Re: Cambrian Explosion

Mark Phillips (mark@ist.flinders.edu.au)
Mon, 15 Feb 1999 08:28:10 +1030

> The claim that the absence of evidence is in fact evidence of absence is in
> fact a logical fallacy called the appeal from ignorance (a particular
> proposition is false because it has not been proved true). To claim, or
> even suggest, that the Cambrian lifeforms could not have evolved because no
> has yet found fossilized ancestors is to engage in this fallacy.

While I agree that we have to be very careful about discounting a
theory, just because there is a portion of evidence not yet found, I
don't think I can agree with your logical falacy point.

Absence of evidence may or _may_not_ be evidence of absence. Suppose
you have a million holes in the ground, and you want to see if at
least one of them contains a marble. You examine 200,000 holes at
random and find no marble. This is good evidence that, if there are
any marbles at all, their number is quite small. It is not however
enough evidence to conclude that there are no marbles at all. If
however you examined 950,000 of the holes and still there were no
marbles found, it would be strong evidence that are no marbles. My
point is that it is possible, at least in principle, to use absence of
evidence as evidence for absence.

I don't believe the "lack of pre-Cambrain fossils argument" correctly
matches the "appeal from ignorance" logical falacy. If no one had
bothered to look for fossilized Cambrian ancestors, and then somebody
claimed that because there were no such specimins they hadn't evolved,
_then_ this would be an appeal from ignorance falacy. But the fact
that people have been looking without success, is admissible evidence.

Don't get me wrong, it may well be that this evidence is ineffective
in discounting evolution. Perhaps ancestors were soft bodied, making
fossilization near impossible --- for example. But my point is that
the reason for the ineffectiveness has nothing to do with "appeal from
ignorance" logical falacy.

Mark.

_/~~~~~~~~\___/~~~~~~\____________________________________________________
____/~~\_____/~~\__/~~\__________________________Mark_Phillips____________
____/~~\_____/~~\________________________________mark@ist.flinders.edu.au_
____/~~\HE___/~~\__/~~\APTAIN_____________________________________________
____/~~\______/~~~~~~\____________________________________________________
__________________________________________________________________________
"They told me I was gullible ... and I believed them!"