Tuesday, September 13, 2005

Pierre Grasse and the `irreducible complexity' of the blood-clotting cascade

I was reading the book "Evolution of Living Organisms" (1977) by "the [late] great French zoologist Pierre-Paul Grasse" (Gould S.J., "An Urchin in the Storm," 1987, p.234), "who for thirty years, held the chair for evolution at the Sorbonne" (Koestler A., "Janus," 1983, p.177), and of whom his opponent Dobzhansky wrote:
"Now, one can disagree with Grasse but not ignore him, he is the most distinguished of French zoologists, the editor of the 28 volumes of `Traite de Zoologie', author of numerous original investigations and ex-president of the Academie des Sciences. His knowledge of the living world is encyclopedic ...." (Dobzhansky T.G., "Darwinian or `Oriented' Evolution?" Review of Grasse P.-P., "L'Evolution du Vivant," Editions Albin Michel: Paris, 1973, in "Evolution," Vol. 29, June 1975, pp.376-378, p.376).
when I found this:
"Take, for example, regulation of the coagulation of blood, a highly complex phenomenon to which biologists seem to have given little thought. Its normal cause is the opening of a vein, artery, or capillaries; the blood brought into contact with the lip of the wound (damaged tissues) becomes the site of chain reactions ending in the formation of a clot. This is only possible because there preexist in the blood reaction agents or their precursors whose end effect is to coagulate certain proteins of the blood plasma. The organism, ready for all eventualities, bears within itself in the latent state its own protective system. Genes control the elaboration of coagulants, proteins, and enzymes. Such a process forms a single whole; a lack of a substance arises, an enzyme is affected, and the system will not work. One does not see how it can have been formed by successive chance effects supplying a protein or an enzyme in any random order. Besides, we know that the effects of mutations on the system are disastrous and form the lengthiest chapter in blood pathology. The system has become functional only when all its components have come together and adjusted themselves to one another. The Darwinian hypothesis compels us to postulate a preparatory period during which selection acts upon something that does not, physiologically speaking, yet exist. Under the necessary conditions of the postulate, the action can only have been prophetic!" (Grasse P.-P., "Evolution of Living Organisms: Evidence for a New Theory of Transformation," [1973], Academic Press: New York NY, 1977, p.152. Emphasis original).
That is, Grasse, in 1973, nominated the vertebrate blood-clotting cascade, as effectively `irreducibly complex'. Here is what Grasse wrote again: "regulation of the coagulation of blood [is] ... a highly complex phenomenon ... [Upon] the opening of a vein, artery, or capillaries; the blood brought into contact with the lip of the wound ... becomes the site of chain reactions ending in the formation of a clot. ... Such a process forms a single whole; a lack of a substance [or] an enzyme ... and the system will not work ... The system has become functional only when all its components have come together and adjusted themselves to one another." (Grasse's emphasis). Grasse points out that it cannot "have been formed by successive chance effects supplying a protein or an enzyme in any random order", i.e. the natural selection of random (unguided) mutations, because "the effects of mutations on the system are disastrous."

This is of course what Mike Behe claimed in his "Darwin's Black Box" (1996), that the (vertebrate) blood-clotting system was irreducibly complex, i.e. it was a "complex organ [or structure] ... which could not possibly [i.e. plausibly] have been formed by numerous, successive, slight modifications":
"Darwin knew that his theory of gradual evolution by natural selection carried a heavy burden:
`If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down.' [Darwin C., 1872, "Origin of Species," 6th ed., 1988, New York University Press: New York, p.154].
It is safe to say that most of the scientific skepticism about Darwinism in the past century has centered on this requirement. From Mivart's concern over the incipient stages of new structures to Margulis's dismissal of gradual evolution, critics of Darwin have suspected that his criterion of failure had been met. But how can we be confident? What type of biological system could not be formed by `numerous, successive, slight modifications'? Well, for starters, a system that is irreducibly complex. By irreducibly complex, I mean a single system composed of several well-matched, interacting parts that contribute to the basic function, wherein the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional. An irreducibly complex biological system, if there is such a thing, would be a powerful challenge to Darwinian evolution. Since natural selection can only choose systems that are already working then if a biological system cannot be produced gradually it would have to arise as an integrated unit, in one fell swoop, for natural selection to have anything to act on." (Behe M.J., "Darwin's Black Box: The Biochemical Challenge to Evolution," Free Press: New York NY, 1996, p.38. Emphasis original).
I emailed Prof. Behe and asked him whether he had seen the above quote by Pierre Grasse on the blood clotting cascade. He replied (with permission to quote him here), "No, I had never seen that before. It's nice to see that an eminent biologist recognized and wrote about the problem."

Here is Prof. Behe's evidence and argument in "Darwin's Black Box" that the blood clotting system (see tagline for his detailed description of it) is irreducibly complex:
"Blood behaves in a peculiar way. When a container of liquid like a carton of milk, or a tank truck filled with gasoline-springs a leak, the fluid drains out. The rate of flow can depend on the thickness of the liquid (for example, maple syrup will leak more slowly than alcohol, but eventually it all comes out. No active process resists it. In contrast, when a person suffers a cut it ordinarily bleeds for only a short time before a clot stops the flow; the clot eventually hardens, and the cut heals over. Blood clot formation seems so familiar to us that most people don't give it much thought. Biochemical investigation, however, has shown that blood clotting is a very complex, intricately woven system consisting of a score of interdependent protein parts. The absence of, or significant defects in, any one of a number of the components causes the system to fail: blood does not clot at the proper time or at the proper place. ... Blood clotting ... requires extreme precision. When a pressurized blood circulation system is punctured, a clot must form quickly or the animal will bleed to death. If blood congeals at the wrong time or place, though, then the clot may block circulation as it does in heart attacks and strokes. Furthermore, a clot has to stop bleeding all along the length of the cut, sealing it completely. Yet blood clotting must be confined to the cut or the entire blood system of the animal might solidify, killing it. Consequently, the clotting of blood must be tightly controlled so that the clot forms only when and where it is required ... the blood-clotting system fits the definition of irreducible complexity. That is, it is a single system composed of several interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system effectively to cease functioning. The function of the blood clotting system is to form a solid barrier at the right time and place that is able to stop blood flow out of an injured vessel. The components of the system ... are fibrinogen, prothrombin, Stuart factor, and proaccelerin. ... none of the cascade proteins are used for anything except controlling the formation of a blood clot. Yet in the absence of any one of the components, blood does not clot, and the system fails. There are other ways to stop blood flow from wounds, but those ways are not step-by-step precursors to the clotting cascade. For example, the body can constrict blood vessels near a cut to help stanch blood flow. Also, blood cells called platelets stick to the area around a cut, helping to plug small wounds. But those systems cannot be transformed gradually into the blood-clotting system any more than a glue trap can be transformed into a mechanical mousetrap. The simplest blood-clotting system imaginable might be just a single protein that randomly aggregated when the organism was cut. ... [but] the simplistic clotting system would be triggered inappropriately, causing random damage and wasting resources. ... [It] is not the final activity ... clot formation ... that is the problem-rather, it is the control system. One could imagine a blood-clotting system that was somewhat simpler than the real one-where, say, Stuart factor, after activation by the rest of the cascade, directly cuts fibrinogen to form fibrin, bypassing thrombin. Leaving aside for the moment issues of control and timing of clot formation, upon reflection we can quickly see that even such a slightly simplified system cannot change gradually into the more complex, intact system. If a new protein were inserted into the thrombin-less system it would either tum the system on immediately-resulting in rapid death-or it would do nothing, and so have no reason to be selected. Because of the nature of a cascade, a new protein would immediately have to be regulated From the beginning, a new step in the cascade would require both a proenzyme and also an activating enzyme to switch on the proenzyme at the correct time and place. Since each step necessarily requires several parts, not only is the entire blood-clotting system irreducibly complex, but so is each step in the pathway." (Behe M.J., "Darwin's Black Box: The Biochemical Challenge to Evolution," Free Press: New York NY, 1996, pp.78-79, 86-87).
Now this is an example of `great minds think alike.' Remember that Grasse wrote: "The system has become functional only when all its components have come together and adjusted themselves to one another. The Darwinian hypothesis compels us to postulate a preparatory period during which selection acts upon something that does not, physiologically speaking, yet exist. Under the necessary conditions of the postulate, the action can only have been prophetic!" Behe wrote (unaware of Grasse), after reviewing the explanation by Prof. Russell F. Doolittle, a world authority on the blood clotting system, "natural selection, the engine of Darwinian evolution, only works if there is something to select-something that is useful right now, not in the future":
"Yet the objections raised so far are not the most serious. The most serious, and perhaps the most obvious, concerns irreducible complexity. I emphasize that natural selection, the engine of Darwinian evolution, only works if there is something to select-something that is useful right now, not in the future. Even if we accept his scenario for purposes of discussion, however, by Doolittle's own account no blood clotting appears until at least the third step. The formation of tissue factor at the first step is unexplained, since it would then be sitting around with nothing to do. In the next step (prothrombin popping up already endowed with the ability to bind tissue factor, which somehow activates it) the poor proto prothrombin would also be twiddling its thumbs with nothing to do until, at last, a hypothetical thrombin receptor appears at the third step and fibrinogen falls from heaven at step four. Plasminogen appears in one step, but its activator (TPA) doesn't appear until two steps later. Stuart factor is introduced in one step, but whiles away its time doing nothing until its activator (proconvertin) appears in the next step and somehow tissue factor decides that this is the complex it wants to bind. Virtually every step of the suggested pathway faces similar problems. Simple words like `the activator doesn't appear until two steps later' may not seem impressive until you ponder the implications. Since two proteins-the proenzyme and its activator-are both required for one step in the pathway, then the odds of getting both the proteins together are roughly the square of the odds of getting one protein. We calculated the odds of getting TPA alone to be one-tenth to the eighteenth power; the odds of getting TPA and its activator together would be about one-tenth to the thirty-sixth power! That is a horrendously large number. Such an event would not be expected to happen even if the universe's ten-billion year life were compressed into a single second and relived every second for ten billion years. But the situation is actually much worse: if a protein appeared in one step 10 with nothing to do, then mutation and natural selection would tend to eliminate it. Since it is doing nothing critical, its loss would not be detrimental, and production of the gene and protein would cost energy that other animals aren't spending. So producing the useless protein would, at least to some marginal degree, be detrimental. Darwin's mechanism of natural selection would actually hinder the formation of irreducibly complex systems such as the clotting cascade. ... The bottom line is that clusters of proteins have to be inserted all at once into the cascade. This can be done only by postulating a `hopeful monster' who luckily gets all of the proteins at once, or by the guidance of an intelligent agent." (Behe M.J., "Darwin's Black Box: The Biochemical Challenge to Evolution," Free Press: New York NY, 1996, pp.95-96. Emphasis original)
The fact that one of the world's greatest biologists, the late Pierre Grasse, in 1973 wrote of the problem for a Darwinian, `blind watchmaker,' step-by-tiny-step, natural selection of random mutations, origin of the vertebrate blood clotting cascade, which Mike Behe again independently discovered and wrote about in 1996, shows that ID's irreducible complexity argument is: 1) science (and therefore so is ID); and 2) has demonstrated the existence of a "complex [system] ...which could not possibly [i.e. plausibly] have been formed by numerous, successive, slight modifications," and so Darwin's theory has absolutely broken down!

Stephen E. Jones, BSc (Biol).
"Problems of Evolution"


"About 2 to 3 percent of the protein in blood plasma (the part that's left after the red blood cells are removed) consists of a protein complex called fibrinogen. ... [which] makes `fibers' that form the clot. Yet fibrinogen is only the potential clot material. .... Almost all of the other proteins involved in blood clotting control the timing and placement of the clot. ... Fibrinogen is a composite of six protein chains, containing twin pairs of three different proteins. Electron microscopy has shown that fibrinogen is a rod-shaped molecule, with two round bumps on each end of the rod and a single round bump in the middle. So fibrinogen resembles a set of barbells with an extra set of weights in the middle of the bar. Normally fibrinogen is dissolved in plasma, like salt is dissolved in ocean water. It floats around, peacefully minding its own business, until a cut or injury causes bleeding. Then another protein, called thrombin, slices off several small pieces from two of the three pairs of protein chains in fibrinogen. The trimmed protein-now called fibrin-has sticky patches exposed on its surface that had been covered by the pieces that were cut off. The sticky patches are precisely complementary to portions of other fibrin molecules. The complementary shapes allow large numbers of fibrins to aggregate with each other ... Because of the shape of the fibrin molecule, long threads form, cross over each other, and (much as a fisherman's net traps fish) make a pretty protein meshwork that entraps blood cells. This is the initial clot (Figure 4-2). The meshwork covers a large area with a minimum of protein; if it simply formed a lump, much more protein would be required to clog up an area. Thrombin, which cuts off the pieces from fibrinogen, is like [a] saw ... thrombin sets in motion the final step of a controlled process. ... if the only proteins involved in blood coagulation were thrombin and fibrinogen, the process would be uncontrolled. Thrombin would quickly clip all of the fibrinogen to make fibrin; a massive clot would form throughout the animal's circulatory system, solidifying it. ... animals would rapidly perish. To avoid such an unhappy ending an organism must control the activity of thrombin. ... The body commonly stores enzymes (proteins that catalyze a chemical reaction. like the cleavage of fibrinogen) in an inactive form for later use. The inactive forms are called proenzymes. When a signal is received that a certain enzyme is needed, the corresponding proenzyme is activated to give the mature enzyme. As with the conversion of fibrinogen to fibrin, proenzymes are often activated by cutting off a piece of the proenzyme that is blocking a critical area. ... Thrombin initially exists as the inactive form, prothrombin. Because it is inactive, prothrombin can't cleave fibrinogen, and the animal is saved from death by massive, inappropriate clotting. Still, the dilemma of control remains. ... If fibrinogen and prothrombin were the only proteins in the blood-clotting pathway, again our animal would be in bad shape. When the animal was cut, prothrombin would just float helplessly by the fibrinogen as the animal bled to death. Because prothrombin cannot cleave fibrinogen to fibrin, something is needed to activate prothrombin. ... the blood-clotting system is called a cascade-a system where one component activates another component, which activates a third component, and so on. ... Figure 4-3. A protein called Stuart factor cleaves prothrombin, turning it into active thrombin that can then cleave fibrinogen to fibrin to form the blood clot. Unfortunately, as you may have guessed, if Stuart factor, prothrombin, and fibrinogen were the only blood-clotting proteins, then Stuart factor would rapidly trigger the cascade, congealing all localize, or remove blood clots. the blood of the organism so Stuart factor also exists in an inactive form that must first be activated. At this point there's a little twist to our developing chicken-and-egg scenario. Even activated Stuart factor can't turn on prothrombin. Stuart factor and prothrombin can be mixed in a test tube for longer than it would take a large animal to bleed to death without any noticeable production of thrombin. It turns out that another protein, called accelerin, is needed to increase the activity of Stuart factor. The dynamic duo-accelerin and activated Stuart factor- cleave prothrombin fast enough to do the bleeding animal some good so in this step we need two separate proteins to activate one proenzyme. Yes, accelerin also initially exists in an inactive form, called proaccelerin .... And what activates it? Thrombin! But thrombin, as we have seen, is further down the regulatory cascade than proaccelerin. So thrombin regulating the production of accelerin is like having the granddaughter regulate production of the grandmother Nonetheless, due to a very low rate of cleavage of prothrombin by Stuart factor, it seems there is always a trace of thrombin in the bloodstream Blood clotting is therefore auto-catalytic, because proteins in the cascade accelerate the production of more of the same proteins. We need to back up a little at this point because, as it turns out prothrombin as it is initially made by the can't be transformed into thrombin, even in the presence of activated Stuart factor and accelerin. Prothrombin must first be modified ... by having ten specific amino acid residues, called glutamate (Glu) residues, changed to y-carboxyglutamate (Gla) residues. The modification can be compared to placing a lower jaw onto the upper jaw of a skull. The completed structure can bite and hang on to the bitten object; without the lower jaw, the skull couldn't hang on. In the case of prothrombin, Gla residues `bite' (or bind) calcium, allowing prothrombin to stick to the surfaces of cells. Only the intact, modified calcium-prothrombin complex, bound to a cell membrane, can be cleaved by activated Stuart factor and accelerin to give thrombin. The modification of prothrombin does not happen by accident. Like virtually all biochemical reactions, it requires catalysis by a specific enzyme. In addition to the enzyme, however, the conversion of Glu to Gla needs another component: vitamin K. Vitamin K is not a protein; rather, it is a small molecule ... Like a gun that needs bullets, the enzyme that changes Glu to Gla needs vitamin K to work ... now we have to go back and ask what activates Stuart factor. It turns out that it can be activated by two different routes, called the intrinsic and the extrinsic pathways. In the intrinsic pathway, all the proteins required for clotting are contained in the blood plasma; in the extrinsic pathway, some clotting proteins occur on cells. Let's first examine the intrinsic pathway. ... When an animal is cut, a protein called Hageman factor sticks to the surface of cells near the wound. Bound Hageman factor is then cleaved by a protein called HMK to yield activated Hageman factor. Immediately the activated Hageman factor converts another protein, called prekallikrein, to its active form, kallikrein. Kallikrein helps HMK speed up the conversion of more Hageman factor to its active forms. Activated Hageman factor and HMK then together transform another protein, called PTA, to its active forms. Activated PTA in turn, together with the activated form of another protein (discussed below) called convertin, switch a protein called Christmas factor to its active form. Finally, activated Christmas factor, together with antihemophilic factor (which is itself activated by thrombin in a manner similar to that of proaccelerin) changes Stuart factor to its active forms. Like the intrinsic pathway, the extrinsic pathway is also a cascade. The extrinsic pathway begins when a protein called proconvertin is turned into convertin by activated Hageman factor and thrombin. In the presence of another protein, tissue factor, convertin changes Stuart factor to its active form. Tissue factor, however, only appears on the outside of cells that are usually not in contact with blood. Therefore, only when an injury brings tissue into contact with blood will the extrinsic pathway be initiated. (A cut ... is the initiating event- something outside of the cascade mechanism itself) The intrinsic and extrinsic pathways cross over at several points. Hageman factor, activated by the intrinsic pathway, can switch on proconvertin of the extrinsic pathway. Convertin can then feed back into the intrinsic pathway to help activated PTA activate Christmas factor. Thrombin itself can trigger both branches of the clotting cascade by activating antihemophilic factor, which is required to help activated Christmas factor in the conversion of Stuart factor to its active form, and also by activating proconvertin. ... Once clotting has begun, what stops it from continuing until all the blood in the animal has solidified? Clotting is confined to the site of injury in several ways. ... First, a plasma protein called antithrombin binds to the active (but not the inactive) forms of most clotting proteins and inactivates them. Antithrombin is itself relatively inactive, however, unless it binds to a substance called heparin. Heparin occurs inside cells and undamaged blood vessels. A second way in which clots are localized is through the action of protein C. After activation by thrombin, protein C destroys accelerin and activated antihemophilic factor. Finally, a protein called thrombomodulin lines the surfaces of the cells on the inside of blood vessels. Thrombomodulin binds thrombin, making it less able to cut fibrinogen and simultaneously increasing its ability to activate protein C. When a clot initially forms, it is quite fragile: if the injured area is bumped the clot can easily be disrupted, and bleeding starts again. To prevent this, the body has a method to strengthen a clot once it has formed. Aggregated fibrin is "tied together" by an activated protein called FSF (for `fibrin stabilizing factor'), which forms chemical cross-links between different fibrin molecules. Eventually, however, the blood clot must be removed after wound healing has progressed. A protein called plasmin acts as a scissors specifically to cut up fibrin clots. Fortunately, plasmin does not work on fibrinogen. Plasmin cannot act too quickly, however, or the wound wouldn't have sufficient time to heal completely. It therefore occurs initially in an inactive form called plasminogen. Conversion of plasminogen to plasmin is catalyzed by a protein called t-PA. There are also other proteins that control clot dissolution, including α2-antiplasmin, which binds to plasmin, preventing it from destroying fibrin clots." (Behe M.J., "Darwin's Black Box: The Biochemical Challenge to Evolution," Free Press: New York NY, 1996, pp.79-85, 87-88)

7 comments:

Tim (Random Observations) said...

I know this is an old article, but I'd be interested to see how you'd respond to this. Just curious, and thanks regardless.

Stephen E. Jones said...

Tim

>I know this is an old article, but I'd be interested to see how you'd respond to this. Just curious, and thanks regardless.

Thanks, but it always has been a point of principle with me not to respond to requests that I check out a URL and then respond to that URL.

One reason is that it is not always apparent to me what is the specific point that I am expected to address.

So, if you have a comment to make, then make it in your own words, i.e. don't just quote the contents of the URL, and will respond to your comment.

Stephen

Kevin Eubanks said...

I'm an English teacher in Texas, but I deal with the Intelligent Design issue in my courses. This week, I had a student write an essay in support of Behe's argument that the blood clotting system is irreducibly complex. In trying to respond to her essay, I got stuck on one issue. If Behe believes in common descent, how does he explain the transition from a more "primitive" blood-clotting system (such as that of jawless fish) to the current one in humans? If, at some point in the past, the ancestor of humans had a different blood-clotting system, were the increasingly complex systems designed separately?

From personal experience, I know how busy you must be! But any help you could offer would be greatly appreciated.

Stephen E. Jones said...

Kevin

>If Behe believes in common descent, how does he explain the transition from a more "primitive" blood-clotting system (such as that of jawless fish) to the current one in humans?

Thanks for your comment and apologies for the delay in replying, due in part to my having gone back to university to become a biology teacher). The other part was that our daughter gave birth to our first grand-daughter this week!

I have decided to respond to your question via a separate blog post, which should be today. I will give the URL of it below when I have posted it.

Stephen E. Jones
May 10, 2009

Stephen E. Jones said...

Kevin

I have posted my reply to your question about Behe at:

Re: If Behe believes in common descent, how does he explain the transition from a more "primitive" blood-clotting system? .

Stephen E. Jones
May 10, 2009.

Kevin Eubanks said...

Thank you for your detailed reply to my previous post. I have had these questions for quite some time, but I have never been able to find help answering them until now.

I hate to try your patience even further, but your response raised another long-standing question of mine. I know that some people accept common descent, but reject natural selection. I’m not sure I understand how the former would work without the latter. In the rise of humans, for example, would a pair of non-human animals give birth to a human child? If so, how would that human child produce human offspring?

Please forgive my ignorance! And if you’re too busy to answer these kinds of questions, could you recommend a place to look for answers?

Thanks again,
Kevin

Stephen E. Jones said...

Kevin

>I know that some people accept common descent, but reject natural selection. I’m not sure I understand how the former would work without the latter.

Thanks again for your question. I will also answer it in a separate blog post.

Stephen E. Jones