Transcript Evolution, 2e

• Evolution: descent with modification
• Unifying theory
• Targets: explaining
– history of life
– causes of biological diversity
– causes of characteristics and adaptations
• Adaptations are “produced by random, purposeless variation acted on by
purposeless natural selection.”
• “Except in the case of human behavior, we need not invoke nor can we find
any evidence for any design, goal, or purpose anywhere in the natural
world.”
Why does this frog
Have extensive
Webbing between
its fingers and toes?
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Old ideas about biological diversity
Aristotle: scale of nature
Ranking system
Ranking represents levels of
fixed diversity
Higher – Lower forms
One tenent of creationism
– fixity of species
– all created at the same time
– persist unchanged
• Idea subsequently altered by
• evolutionists such as Lamarck.
Lamarkian and Darwinian Evolution
Anagenesis: Yes, but not this example!
Example of an
adaptation.
Giraffe neck size
Why do giraffes have
Long necks?
Lamarck’s hypothesis:
Facilitates feeding from
high branches
Inheritance of acquired
characteristics.
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Evidence
Two bull giraffes
• Why do giraffes have long necks?
• There is a difference in neck size among bulls.
• Competition for females during a brief reproduction
season. Males engage in combat; necks are used.
• Neck length accompanied by a gain in mass
• Sexual selection: males with stronger necks have greater
mating success.
• Alleles resulting in stronger necks tend to be passed on to
progeny and increase in the population.
• The population changes over time.
• Something missing from Darwin’s original theory
• The particulate nature of transmission genetics.
• Mendel: experimental results published in
Proceedings of the Brünn Natural History Society in
1866.
• Although published, Darwin was unaware of this
info.
The modern synthesis
George Stebbins
George Simpson Theodoseus Dobjensky
• Ma
Ernst Mayr