What Is a Vestigial Structure?

Webster's Third New International Dictionary defines a vestige as "a small and degenerate or imperfectly developed bodily part or organ that remains from one more fully developed in an earlier stage of the individual, in a past generation, or in closely related forms." It is those vestigial organs that show signs of coming from past generations that support the theory of evolution.

From the beginning, creationists have disputed either the existence or importance of vestigial organs. Robert Kofahl declares in his Handy Dandy Evolution Refuter:

Advancing knowledge and physiology has shown that most of the supposed vestigial organs are useful and even essential. If there are any true vestigial organs, they show the loss of structure and design, not the production of something new. But to support the theory of evolution, evidence for the production of new organs is required.

On the other hand, leading scientists, such as the late zoologist and geneticist, Theodosius Dobzhansky, have continued to support vestigial organs as evidence for evolution. In his text, Evolution, Genetics, and Man, Dobzhansky wrote, "There is, indeed, no doubt that vestigial rudimentary organs silently proclaim the fact of evolution."

To speak to the statement by Kofahl, then, seems to be in order. Let us take his statement one sentence at a time.

When Kofahl says that advancing knowledge has discovered uses for most of what were thought to be vestigial organs, he is at least partly correct. Compared to what scientists thought in the last century, scientists today regard fewer organs as truly vestigial. Among the recent scientists who have been noting uses for formerly held vestiges is Russian zoologist Alexy Yablokov. His book, Variability of Mammals, discusses the important functions played by the pelvic bones and whiskers of whales—two features that were formerly regarded as vestiges.

Does this signify that, given enough time, scientists will soon find uses for all so-called vestigial organs and that we would be well-advised today in giving up the vestigial-organ argument as a case that is doomed? This is what creationists would like us to suppose. But this attitude is based on a misunderstanding of why many structures regarded in the past as vestiges are today regarded as something else.

In a chapter entitled "Variability and the Problem of Vestigial Organs," Yablokov helps us clear up the misunderstanding. He sees much of the problem as having been caused by "vague definitions of the concept of vestigial organs," particularly "the vague or imprecise understanding of the concept of vestigial organ present in the works of Darwin ..." (pp. 232-233). His purpose is to tighten up the definitions in order to provide scientists with a clearer idea of what criteria must be met before a structure can be called vestigial.

But even with tighter definitions, the organs no longer labeled as vestigial do not cease to have value in demonstrating evolution, as creationists might think. For example, when Yablokov denies that pelves and whiskers in whales are truly vestigial, he continues to affirm that they are clear throwbacks to an earlier evolutionary stage. As he states on page 240, "The structure of these organs was modified by a significant change in function at some time in their evolution." Because of his tighter definitions, he prefers to speak in such cases "about the vestigiality of functions rather than the vestigiality of organs" (p. 246). This means that creationists gain very little by the "advancing knowledge" that keeps discovering useful, but altered, functions for organs formerly defined as "vestigial." These organs still demonstrate descent with modification.

In Yablokov's view, the problem with most of the previously held examples of vestigial organs is that they were organs "present in all the individuals of a given species." But, "it is observed in all cases that such organs or structures, inherited by the whole population, have a functional significance and logically cannot be named as vestigial." To Yablokov, an organ should be taken as vestigial only if it is one which develops in some individuals but is not characteristic of the whole population (p. 241). And he adds, "It has been known for a long time that such organs exist in animals."

Armed with this clearer concept of vestigial organs, we can now look at the second sentence in Kofahl's statement. Here he says that any true vestigial organ would show the loss of structure and design instead of the development of something new. If we drop "design," Kofahl is perfectly correct. A true vestigial organ is indeed an organ that has lost its original structure. It has also lost its function. Individuals possessing a vestigial organ don't differ in fitness from those without it. The organ is simply a leftover. Therefore, Kofahl seems to be accepting the concept.

But when he speaks of "design," he implies a designer, a master architect who puts the organs in place; animals were perfectly made by the perfect maker who knew exactly what was to be done.

Given such a position, it would seem frivolous if this maker put some parts in that were of no use. But "design" is a concept that has no usefulness in science. As Richard Aulie points out:

We do not observe design in nature. Rather our minds seem to be constructed so that we can perceive regularities to which, if we have religious presuppositions, we apply the concept of design. Furthermore, to make of design a biologic principle . . . is to reduce the need to interpret biologic processes as precursors of the adaptation that evokes wonder.

This brings us to Kofahl's last sentence. There he states that, since vestigial organs show a loss of structure, they don't help evolution, since evolution requires "evidence for the production of new organs...." This sentence shows Kofahl's misunderstanding of why vestigial organs are used as evidence in support of evolution.

Vestigial remains hark back to an earlier evolutionary stage because these vestiges are organs or parts that have ceased to exercise their original function and have become unnecessary and atrophied. Yablokov considers them examples of atavism, "organs appearing in the development of present forms and indicating the condition of their ancestors (atavus = ancestor in Latin)" (p. 244). Production of new organs has nothing to do with the matter. This is an entirely separate evolutionary issue.

The Appearance of Limbs in Cetaceans

Now that we have a fuller understanding of what constitutes a true vestigial structure, we can proceed to look for a concrete example. The cetaceans (whales and dolphins) are commonly regarded as possessing many vestiges. Of course, it is precisely these mammals that have been used by Yablokov to demonstrate the errors scientists have made in regard to vestigial structures. So we must ask, does Yablokov find any evidence for true vestigial structures in the cetaceans? Yes, he does, and much of his data is based on personal investigation.

Among the vestigial structures in cetaceans that he accepts are vestigial hind limbs. He is aware of six cases in sperm whales alone. One in particular, which was later passed on to him for personal study, he discusses on page 242.

In June 1962, V. 1. Borisov observed a sperm whale with well-developed protuberances on the ventral region of the body, while working in the whale factory at Skalistii (Central Kuril Islands). One of these protuberances could even be X-rayed.

Yablokov himself observed a remnant of a femur in a male sperm whale in the factory at Podgornyi (North Kuril Islands).

Other investigators are also aware of this type of evidence. William King Gregory, writing in 1962 in the Encyclopedia Britannica, provided the following account.

In July 1919, a female Humpback Whale (Megaptera nodosa) with two remarkable protrusions on the ventral side of the body, posteriorly, was captured by a ship operating from the whaling station at Kyuquot, on the west coast of Vancouver Island, British Columbia. One of the protrusions was cut off by the crew of the vessel but the other was photographed in situ by the superintendent of the station.

At the request of Roy Chapman Andrews, the skeletal remains, which consisted of two bones and two heavy cartilages, were sent from Canada to the American Museum of Natural History in New York City. The specimen as found had elementary legs protruding from the body about four feet, two inches, covered with blubber about one-half inch thick. Andrews identified the bones as tibia and metatarsal, the cartileges as femur and tarsus, and published his findings:

After studying the material and discussing it with various scientists, I have come to the conclusion that the protrusions actually do represent vestigial hind limbs and show a remarkable reversion to the primitive quadrupedal condition.

Professor Andrews had sufficient anatomical reasons to reject the idea that the limbs were merely abnormal malformations with no reversionary significance. He concluded his research on this remarkable specimen with the following observations:

Since Kukenthal's and Guldberg's researches have shown that external hind limb rudiments are still present in some cases in embryonic life, it is by no means impossible that these vestigial organs should continue their growth and persist until the adult stage. I believe that that is exactly what has occurred in the specimen which I have described above, and that we are confronted with a clear case of partial reversion to a primitive quadupedal condition.

The limbs, according to the statements of the whalers, were symmetrical; they are in the exact position in which the hind limb rudiments have been found in embryonic Megaptera; there are strong indications that the cartilaginous femur was attached to the pelvic elements.

The report, entitled "Remarkable Case of External Hind Limbs in a Humpback Whale," was published in June 1921.

In 1953, Teizo Ogawa, writing "On the Presence and Disappearance of the Hind Limb in the Cetacean Embryos" in The Scientific Report on Whales Research, concluded that:

... in my opinion the disappearance of the paired hind limbs in the Cetacea seems to have an intimate causal nexus with the appearance of the paired caudal flukes of them. . . . In a 14 mm long embryo of the dolphin, Prodelphinus caeruleoalbus, and in a 20 mm long embryo of the Humpback, Megaptera nodosa, the paired elevations of the hind limb are pretty well developed. Photographs of them arc shown. Further consideration was given to the simultaneousness of the disappearance of the hind limb elevation with the first appearance of the caudal flukes in the cetacean embryos. (p. 131)

In 1957, Tezio Ogawa and Toshiro Kamiya, writing in the same journal, reported on "A Case of the Cachalot with Protruded Rudimentary Hind Limbs."

Needless to say, no protrusion of the hind limb is seen in all the Cetacea in their postnatal life. Only in the early embryonic stage they show a pair of protruded hind limbs, which but soon disappear. On the other hand, the existence of a pair of small pelvic bones is known as to nearly all of the Cetacea, lying far apart from the vertebral column on both sides of the genital opening. In the fin and blue whales and in the humpback, the femur too is present near the pelvis, and in the right whale even the tibia exists. Of course, these bones are deeply buried under the skin, causing no protuberance on the body surface. (p. 197)

After some discussion of the 1921 Andrews report, the authors continued:

Recently another individual belonging, however, to the Odontoceti [sperm whale] and possessing likewise a pair of protruded hind limbs was encountered in Japan.... According to the report presented from the whaling station, it was a female measuring 10.6 m in length. The protuberances were present on both sides of the genital opening.... (p. 198)

The difference between the two cases is never essential but rather a problem of the quantity of materials for study.

In their summary, Ogawa and Kamiya stated:

In a nearly adult female Cachalot captured in November of 1956, off Kinkwazan in Japan, a pair of budlike vestigial hind limbs were present. The height of the protuberance was 5.35 cm on the right side and 6.56 cm on the left side. Upon examining the interior of the left limb, three partially cartilaginous hones were found. They corresponded to pelvis, femur, and possibly to tibia, but no joints exist between them. Pretty strong muscles connect between pelvis and femur, while two weak muscles are extended between femur and tibia... .

This case can be understood by assuming abnormal retention of the early embryonic state and shows very probably an atavism back to the quadrupedal condition of the whale's remote ancestors. It can never be a malformation of no phylogenetic significance. (p. 207)

These examples of rudimentary hind limbs meet Yablokov's criteria of being nonfunctional as well as uncharacteristic of the whole population. To demonstrate their noncharacteristic nature, a report by Seiji Ohsumi is instructive.

On December 16 in 1963, a herd of about 450 blue white dolphins (Stenella caeruleoalba) was caught by fishermen at Kawana Beach in the eastern coast of Izu Peninsula, Japan. In the course of biological investigation on the herd, I found an individual with protruded rudimentary hind limbs ... protruded on either side of just the mammary slit. (p. 135)

Out of 450, he found only one example.

Other vestigial reports on sea mammals could be cited, but enough has been presented to show that these rudimentary hind limbs do exist in cetaceans and are truly vestigial. Being vestigial, they point to an earlier stage of evolutionary development. Because of this and other evidence, William King Gregory concluded in his Encyclopedia Britannica article, "that the Cetacea have been derived from terrestrial, quadrupedal placentals."

The very word vestigial comes from the Latin vestigium, which means footstep or track. Vestigial organs are traces of organs previously functional. In a sense, vestigial remains are like footprints leading us back to an earlier time when they were fully developed, a time when the ancestral animal had a significantly different body structure and a totally different way of life from the example alive today. That is what we have discovered in the case of the cetaceans.