evolution

This time, I’m talking not about my blog but the science. I won’t be filing for tax-exemption any time soon.

A tired argument put forth by some “intelligent design” advocates is that evolution is really just another religion; convenient because the “intelligent design” people can’t compete in the realm of science (or, rather, they haven’t), so they try to compete in the realm of religion — which, in this Christian-dominated society, they are more likely to persuade persons who have been inculcated in Christian (or some other religious) values since birth but who, like me, may not be experts in evolutionary biology.

Part of the article cited above, which was by Mustafa Akyol (a Muslim who testified before the Kansas State Board of Education’s show trial) in NRO (which is not quoted in the original post) deals with evolution as a means of social development, which I won’t deal with, simply because those theories are far less well-worked out (and like many sociological theories, much harder to offer proof of; and that I don’t accept them myself). Akyol’s notion of evolution as an argument or justification for materialism is suspect; but, again, I don’t want to deal with that. The theory of evolution as a biological process deals with neither of these things. I want to focus on evolution as a biological science.

First, from the NRO article:

Of course, ID — like any other scientific theory — stands or falls not according to its political and diplomatic utility, but according to the evidence. So: Is ID true?

There is a huge and growing body of ID literature produced by some of the world’s finest minds, and I won’t attempt even to summarize the overwhelming evidence it presents for design in nature. Yet I think an examination of the main premise behind the current opposition to ID might be helpful.

To see that premise, we first have to note how ID theorists criticize Darwin. They do this by applying his own criterion for falsification. “If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications,” said Darwin, “my theory would break down.” ID theorists, such as biochemist Michael J. Behe, apply this criterion to complex biochemical systems such as the bacterial flagellum or blood clotting and explain that they could not have been “formed by numerous, successive, slight modifications” — because they don’t function at all unless they are complete.

What is the Darwinian response to this? Here’s Jerry Coyne again, in The New Republic: “In view of our progress in understanding biochemical evolution, it is simply irrational to say that because we do not completely understand how biochemical pathways evolved, we should give up trying and invoke the intelligent designer.” Note that Coyne is here denying the falsification criterion that Darwin himself acknowledged. According to Darwin, if you demonstrate “that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications,” the theory will break down. According to Coyne, you will only be pointing to a system about which “we do not completely understand how [it] evolved.”

The examples of bacterial flagellum and blood clotting as systems that could not have evolved from scratch without going through a series of minor revisions, therefore disproving Darwin’s original theory, are presented here without evidence.

I found a refutation of that notion here, by Ken Miller of Brown University. It appears in his book Finding Darwin’s God: A Scientist’s Search For Common Ground. Miller presents his notion of how such systems could have developed, citing examples from nature. It’s rather long and technical, and I won’t reprint it here. As I understand it, blood clotting systems develop from proteins in a manner appropriate to the organism’s chemical makeup. As the organism becomes more complex, so too does the clotting system. Organisms naturally ingest other organisms, giving each a different set of proteins to work with; and natural selection does the rest — those with better blood clotting systems live longer, and that biochemistry is passed down through generations.

Miller writes of his explanation:

Can we know for sure that this is how blood clotting (or any other biochemical system) evolved? The strict answer, of course, is we cannot. The best we can hope from our vertebrate ancestors are fossils that preserve bits and pieces of their form and structure, and it might seem that their biochemistry would be lost forever. But that’s not quite true. Today’s organisms are the descendents of that biological (and biochemical) past, and they provide a perfect opportunity to test these ideas.

In other words, we find evidence and then test theories. That’s how science works. Miller goes on:

Even a general scheme, like the one I’ve just presented, leads to a number of very specific predictions, each of which can be tested. First, the scheme itself is based on the use of well-known biochemical clues. For example, most of the enzymes involved in clotting are serine proteases, protein-cutting enzymes so-named because of the presence of a highly reactive serine in their active sites, the business ends of the protein. Now, what organ produces lots of serine proteases? The pancreas, of course, which releases serine proteases to help digest food. The pancreas, as it turns out, shares a common embryonic origin with another organ: the liver. And, not surprisingly, all of the clotting proteases are made in the liver. So, to “get” a masked protease into the serum all we’d need is a gene duplication that is turned on in the pancreas’ “sister” organ. Simple, reasonable, and supported by the evidence.

Next, if the clotting cascade really evolved the way I have suggested, the the clotting enzymes would have to be near-duplicates of a pancreatic enzyme and of each other. As it turns out, they are. Not only is thrombin homologous to trypsin, a pancreatic serine protease, but the 5 clotting proteases (prothrombin and Factors X, IX, XI, and VII) share extensive homology as well. This is consistent, of course, with the notion that they were formed by gene duplication, just as suggested. But there is more to it than that. We could take one organism, humans for example, and construct a branching “tree” based on the relative degrees of similarity and difference between each of the five clotting proteases. Now, if the gene duplications that produced the clotting cascade occurred long ago in an ancestral vertebrate, we should be able to take any other vertebrate and construct a similar tree in which the relationships between the five clotting proteases match the relationships between the human proteases. This is a powerful test for our little scheme because it requires that sequences still undiscovered should match a particular pattern. And, as anyone knows who has followed the work in Doolittle’s lab over the years, it is also a test that evolution passes in one organism after another.

There are many other tests and predictions that can be imposed on the scheme as well, but one of the boldest was made by Doolittle himself more than a decade ago. If the modern fibrinogen gene really was recruited from a duplicated ancestral gene, one that had nothing to do with blood clotting, then we ought to be able to find a fibrinogen-like gene in an animal that does not possess the vertebrate clotting pathway. In other words, we ought to be able to find a non-clotting fibrinogen protein in an invertebrate. That’s a mighty bold prediction, because if it could not be found, it would cast Doolittle’s whole evolutionary scheme into doubt.

Not to worry. In 1990, Xun Yu and Doolittle won their own bet, finding a fibrinogen-like sequence in the sea cucumber, an echinoderm. The vertebrate fibrinogen gene, just like genes for the other proteins of the clotting sequence, was formed by the duplication and modification of pre-existing genes.

Now, it would not be fair, just because we have presented a realistic evolutionary scheme, supported by gene sequences from modern organisms, to suggest that we now know exactly how the clotting system has evolved. That would be making far too much of our limited ability to reconstruct the details of the past. But nonetheless, there is little doubt that we do know enough to develop a plausible and scientifically valid scenario for how it might have evolved. And that scenario makes specific predictions that can be tested and verified against the evidence.

That pesky science thing again. It does what the “intelligent design” advocates have thus far failed to do. The “ID” crowd makes a specific prediction (“Systems are too complex to have evolved, therefore they were ‘intelligently designed’ by a divine designer”), but offers no means to test it against evidence, and at that they offer no evidence, other than your wonderment at the nature of things.

The most egregious part of the NRO article Nathan quotes is this:

Of course, Darwinians have the right to believe in whatever they wish, but it is crucial to unveil that theirs is a subjective faith, not an objective truth, as they have been claiming for more than a century. This unveiling would mark a turning point in the history of Western civilization, by reconciling science and religion and letting people become intellectually fulfilled theists. Moreover, it would mark a turning point in the history of the world, by changing the meaning of “the West” and “Westernization” in the eyes of Muslims. They have been resisting the influx of godlessness from the West for a long time; they would be much less alarmed in the face of a redeemed West.

Phillip E. Johnson once said that the ID debate is about the question whether the U.S. is a nation under God or a nation under Darwin. We Muslims see the latter as a plague; we have no problem with the former. We might have disagreements, but we agree on the most fundamental truth of all — that there really is a God out there, and He is the One to Whom we owe our very life and existence.

Both of these bolded sentences are simply false. No serious scientist can claim that evolution — or any other scientific theory — is an absolute truth. Science makes predictions based on evidence and tests them, and uses the results to make further, refined predictions on future events — which can be tested when new evidence is gathered, and so forth. Evidence evolutionary biologists have is vast. Evidence “intelligent design” advocates have is minimal, if not zero.

Secondly, as to the notion of a conflict between God and science — there simply isn’t one, and evolutionary biologists do not seek to create one through their science. Steven Jay Gould, while reflecting on his trips to the Vatican:

The net of science covers the empirical universe: what is it made of (fact) and why does it work this way (theory). The net of religion extends over questions of moral meaning and value. These two magisteria do not overlap, nor do they encompass all inquiry (consider, for starters, the magisterium of art and the meaning of beauty). To cite the arch cliches, we get the age of rocks, and religion retains the rock of ages; we study how the heavens go, and they determine how to go to heaven.

There can be (or, rather, there should be) no conflict between evolution and “intelligent design”. The former is science. The latter is not.

MORE: Courtesy of the Commissar, links that specifically address the examples of bacterial flagellum and blood clotting. Also related is this piece at Thoughts from Kansas, Kansas’s favorite Leftie blog.

This entry was posted on Saturday, December 3rd, 2005 at 18:37 and is filed under science. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.