Evidence and Evolution: The Logic Behind the Science by Elliott Sober

Author:Elliott Sober [SOBER, ELLIOTT]
Language: eng
Format: epub, pdf
Tags: General, Life Sciences, Science, Philosophy, Philosophy & Social Aspects, Evolution (Biology), Evolution, Natural Selection, Epistemology, Probabilities, Probabilities - Philosophy, Evidence, Evolution (Biology) - Philosophy, Natural Selection - Philosophy
ISBN: 9780521692748
Google: c1VehakcuuQC
Amazon: 0521692741
Publisher: Cambridge University Press
Published: 2008-01-15T10:00:00+00:00

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Natural selection

An important theme from Chapters 1 and 2 was that testing is con-

trastive: To test a theory, you need to test it against alternatives.1 This seems to entail that testing evolutionary theory means testing it against

creationism. If so, why is creationism so rarely discussed in scientific

publications? Are biologists willfully burying their heads in the sand? In

the last chapter I argued that the hypothesis that an intelligent designer

made the complex and useful traits that we observe organisms to have is

untestable. However, if intelligent design is a sorry excuse for a scientific

theory, where is evolutionary theory to find a more worthy opponent? If

testing is contrastive, there must be one. This line of questioning has a

false presupposition. Evolutionary theory describes a number of possible

causes of evolution. There is natural selection but there also is mutation,

migration, random genetic drift, recombination, linkage, inbreeding, as

well as others. The theory allows for the possibility that different traits in

different lineages might evolve for different reasons; there is no presup-

position that one size fits all. What evolutionary biologists spend their

time doing is testing one evolutionary hypothesis against another. For

example, an important project in population genetics involves using data

on the DNA sequences present in different species to test selection against

drift, an undertaking I’ll discuss in §3.9. Contrastive testing occurs within

evolutionary biology, not between evolutionary biology and something

outside. To talk about testing evolutionary theory is a bit like talking

about testing chemistry. Evolutionary biology, like chemistry, is a field or

discipline that contains many theories; evolutionary biologists test evolu-

tionary hypotheses against each other.

Does this mean that there are presuppositions internal to evolutionary

biology that never get tested? For example, when population geneticists

use sequence data to test selection against drift, they usually assume that

the species considered all derive from a common ancestor. Not only that,

they usually assume a specific phylogenetic tree, one that describes which

species are closely related to each other and which are related only more

distantly. It is true that population geneticists usually make these

phylogenetic assumptions, but it is false that those ‘‘assumptions’’ are

merely assumptions. As we will see in the next chapter, the hypothesis of common ancestry can be tested, and the same is true of more detailed

claims about phylogenetic relationship. It is important to distinguish the

1 This isn’t true for theories that (together with independently justified auxiliary propositions) have deductive implications about observations; however, for theories that merely confer nonextreme probabilities on observations, the dictum is correct.

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