts in the pollutants covering the foliage of trees have mutagenic properties.

• Exposure to these salts has led to this mutation.

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To Sum it Up…

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Cooke’s TheoryIncreasingPollution

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Tutt & Ford’s TheoryIncreasingPollution

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Heslop Harrison’s TheoryIncreasingPollution

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What is a theory?

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How do scientists choose between competing theories?

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