NOTES ON TIM LEWENS, DARWIN, CHAPTER FOUR
I.
Question: What makes a scientific theory a good one?
Answer: “[T]he fact that a theory is able to successfully explain diverse phenomena is, Darwin thinks, strongly
indicative of the theory’s truth” (p. 98)
II.
This “mode of reasoning” = INFERENCE TO THE BEST EXPLANATION (IBE)
An Example of IBE: “Why do we think it is likely that the butler killed the Earl of Wensleydale? Because if the
butler did kill him, then this would best explain our data—the Earl’s blood on the butler’s jacket, the Earl’s blood on
the knife found under the butler’s bed, the sighting of the butler running away from the crime scene just after the
Earl died. When a hypothesis explains the data better than its rivals, we often think the hypothesis is true” (p. 98).
The structure of a typical IBE argument is as follows:
1. There exists some phenomenon P.
2. E provides the best explanation for P.
3. Therefore, it is probable that E is true.
III.
Problems with IBE arguments (pp. 99-101)
IV.
Note John Herschel’s influence on Darwin: scientific theories should appeal only to “true causes.” A theory should
“command our assent” only when the causes it appeals to pass three tests:
(1)
(2)
(3)
They must be shown to exist;
They must be shown to be capable of producing the phenomena we seek to account for;
They must be shown to be responsible for producing the phenomena we seek to account for.
We can apply these tests to Darwin’s structuring of his argument in The Origin of Species (pp. 105-107).
V.
Note, too, William Whewell’s influence on Darwin: scientific theories should give evidence of a “consilience of
inductions” (p. 103).
VI.
Now consider the Natural Selection/Intelligent Design Debate in light of these considerations of what counts as a
good scientific theory. According to Michael Behe, a contemporary advocate of Intelligent Design, Darwin’s theory
of natural selection cannot adequately explain the presence of the flagellum structure in some bacteria. His
argument has four steps:
(1)
(2)
(3)
(4)
Natural selection cannot explain the flagellum.
Chance is a poor explanation of the structure of the flagellum.
The intelligent design hypothesis is a good explanation of the structure of the
IBE demands assent to the intelligent design hypothesis.
flagellum.
VII.
There are explanatory problems with the Intelligent Design Hypothesis.
VIII.
The upshot is that natural selection remains compatible only with a conception of God who is “not a vulgar plate
spinner, ceaselessly intervening in worldly affairs to produce a species here, or fine-tune an adaptation there, but a
God who sets up a small number of elegant laws, which by their own action produce the full range of phenomena we
see around us. Intelligent design’s image of a creator who fiddles with bits of bacteria is, Darwin writes, ‘beneath
the dignity of him, who is supposed to have said let there be light & and there was light’” (p. 124).