Control Systems and Evolution

THE ARGUMENT about the most plausible explanation for the origin of plants and animals on this planet is difficult to win. The idea of Creation can receive only indirect support from scientific evidence, because the creative acts were supernatural events and therefore lie outside the realm of science. And although most scientists would agree about the high improbability that natural processes can account for the intricacies of plant and animal life, it is hard for them to exclude the evolutionary postulate completely.

However, the picture changes when we consider the "control systems" that have been provided at all levels of function in animals and plants. The huge range of automatic devices designed for such tasks as saving fuel, detecting poisons, and avoiding production bottlenecks is most difficult to account for by the theory of natural selection. At the same time these contrivances suggest more strongly than anything else that the characteristics of plants and animals were designed at one time and not added piece by piece. It is in focusing on automatic control devices that the evolutionary mechanism appears most improbable, perhaps actually impossible.

Control of Enzyme Synthesis

The most remarkable examples and the most difficult to explain are the switching mechanisms found within the single cell. Between 1950 and 1960 biochemists came to appreciate the relation ship between the enzymes responsible for the chemical activity of cells and the genes responsible for the enzymes. To each enzyme there corresponds a specific section of DNA somewhere along the length of one of the chromosomes of the cell. Along the length of this section is written in a chemical code the specification for the construction of the enzyme. What was not initially appreciated was that there also exist many lengths of DNA in the chromosomes that are concerned, not with instructions for building enzymes ("structural genes"), but with controlling the assembly of enzymes so that they are produced only when they can actually benefit the cell.

The first example of a "control gene" to be discovered was found in a species of bacterium that in habits the human alimentary tract and is known as Escherichia coli. E. coli is capable of surviving under very stringent conditions, taking advantage of whatever foodstuff happens to be available. To facilitate this survival, it has available a range of enzymes to help it "digest" the kinds of food it happens to come in contact with and, accordingly, it possesses genes enabling it to produce these enzymes.

E. coli possesses only one chromosome and has genes for only about 3,000 enzymes, which is why it is so convenient to study. (The fact that the specifications for 3,000 separate proteins, each with an average of 400 amino acids in precise sequence, can be called "convenient" gives a hint of what may be expected in more complex cells!) Quoting the number of 3,000 makes it clear why control of synthesis of the enzymes is necessary. Enzyme synthesis is so efficient that the cell would quickly burst if this process were not checked.

One set of E. coli genes contains the code for a set of enzymes required for the breakdown of lactose, often called milk sugar. Although a relatively uncommon nutrient, lactose is sometimes used by the bacteria, and this special set of enzymes is therefore held in readiness. However, the cell never bothers to synthesize these enzymes from the instructions available in the genes until the genes are switched on, and this does not occur unless lactose is actually available to the cell as a foodstuff. (See Fig. 1.)

The switch mechanism works like this. 1 All the genes required for production of the lactose-split ting enzymes are clustered in one part of the bacterial chromosome, and in that same location there are two additional lengths of DNA. One of these contains instructions that enable the cell to construct a substance known as "represser," which is of such a design as to attach itself specifically to the other length of chromosome located just ahead of the three lactose genes. Whenever "represser" is in position in that location it prevents the DNA code for the three enzymes from being decoded and the enzymes synthesized.

But if the cells are growing in a medium that contains lactose, the lactose molecules are occasionally transported through the membrane of the cell and metabolized, and one of the products attaches itself to "represser," which is specially shaped to permit this attachment. When this attachment is made "represser" is no longer able to attach itself to the DNA, the "roadblock" is removed, and normal transcription and translation of the code and synthesis of the enzymes proceed. ²

It is no simple matter to design a protein such as "represser," capable of being tightly bound to two very different substances, one of which prevents the other one from being bound, but not vice versa. Apparently it is worthwhile for the cell to go to this trouble, in spite of the fact that represser molecules are large and complicated proteins with no function other than regulation. Many other enzyme systems are regulated in the same way, and chaotic over production in the cell is avoided. The device is very efficient. In E. coli the lactose-splitting enzymes are 1,000 times scarcer when the genes are repressed than when lactose is present and their synthesis is switched on.

In the case of the enzymes required to synthesize histidine the problem is rather different. Histidine is an amino acid required for the synthesis of enzymes (including the enzymes required for the synthesis of histidine!), and no bacterium can ever be sure that it will not have to manufacture it for itself hence the existence of a set of nine enzymes that convert a readily available substance to histidine in eleven steps (two of the enzymes are used twice over). On the other hand, it is costly to manufacture such a large packet of complicated proteins if histidine is already available in the diet, so a mechanism exists to switch the whole synthetic process off.

What the Regulation of Enzyme Synthesis Implies

There are three problems for any naturalistic theory of origins that are exposed by enzyme-synthesis control systems. The first problem occurs whenever the word enzyme is used. It occurs because of their ability to perform one particular task with high efficiency in biochemical terms, their specificity. A protein produced by regulatory genes can:

1. assume a stable, folded structure and, in some cases, build itself to correct size by attaching to other identical proteins to form an "oligomer" (literally, a small segment);

2. adhere specifically to the section of chromosome just ahead of the appropriate structural genes it is designed to regulate; and

3. link with an inducer molecule in such a way as to disrupt its attachment to the operator site.

This is evidence of high precision in their design, something difficult to imagine as the result of random mutation in previously existing proteins with completely different functions. In the "lac operon" (Fig. 1) the represser protein is able to recognize and bind a specific section of DNA only 0.001 percent of the total length of the chromosome, do it efficiently, and never choose the wrong site.

Evolution by natural selection implies that each mutation produced an advantage to the species sufficient to ensure that other organisms without it would die out. With such precise design it is clear that large numbers of mutations would be required before the required sequence of amino acids could be achieved. It is unthinkable that each intermediate mutational step could be accompanied by the required advantage to make natural selection possible.

The other problems pinpointed by represser proteins are in a slightly different category. They concern (1) the positioning of the genes on the chromosome and, (2) the fact that the binding of a "represser" to the operator site is prevented by the molecule whose presence or absence is the reason for the regulation, such as lactose or histidine.

In the first case, there is the difficulty of accounting for the presence of the structural genes in adjacent positions immediately following the operator site. Since the repression of synthesis depends on stopping the cell's decoding machine as it moves along the chromosome, it is vital that the operator site be located precisely at the head of the structural genes and that they be all located together.

However it is exceedingly difficult to contemplate how they could migrate from some other part of the chromosome (where they were produced randomly), and even harder to see how they could have been randomly produced all in the same place. One possible way to solve the problem has been suggested but rejected because the evidence is against it. ¹ With as many as nine genes, as in the histidine case, the probability of such events' occurring by random processes is infinitesimal.

The dual binding ability of a represser molecule poses what might be called a "logical problem" for evolutionary explanations of origins.

The advantage of developing a represser (presuming, among other things, that the structural genes are already aligned and ready to be repressed) depends on the represser's ability to bind both the effector (e.g., lactose) and the operator site. But developing a represser by natural selection would be a long job. To produce a protein as large, as accurate in its recognition of the correct operator site, and as effective in its binding would require many hundreds of mutational steps, taking at the very least, thousands of generations.

The advantage of having a re presser to bind to the operator site applies only if the inducer molecule is absent during this time, which it cannot be, because it must be present to confer the other half of the advantage "switching-on." If only half of the advantage is sought, then a represser is not needed at all! Either leave the structural genes to be continuously synthesized or delete them altogether. But to develop the advantage or a control system gradually it is necessary for lactose (or histidine, et cetera) to be simultaneously present and absent!

Control of Enzyme Activity

Many enzyme systems avoid the "too-much-of-a-good-thing" problem by using the "negative feedback" idea utilized in the ballcock commonly used in water cisterns and reservoirs. As the water rises to the level specified the floating ball gradually closes the cock. Likewise, rising concentrations of enzyme products (such as the amino acid isoleucine, produced by an important chain of enzymes in many organisms) permit them to be caught and bound by one of the enzymes, usually the first in the chain. This enzyme is designed so that any attachment of the end product prevents the normal enzyme function from being carried out, and the production line stops until the excess supply of the product is used up.

More ingenious still are the control systems designed to keep up supplies of a product used by the cell for several distinct purposes. Here there are provided several distinct enzymes (called isoenzymes) capable of producing the same product, but each designed to be inhibited by a different end product, so that excess of one of them switches off only a part of the production line and does not close it down completely!

Another method of control is the use of some appropriate sub stance to activate the enzyme when it is needed, otherwise leaving it in "mothballs." One example of this method is the use of glucose phosphate to stimulate the final enzyme involved in the conversion of glucose (blood sugar) to glycogen (the form in which excess carbohydrate is commonly stored in the human body). Even if these systems do not generate the logical paradox in as acute a form as happens with suggestions of an evolutionary origin for represser proteins, they still confront that hypothesis with the obstacle of explaining how the development of a "switched-off" enzyme could ever be beneficial to the cell.

The list of regulatory devices is long, but all parts of it tell the same story that living cells were designed and produced as going concerns. Modification and diversification by natural selection has certainly operated in the plant and animal kingdoms ever since their creation, but the conclusion that there was originally a Creation is hard to escape. The complex interlocking of the molecular mechanisms inside cells and the calm strategy with which they are regulated are among the clearest evidences of divine design to be found anywhere in nature.