The Search for a Purpose in Harvey and Modern Biology

by Bob Kopp
10 February 02001

Although Aristotle considered the search for teleological causes -- ultimate ends or purposes -- to be one of the primary goals of science, modern physical scientists generally deprecate this quest. A search for the purpose of the laws of gravitation would be considered a religious search, not a scientific one. In the biological sciences, teleology is a bit more common, as the presence of Darwinian selection lends a bit more meaning to terms like 'purpose' and 'final cause.' For this reason, the teleological arguments William Harvey offers in his investigation of the circulatory system do not all fall outside the bounds of scientific inquiry. In De Motu Cordis, Harvey productively employs teleological reasoning as a source and support for his empirically-testable hypotheses and, less productively, as a source for some hypotheses impossible to investigate in his day.

The existence of final causes requires some form of intentionality. It is, for instance, valid to talk about the purpose of a computer keyboard because keyboards are designed by intelligent beings; their creators made them so that computer users could enter data into computers. Where intentionality is absent, as it is in the physical universe, talk of final causes is meaningless. Few scientists would agree with Johannes Kepler's statement that the Sun exists to provide light to the inhabitants of the Earth, or with his hypotheses that the planets of the Solar System are located in their current positions in order to exhibit geometrical and musical harmonies. Such statements would only have meaning if the layout of the Solar System were the product of an intelligent designer.

In the biological domain, on the other hand, there is a quasi-intentional actor: natural selection. Darwinian selection ensures that genes and the species they produce only survive if they are well-adapted to their environment. Surviving organisms are therefore well-designed to pass on their genes, and one could say that the ultimate end of such organisms is reproduction. In investigating organisms' anatomy, one can therefore define the purposes of their component systems with respect to the organism's reproductive purpose, and the associated purpose of surviving to reproductive age. It is, therefore, perfectly reasonable to say that humans have eyes so that they can see; vision helps them find food, avoid danger and engage in social activity.

But although such teleological statements are philosophically sound, they are not always of scientific value. Scientific hypotheses must be falsifiable; teleological statements are generally not, but they can sometimes act as 'intuition pumps,' assisting a scientist in the invention of testable theories. This is one of the main uses for which Harvey employs teleological argument.

Several basic principles underlie Harvey's teleological reasoning. The most fundamental of these is Harvey's assertion of Nature's efficiency: "Nature being perfect and divine . . . [makes] nothing in vain" (113). Although Harvey lacks a rigorous theoretical framework for this statement, and although organisms do not always have efficient structures, modern biology agrees that natural selection does tend to encourage efficiency in the design of organisms. From this efficiency principles derives a second principle, that systems with similar structures or performing similar activities have similar purposes. Conversely, if two systems have different structures, it is unlikely they serve the same purpose. Again, these principles are not in complete agreement with modern biological theories, but because it takes fewer genetic alterations to replicate a complex structure than to make a different structure with the same function, these principles do tend to be true.

Harvey's investigation of the heart and the circulatory system is, in large part, spurred by the conflict between his teleological principles and the prevailing contemporary understand of human anatomy, due primarily to the Greek physician Galen. In the Galenic theory, respiration and pulsation both involve the intake of air; the heart and the arteries swell as they take in air through pores in the skin. This view conflicts with Harvey's opinion that systems with different structures serve different purposes; he writes, "since the motion and constitution of the heart is different from that of the lungs, and the motion of the arteries different from that of the breast, it is probable that divers uses and utilities should follow" (2).

Conversely, Galenic theory ascribes quite different purposes to the two ventricles of the heart, despite their similar structures. In the Galenic view, the right ventricles exists to send blood from the veins into the lungs, where it is consumed for nutrition. The left ventricle takes air from the lungs through the pulmonary vein, mixes the air with blood that enters from the right ventricle through invisible pores in the septum and then is sent through the aorta to the entire body. This again runs counter to Harvey's teleological principles. "Why," he asks, "should we think [the two ventricles] were appointed to such diverse different uses, seeing action, motion, pulse is the same in both?" (9).

Another aspect of the Galenic physiology of the heart runs counter to Harvey's principle of natural efficiency: the use of the septum to transmit blood from the right ventricle to the left ventricle. The septum, Harvey notes, is one of the densest objects in the body; it is "thicker and more compact than any part of the body, except the bones and the nerves." He doubts that Nature would employ "hidden, invisible, incertain, and obscure pores" in such a substance for the transmission of blood (13). Rather, he suggests that blood enters the left ventricle through the pulmonary vein, a conduit resembling others in the body clearly used for the transmission of blood and with a much more efficient design for that purpose than the septum.

Having identified these and other flaws in the Galenic system, Harvey proposes an alternative, correct theory which is more in line with his teleological principles. In it, pulsation is caused by the flow of blood as the ventricles of the heart contract and push it through the body. The right ventricle pumps all the blood of the body through the lungs, and the blood then travels to the left ventricle by way of the pulmonary vein and the left auricle. The left ventricle sends the blood through the arteries, and the blood returns to the heart by way of the veins.

But while this theory is inspired by teleology, teleology serves Harvey here only as an intuition pump. Having proposed the theory, Harvey proceeds to substantiate each step of his argument using diverse methods of scientific argument, including empirical testing, arguments from fluid dynamics and calculation. For example, he observes the motion of the heart in dying animals and concludes that the heart contracts and forces blood into the arteries which causes their expansion. He argues from calculation that if blood in a body did not travel in circuit, it would be used up in a short period of time. He performs experiments involving the ligation of veins and arteries to examine the movement of blood through these conduits.

Although most of Harvey's supporting arguments are not teleological, he does offer some arguments from teleology. The most important of these are Harvey's arguments from comparative anatomy. This form of argument is original to Harvey and depends on his teleological principles. Previous anatomists had examined animals like dogs and monkeys and assumed that the structures in these animals were identical to those in humans; Harvey was among the first to study animals for the sake of comparison. Harvey examines the motions of a living heart in creatures with no lungs, such as fish, and shows that in these animals, blood travels from the veins to the arteries by way of these animals' single auricle and single ventricle. Because similar structures -- the hearts of lungless animals and the hearts of lunged animals -- should perform similar functions, Harvey argues that this suggests blood passes from the veins through the heart to the arteries in humans as well. He writes, "The case is just so with them as it might be with a man, the enclosure of whose heart were pierced through, or taken away, and so both the ventricles became one" (42).

Harvey continues this line of investigation by looking at human fetuses. In the fetus, the lungs are inactive. The two auricles are connected through foramen ovale, an oval hole in the undeveloped septum; and the pulmonary artery joins the aorta through the ductus arteriosus. As in lungless animals, it is clear that it the human fetus, blood passes from the veins through the heart to the arteries. As Harvey writes, "whilst the lungs are idle . . . Nature makes use of both the ventricles of the heart, as of one for the transmission of blood" (46). Since Nature does nothing in vain, it is unlikely She would have so radically altered the design of the adult body so as to stop the flow of blood from the veins to the arteries. The question remains, however, "why it is better that Nature (for Nature always does that which is best) hath altogether shut up those open ways" and "would rather have the blood to be squeezed through the streyner of the lungs, than through most patent passages" (48). This teleological question, however, is part of the investigation of the respiratory system, and is not relevant to Harvey's investigation of the circulatory system; he therefore does not pursue it further in this work.

In the final chapter of his investigation, Harvey returns to comparative anatomy and, relying heavily on the principle of natural efficiency, offers confirming evidence for his theory. He shows how Nature has fitted each organism with a heart and a circulatory system appropriate for its needs. Fairly inactive "Plant-animals" such as oysters and sponges have no distinct heart; they distribute nutrition through their small bodies by contracting and expanding as a whole unit. In animals such as shrimp, there is a bladder that only occasionally contracts. Lungless animals like fish, as previously noted, have an auricle and a ventricle; animals with lungs have two ventricles and at least one auricle, and these organs are stronger than in lungless animals. Further, in stronger animals, the heart is accompanied by auxiliary muscles that make its contraction even stronger. These muscles are more common on the left ventricle, which propels blood through the whole body, then on the right ventricle, which has only to send blood the shorter distance to the lungs. Harvey also notes that there are variations in the strength of the heart even among different men; more muscular men have stronger hearts than weaker men. Harvey concludes,

all creatures, men likewise, by how much the habit of their flesh is harder and more solid, and by how much more their outward members are more fleshy, and farthest from the heart and brawnie, so much more fibrous, thick, robust, and musculous a heart have they. (108)

Harvey identifies similar effects with respect to the strength the auricles and the efficiency of the three-forked portals that prevent the flow of blood backwards from the heart into the veins. Nature, Harvey concludes, has given each organism a heart that "acquires its perfection in them all" (113).

Harvey also supports his theory by showing how, within the human body, Nature has provided structures ideally suited for their purposes. The muscles of an artery, for instance, serve to hold the artery together against the force provided by the contraction of the heart. The farther arteries from the heart must work counteract a weaker force and so are themselves weaker. "The nearer the arteries are to the heart, the more they differ from the veins in their constitution, and are more robust . . . but in the furthest dispersions . . . they are so like in their constitution, that . . . it is a hard business to know one from the other" (115). Similarly, Harvey notes how the pulmonary artery -- which Harvey and his contemporaries call the arterial vein, because it is on the same side of the heart as the veins -- has the structure of an artery because it has the function of the artery. Just as the other arteries receive blood pumped out of the left ventricle, so the pulmonary artery receives blood pumped out of the right ventricle. In a like fashion, the pulmonary vein, which Harvey and his contemporaries call the veinous artery, has the structure and function of a vein. "Both in function, constitution, and all other things, [the arterial vein] is an arterie, and [the veinous artery] a vein, otherwise than is commonly believed" (118).

Although teleology largely serves Harvey as an able assistant in his reasoning, it occasionally leads him astray, into quasi-mystical speculation. The most significant instance occurs when Harvey speculates about the purpose of circulatory system. Accepting Aristotle's statement that death is caused by lack of heat, he contends that one of the purposes of the heart is to "be a place and beginning of heat . . . by which the nursery of Nature, and the first beginnings of inbred fire may be contain'd" (92). The purpose of circulation, then, is to return blood to the heart, where it may be warmed after having been exposed to the coldness of the body's extremities. Unlike most of the teleological reasoning Harvey employs, this speculation does not suggest any new, testable hypotheses.

Nevertheless, this flawed teleological argument is auxiliary to Harvey's main argument. Indeed, almost all the teleology in De Motu Cordis serves as a supplement to other, more standard forms of scientific reasoning. Harvey's argument from comparative anatomy about the connection of the veins to the artery is the main instance in which teleology plays a primary role. Even this argument, however, is later supported by other arguments demonstrating the circulation of blood through the body. Furthermore, thanks to the agreement between Harvey's personified Nature and natural selection, Harvey's teleological reasoning stands in general agreement with the views of modern biology.

Citations from Harvey, W. The Anatomical Exercises. G. Keynes, ed. New York: Dover, 1995.