Tuesday 29 April 2008

Is there a difference between evidence that supports a theory and evidence that is merely consistent with a theory?

This post comes from a post by Stephen Law on the same subject in relation to Creationism and subsequent discussions on his blog. One of Stephen’s main criticisms of the Creationist position is that they subtly change their theory in order to save it in the face of evidence. The result is a theory that is compliant with evidence, but not supported by it. Much of the discussion (at least from me) centred around Stephen’s requirements for a theory to be capable of being supported by evidence:

“o First, the theory must allow us to deduce observational consequences:
consequences that can be clearly and precisely stated.
o Second, there should
be a sense in which the prediction is surprising and unexpected.
o Third, the
prediction should turn out to be true.”

I advanced the (not very well worded) thesis that this reduced to Popper’s concept of corroboration: evidence supports theory-x only if its absence would falsify theory-x. Creationism’s tendency to hedge its bets progressively removes any support it has from the evidence. This post is an attempt to bring more clarity to the thesis.

Starting Point
Let us, first of all, characterise "Creationism" and "Evolutionism":

Creationism: “God created all the species on the planet within six 24 hour days less than 10,000 years ago” we will call this ψ (“psi”)

Evolutionism: “The species evolved from a small number of common ancestors by means of evolution over a period in excess of 4 billion years”. We will call this φ (“phi”)

ψ entails certain things, it means certain things. If we were to give the full meaning of ψ we would list out an infinite number of things that result from the truth of ψ. ψ means ‘A and B and C and D….’. Using a full-stop for “and”, an arrow → for “means” gets us to ‘ψ→A.B.C.D.E.F….’. For the purposes of this illustration I shall truncate the meaning to just the first four propositions entailed:

1. ψ→A.B.C.D (psi means A and B and C and D)

If one of these (A, B , C or D) is incorrect then, in that respect ψ is incorrect. If one of these is correct then, in that respect ψ is correct. I shall characterise the meaning of φ as follows:

2. φ→G.H.I.J (phi means G and H and I and J )


Possible Changes
If the adherent to ψ subsequently finds out, say, ¬A (‘not A’) he has four options:

Drop the belief in ψ:

3. ¬ ψ (not ψ)

Drop the entailment of A by ψ:

4. ψ→B.C.D (ψ means, just, B and C and D)

Add additional possible outcomes (with “v” as “or”):

5. ψ→(AvL).B.C.D (ψ means “A or L” and B and C and D)

Replace the entailment of A with the entailment of something else:

6. ψ→L.B.C.D (ψ means L and B and C and D)

If more negative evidence is found the same choices are open.

At the limit (all entailments appear negative) we get to:

3*. ¬ ψ

4*. ψ→ (ψ means nothing)

5*. ψ→(AvL).(BvM).(CvN).(DvO)

6*. ψ→L.M.N.O

(Notice that in 4,5,6,4*,5* and 6* the meaning of ψ changes. None of “A.B.C.D”, “B.C.D”, “(AvL).B.C.D”, “L.B.C.D”, “ ”, “(AvL).(BvM).(CvN).(DvO)” or “L.M.N.O” are identical.)

Following the strategy in 3 and 3* the adherents of ψ stop being adherents of ψ. Following the strategy in 4 and 4* the adherents of ψ remove all meaning from ψ.
What of the situation in 5*: (AvL).(BvM).(CvN).(DvO)? Well “L” most decidedly is not “A”, we got to “L” from our evidence “¬A”. We got to “M” from our evidence “¬B” and so on. ¬A.¬B.¬C.¬D together with (AvL).(BvM).(CvN).(DvO) entail:

7. (Av¬A).(Bv¬B).(Cv¬C).(Dv¬D).

Each of those disjunctive pairs entails nothing, thus, means nothing and can be discounted. However ψ does say something, we also added entailments to the meaning of ψ. In full what we have is:

8. ψ→(Av¬AvL).(Bv¬BvM).(Cv¬CvN).(Dv¬DvO)

Again each of the meaningless disjunctive pairs can be discounted, with the result:

9. ψ→L.M.N.O

This is the same as the result of following the strategy in 6 and 6*.

Evidence

We may be able to check whether A or ¬A holds. If so then A or ¬A, whichever does hold, can count as evidence. If there are entailments of ψ that we are unable to check up on, say B and ¬B, these may still form part of the meaning of ψ but cannot be either evidence for or against ψ (or indeed evidence for or against any proposition).

Let now expand our conception of ψ a little. We shall say that ψ means:

a) Evidential statements L, M, N and O
b) Non-evidential statements P, Q, and R

10. ψ→L.M.N.O.P.Q.R


Bring Evolutionism Back Into Things

Of course whilst all this adaption of ψ has been going on the evolutionists have been up to the same tricks, φ has been revised as well. Let’s say:

11. φ →L.M.N.O.S.T.U

With S, T and U being non-evidential statements.

We can notice two things:

a) Neither proposition can be proven. Proving ψ requires ascertaining P, Q and R the truth of which we cannot ascertain. Proving φ requires ascertaining S, T and U the truth of which we cannot ascertain.
b) The totality of their evidential statements, (L, M, N and O), are exactly the same.

For the purposes of assessing the evidence we may drop the non-evidential statements from our definitions:

12. Evidentially, ψ→L.M.N.O and
13. Evidentially, φ→L.M.N.O

Evidentially speaking ψ and φ are the same proposition.
In this situation our choice between the two propositions cannot be based on evidence. Assuming:
- The above definitions are complete definitions of ψ and φ
- ψ and φ are the only propositions under consideration
- L, M, N and O hold true
Then based on the evidence we must adopt either ψ or φ. The evidence supports “either ψ or φ”.

L, M, N and O do not prove either proposition
L, M, N and O are evidence for the propositions because they force us to accept part of what they mean
L, M, N and O are no evidence at all for “P and Q and R” or “S and T and U”, there is no “force” to accept either of them.


A Difference

Right, let’s bring in a number of ways in which ψ and φ can be different:

14. ψ→L.M.N , φ→L.M.N.O
15. ψ→L.M.N.(Ov¬O) , φ→L.M.N.O
16. ψ→L.M.N.¬O , φ→L.M.N.O

In situation 14. “L.M.N” can be taken to be evidence for either ψ or φ it gives no indication as to which one to adopt. “O”, on the other hand is evidence for φ. It forces us to accept at least part of φ. It is not evidence for ψ, it does not force us to accept any of ψ.

In situation 15. we can rewrite “(Ov¬O)” as a blank “” bringing us back to the situation in 1. “O” is evidence for φ but not for ψ.

In situation 16. “O” is evidence for φ and evidence against ψ. Where O to hold ψ would have to be revised either to:

16.a ψ→L.M.N
16.b ψ→L.M.N.O

And we would be back to either 14. or the propositions would be evidentially similar.

Notice that O to be evidence for ψ we have to be able to write out ψ→O without adding ¬O. If we ascertain ¬O having stated ψ→O then we have to revise ψ. If we are in a situation where we do not have to revise ψ after ascertaining ¬O then we must either have started with

17. ψ→¬O or
18. ψ→(Ov¬O)

In neither situation is O evidence for ψ.

O is evidence for ψ if and only if ¬O forces a revision in ψ

The Fossil Record

Evolutionism makes some predictions about the fossil record. Not very precise ones and not very many, but some. For example evolutionism never says “There will be a fossil right there”, “FRT”. If we do not find an FRT we do not revise evolutionary theory. Thus evolutionary theory, φ, predicts “either there will be an FRT or there won’t be an FRT” or φ→(FRTv¬FRT).

Evolutionism does not say that there will be lots of fossils (LOF), that they will contain certain types of fossil (CTF) etc etc.

19. φ→(FRTv¬FRT).(LOFv¬LOF).(CTFv¬CTF), which cancels down to φ→

To have any meaning for evolutionary theory in the fossil record we have to find something that would force a revision in evolutionary theory. What could that be? One reply is “A rabbit fossil in the in the pre-cambrian”. Not much of a prediction but it is a predicition. Evolutionary theory means we do have a Rabbit Free Pre-Cambrian Type Fossil Record (RFPC).

21. φ→RFPC

RFPC is evidence for Evolutionism

And Creationism? Well RFPC is consistent with creationism. ¬RFPC is also consistent with Creationism. It does not say either way. So:

20. ψ→(RFPCv¬RFPC)

Which cancels down to ψ→.

RFPC is not evidence for Creationism

Surprise!

Let us say that both ψ→O and φ→O. O is evidence for ψ and φ. O is either evidence equally for ψ and φ or is not evidence at all for at least one of them. Very crudely, if ψ and φ were the only two propositions that →O, O would support them both 50%.

Let us add a third, χ (“chi”). χ→O. There are now three propositions ψ, φ and χ for which O is evidence. Very crudely again, O supports them 331/3% each. Add another, ω (“omega”) and the crude measure of evidential support becomes 25%.

Lets add a fifth, κ (“kappa”) but say that κ→(Ov¬O). We know that ¬O does not force a revision in κ, so O is not evidence for κ. There remain just the four theories that →O and so each remains supported 25% by O.

We could go on through the Greek alphabet and beyond but I think we have demonstrated the point.

The existence of support of ψ by O depends upon whether ¬O forces a revision in ψ. The amount of support of ψ by O depends upon the number of other theories where ¬O also forces a revision.

Now supposing we had ψ, φ, χ and κ all equally likely. How likely are we to have O? Well, ψ, φ and χ all firmly predict O if ψ, φ or χ are true then O is definite. If κ is true then we have no idea either way, 50%. The total likelihood of O is [(3x100%) + (50%)]/400% = 87.5%

Now suppose that φ, χ and κ do not predict O either way. The total likelihood of O is now [100% + (3x50%)]/400% = 62.5%

Suppose that φ, χ and κ predict ¬O. If they were true the likelihood of O would be zero. The total likelihood of O would be [100% + (3x0%)]/400% = 25%

As the number of rival theories not predicting O or firmly predicting ¬O increases the likelihood of O decreases. The term “surprising” springs to mind. As the number of rival theories not predicting O or firmly predicting ¬O increases the amount of support by O increases.

“Surprising” = exclusivity of firm prediction = amount of support


Now…

The situation right now is that there are bundles of evidence for evolution. Much of this is compatible with Creationism (Creationism has been changed to fit it) but is not a firm prediction of Creationism. Creationism does not say “if Creationism then Evidence”, it says “if Creationism then the Evidence or Not the Evidence”.

Much of the evidence for Evolutionism is surprising. We would not expect it if Evolutionism were not as it is. The apparent fusing of two ape chromosomes to produce one human chromosome is not just surprising it is, frankly, flabbergasting. (Have your flabber-gasted at this link)

Creationism on the other hand presents no evidence what-so-ever that is not also evidence of Evolution. There is nothing that forces a revision of Creationism that would not also force a revision of Evolutionism.

If Author thinks there is any evidence for Creationism he is welcome to put it forward. Just make sure that:

21. Creationism would have to be revised if it were to be false
22. Godless-communist-fag-Evolutionism would not also have to be revised were it to be false.

8 comments:

Anonymous said...

Hi, and thank your for your post.

I just started reading your post, and I haven't finished it yet. So far it seems fairly well reasoned. But before I finish reading it I have a few preliminary comments I would like to share with you right away.

Just so you know what my personal views are on creation and where I stand, I do not necessarily agree with the majority of creationists or Intelligent Design proponents on how creation took place or how long it took. In these discussions, I am only representing my own views, not the views of others. Sometimes in discussions like this, evolutionists assume I am arguing for points that others hold about creation, points which I do not agree with at all.

I would like to suggest different definitions of evolution and creationism that focus less on the time-frame and more on the mechanism. To me, it is the mechanism that is at the heart and core of the controversy. This may not be true for everyone, some may feel the time-frame is more important.

Anyway, this would be how I would define evolution and creation:

Evolution is the teaching that the variety of species came about through natural forces only, mutation and natural selection being examples of some of the natural forces that developed the species.

Creation is the teaching that the variety of species came about through the supernatural design and intervention by God. That is, God through some supernatural means created or modified the genetic coding that determines the species.

Notice that I say nothing about the time-frame. This makes my definition of creation more broad than the one in your post because my definition of creation does not rule out the possibility that God created the species incrementally over millions of years, and it does not rule out the possibility that God used the mechanism of common descent and through supernatural means made small modifications in the genetic code from one generation to the next to produce new species.

In the Stephen Law blog, some evolutionists had an issue with my definition of evolution. Some of them objected, saying that evolution does not rule out the intervention of God in the process of gene modification, that evolution only specifies common descent and does not specify the mechanism for gene modification. I do not remember everyone who said this, but I think Stephen Law was someone who took this position. But he is a philosopher, not a scientist. Ironically, from other statements he made, it seems he feels he has strong evidence that there is no God, so even while he gives a broad definition to evolution that can include devine intervention, he personally feels sure that there has been no such intervention. But at least one evolutionist seemed to agree with me. Steelman in one of his comments seemed to be saying that evolution teaches development of species through natural forces only.

I was wondering what your position is on this.

Are students taught evolution through natural forces only, or are they taught evolution with the mechanism unspecified and can include supernatural intervention by God?

I want to finish reading your post because you go into a lot of detail about how to compare evidence with a theory. I think this can be a useful technique perhaps for evaluating what I would call the reasonableness of a theory. I am looking for a way to discuss the reasonableness of belief in God as a supernatural cause for the origin of things, including species, compared with the reasonableness of "spy-dogs from Venus" and other analogies presented in debates like the one at the Stephen Law blog.

One more thing that struck me when I started reading your post. You use criteria for evaluating a theory such as, "the theory must allow us to deduce observational consequences", "there should be a sense in which the prediction is surprising and unexpected", and "the prediction should turn out to be true".

These are principles of the scientific method, is that correct? And the scientific method is the basis for all scientific investigation, is that correct?

Is the scientific method the only valid method for acquiring knowledge or learning truth? In science it is the only method used, unless I am wrong about that. But science is a limited field, and that is the point I am trying to get across. Science is limited to the study of physical processes only, and the scientific method was developed by the scientific community through trial and error over many years as the most effective method for studying physical processes.

Within science, the scientific method may not seem like a limitation. Among evolutionists and many scientists, it may not seem limited because they believe that physical processes are the only processes that exist. So a method that is used to learn only about physical processes is not limited if the only processes that exist are physical processes.

But if physical processes are not the only processes that exist, if there are supernatural processes in the universe, then the scientific method would be limited. It can study some processes, that is physical processes, but not all processes including supernatural ones. If an intervening God exists, the scientific method is not a valid method for investigating God and His interventions. Do you agree or not? If, not, let me know and I can go into more detail as to why I think that method fails if you try to use it to investigate God.

Science is not the only valid field in the search for knowledge. There are other fields that deal with knowledge, such as religion and theology. And within these other fields, the scientific method is not a valid way of learning knowledge. These other fields can look outside themselves at science and see that the scientific method is very good for investigating everyday, repeatable, physical processes. But they disagree with science that the scientific method should be used for learning about origins of things. And I think the scientific community as a whole, not every scientist, but the science community itself does not look outside itself at fields of religion and theology and acknowledge the validity of their methods for discovering truth. They tolerate those fields, but they look at them differently than those within those fields. For example, science might look at people's "need for religion" and try to understand how natural selection might have shaped the human brain and thinking process to have a need for religious beliefs and thought to comfort us. But science doesn't take those fields seriously as those fields take themselves.

But the evolution vs. creation controversy is where two fields of knowledge, each with different methods for discovering knowledge and gaining understanding, overlap. Both science and religion have something to say about origins, including origin of species. Both science and religion try to investigate questions of origins, each with its own methods.

For repeatable physical processes, I am in favor of the scientific method and would use it myself for trying to learn about those processes. For questions about the origins of things, I do not use the scientific method. I might use parts of it at times when it is appropriate, but not the whole package. I have more tools at my disposal than the scientific method provides.

So I would not agree that an explanation for how God may have created the species needs to be a theory that allows us to deduce observational consequences, that there should be a sense in which a prediction is surprising and unexpected, and that the prediction should turn out to be true.

I will continue reading your post and try to respond in more detail later.

Steelman said...

"For example evolutionism never says “There will be a fossil right there”, “FRT”."

I'm not so sure about that. It can predict, with the aid of other scientific disciplines, that "right there" is where a fossil would most likely be, and what type of fossil as well.

Knowledge of biological evolution, and geology, allowed paleontologists to predict where to dig for a particular type of fossil: Tiktaalik (scroll down to the "Discovery" heading).

Unfortunately, from the comment above, I see that Author is once again throwing out whatever scientific evidence he finds inconvenient (time frames, which includes geology and physics, at the moment).

Generally, scientific theories are comprehensive (all the evidence), predictive (see above), and falsifiable. Science sets a high standard for what it calls evidence and (contingent) knowledge. Predictions about the natural world that are based on religious beliefs continue to be proven false; the standards of evidence (baggage carted along from primitive times), are much lower, go figure.

Could there really be an undetectable, supernatural influence behind phenomena, for which science has already provided a natural explanation (i.e., theory)? Well, if you equate pure speculation with knowledge, then you'll never ask yourself the following question: "What's the difference between an undetectable influence and no influence at all?"

The influence of the supernatural, if it exists, can only be measured by its affects on the natural world. Scientific methods could certainly be employed to examine any such affects. However, there's no good reason, even for religious believers, to assume a supernatural explanation where a natural one is already sufficient. That's why most of us (even most Catholics!) prefer prescription drugs, rather than exorcisms, as a solution for what ails us.

Sorry, Author, science must remain agnostic about that which its methods cannot detect. There's no more impetus for science teachers, of any discipline, to make disclaimers in the classroom regarding the possibility of speculative, and/or superfluous, entities. This includes the workings of gods, demons, fairies, space aliens, etc. Their only job is to advise the student body of what science has discovered, and how it has done that discovering, and leave the rest to people's private imaginings, or at least to world religions or philosophy classes.

In other words, Author, it's fine for a science teacher to say, "we don't yet know the cause of X," but not to say, "we don't yet know the cause of X, but we've never disproved supernatural causes A, B, C, D...", and certainly silly to say, "we do know the cause of X, but, hey, [insert whatever you like here] could be secretly working behind the scenes!"

Tony Lloyd said...

Hi Author

Thanks for your comments.

On the “definition” of evolution I would say that it is “those things predicted by the theory that would necessitate a revision of the theory if they were found to be false”. Which is a bit of a mouthful, which I use to try and leave as open as possible the propositions that would require a revision and, thereby, avoid positivism. If we were to think of the meaning as just “propositions we can verify/falsify” we limit the meaning to evidence. The meaning of a proposition is everything that would falsify it, whether we can know that thing or not, whether we even know that it would falsify it or not.

Does Evolution “rule out the intervention of God in the process of gene modification”? Well part of what evolution says is that the reason we have a diversity of species is that we have
(A) descent with modification,
(B) a constant tendency to overpopulation and
(C) natural selection.
Recently neo-Darwinism has said that
(D) all of the reason for descent with modification is due to changes in the genome.
(E) It is thought that most of these changes come from mutation.
(F) The mutations come from a reconfiguration of base-pairs within DNA.

Now if mutations came from something other than a reconfiguration of base-pairs in the DNA then this would require a change in evolutionary theory. Two things are worth mentioning here:

1. It would still be an “evolutionary theory”, just a different one.
2. I haven’t mentioned God.

If we found out that God was responsible, supernaturally, for causing the end configuration of those configurations would that necessitate a revision to the theory sketched out above? Clearly not. If we found out that God was responsible, supernaturally, for causing the end configuration of those configurations would that necessitate a revision to the theory sketched out above? Clearly not.

So evolution does not mean that either God does, or does not intervene at that level. But notice something else. If you agree with all of A, B, C, D, E and F you agree with evolution. It is recognisably an evolutionary theory. What you are arguing for, it seems, is Evolution + Intervention. It’s a little strange to call that “Creationism”, most people call it “theistic evolution”. But notice further, if Evolution + Intervention is true then Evolution is true. It seems reasonable to teach a true theory in schools.


On the question of scientific method I deliberately did not distinguish “scientific evidence” from “evidence”. The whole things was on evidence, so I did concentrate on evidence. Basically anything that would necessitate a revision of a theory if it were false would count as evidence if we had access to it. So a historical manuscript is evidence for historical events. Not very scientific evidence (and its usually not very reliable) but it is evidence.

Science progresses by trial and error, I think all parts of knowledge progress by trial and error. What science has found (and to defend Stephen’s profession it’s actually philosophers have found!) is that there is no way of making sure our trials are better. All we can improve is our error detection. So any field of equiry where we can detect error is a field we can progress in. Conversely any field in which we cannot detect error or we have decided to prevent detection of error is a field that will not progress.

The great thing about evidence is that its just so good at detecting error. (A discussion about whether or not all swans are white could go on forever, but would be cut short if someone stuck a black swan under the disputants nose!).

Anonymous said...

In spite of the fact that, in discussion in textbooks of the details of how the genetic code changes from one generation to the next, you can find places where intervention by God can be inserted (because the evolutionary text does not openly state that it is excluded), there is an overall message to students that there has been no such intervention. Everyone reads between the lines. If science considered God's intervention a possible cause, it would be expected that science would mention it. Silence sends a message in this case.

Science does not treat possible supernatural intervention on an equal level with natural causes in considering the origin of species. If that were the case, science would mention it in texts that explore how to resolve the difficulties in interpreting the fossil record. For example, when a problem is encountered, such as the abrupt change from one species to another, or in trying to explain how an organ that requires many elements of a complex structure to be in place before any of them can confer a reproductive advantage, you will never read that "perhaps God designed and implemented certain organs that could not have developed gradually". Whenever any problem is encountered, the whole tone and practice of the discussion is that if science cannot discern a natural explanation, then science just needs to learn more and eventually a natural explanation will be found. This sends a message that there is no God that has intervened.

And I think there is a constitutional problem with doing this in government supported and mandated public schools.

What some call "theistic evolution" is really very different from "evolution", and it is very different from what is taught in public school classrooms.

Anonymous said...

Hi,

Theory: 'It is always raining'

I can deduce from this: 'The streets are always wet or grass is green.' (Call this A)

Grass is green, therefore A is true. Therefore I have evidence (and lots of it) for my theory.

Your criteria seem to suggest this.

Tony Lloyd said...

Hi Anonymous

"A v B" is true just in those cases where one or both of A and B is true. It is false only when both A and B are false.

So from "It is raining or grass is green" and "it is not raining" you can deduce "grass is green" (one of them must be true, it isn't "it is raining", so it must be "grass is green").

Or from "It is raining or grass is green" and "grass is not green" you can deduce "it is raining".

Basically from "A v B" and the FALSITY of one you can deduce the truth of the other. From the truth of one you cannot dedcue anything from the other (one OR BOTH may be true)

I'll reply to Author when I'm sober (it is Friday night, after all).

Tony Lloyd said...

Hang on a minute Anonymous I've just realised that I've mis-read your post (and can only plea a couple of very nice Belgian beers in my defence).

I did make it clear that we have to deduce "B" WITHOUT "¬B" for B to count as evidence. If B and ¬B were deductible then the theory would not need revision either if B presented itslef or ¬B.

From "it is raining" you can deduce "It is raining or (the grass is green or the grass is not green)". The two statments about the grass cancel out so the theory is just saying "it is raining".

Tony Lloyd said...

Hi Author

Stephen Law’s original post was about evidence. It was about how we distinguish between non-falsified, non-proven theories. It was Stephen’s contention that we make can make a decision on the rationality of the theories by whether and how much evidence for them they have. Stephen illustrated this by taking a theory we all agree is wholly irrational, that dog’s are venusian spies, and showing how there is no evidence for it, despite it being consistent with all evidence.

Stephen also contended that creationism is a similarly irrational theory. It complies with, but is wholly unsupported by evidence. My post was an attempt to make the understanding of what counts as evidence more explicit and formal and then to offer two examples of evidence for evolution and challenge creationists to come up with evidence for creation.

A further thesis contained in Stephen’s piece was that creationism puts itself in this irrational position by running away from contrary data. The creationist position says less and less as it seeks to make itself compliant. I must say that your posts are very good evidence for this latter thesis. It appears that your objection to evolution in schools boils down to an incredibly fine point accusing evolution at the extreme boundaries of knowledge of not explicitly stating that your particular creationist thesis is, in this tiny little area, not actually ruled out by all that we know. Every single thing in an evolutionary textbook is quite fine to say: it should just add this little bit because, without this little addition it says “not little addition”.

As a basis we can say that if I say "A" I say "A" and do not, simply from saying "A", say "A and not B" or "A and not C" or anything else.

On that basis your assertion that evolution as taught in schools implies anything about the supernatural where no natural cause is specified is simply false.

How could it be true? Of course it WOULD be true if what was said ENTAILED the unsaid. For example if I say "this glass is full of beer" I do also say "this glass is not full of wine". "This glass" cannot be full of wine if it is full of beer so if I say it is full of beer I say it is empty of wine without actually having to verbalise the assertion. If I said "this glass is full of beer" I do not say "Led Zeppelin are a great rock band" because my verbal assertion fails to entail the other assertion. If someone said that I had implied that "Led Zeppelin are a great rock band" simply because I had failed to say that they were a terrible rock band I think both you and I would call the men in white coats.

Now if saying "variations arise from changes in DNA" entails "God had no part in the changes in DNA" then you are correct: science in falling silent on the matter makes the assertion as much as if it were to explicitly state it. Does "variations arise from changes in DNA" ("X") entail "God had no part in the changes in DNA". ("Y"). If X entailed Y it would be impossible for someone to maintain the negation of Y whilst also maintaining X. Who maintains the negation of Y whilst also maintaining X? Why the theistic evolutionists of course! Are they being inconsistent? No, I do not think they are and have never seen anything approaching an argument that shows that they are. I've seen plenty of arguments saying that they are WRONG, just as anyone saying Led Zeppelin are a terrible rock band would be totally deluded. But, deluded or not, someone saying “Led Zeppelin are a terrible rock band” are not being inconsistent with glasses being full of beer and, likewise, saying “God had some role in the changes in DNA” is not inconsistent with “variations arise from changes in DNA”.

Hypotheses non fingo. The motive behind not speaking, either way, on the cause of effects that cannot be supported by any evidence and which do not form a necessary part of the theory could well be the perfectly proper wish not to start going on about things for which one has no evidential support and no necessity to talk about. There are an infinite number of things not entailed by and not ruled out by any theory. It is not possible to list them all in a class on evolution. Why mention this particular one? Because you like it? Because you think it important? Why select this one, particular non-entailment of evolution to emphasise its non-negation? Just as good an argument can be made for forcing teachers to outline “evolution does not rule out the possibility of Led Zeppelin being a good/terrible rock band” as for forcing them to teach “evolution does not rule out the possibility of divine intervention”.