Science and Religion: Fetal Circulation—Design or Happenstance?

A look at the complex system involved provides a basis for evaluation.

M. E. Clark is professor of theoretical and applied mechanics and bioengineering in the College of Engineering, University of Illinois at Urbana-Champaign, Illinois.


The word design indicates "deliberate, purposive planning" by a person or group. In all facets of life we see evidence of design that we readily ac knowledge as coming from the mind and hand of a designer. No one looks at the intricacies of a watch, an engine, or an airplane and says, "What a fortunate happenstance!" Yet when we leave the realm of manufactured articles to con template living things, the tune changes.

Although the simplest living entity is in finitely more complex than any manufactured item, the evolutionist tells us that it exists not by "creative design" but rather by "fortunate happenstance."

By the very nature of the case, one can prove neither creationism nor its alternative, evolutionism. Both require faith. One can, however, select a sub system from the total world around him, look carefully at what actually exists therein, and make an informed choice regarding which of these two views of life is the more believable. The subsystem to be considered here is the fetal circulation.

When humans design something, their lack of total knowledge allows errors to be incorporated. Failures can ensue. But when an omniscient Being designs, the end result should be free of error. Furthermore, when humans design, it is extremely unlikely that the first design will fully accomplish the desired result. Only after a series of modifications and redesigns is the end result optimized so that the mechanism operates most efficiently. When an omniscient Being designs, however, the optimizing process should be noticeably absent. The first result should be the optimal one.

The evolutionist, of course, rejects all such teleological considerations in connection with living things. He believes that the end result has undergone mil lions of modifications, and that he has mechanisms just as capable of producing optimization as does the creationist. How, then, can the choice be made be tween evolution and Creation? It must be made on the basis of "reasonableness." The creationist accepts the concept of God, and thereafter problems connected with the formation of the intricate world about him vanish, for he believes God to be omniscient and omnipotent. The nontheistic evolutionist rejects God out of hand, and thereafter his problems begin, for he must explain the development of an intricate world without the least shred of help from a guiding intelligence.

What mechanisms does the evolutionist consider adequate and acceptable in explaining the human body's present state of harmonious operation? In the final analysis, he sees all of evolution as a result of random mutations and natural selection. Occurring over phenomenally long periods of time, these processes are considered capable of producing any living thing. However, one should re member that random mutations are, in reality, "mistakes" in the proper genetic code of the organism, and natural selection is only a screening process whereby the lesser fit are eliminated. Although the evolutionist admits to this role for mutations, he has faith that once in a while a "good mistake" will contribute to the optimization process.

Thus, according to the evolutionist, random mutations and natural selection are the main forces that have changed life forms from amoeba to man. Al though not one iota of intelligence guides these mechanisms, and although the mutation mechanism by definition involves mistakes, yet, in some paradoxical manner, the results are infinitely complex and the life processes are optimized! How reasonable is this explanation? An examination of fetal circulation will be used to contrast the two positions and perhaps provide the basis for the test of "reasonableness."

Description of fetal circulation. During gestation, the mother carries on the functions of respiration, digestion, and elimination for the fetus. Since the lungs are not functionally active, oxygen is supplied to the fetal blood in the placenta. By the eleventh week, the fetal heart has developed into a four-chambered organ with its corresponding arterial vessels. A problem now arises concerning the activity to be carried on by the right side of the heart during gestation, when it is not needed to pump blood through the pulmonary circulation. It cannot lie dormant, for then it would not be sufficiently developed at birth to assume its necessary rigorous pumping activity.

The solution to this problem rests on the fact that the heart is actually two separate pumps that eventually are to function in series. However, by means of a temporary additional passageway and a temporary vessel, the fetal heart can be made to pump in a parallel arrangement, with both left and right sides pumping blood through the systemic circulation (see figure 1).

The amazing manner in which fetal circulation operates and the provisions that make possible the rapid accommodation from a parasitic existence as a fetus to the independent status of the newborn baby can be attributed, of course, either to a huge juxtaposition of chance happenings (the evolution model) or to the intelligent design of an omniscient Designer (the Creation model).

A priority system for oxygen. Of all the nutrients delivered to the fetal blood in the placenta, none is of greater importance than oxygen. Its presence is necessary to the metabolic processes that occur in all the various tissues. There fore, a priority system must be established in the circulation of blood to the various organs of the fetus. (With some modifications, nonfetal circulation is also organized upon this concept.) Since the heart and the brain are high on the priority list, the vessels that supply these organs receive oxygen-rich blood directly from the left side of the heart. As we shall see, it is only after these organs have taken off their share that the oxygen-poor blood from the right side of the heart enters the systemic circulation. Is it merely a coincidence that a striking series of events transpires to deliver the blood with the highest oxygen content to the heart and the brain?

Laminar blood flow. Once it is oxygenated in the placenta, blood passes back to the fetus through the umbilical vein (see figure 2). Most of it is then diverted through the liver, although some moves directly to the heart through the ductus venosus. At the entrance to the right atrium of the heart, the inferior vena cava also carries deoxygenated blood from the lower trunk and extremities (see figure 2). Even here a significant event of fluid mechanics occurs. One would normally expect that blood from these two sources would mix within the inferior vena cava and that the oxygen content would reach a uniform level. Not so, however! Streams of blood from both the placenta and from other parts of the fetus tend to maintain their identity and their individual oxygen contents.

Foramen ovale. The oxygen-rich blood now needs to be delivered to those vessels feeding the heart and brain. Upon entering the right atrium, blood from the inferior vena cava with its differing oxygen levels is divided into unequal streams by the crista dividens, an edge of the interatrial septum. The smaller stream passes into the right atrium and mixes with blood from the superior vena cava; the larger stream, primarily oxygen-rich blood from the placenta, moves into the left atrium through the foramen ovale, a hole in the dividing wall between the two sides of the heart (see figure 2).

Thus the foramen ovale allows oxygen-rich blood from the placenta to move across from the right side of the heart into the left, where it preferentially provides the coronary and cerebral circulations a well-oxygenated supply of blood. The priority system is satisfied, and the most important organs receive the "best" blood available. Where did the foramen ovale originate? How did it not only come to be, but come to be in the most advantageous place? Depending on the point of view, it's either a fortuitous happenstance or a master piece of ingenuity from the mind of the Creator Himself.

Ductus arteriosus. Still more amazing processes are to be found in the fetal circulation. Oxygen-poor blood from the right atrium is pumped out of the right ventricle into the pulmonary artery. After birth this blood will go to the lungs and be oxygenated. But in the fetal state less than a third of the blood goes to the lungs—the amount that is required to nourish that developing organ. What happens to the rest? There just "hap pens" to be an artery—called the ductus arteriosus at the optimal place to carry the remaining two thirds into the systemic circulation. Again the question comes—chance or design?

The ductus forms a straight chute for most of the oxygen-poor blood to move directly into the aorta downstream from the places where the coronary and cerebral arteries have taken off their oxygen-rich supply (see figure 1). Now the two streams in the aorta proceed to feed the rest of the systemic circulation while at the same time sending about half the blood supply back to the placenta to replenish its oxygen and other nutrients. Here is a parallel pump arrangement—both left and right sides of the heart working mainly to feed the systemic circulation. A slightly greater pressure in the right side of the heart at this time causes the flow from pulmonary artery to aorta.

Conversion from parallel to series pumping. As amazing as these processes are, others just as astounding follow as the fetus is delivered and starts an independent existence. Now, instead of both sides of the heart pumping in parallel to supply the systemic circulation, the pulmonary and systemic circulations each have their own pumping in a series con figuration. Only a minimum of "plumbing" is needed for the change. The first processes are external and manual the umbilical cord is clamped and breathing is started. Subsequent changes are internal and automatic a valve flap over the foramen ovale closes, the ductus arteriosus begins to constrict, and the ductus venosus closes by means of a sphincter muscle. When the umbilical vessels are closed, systemic pressure in creases. At the same time, the lack of oxygen activates the respiratory center. When the lungs are filled with air, the pulmonary vascular resistance decreases, greatly increasing the pulmonary flow as well as the flow into the left atrium. Thus, pressures on the right side of the heart are decreased; those on the left side are increased. These pressure changes induce a reversal of flow in both the foramen ovale and the ductus arteriosus. This reversed blood flow moves a valve flap (the valvula foraminis ovalis) to close the opening of the foramen ovale. Fusion of the flap with the atrial wall usually occurs during a period of several days.

Closure of the ductus. The closure of the ductus arteriosus is much more involved than that of the foramen ovale, and has been the subject of much re search. Closure appears to be initiated by the passage of blood saturated with oxygen because of a complex interaction between oxygen-rich blood and the ductus walls. The composition and structure of this artery's walls differ greatly from those of both the pulmonary artery and the aorta, which are in direct contact with it. This fact should cause the evolutionist to pause.

The embryonic development of the cardiovascular system shows a series of five or six arches, all of which disappear within the first month or so of pregnancy, with the exception of the left fourth arch, which becomes the aortic arch, and the left sixth arch, which be comes the ductus arteriosus. The ductus is looser in structure, is relatively more muscular, and contains less elastic tissue than the arteries that surround it. Its internal layer has peculiar properties that help produce protuberances or mounds when closure is initiated.

It is one thing for this unique vessel to develop in such a "fortunate" position, but for it to have properties and structure strangely different from the surrounding vessels and yet distinctly appropriate for its special purpose is quite another thing. And the evolutionists do pause before these facts. Cassels notes, "It is difficult to understand how this short vessel, a part of the brachial arch system, differs so in structure and function from the other derivatives of that system, or from any other part of the surviving vascular tree."

Role of oxygen-saturation level. Studies by Born and others confirm that oxygen level plays an important role in the closure of this special artery. In fetal lambs, delivered by Caesarean section, the ductus arteriosus became constricted when the oxygen saturation was in creased by ventilating the lungs. Contrariwise, it dilated when the oxygen content of the inspired air was decreased. Experiments on isolated heartlung preparations showed the same results, demonstrating that the response was not initiated through the central nervous system.

Although the placenta! system provides the fetal circulation with oxygenated blood, the oxygen-saturation level is lower than that provided by the baby's own respiratory system after birth. Thus, when the baby takes its initial breaths, the ductus experiences, for the first time, blood with a high oxygen-saturation level. The specially designed walls then begin to execute their complex maneuvers that eventually result in closure.

The intricacies of the fetal cardiovascular system that have been described show deliberate, purposeful planning. How else could the result so closely harmonize with the need? How could "chance" provide something for the right side of the fetal heart to do in order to strengthen and develop its muscles while waiting for the termination of gestation? How could the flow concepts associated with the foramen ovale and the ductus arteriosus be developed with out the knowledge associated with Deity? Who but God could decide be forehand the need for those special properties of the ductus, so different from all the surrounding vasculature? As difficult as it is to conceive of the development of such a complex system guided only by the genes, isn't it unreasonable to postulate that the system design and the genetic mechanism arose independent of a guiding Intelligence?



Barclay, A. E., K. J. Franklin, and M. M. L. Prichard. The Foetal Circulation and Cardiovascular System. London: Oxford, 1944.

Berne, R. M., and M. N. Levy. Cardiovascular Physiology. 2d ed. St. Louis: C. C. Mosby Co., 1972.

Born, G. V., G. S. Dawes, J. C. Mott, and B. R. Rennick. Constriction of the ductus arteriosus caused by oxygen and asphyxia in newborn lambs. J. Physiol. (London) 132: 304-342.

Burton, A. C., Physiology and Biophysics of the Circulation. Chicago: Yearbook Medical Publishers, 1965.
Cassals, D. E., The Ductus Arteriosus. Springfield, 111.: C. C. Thomas, Publisher, 1973.

An extended treatment by Professor Clark of this and similar circujatory examples is available from the Institute for Creation Research, San Diego, California, as ICR Monograph No. 5, entitled Our Amazing Circulatory System.

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M. E. Clark is professor of theoretical and applied mechanics and bioengineering in the College of Engineering, University of Illinois at Urbana-Champaign, Illinois.

September 1979

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