Wednesday, May 21, 2008

Homology, Darwinism, and Logic

[This is a section from one of my chapters on Darwinism and Intelligent Design.]

One argument from homology to Darwinism is philosophical and does not rely on any empirical factors. The objection is made that a conscious designer would never use similar structures in different organisms to accomplish different tasks. Therefore, the random process of natural selection is the better explanation.

The empirical evidence for homology is very questionable (see Jon Wells, Icons of Evolution and M. Denton, Evolution: A Theory in Crisis), but the logic behind the philosophical argument is flawed as well. Why, pray tell, should a designer employ entirely different structures for different purposes—say for a wing and for a hand (which have some structural bone similarities)—when similar structures accomplish various goals quite well? How can the Darwinists read the mind of the nonexistent (or at least nondesigning) God? There seems to be no moral or logical principle at hand to invoke against such a designer. Moreover, many human designers employ similar structures for divergent purposes. If this is the case for human designers, why not so for a nonhuman designer of the structures of living things themselves?

14 comments:

pgepps said...

Sure makes sense to me. And from a theological and aesthetic standpoint, certain forms which resemble each other to greater and lesser degrees may have purposes utterly alien to their physiological or survival function.

Why should a platypus be "duck-billed"?

And why shouldn't two eyes on the front of a face seem "more human" to us?

If, for example, varying types and degrees of resemblance to humans and human projection onto animals were key reasons for a diversity of animal forms . . . so that we would "see ourselves in" creatures in different ways and relate to them--and to God, and He to us--among them. . . .

Wouldn't function-irrelevant homology be some part of that aesthetics of Creation?

scripto said...

"Moreover, many human designers employ similar structures for divergent purposes."

They may indeed, but they don't have to. Evolution has to cobble together novel structures from existing structures. Are you suggesting the "non-human" designer is constrained by this when human designers aren't. Unless you are proposing an unending sequence of design events this idea does not jibe with certain aspects of the fossil record. What are we to make of the apparent whale sequence found here? Are the intermediate forms just practice?

Looks more like descent with modification to me.

John Stockwell said...

The arguments that you make here against
homology are pretty outdated. You need
to study up on the modern view of developmental
evolutionary biology. There books by
Sean B. Carroll are a good start.

Homology of structures between species is
governed by genes called "hox" genes. The
differences in structures occur through
duplication of hox genes, and through the
changes in timing of the action of these genes.

Doug Groothuis said...

Scripto:

You beg the question about evolution having to be constrained. I question the sufficiency of natural selection and mutation to account for everything in the biosphere.

Some development within species is compatible with my view, but not macro-evolution according only to natural, unintellignet causes. The whale case is much disputed, in any case.

Stockwell:

You avoided my philosophical point. I'll look into hox genes, but I doubt they will explain everything adequately.

scripto said...

"You beg the question about evolution having to be constrained."

I don't understand what you mean.

"I question the sufficiency of natural selection and mutation to account for everything in the biosphere."

You're not alone. I believe there are other mechanisms such as genetic drift that may play an important role. But there is no evidence that anything beyond natural processes are required.

"Some development within species is compatible with my view, but not macro-evolution according only to natural, unintellignet causes. The whale case is much disputed, in any case."


You can always dispute direct ancestry. I doubt if that case is provable and if you are looking for certainty you won't find it in paleontology. The pattern and timing of the distribution is what is important here. Whether direct ancestors or kissing cousins what other process other than descent with modification could be at play?

Since the species that exist now didn't exist for the most part 60, 100, or 500 million years ago why would you think that there is some sort of dividing line beyond which natural evolutionary processes can't cross. Again, is the alternative innumerable multiple creations or some sort of continual interference by an undected agent?

pgepps said...

Stockwell's moving-goalposts doesn't seem very interesting.

I find the attempt to decide exactly where microevolution and macroevolution differ less interesting than the question of whether descent with modification from a high-genetic-potential population of a few distinct kinds, or descent with modification from zero genetic potential into some nonzero amount, makes more sense.

I have no problem with natural selection, up to the point where natural selection ceases to be the uncontrolled version of breeding efforts and becomes the hero of Darwin's mythopoeic works--and his grandson's, too.

(Charles Darwin was the grandson of radical, naturalist, and bad poet Erasmus Darwin, who wrote to long verse narratives attempting to argue for the theory his grandson later wrote a prose epic about.)

John Stockwell said...

Dr. Groothuis wrote:

You avoided my philosophical point. I'll look into hox genes, but I doubt they will explain everything adequately.

... the philosophical point...

One argument from homology to Darwinism is philosophical and does not rely on any empirical factors. The objection is made that a conscious designer would never use similar structures in different organisms to accomplish different tasks. Therefore, the random process of natural selection is the better explanation.


That simply is a strawman that you are demolishing. First of all,
there isn't any such thing as "Darwinism", at least not in this
century. Second, "arguments from
bad design" are usually used
against creationists as a response
to claims by creationists that
"design is obvious".

Such discussions really don't occur
in the scientific community, because
you would have to have an actual
scientific theory of manufactured
biology to propose such hypotheses,
and such a thing does not yet exist.

John Stockwell said...

pgepps wrote:
Stockwell's moving-goalposts doesn't seem very interesting.


No goal post moving here. I am just
trying to keep Dr. Groothuis honest.
He will appreciate what I say in
the longrun.

Doug Groothuis said...

Stockwell:

1. Is Stephen Jay Gould a straw man? He used this argument, as do other Darwinists in their case agasnst design.

2. Of course, Darwinism still exists! Other mechanisms besides natural selection and mutation have been added, but those are nonnegotiable and Darwinian. It is called the newo-Darwinian synthesis.

3. Supoptimal design does not equal no design. That is really a bad argument.

Doug Groothuis said...

Scripto:

You beg the question again. If certain species exist now and did not, say, 50 million years ago, that does not prove that they came about through only natural, unintelligent causes. It simply means they did not exist then, if that is true at all. There are genetic limits to species change. Mutations are usually harmful, not helpful.

I am arguing for design as an explanatory category, not for innumerable special creations all over the place. That is a straw man. There may be considerable change within life forms over time, but within certain forms.

Does "undected" agent mean "undetected agent"? If so, the agent is detected through the signs of intelligences: the irreducible complexity of aspects of the cell, the fine tuning of the unverse, the specified complexity of information in DNA, etc.

scripto said...

"You beg the question again. If certain species exist now and did not, say, 50 million years ago, that does not prove that they came about through only natural, unintelligent causes."

The point is that species or "kinds" or whatever you want to call the classification is not static.

"There are genetic limits to species change."

How did you determine this and what are they?

"Mutations are usually harmful, not helpful."

They are usually neutral. Neutral mutations may very well supply some of the material for future genetic change.

"I am arguing for design as an explanatory category, not for innumerable special creations all over the place. That is a straw man. There may be considerable change within life forms over time, but within certain forms.


I don't think so. I'm asking for a coherent alternative to descent with modification. If say, 63 million years ago, all placental mammals were shrew-like animals (which fits the fossil evidence, how can you say that change is limited to certain "forms" (whatever that means) and still explain the diversity of placental mammals today?

"Does "undected" agent mean "undetected agent"?

Yep. I'll try to keep it in English.

"If so, the agent is detected through the signs of intelligences:"

And this is determined through a weak analogy to human design. No process, no timeline - no dice. It is a less than compelling alternative to evolutionary theory. If fact, you cannot even compare them on equal terms.

John Stockwell said...

Douglas Groothuis wrote:

1. Is Stephen Jay Gould a straw man? He used this argument, as do other Darwinists in their case agasnst design.


2. Of course, Darwinism still exists! Other mechanisms besides natural selection and mutation have been added, but those are nonnegotiable and Darwinian. It is called the newo-Darwinian synthesis.


What other mechanism? Basically the
claim of design has no mechanism.
Not merely that, it is the claim
of *no possible mechanism*.

The term Darwinian synthesis refers
to the notion of studying "descent
with modification and natural selection"
in the context of genetics.

Actual, "Darwinism" which is to say
the strict adherence to the principles
outlined by Darwin has been supersceded
by a more modern view. Consequently,
there aren't any more Darwinists.



3. Supoptimal design does not equal no design. That is really a bad argument.


You just don't get it. The claim of
design has no theory that will tell us
what to expect in terms of "design".

The creationist argues that the
structure is evidence of "good design",
yet he or she cannot refute the argument
that the same structure is evidence of
"bad design". Hence, apparently designs
are all simultaneously both good and
bad, rendering the concept of design
impotent in biology.

Ed Darrell said...

You raise a good question, Doug: Why should God strive for good design, when merely adequate design will work? God's economics don't work the same as human economics -- quality is probably not a function God needs to achieve in order to get the most design for his buck.

But I fear that quickly decays as an argument. Is God arbitrary and capricious? Really? Sez who?

Jon said...

I saw an interesting video in which Dawkins stated that flatfish are evidence against design because "no one would ever design a fish like this", which of course really means, "I wouldn't have designed it like this, so therefore it cannot have been designed."