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evolution-digest Tuesday, February 16 1999 Volume 01 : Number 1305
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Date: Mon, 15 Feb 1999 17:51:02 -0800
From: Brian D Harper <bharper@postbox.acs.ohio-state.edu>
Subject: Re: Cambrian Explosion
At 11:15 AM 2/16/99 +1030, Mark wrote:
>When you say "absence of evidence can never be evidence of absence", I
>think the key is what exactly is meant by "absence of evidence". In
>its purest sense: absence of evidence for or against a proposition,
>you are completely right. But that is not the sense meant when
>talking about a pre-Cambrian fossil search. Here "absence of
>evidence" means "a search has failed to produce any pre-Cambrian
>fossils". As I will expand upon below, in this sense, "absence of
>evidence" can produce evidence of absence.
>
I thought I would throw my two cents on this, hope you
don't mind :). This insistence by some that absence of
evidence is not evidence of absence has always bugged me
since, for one thing, it seems totally contrary to the
way science normally works. If someone proposes a theory
it is natural to ask that person what the evidence is for
that theory. But if absence of evidence is not evidence of
absence then what, pray tell, is the purpose of such a
question? Suppose that: (a) there is an absence of evidence
that I robbed Fred's Bank on High Street yesterday and
(b) there is an absence of evidence that Fred's Bank on
High Street was robbed by anyone yesterday. Should this
absence of evidence be considered evidence that I did not rob
Fred's Bank on High Street yesterday? Or, more in context,
does the absence of evidence for a global flood indicate
evidence that such a flood never occurred?
Yes, there are exceptions of course. Primary seems to be
pointing to a lack of evidence where there are good reasons
to say that no evidence of this type should be found. Whether
this applies wrt pre-Cambrian fossils I can't say. Perhaps.
Brian Harper
Associate Professor
Applied Mechanics
The Ohio State University
"He who establishes his arguments
by noise and command shows that
reason is weak" -- Montaigne
- ------------------------------
Date: Tue, 16 Feb 1999 16:21:49 +1030
From: Mark Phillips <mark@ist.flinders.edu.au>
Subject: Re: Where is evolutionary theory?
> Pim: Does this explain why Philip Johnson is so succesful in the
> field if ID ?
Forgive my ignorance, but what does "ID" stand for? Intelligent
Design perhaps?
Cheers,
Mark.
_/~~~~~~~~\___/~~~~~~\____________________________________________________
____/~~\_____/~~\__/~~\__________________________Mark_Phillips____________
____/~~\_____/~~\________________________________mark@ist.flinders.edu.au_
____/~~\HE___/~~\__/~~\APTAIN_____________________________________________
____/~~\______/~~~~~~\____________________________________________________
__________________________________________________________________________
"They told me I was gullible ... and I believed them!"
- ------------------------------
End of evolution-digest V1 #1305
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------------------------------
Date: Tue, 16 Feb 1999 10:15:45 -0600 (CST)
From: pnelson2@ix.netcom.com
Subject: Re: Cambrian Explosion
Jonathan Clarke wrote, in part:
>So in about 25 million years, less than half the length
>of the Tertiary, we see the appearance of all the skeletonised
>phyla. There is no other period in the fossil record like it.
>
>The problem is not intractable. Molecular genetics can give
>us phylogenies and mechanisms by which new body plans develop.
>
>[...]
>
>We know a lot more than we did 20 years
>ago, especially about how changes body plans happen at the level
>of developmental biology and genetics [...]
I wonder if you could say more, Jonathan, about how you see
molecular genetics having illuminated how new body plans develop,
or how they change viably.
I ask because I see the situation quite differently. Saturation
mutagenesis in both Drosophila and zebrafish, and indeed the
perturbation of development in all known model metazoans, gives
no evidence that these body plans ever want to change (so to speak).
Indeed, the absence of viable mutants which might provide the
basis of higher-level evolution (at the origin-of-novel-body-plans
level) has led Gould and others (e.g., Douglas Erwin) to propose
profound temporal asymmetries in evolutionary processes. In brief,
ontogenies have now "hardened" irreversibly; so that a fruit fly
or zebrafish population under mutagenesis nowadays will die, sicken,
or otherwise tumble off its adaptive peak -- but things were very
different in the Cambrian radiation. Ontogenies were labile and
permitted rapid morphological change.
Whatever that means.
So I'm wondering if you can point to experiments illuminating
what you mean by the "mechanisms by which new body plans develop."
Paul Nelson
------------------------------
Date: Wed, 17 Feb 1999 07:34:08 +1100
From: Jonathan Clarke <jdac@alphalink.com.au>
Subject: Re: Cambrian Explosion
Dear Paul
Did you have to ask a question on molecular genetics where I am but an
interested spectator? Only kidding! I will do my best.
pnelson2@ix.netcom.com wrote:
> Jonathan Clarke wrote, in part:
>
> >So in about 25 million years, less than half the length
> >of the Tertiary, we see the appearance of all the skeletonised
> >phyla. There is no other period in the fossil record like it.
> >
> >The problem is not intractable. Molecular genetics can give
> >us phylogenies and mechanisms by which new body plans develop.
> >
> >[...]
> >
> >We know a lot more than we did 20 years
> >ago, especially about how changes body plans happen at the level
> >of developmental biology and genetics [...]
>
> I wonder if you could say more, Jonathan, about how you see
> molecular genetics having illuminated how new body plans develop,
> or how they change viably.
>
> I ask because I see the situation quite differently. Saturation
> mutagenesis in both Drosophila and zebrafish, and indeed the
> perturbation of development in all known model metazoans, gives
> no evidence that these body plans ever want to change (so to speak).
> Indeed, the absence of viable mutants which might provide the
> basis of higher-level evolution (at the origin-of-novel-body-plans
> level) has led Gould and others (e.g., Douglas Erwin) to propose
> profound temporal asymmetries in evolutionary processes. In brief,
> ontogenies have now "hardened" irreversibly; so that a fruit fly
> or zebrafish population under mutagenesis nowadays will die, sicken,
> or otherwise tumble off its adaptive peak -- but things were very
> different in the Cambrian radiation. Ontogenies were labile and
> permitted rapid morphological change.
>
> Whatever that means.
I think you are correct. We don't see phyla-level body plans evolving
today, we haven't seen this since the beginning of the Ordovician.
>
>
> So I'm wondering if you can point to experiments illuminating
> what you mean by the "mechanisms by which new body plans develop."
I was referring to the experiments on the effects of Hox gene mutations,
which from memory (it is early morning and there is no way I can get to
a source for this) appear to be able to effect major changes in body
plan. Some appear to be able to effect changes at the phyletic level
(segmentation, endoskeletons vs exoskeletons etc.). As you point out,
the results of the experiments are non-viable, whether this was always
the case, remains to be seen. I should have said something like "the
way new body plans developed".
It is a matter of degree though. I don't see any reason why leglessness
should not develop now, and many lizards seem to be doing so. This
requires Hox gene mutation also.
Hope this clarifies my tortuous explanations of my muddy mental
processes.
>
>
> Paul Nelson
God Bless
Jonathan
------------------------------
Date: Tue, 16 Feb 1999 14:07:52 -0700
From: "John W. Burgeson" <johnburgeson@juno.com>
Subject: Kevin later wrote:
kevin later wrote:
"But there has never, to my knowledge, been a case when a physical law
was
found to be false by new evidence. All theories that violate known
physical
laws are proven wrong in time."
Wow!
Too bad about Einstein. Not to mention a few others.
Burgy
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------------------------------
Date: Tue, 16 Feb 1999 14:00:58 -0700
From: "John W. Burgeson" <johnburgeson@juno.com>
Subject: Kevin (I think) said recently:
Kevin (I think) wrote recently:
" Imagine someone excavating
Jericho found two golden spheres that, when they collided, always had a
momentum sum greater after the collision than they had before. Though no
doubt all sorts of weird natural explanations would be concocted to
explain
the phenomenon, by definition it is a distinctly non-natural phenomenon."
In my physics education, admittedly many years back, I remember
exploring thought problems of this sort. The conclusion we reached
was that such a finding would NEVER lead to a non-natural
explanation, but ALWAYS to an exciting new science of new laws of nature
we had not previously suspected were there.
So I must politely disagree with your definition, my friend.
Burgy
___________________________________________________________________
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------------------------------
Date: Tue, 16 Feb 1999 14:26:05 -0700
From: "John W. Burgeson" <johnburgeson@juno.com>
Subject: The End of Science
I reviewed Horgan's THE END OF SCIENCE last year for
PERSPECTIVES.
Since it has gotten some comments here recently, here is the review.
Burgy
TEOS.WPS
As published in PERSPECTIVES, the quarterly journal of the American
Scientific Affiliation, Volume 49, Number 3 (September, 1997), page 200.
Bu John W. Burgeson
Book Review -- THE END OF SCIENCE, by John Horgan
THE END OF SCIENCE, Facing the Limits of Knowledge in the Twilight of the
Scientific Age, by John Horgan. New York, NY; Addison-Wesley Publishing
Company, Inc., 1996. 308 pages, index and footnotes. Hardcover; $24.00.
An American fable, probably apocryphal, tells of an executive in the
Patents Office resigning his job in 1890 because, he said, "nearly
everything that can be invented now has been!" Now comes John Horgan,
science writer for the Scientific American (that journal which has the
self-appointed task of telling us all how to think about Science),
interviewing dozens of scientists and philosophers on a similar issue.
Horgan poses the question this way:
1. Have the BIG questions all been answered?
2. Is the age of great discoveries now behind us?
3. Are scientists now reduced to puzzle-solving, just adding details, and
possibly precision, to today's existing theories?
Horgan argues persuasively for "endism," a "yes" answer to all the
questions above, and sees science, as a result, losing its place in the
hierarchy of disciplines, becoming, in time, much like the field of
literary criticism (which he apparently does not admire). His arguments
are based, not so much on his own ideas, but on ideas freely shared by
the people he interviews. Most of the "big" names are included, Popper,
Kuhn, Feyerabend, Weinberg, Wheeler, Dawkins (of course), Chomsky,
Eccles, many many others.
This is a frustrating book; one wishes to enter into the interview, to
ask the questions Horgan glosses over, to clarify points. It is also
exciting, for it covers a common topic across many disciplines. It is a
depressing book; one comes away from it with an impression much similar
to the writer of Ecclesiastes; all is vanity. Yet, it is an uplifting
book for the Christian; I see in it the logical end of treating "science"
as a faith position.
This may be a short-lived book, for it is very much bound to the "state
of the art" of the early 90s. The subject it covers, however, will
continue to be an issue for decades to come, and I foresee extensive
quotations from it for many years to come.
Horgan writes with insight into the end of progress, philosophy, physics,
cosmology, evolutionary biology, social science, neuroscience, and so on.
In an epilogue, titled "The Terror of God," Horgan speculates what this
means. He writes (page 266), "The ostensible goal of science, philosophy,
religion and all forms of knowledge is to transform the great 'Hunh' of
mystical wonder into an even greater 'Aha' of understanding. But after
one arrives at THE ANSWER, what then? There is a kind of horror in
thinking that our sense of wonder might be extinguished, once and for all
time, by our knowledge. What, then, would be the purpose of existence?
There would be none." The book ends with this plaintive wail, "And now
that science -- true, pure, empirical science -- has ended, what else is
there to believe in?" The Christian, of course, can
answer that question.
I recommend this book to all ASA members. It ought to be readable by most
persons at the college level; perhaps even by some advanced high school
students. The issues raised are important, and the views it collects
under a single cover are a unique look at science not found in the
textbooks. Much time and effort went into its research, and the results
are well worth our attention. It is easy to read, controversial and,
above all, entertaining.
>From PERSPECTIVES,
the journal of the American Scientific Affiliation
Volume 49, Number 3 (Sept 1997)
John W. Burgeson
IBM Corporation (retired)
Burgy@Compuserve.com
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------------------------------
Date: Tue, 16 Feb 1999 17:07:08 -0600
From: "Karen G. Jensen" <kjensen@calweb.com>
Subject: Re: Out of order fossils
Does anyone on the list know about these claims of Devonian insects?
I read about finds of centepedes, arachnids, and insect remains preserved
in exquisite detail in Devonian rock form upstate New York, "similar to
modern forms" (Science News 123:356-357, June 4, 1983) -- have these been
found to be contamination?
Karen
=====
Kevin's answer to my question [Mon, 8 Feb 1999 23:07:48 -0700]:
>>What would "out of order" fossils mean?
>>
>How about a pod of dolphin skeletons in unfaulted, unaltered, uniform
>Devonian deposits? How about a modern human skeleton found inside the rib
>cage of a Tyrannosaurus rex?
>
I wouldn't expect to find those!
The fossil record shows order.
But I did read about finds of centepedes, arachnids, and insect remains
preserved in exquisite detail in Devonian rock form upstate New York,
"similar to modern forms" (Science News 123:356-357, June 4, 1983) -- have
these been found to be contamination?
Karen
------------------------------
Date: Tue, 16 Feb 1999 21:13:23 -0600
From: andrew <amandell@jpusa.chi.il.us>
Subject: RE: Where is evolutionary theory?
Hi Pim van Meurs
I have just read my two notes after a night of sleep and feel pretty bad. I
do have some strong feelings and beliefs here but they are not coming
across. Worse than that I feel I have said things so poorly as to feel I
must apologize.
1 first off I was not ready to offer intelligent clear debate and should
have waited
2 i don't feel I have the years of research or reason to say things like
"johnson aside" or "I see the shortcomings of Johnson's work"
or any of a large amount of arrogant sounding stuff I said. It was not in
my heart I think I just wrote very foolishly. Much of it might be in line
for some with more dues paid but I am sorry I wrote with the style I did. I
am no ID spokesman I am just learning myself.
I hope I can talk this out with Pim van Meurs as it is still imp. to me to
keep going but I want to apologize for wasting folks time with my comments.
When posting to the list in the future I will try not to repeat this
shameful slop.
Sorry.
Andrew
------------------------------
Date: Tue, 16 Feb 1999 17:52:25 -0700
From: "Kevin O'Brien" <Cuchulaine@worldnet.att.net>
Subject: Re: Kevin later wrote:
>kevin later wrote:
>
>"But there has never, to my knowledge, been a case when a physical law
>was
>found to be false by new evidence. All theories that violate known
>physical
>laws are proven wrong in time."
>
>Wow!
>
>Too bad about Einstein. Not to mention a few others.
>
Too vague; do you have any specific examples to offer?
Einstein's theory of relativity did not prove any physical law to be false,
to my knowledge; all it did was to refine those laws so that they were more
accurate under specific circumstances.
Kevin L. O'Brien
------------------------------
Date: Tue, 16 Feb 1999 18:12:41 -0700
From: "Kevin O'Brien" <Cuchulaine@worldnet.att.net>
Subject: Re: Kevin (I think) said recently:
>Kevin (I think) wrote recently:
>
>" Imagine someone excavating
>Jericho found two golden spheres that, when they collided, always had a
>momentum sum greater after the collision than they had before. Though no
>doubt all sorts of weird natural explanations would be concocted to
>explain
>the phenomenon, by definition it is a distinctly non-natural phenomenon."
>
>In my physics education, admittedly many years back, I remember
>exploring thought problems of this sort. The conclusion we reached
>was that such a finding would NEVER lead to a non-natural
>explanation, but ALWAYS to an exciting new science of new laws of nature
>we had not previously suspected were there.
>
>So I must politely disagree with your definition, my friend.
>
I have no problem with that (you disagreeing that is). However, the fact
that you and your classmates missed the point does not refute my conclusion.
The law of conservation of momentum is a fundamental physical law; so much
of modern science is based on it that if it were proven to be false, or if
exceptions were to be found, the vast majority of accepted theories in most
disciplines would either collapse or have to be reconfigured. On top of
that, the law of conservation of momentum is so inexorably tied into the
very nature of the physical universe itself that if even one exception was
found we would have to rethink our concepts of what the universe is really
like.
That's why I called such an exception a non-natural phenomenon, because it
would violate the very nature of the physical universe as we understand it
to be. And if that were the only exception extant, it would be more likely
to be a non-natural anomaly rather than a representation of new physical
laws.
Kevin L. O'Brien
------------------------------
Date: Tue, 16 Feb 1999 19:30:14 -0700
From: "Kevin O'Brien" <Cuchulaine@worldnet.att.net>
Subject: Re: Cambrian Explosion
>When you say "absence of evidence can never be evidence of absence", I
>think the key is what exactly is meant by "absence of evidence". In
>its purest sense: absence of evidence for or against a proposition,
>you are completely right.
>
According to the philosophy of science, you can only get one of three
results whenever you test a concept: positive evidence that verifies the
concept, positive evidence that refutes the concept, or negative evidence,
which is generally defined as a lack of positive evidence; the implication
being that if you get negative evidence you cannot say whether the concept
has been verified or refuted. So the "purest" sense of what is meant by
absence of evidence -- namely that it constitutes negative evidence as
defined by the philosophy of science -- is the correct way to look at this
problem. Any other way tends to be subjective.
>
>But that is not the sense meant when
>talking about a pre-Cambrian fossil search.
>
On the contrary, the Precambrian fossil search is a perfect example of this
kind of confusion.
>
>Here "absence of
>evidence" means "a search has failed to produce any pre-Cambrian
>fossils".
>
No, that is not what it means; as I outlined it above, it would properly
mean that "a search of Precambrian sedimentary layers has so far failed to
produce any positive evidence that either verifies or refutes the existence
of Cambrian ancestors". The only way it could mean how you wish to define
it is if every Precambrian sedimentary rock layer has been thoroughly and
exhaustively searched in a systematic manner. Since that has not been done,
since that has not even been begun, it is rather arrogant to believe that
the extremely limited and poor results so far obtained can serve as evidence
that tends to refute the concept in question.
>
>As I will expand upon below, in this sense, "absence of
>evidence" can produce evidence of absence.
>
But since your sense of what "absence of evidence" means is incorrect, your
conclusion that it can constitute "evidence of absence" is also incorrect.
>
>> >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.
>>
>> Assuming that the marbles were themselves distributed randomly, which you
>> did not specify. Otherwise there could be 500,000 of them, but placed in
>> specific arrangements meant to defeat a random search. As such, your
lack
>> of evidence at this point really tells you nothing about how many there
are.
>
>No assumptions need be made about the distribution of the marbles.
>The fact that the search is _random_, means that there is _no_
>distribution strategy which can defeat it. It would be impossible to
>arrange the marbles in such a way as to defeat the search because
>there is no way of predicting, ahead of time, which holes will be
>searched.
>
There is no such thing as a truly random search in practical terms; as such,
it is theoretically possible to predict which holes will be searched. There
is in fact an entire field of probability statistics that studies exactly
this problem. I understand very little about it, but from what I've read
the statisticians are convinced that any quasi-random search pattern can be
predicted if you know what the underlying order of the pattern is. Some of
these theories are being used to create and break new mathematical codes.
My point is that since no search can be truly random, you cannot say after
searching only 200,000 holes what is really going on. Had you instead
specified a random distribution of marbles coupled with a systematic search,
however, then your claim after 200,000 holes would be on firmer ground, as I
admitted in my last post.
>
>Suppose there were in fact 100 marbles. The chance of not finding one
>after 200,000 searches, can be calculated. It is:
>
> 999,900 999,899 999,898 799,901
>---------.---------.---------. ... .---------
>1,000,000 999,999 999,998 800,001
>
>which is a _very_ small number --- we're talking around 1/100,000,000.
>
>In fact, further calculations would show that if no marble were found
>after 200,000 searches, we could have 99% statistical confidence that
>there were fewer than 20 marbles.
>
Those calculations are based on the assumptions that the marbles were
randomly distributed and that the search was orderly and systematic, which
is the simplest case. I cannot reproduce the mathematics (I barely
understood them when I first encountered them) but I know that if you assume
a non-random distribution coupled with a random search, you get a very
different result, one in which the chance of finding no marble after 200,000
searches is much higher. Those results also indicate that no statistical
confidence can be applied to any specific number of marbles.
>
>> >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.
>>
>> Not really. Your hypothesis is that there is at least one marble
present,
>> but nothing is said about the probability of there being more than one.
>
>"at least one marble present" is mathematical speak for "one marble,
>or two marbles, or three marbles, or four marbles, ..." --- in other
>words, it is an expression often used when one wants to talk about the
>probability of there being "one or more than one" marbles present. I
>hope this clarifies things --- a technical point in any case.
>
It's still too vague a statement to make a simple straight-forward testable
hypothesis; the null hypothesis would be too complex and virtually
meaningless, rendering any result that was not an exact verification of the
hypothesis too ambiguous to interpret.
>
>> That makes the null hypothesis that there are no marbles. As such,
>> to verify or refute either hypothesis you would have to examine every
single
>> hole; even 950,000 holes would be insufficient to verify or refute either
>> hypothesis. Even 999,999 holes would be insufficient because the last
hole
>> still has a 50/50 chance of containing a marble.
>
>It is _possible_, after searching 999,999 holes without success, that
>the last hole contained the marble, but _very_ _very_ improbable ---
>certainly not 50/50! A 999,999 hole search would not give you
>_absolute_ certainty of no marbles, but it would give you extremely
>high _statistical_confidence_ of no marbles.
>
That would only be true at the beginning of your search, and even then it
would not be strictly true. At the beginning of your search (# of holes = n
= 1,000,000) the chance that any **specific** hole had that one marble would
be so low as to be negligable (specifically 0.5^1,000,000; which my
calculator could not solve), but the chance that **any** random, unspecified
hole would have the marble would be 50/50 (or 0.5^1). As you eliminated
holes that had no marble (n < 1,000,000) the chance that a **specific** hole
would have the marble would increase (0.5^800,000; 0.5^600,000; 0.5^400,000;
0.5^200,000; and so on), until finally when you had eliminated every hole
but the last one (n = 1) you would reach the maximum probability of 50/50
(or 0.5^1). So again, even after you have searched all but one hole you
still can make no definitive statement about whether a marble is present in
any of the holes.
>
>> Despite appearances, however, this is not a case where a lack of
>> evidence verifies one hypothesis and refutes another, because in
>> this kind of study the lack of marbles is not a lack of evidence;
>> you would expect to find some holes empty in any event.
>
>Well this "marbles scenario" is analogous to the "missing fossil
>scenario", though the latter is obviously not so neat. There are a
>finite number of potential fossil locations on earth (though we may
>not know where they all are). Theoretically we could break this up
>into small regions --- our "holes". Finding a pre-Cambrian fossil in
>a region is equivalent to finding a marble. Clearly there are lots of
>complications, and probability calculations are much more difficult
>than in the marble scenario, but the essential idea is still there.
>
And when examined correctly the marble example tells us that we should
expect to find empty holes; i.e., regions that are devoid of fossils. As
such, our current lack of success based on a so-far limited search cannot
definitively tell us anything about our overall liklihood of success.
>
>My point is that just as "finding many empty holes" is admissible
>evidence as to the number of marbles, so too is "finding many fossil
>beds with no pre-Cambrian fossils" evidence as to the number of
>pre-Cambrian fossils.
>
My second marble example, in which 100,000 marbles are randomly distributed
throughout the holes, and in which no marbles are found after a search of
200,000 holes, is closer to the reality of our search for Precambrian
fossils than your at-least-one-marble example or my single-marble example.
In that second example I established that finding 200,000 empty holes would
refute the hypothesis that 100,000 marbles were distributed randomly
throughout the holes, though I could not say what was invalid, the number of
marbles or that they were distributed randomly. In any event, while this
would constitute a **negative result** (hypothesis refuted) it would not
constitute **negative evidence** (an absence of positive evidence that
verifies or refutes the hypothesis) because in fact the result constitutes
definitive evidence that contradicts the hypothesis and verifies the null
hypothesis. So rather than being an example of an absence of evidence that
provides evidence of absence, it is in fact an example of the presence of
evidence that directly refutes the hypothesis in question.
At our current point in our search for Cambrian ancestors, however, the lack
of fossils is due more to a lack of holes (i.e., a lack of regions) rather
than a lack of marbles. A lack of holes would constitute a true absence of
evidence -- i.e., a lack of positive evidence that verifies or refutes the
hypothesis; in other words, negative evidence -- but we cannot say that this
constitutes evidence of absence because we are lacking the very data we
would need to make that determination.
>
>> >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.
>>
>> The fallacy doesn't depend upon whether you look for the evidence or not;
it
>> only depends upon whether you use a lack of evidence to try to prove or
>> disprove a concept. The fallacy doesn't say, claiming a concept is false
>> because no one has tried to prove it true; it says, claiming a concept is
>> false because it hasn't been proven true. The implication is that people
>> could have been trying to prove it true but had not yet succeeded.
>
>You are correct in suggesting that _trying_to_prove,_without_success_
>does not invalidate a claim --- *providing* the very process of
>_trying_to_prove_ does not in itself yield evidence in favour of the
>counter claim.
>
True, but it would have to yield positive evidence that verifies the
counter-claim, not negative evidence that neither verifies or refutes any
claim. That's why the appeal from ignorance is a fallacy.
>
>I am saying that, a large enough search for pre-Cambrian fossils which
>results in none being found, can be taken as positive evidence in
>favour of the proposition that no pre-Cambrian fossils exist. And
>thus, this kind of argument cannot be classified as an "appeal from
>ignorance" falacy.
>
That is true only after a "large enough search" has been done (which it
hasn't) and only if that search turns up positive evidence that refutes the
claim that Cambrian ancestors exist. So far all we have is negative
evidence that neither verifies nor refutes any claim; attempting to use this
negative evidence as an argument for claiming that Cambrian ancestors do not
exist is classified as an "appeal from ignorance" fallacy.
PS -- A few quick technical notes: it's "Precambrian", not "pre-Cambrian";
Precambrian fossils have been found, but the point of this discussion
concerns fossils that should be older still; and it's "fallacy", not
"falacy".
Kevin L. O'Brien
------------------------------
Date: Tue, 16 Feb 1999 20:20:13 -0700
From: "Kevin O'Brien" <Cuchulaine@worldnet.att.net>
Subject: Re: Cambrian Explosion
Brian wrote:
>
>I thought I would throw my two cents on this, hope you
>don't mind :).
>
As a worthy opponent you are most heartily welcome. Come, let us toast each
other's bravery and fortitude. Slantha!
>
>This insistence by some that absence of
>evidence is not evidence of absence has always bugged me
>since, for one thing, it seems totally contrary to the
>way science normally works.
>
Not really. Science is based on the idea that you need definitive,
unambiguous evidence that specifically validates or refutes hypotheses. As
I explained to Mark in my latest reply, you can expect one of three basic
results from any experient: positive evidence that verifies the hypothesis,
positive evidence that refutes the hypothesis, or no positive evidence,
which is then called negative evidence. It is negative evidence that the
appeal from ignorance specifies when it refers to "absence of evidence".
Practically speaking, negative evidence is either no evidence whatsoever
(such as from a failed experiment) or evidence too ambiguous to interpret;
it is not positive evidence that refutes the hypothesis (hence producing an
"absence" of positive evidence that would have verified it instead).
>
>If someone proposes a theory
>it is natural to ask that person what the evidence is for
>that theory. But if absence of evidence is not evidence of
>absence then what, pray tell, is the purpose of such a
>question?
>
To test the theory against physical reality, you silly person ;-). Since
any proper theory must have some supporting evidence from the start
(otherwise it is only speculation), this is not what verifies or refutes it.
Instead you use the theory to make predictions about experimental results,
then do the experiments to try to get those results. As such, only positive
evidence that directly and unambiguously verifies or refutes the prediction
will have any impact on the theory. Negative evidence, which by definition
cannot either verify or refute the prediction, can tell you nothing about
the theory. As such, any attempt to use this "absence of evidence" to
refute the theory is a fallacy.
Creationist "theories" tend to be speculation disguised as theory, so they
can be refuted without testing them by revealing their lack of supporting
evidence. This doesn't really involve the appeal from ignorance fallacy,
however, because the speculations-disguised-as-theories don't really
qualify.
>
>Suppose that: (a) there is an absence of evidence
>that I robbed Fred's Bank on High Street yesterday....
>
In other words there is no positive evidence that proves OR disproves that
you robbed that bank.
>
>...and
>(b) there is an absence of evidence that Fred's Bank on
>High Street was robbed by anyone yesterday.
>
In other words there is no positive evidence that proves OR disproves that
the bank was even robbed.
>
>Should this
>absence of evidence be considered evidence that I did not rob
>Fred's Bank on High Street yesterday?
>
No. At best it constitutes evidence that you both did and did not rob the
bank; at worst it constitutes no evidence at all. Either way, based on all
this negative evidence alone no one can make a claim whether a robbery even
occurred, much less whether you were the robber. In other words, the
evidence tells us that we can neither confirm nor deny that a robbery took
place and can neither confirm nor deny that the culprit was Brian Harper.
Practically speaking, however, the end result is the same as if the absence
of evidence were evidence of absence.
>
>Or, more in context,
>does the absence of evidence for a global flood indicate
>evidence that such a flood never occurred?
>
No, because a global flood is not refuted by a lack of positive evidence
that verifies it (i.e., negative evidence), but by the presence of positive
evidence that refutes it. Again, however, the practical results are the
same, hence the confusion.
>
>Yes, there are exceptions of course. Primary seems to be
>pointing to a lack of evidence where there are good reasons
>to say that no evidence of this type should be found. Whether
>this applies wrt pre-Cambrian fossils I can't say. Perhaps.
>
It does in some cases; I believe it would apply in most, but there should
still be some good fossil-bearing strata left to explore in any case.
Kevin L. O'Brien
------------------------------
End of evolution-digest V1 #1306
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