Re: Cambrian Explosion

Kevin O'Brien (
Sun, 7 Mar 1999 21:06:16 -0700

>"Kevin O'Brien" wrote:
>> "Brian D Harper" wrote:
>> >When I think of lack of evidence in a scientific setting
>> >I'm thinking mainly of two possibilities:
>> >
>> >1) There is a particular piece of evidence which would really
>> >bolster a theory were it available. Unfortunately, it is not.
>> >
>> >2) The theory makes a specific prediction that such and such
>> >evidence should be found in such and such a fashion. But this
>> >evidence is not found.
>> >
>> >How would you define these two "lack of evidence" situations
>> >using your terminology?
>> Both are clearly cases of negative evidence, since we lack positive
>> evidence that would support the theory, but we do not have any
>> evidence that refutes the theory either.
>I don't see how 2) is a "clear case of negative evidence"!! If a
>theory makes a specific prediction that such and such evidence should
>be found in such and such a fashion --- but the evidence is not there
>--- then the theory has been falsified! This "lack of evidence" then
>constitutes _positive_evidence_ against the theory.

Your conclusion is flawed for two reasons. The first is that Brian himself
gave an example of a failed prediction that DID NOT falsify a theory. So it
cannot be true that a lack of positive evidence in favor of a theory
automatically constitutes positive evidence against a theory.

The second reason is that you are ignoring all the evidence that was used to
develop the theory in the first place. That evidence can be considered
positive evidence in favor of the theory. To refute the theory you have to
refute that evidence. A failed prediction does not refute this supporting
evidence, so a failed prediction by itself does not falsify the theory.
Only if the result directly contradicts the theory by refuting some of this
supporting evidence (or directly contradicts known physical laws or other
more strongly verified theories) can it then be considered positive evidence
against the theory.

Kevin L. O'Brien