Science in Christian Perspective

MODES OF EXPLANATION IN BIOLOGY
V. ELVING ANDERSON*

From: JASA 16 (December 1964): 103-107.

I am impressed with your wisdom in choice of general theme for this symposium." The nature of explanation is a central problem in the sciences, although seldom recognized as such. Which of two explanations is a better one? This question infers some criteria for choice.

The problem is also a central issue in relating science with faith. One of the claims made for faith is that thereby one can have better answers (or explanations) than science is able to provide. Let us consider, for example, two different statements: (a) Now that science has produced a satisfactory explanation, it is no longer necessary to believe in God. (b) What science has found is merely a description not really an explanation. The failure of science to find a final explanation is, in fact, evidence that God must be operating here.

These claims are clearly incompatible if they are phrased in the same language. It is possible, however, that "explanation" is being used in different senses, and the statements may not really be in opposition. I shall try to show that the apparent conflict results from different understandings of "explanation". Furthermore, in my opinion, neither conclusion is justified.

The person in search of an explanation should be prepared to answer two questions:, (a) What is it you want explained? (b) What kind of explanation do you want? In the first question the general area of explanation is marked out. I am to limit myself to biology, but even this is a tremendous area. If I were to give each of you a chance to write one question, the variety in response would be great, representing different interests an d backgrounds. Furthermore, the questions we ask now are quite different from those we asked as children. There are some questions we never answer; we simply get over them.

But we must also consider what kind of explanation we wish. We have all had the experience of asking a

* Dr. V. Elving Amderson is Assistant Director, Dight Institute for Human Genetics, University of Minnesota and President of the American Scientific Affiliation.

** An address presented at the third biennial science symposium at Wheaton College, February, 1964.

question only to receive an answer in terms far too difficult for us, or far too simple. Thus the acceptability of an explanation involves personal choice. Braithwaite (1, p. 348) considers an explanation to be "an answer to a 'WhyT question which gives some intellectual satisfaction." An answer that gives partial or complete intellectual satisfaction to one person may give none whatever to another person at a different stage of intellectual development.

Now let me ask a simple biological question: Why does a cat purr? The question occurred to me as I watched the two cats in our house - one a pure Siamese female, the other a half-Siamese male. The Siamese female purrs only occasionally and then very quietly. The male purrs loudly at the slightest sign of attention. So I wondered, why does a cat purr anyway?

Your answer to this question might take the form: 

(a) Because it is contented, or

(b) In order to get further attention, to show you that he likes you. These are quite different explanations, and different answers would satisfy different persons. Furthermore any such answer is subject to further questions:

(c) What apparatus does the cat possess to make purring possible?

(d) What elicits purring? Is it intentional or not?

(e) What function does this behavior have?

(f) How did it all get started? Why are the genes maintained?

Braithwaite (1, p. 347) pointed out that: "At each stage of explanation a 'Why' question can significantly be asked of the explanatory hypotheses; there is no ultimate end to the hierarchy of scientific explanation, and thus no completely final explanation."

To some, this may come as a disappointment, or as evidence of some weakness in science. Would it not be more satisfactory as an explanation to answer that "God made cats that way." This is a perfectly acceptable statement concerning any natural phenomenon, but it is a different kind of answer. I would prefer to call it an "affirmation" rather than an "explanation." I would not wish to be given a choice but would prefer to have both affirmation and explanation.

Now let us try a more serious biological question. What is the cause of complex malformations in man? Perhaps the best known of these is mongolism, which involves defects in the brain, heart, skeletal system and other parts of the body. What can interfere with so many processes at once? Many speculations were proposed (such as fluorides in the drinking water or airplane trips by the mothers during pregnancy), but in 1959 the presence of an extra chromosome in affected children was discovered. This "explanation" produced a tremendous intellectual excitement and satisfaction among scientists. It was not long, however, before new questions became apparent, requiring explanation at a different level. What causes the error in germ cell formation that leads to the presence of the extra chromosome? How does the extra chromosome produce this particular set of malformations?

From this problem, let me shift to the complexity of life in general, particularly as seen in cells. After the development of the microscope revealed the cellular nature of living material, it was realized that the mystery of life must somehow reside in these cells. The living stuff that made up the cells was called protoplasm."

At this early period many scientists assumed that the phenomena of living matter could eventually be explained in terms of physical and chemical principles. Thus, protoplasm was described as the "physical basis of life." They did not claim to understand everything at that time, but insisted that in principle this description was possible.

To other scientists this approach seemed to be too simple, and too materialistic. These workers insisted that some other factor must be present in living material - a factor X, or entelechy, or elan vital. Probably many religious people followed this idea of vitalism, since it seemed to offer some room for God. The major difficulty was that such a life force was in principle considered not subject to investigation and therefore outside the scope of science.

It should be no surprise, therefore, that biologists were not particularly interested in forces they could not study, and the concept has fallen into disuse. Furthermore, the progress of biology has identified reasonable explanations for questions which the early vitalists insisted could be explained only by a vital force. In addition, it is my impression that vitalism is really foreign to a Christian doctrine of creation, even though it may superficially appear attractive. Does this exclude God? No, for our doctrine of creation must include the idea that all matter and energy spring from God and are held together by Him.

The vitalists did point up a problem, however. The explanation of the phenomena of life does require principles other than those currently available in physics and chemistry. George Gaylord Simpson has recently argued that biology is at the center of all science. "All known material processes and explanatory principles apply to organisms, while only a limited number of them apply to nonliving systems." (5, p. 87) The claim for the central role of biology may seem presumptuous, but the recognition of the complexity of living systems serves as an antidote to vitalism.

Simpson went on to identify three kinds or modes of explanation:

(a) The question "How?" - answered in terms of mechanism (reductionist explanation).

(b) The question "What for?" - answered by analysis of function (compositionist explanation).

(c) The question "How Come?" - answered by conoideration of history (historical explanation).

The first of these kinds of explanation involves the 'use of physical and chemical principles. The significance of this mode of explanation is apparent to anyone familiar with current biological research. Several decades ago it was relatively easy to identify a biology laboratory by the presence of microscopes and the smell of formaldehyde. But today many biologists use the techniques and tools of the physical sciences. It is not possible to identify the nature of a research project by a cursory glance through the laboratory door.

One implication of this fact is that college students anticipating graduate work in biology must be well trained in physics, chemistry, and mathematics. Preparation for graduate work should be more broadly based and more rigorous along these lines than the program usually suggested for premedical students. Some of the significant advances in recent years have not been made by biologists at all, but by persons trained in such fields as physical chemistry.

Perhaps the most striking breakthrough has come in the discovery of the DNA code. I wish to review some of the major points in this development to illustrate the value of physical and chemical principles in biological explanations.

For some years now we have realized that the growth of organisms depends upon three essential factors: raw materials, energy, and information. This may be compared with the growth of a building, requiring building materials, energy in the form of men or machines, and information contained in the blueprints.

Studies with electron microscopes have revealed a very complex internal architecture within cells. Enzymes are localized in small structures or on their surfaces. Energy is stored in the form of compounds with high energy chemical bonds. The building blocks of proteins are available as amino acids - 20 different kinds in all. How does the cell know how to put these amino acids together in the proper arrangement to form the many different products needed by the cell?

From other lines of evidence, it became clear that the necessary information is stored in the nucleus of the cell, more specifically in the chromosomes. Chemical studies of chromosomes showed them to be composed of proteins associated with a special type of compound, DNA. It was just over 10 years ago (in 1953) that Watson and Crick postulated that DNA is in the form of a long molecule shaped much like a spiral staircase, with the stair treads made of pairs of chemical bases. There are only four possible kinds of stair treads, but they can be arranged in many different combinations or sequences up the staircase.

With this model in mind, teams of scientists have now "cracked the DNA code." Let us suppose that we walk up one side of the staircase and find that each step has one of four letters of the alphabet. The first three spell CAT, the next three TAG, and the next set TTT. It is obvious that we have a sort of code. It turns out that each three-letter word stands for one of the amino acids. We then can find out the sequence of amino acids specified by the code.

This DNA code, of course, is inside the nucleus while the work of the cell takes place out in the cytoplasm. Copies of the DNA code are made in the form of ,'messenger RNA." These copies are then free to migrate to the cytoplasm where they are lined up on ribosomes. Amino acids are moved into proper position by transfer compounds (also RNA) which can read the code. Finally, the amino acids are joined together in this order by the formation of chemical bonds (and in this process energy is used).

Here then is a physico-chemical explanation of a fundamental process in living matter. What are some of the implications?

(a) Once the amino acids have been lined up in the proper order, the molecules of protein automatically fold into the three-dimensional structure characteristic of that particular protein. In a favorite parlor riddle we are asked how long it would take a group of monkeys pecking away at typewriters to produce one of Shakespeare's sonnets. It might be possible to calculate the probability for a sonnet, but we will be way off when it comes to organic molecules. Who would have guessed that a complex-shaped protein molecule has a probability of one, given a linear sequence of amino acids?

(b) It now appears likely that a given 3-letter code stands for the same amino acid in all forms of life, from viruses to man. The idea of such a universal code staggers one's imagination.

(c) Many mutations have been traced to a change in just one of the letters in the code, making possible a new approach in the study of mutations.

(d) In many organisms enzymes are not formed until they are needed. This type of adaptation can now be explained. Many of the genes in a cell are kept inactive by repressors. When a chemical enters a cell and makes a specific enzyme necessary, this new chemical removes the brake (or derepresses the gene) so that messenger RNA is formed and the enzyme produced.

In these, and many other ways, we are learning to explore the complex biochemical pathways and feedback systems within cells. We are deeply indebted to such explanations of the first type - answering the question "How?" in physico-chemical terms.

The success of molecular biology, however, is creating new tensions among biologists. Some argue that only this approach is true biology and that other methods are doomed to rapid extinction. Others strongly urge that many biological problems cannot possibly be studied by biochemical means, at least at present.

Therefore, let us turn to the second mode of explanation, which I have termed the analysis of function. Simpson would include here the adaptive usefulness of structures and processes, for the entire organism and for the species to which it belongs. Questions of ecological function would also be included.

By the end of the 19th century it had virtually become a dogma that a scientist must not ask "What for?" Such a question was considered meaningless or unanswerable in scientific terms.

The difficulty. however, is that "organisms are clearly adapted to live where and how they in fact live . . . In fact they plainly have the adaptations in order to live as they do. The question, then, is how these key words in order to are to be interpreted." (5, p. 86) These questions of purpose and purposiveness are included under the topic of teleology.

It has become traditional to insist that a scientist can have no truck with teleolog y, but this opinion conflicts
with the statement of Mayr (3, p. 1503) that "no dis cussion of causality is complete which does not come
to grips with the problem of teleology." And that of Simpson: (5, p. 86) "Many biologists threw out the
baby with the bath water. In seeking to get rid of nonscientific teleology they decided to throw out all
the quite real and scientific problems that teleology had attempted to solve."

One aspect of current thinking can be seen in the biologist's attitude toward structures for which no function is known. Formerly it was customary to dismiss such structures as "vestigial" - an historical explanation. It is now more common to say that the persistence of such an organ makes one suspect that it must have a function for the organism. There has been a recent breakthrough in study of the thymus, which is now known to be an essential for the formation of antibody-producing system6. The appendix in the rabbit is also essential for normal antibody-production. Early removal of the thymus in mice will prevent the development of leukemia.

How does one explain the actions of an animal that appear purposeful - a bird that starts its migration, an insect that selects its host plant, an animal that avoids a predator, a male that displays to a female? Mayr (3, pp. 1503-4) speaks of these as instances of "programmed behavior." This term makes more sense to us in this day of electronic computers. "The completely individualistic and yet also species-specific DNA code of every zygote (fertilized egg cell) . . . is the program for the behavior computer of this individual." Because the term teleology has so many other implications, the term teleanomic has been proposed to describe systems operating on the basis of such a programmed code of information.

The third mode of explanation in biology is historical. It is not enough to understand the present mechanism and function of any biological system. One must also ask: How come? This question is usually inappropriate concerning strictly physical phenomena, but in biology it is both appropriate and necessary.

The use of radioactive tracers illustrates one type of historical reasoning. It is possible to analyze the contents of a cell and determine how much biochemical turnover there has been. For example, certain compounds in the fluid part of the eye show an almost complete exchange in 80 minutes. When radioactive techniques are applied to dividing cells, we learn that the DNA molecule replicates by splitting the staircase down the middle of'the treads and forming new parts.

An awareness of future history is shown in our concern over the effects of radioactive fallout. We realize that extra mutations in our gonads will affect future generations - persons we may never see and won't have to like.

Turning to past history it is clear that natural selection has helped to determine the frequencies of different genes. Those gene patterns associated with a higher reproductive rate tend to become more common in the population. One of the best illustrations in man involves a type of hemoglobin called "sickle cell hemoglobin" or "Hemoglobin S.11 Persons with two genes for HbS have red blood cells that assume a sickle shape and result in a severe anemia. Few of these persons live to reproductive age. But sickle cell anemia in certain areas of Africa and the Mediterranean is too common for a disease with such a severe effect. Geneticists were puzzled until they found out that persons with only one gene for HbS were quite resistant to malaria. Thus the gene was favored by natural selection because of its advantage in carriers, even in spite of its harmful effect in those with a double dose of the gene.

A related problem -is that of "final cause," which began with Aristotle's classification of causes. I must confess that I do not understand the implications of this concept. Mayr (3, p. 1503) quotes a definition of "final cause" as "the cause responsible for the orderly reaching of a preconceived ultimate goal." I suspect that this refers to a goal-seeking tendency built into the universe which has controlled its development from the beginning to the present order. This sounds like a type of deism rather than a Biblical concept of God as creator. The ideas of writers such as Lecomte du Nuoy have been described as a type of "finalism." There is a great temptation for a Christian to buy such an idea because it appears to explain purpose.

There may be a great danger that in defending the concept of "final cause" we may be defending Aristotle rather than God's Word.

We have thus considered the general nature of explanation and the three major patterns of explanation in biology. It is important to realize that many arguments about the "cause" of a phenomenon result when the opponents are talking about different aspects of causation.

One illustration is seen in the book The Genesis Flood by Whitcomb and Morris (6). The authors consider the question as to how the animals were brought to the ark and as to how they could be cared for. They then suggest that God may have introduced at that time the phenomena of migration and hiberation. A migratory instinct may have directed the animals to flee from their native habitats to the place of safety. Then having entered the Ark, they received from God the power to become more or less dormant, thus simplifying the problem of survival in the Ark.

For our discussion today, we must note that a major part of the authors' argument is that "thus far . . . science has been utterly unable to explain (these powers), in spite of their great importance in animal physiology and ecology . . . One might even be justified in saying that the marvelous migratory instinct and the equally remarkable power of hibernation can only be explained teleologically. We do not deny that some truly physiological explanation of these capacities may some day be developed, although none is in sight as yet, but even this would only constitute a description of that which God Himself originally endowed." (6, pp. 73-74)

It is interesting to compare this discussion with that by Mayr. (3, pp. 1502-3) To the question "What is the cause of bird migration?" Mayr lists four. aan-swers: (a) Ecological cause. An insect eater must migrate. (b) Genetic cause. The bird has acquired a genetic constitution which induces it to respond appropriately to the proper stimuli from the environment - an illustration of programmed or teleonomic behavior. A screech owl lacks this constitution and fails to migrate. (c) Intrinsic physiological cause - photoperiodicity. The bird is ready to migrate as soon as the number of hours of daylight have dropped below a certain level. (d) Extrinsic physiological causes - a sudden drop in temperature on the night of the 25th of August.

Morris and Whitcomb claim that there are no scientific explanations for migration, while Mayr thinks there are. Clearly they are talking about different things. Even if migration had been introduced by God at the time of the flood, we still want to know what genes are involved in transmitting the ability through all intervening generations, and how these genes act to bring about this unique pattern of response to environmental changes.

In my opinion, it is not necessary or wise to base an argument for God upon the absence of scientific explanation. Our belief in God as creator is based upon the Scriptures, not upon what science has, or has not, discovered.

But there is another side to the same point. Biologists have no business basing a denial of God upon the presence of scientific explanation. Unfortunately some prominent scientists have yielded to this temptation.

Mayr: "If an organism is well adapted, if it shows superior fitness, this is not due to any purpose of its ancestors or of an outside agency, such as 'Nature' or 'God' who created a superior design or plan." (3, p. 1504).

Huxley: "In the evolutionary pattern of thought there is no longer either need or room for the supernatural." (2, p. 252).

Simpson: "There has been disagreement and indeed confusion through the ages regarding to whom and for what man is responsible. The lower and higher superstitions have produced their several answers. In the post-Darwinian world another answer seems fairly clear: man is responsible to himself and for himself." (4, pp. 973-4).

In these statements our attention is turned toward the nature of man. It should be clear that the three modes of explanation do apply to man. In fact, a major part of my professional career is devoted toward understanding the biological explanations of man in terms of mechanism (physics and chemistry), function, and history. But I still hold that these do not fully describe man's nature. As a Christian, I hold to the affirmation that man was created with the ability to respond to God. I call this an affirmation since it is not based upon empirical data, but is an article of faith.

In summary, I have tried to point out that scientific explanations occur in layers and are never exhaustive. Explanations in biology may be grouped into three major categories. As a Christian I am committed to a Biblical view of creation, but not to vitalism or finalism. My faith does not rest on the presence or absence of scientific explanations. Realization of these essential points should clarify our witness to informed persons.

1. Braithwaite, Richard Bevan. 1953. Scientific Explanation. Harper Torchbook edition, published 1960.

2. Huxley, Sir Julian. 1960. The evolutionary vision. Pp 249-261 in Evolution After Darwin. Vol. 111. Issues in Evolution, ed. by Sol. Tax., Chicago: University of Chicago Press.

3. Mayr, Ernst. 1961. Cause and effect in biology. Science 134: 1501-1506.

4. Simpson, George Gaylord. 1960. The world into which Dar. win led us. Science 131:966-974.

5. Simpson, George Gaylord. 1963. Biology and the nature of science. Science 139:81-88.

6. Whitcomb, John C., Jr., and Morris, Henry M. 1962. The Genesis Flood: The Biblical Record and Its Scientific Implications. Philadelphia: The Presbyterian and Reformed Publishing Company.