Monday, August 09, 2004

Hunter, Part 2

I now continue with my analysis of Cornelius Hunter's contribution to William Dembski's anthology, Uncommon Dissent.

In the first part of this series I analyzed Hunter's arguments about the fossil record. I pointed out that his entire argument collapses because he conflated two different questions: “Is the history of life as revealed in the fossil record consistent with evolution?” on the one hand, with “Can we determine specific lines of descent from the fossil record?” on the other.

Another place where Hunter gets things badly wrong is in his discussion of the universal genetic code. He writes:


The DNA code is routinely used as strong evidence for evolution, but why? Everyone knows that one cannot use a code without having a method for encoding and decoding the information that is being transmitted. And, of course, the sender and receiver must be using the same code for the system to work. Volumes have been written on the cellular machinery that is involved in nature's scheme for using the DNA code, and we still don't understand all the details. It is phenomenally complex and it is not easily explained as a product of Darwin's evolutionary process. (P. 208)


Let's take this one sentence at a time:


  • The DNA code is routinely used as strong evidence for evolution, but why? Actually, the universality of the DNA code, and the universality of the cellular machinery used to translate that code, are evidence for a universal common ancestor. If these universals were not present it would be essentially impossible to argue that any two modern species share a common ancestor somewhere in the past.

  • Everyone knows that one cannot use a code without having a method for encoding and decoding the information that is being transmitted. I have no idea what the point of this sentence is. What does this have to do with whether different species use different codes, or have different cellular tools for encoding and decoding?

  • And, of course, the sender and receiver must be using the same code for the system to work. The “sender”, and “receiver” in this analogy are the parents and offspring of a given species. So, yes, the offspring must be using the same genetic code and possess the same cellular machinery as the parents. Again, what does that have to do with whether these are different codes in use in different species?

  • Volumes have been written on the cellular machinery that is involved in nature's scheme for using the DNA code, and we still don't understand all the details. Well, at least we agree on something.

  • It is phenomenally complex and it is not easily explained as a product of Darwin's evolutionary process. And here we have the standard conflation of evolution with the origin of life. Evolutionary theory has nothing to say one way or the other about the origin of the code. The code is simply taken as a given. Evolution also does not explain the motions of the planets around the Sun, but no one thinks that's a legitimate objection to Darwin's theory.


But Hunter disputes the idea that evolution predicts a universal code. Picking up from where the last quote left off we find:


Furthermore, evolution does not predict there to be a universal DNA code. A number of explanations of the code's supposed evolution are currently under consideration. In one way or another, the code is supposed to have evolved from simpler codes; but if the code could have evolved over time, then it is easily conceivable that it could have evolved into several different codes. In other words, evolutionary theory could explain the existence of multiple codes in nature. As such, evolution does not require there to be a single DNA code. (P. 208)


Evolution does not require a single code, but universal common ancestry does. In principle life could have formed several times on Earth, with each origination event producing a different code. After these events life could have evolved by the standard mechanisms. As a hypothetical scenario this is fine.

But such a scenario would be hard to square with the patterns of descent suggested by all the various anatomical homologies that we find, and it is hard to square with the fossil record. In other words, we have copious evidence from fossils and homologies that there is a universal common ancestor for all life. If it then turned out that there were multiple genetic codes, each one leading to a different evolutionary experiment, we would have some serious dissonance in the data. So it is comforting that the code is, in fact universal.

Let's go a little bit further. Picking up where the last quote left off:


The universal genetic code doesn't seem like a good candidate to serve as strong evidence for evolution. Evolution has trouble explaining how the code and its attendant machinery came about, and evolution does not require there to be a single code. How then does the universal genetic code support evolution so strongly? The answer is that evolutionists believe that if the species had been created independently, they would not share the same code. (P. 208-209)


Here Hunter makes explicit the error of conflating evolution with the origin of life. And we have already discussed what evolution expects about a universal code. I would like to examine that last sentence, however.

Hunter includes a footnote to back up his assertion about special creation predicting that the code should not be universal. He refers us to Mark Ridley's textbook Evolution. Sadly, Hunter's footnote refers us to the first edition of the book, whereas I only have the second edition. So I will leave open the possibility that Ridley says something different in the first edition.

But in the second edition Ridley does not say anything remotely like what Hunter attributes to him. Ridley does discuss the relevance of the universal genetic code, but he does so in terms that are similar to what I have provided here. I'd be surprised if you could find a single scientist making the argument Hunter describes above.

The simple fact is that scientists to not defend evolution by speculating about what an intelligent designer would do and then showing that these expectations are not met. Scientists do sometimes argue this way when they are criticizing creationism, however. That is entirely reasonable. Creationists believe that God has certain attributes such as omnipotence and omnibenevolence, and it is natural to ask how those characteristics would be reflected in the creation.

Criticizing creationism is not the same as defending evolution, though most creationists fail to see the distinction.

The relevance of the fossil record to assessing the validity of evolution, and the significance of the univeral genetic code are not hard to grasp. Hunter, nonetheless, seems not to have grasped them.

13 Comments:

At 5:29 AM, Blogger Richard Wein said...

Nice blog, Jason. I haven't read "Uncommon Dissent", but, from the passages you've quoted so far, it seems like typical creationist nonsense.

Anyway, I'd like to pick you up on a couple of points.

JR: "And here we have the standard conflation of evolution with the origin of life. Evolutionary theory has nothing to say one way or the other about the origin of the code. The code is simply taken as a given. Evolution also does not explain the motions of the planets around the Sun, but no one thinks that's a legitimate objection to Darwin's theory."

Evolutionary processes occurring before the origin of the first full-fledged cell may be considered by some to be non-biological and therefore a matter of OOL, but they're only divided from biological evolution by a rather arbitrary definitional line. They're nowhere near as far divorced from biological evolution as is astronomy. I don't think it would be unreasonable for Hunter to raise the subject under the general heading of "evolution" _if_ he had something useful to say about it. But all he has to say (if your quotes are representative) is that "it is not easily explained". Well, what a shock! And I thought that science was supposed to be easy.

JR: "Evolution does not require a single code, but universal common ancestry does."

Not necessarily. The code has already accrued minor variations in some lineages, and it's possible--at least in principle--that it could change beyond recognition. So distantly-related species could have quite different codes, as Hunter claims. (You might argue that the code is strongly preserved, so it would change too slowly for this to be a realistic possibility, but you haven't made that argument and it might be a difficult one to make.)

I think Hunter's point is something like this: a common code is evidence of a common _origin_, but why should scientists assume that this means common descent rather than separate creation by a common designer? I would answer that common descent is merely an extrapolation of processes which are readily observed, such as birth and heredity, while separate creation requires the invocation of a designer who is difficult to explain (where did he come from?) and for whom we have no independent evidence.

 
At 10:46 PM, Blogger Jason said...

Hi, Richard. Thanks for the comments. Your points are well taken.

My remark about evolution not explaining the motions of the planets around the sun might have been a bit extravagant, but I think the line between OOL and evolution is not just a matter of arbitrary definitions. Evolution takes it for granted that you have competition between imperfect replicators. If you are concerned with a time before such replicators existed, then you are not studying evolution. Not in the biological sense, anyway. I agree that the OOL is a question that is closely related to evolution, and it is natural to discuss them together. But Hunter clearly implied that it was a defect in Darwin's theory that it does not account for the origin of the genetic code. That is like blaming a hammer for being lousy at sawing wood.

Regarding your second point, I should have been more careful with my wording. When I said that universal common ancestry requires a universal code, I was thinking more of the cellular apparatus that is used to translate the code. The code can evolve in the sense that the same triplet might code for two different proteins in two different organisms. But I don't think universal common descent could survive the discovery that there are two fundamentally different mechanisms for converting DNA into proteins in two different organisms. Similarly, universal common ancestry could not survive the discovery that in some organisms DNA is the molecule of heredity while some different molecule is at work in other organisms.

I think you could argue that the code is strongly preserved, since in four billion years only a handful of minor variation have cropped up. And such variations as have been discovered are themselves in accord with common descent. As I recall, Ken Miller has an essay on this subject up at his site.

 
At 1:33 PM, Blogger Richard Wein said...

Hello, Jason.

JR: "...but I think the line between OOL and evolution is not just a matter of arbitrary definitions. Evolution takes it for granted that you have competition between imperfect replicators. If you are concerned with a time before such replicators existed, then you are not studying evolution."

In my experience, many people consider the OOL to be the appearance of the first cell, not the first replicator. The first replicator may not have been anything that would be recognised as a living organism.

Given that you take the OOL to be the appearance of the first replicator, your criticism of Hunter (that the origin of the genetic code is a matter of OOL) entails that the first replicator already possessed the code translation apparatus. This seems implausible to me.

JR: "I think you could argue that the code is strongly preserved, since in four billion years only a handful of minor variation have cropped up."

I think this argument requires the premise that common descent is true, which was the point in question. I was looking for an a priori reason to think that the code _could_ not change significantly.

I don't know much about the subject, so I did a web search and found the following relevant passage at Talkorigins:

[quote]... What is known, however, is that the scientists who cracked the genetic code in the 1950's and 1960's worked under the assumption that the code was universal or nearly so (Judson 1996, p. 280-281). These scientists, which included Francis Crick, Sydney Brenner, George Gamow, and several others, all made this assumption and justified it based upon evolutionary reasoning, even in the complete absence of any experimental evidence. In fact, this assumption was instrumental in their success in solving the code. For instance, in 1957, nearly ten years before the genetic code was finally solved, Sydney Brenner published an influential paper in which he concluded that all overlapping triplet codes were impossible if the code was universal (Brenner 1957). This paper was widely considered a landmark work, since many researchers were leaning towards an overlapping code. Of course, it turned out that Brenner was correct about the nature of the true code. In 1961, five years before the code was deciphered, Crick and others also concluded that the code was (1) a triplet code, (2) non-overlapping, and (3) that the code is read from a fixed starting point (i.e. the "start" codon) (Crick et al. 1961). These conclusions were explicitly based on the assumption that the code was essentially the same in tobacco, humans, and bacteria, though there was no empirical support for this assumption. These conclusions turned out to be correct. In fact, in 1963—three years before the code was finally solved—Hinegardner and Engelberg published a paper in Science specifically explaining why the code must be universal (or nearly so) if universal common descent were true, since most mutations in the code would likely be lethal to all living things.[/quote]
http://www.talkorigins.org/faqs/comdesc/camp.html

So it seems there are reasons to think that the code could not change significantly. I think the reason as stated here ("since most mutations in the code would likely be lethal to all living things") is insufficient, but presumably the cited sources make the case more comprehensively.

 
At 10:45 PM, Anonymous Anonymous said...

Comments:
My reply to Jason Rosenhouse is at the ISCID Brainstorms:

http://www.iscid.org/ubb/ultimatebb.php?ubb=get_topic;f=6;t=000540

 
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