Citing Scadding (1981) and Misunderstanding Vestigiality

Cuiusvis hominis est errare, nullius nisi insipientis in errore perseverare.
—Marcus Tullius Cicero, Philippica XII, ii, 5

Introduction • Scadding's Paper • Naylor's Response • Scadding's Response • Evidence of Inutility • More than Mere Homology • Conclusion
Sidebar: Definition of Vestigial • SideBar: Creationists Citing Scadding
References

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"Vestigial" does not mean "non-functional"; vestiges can have functions. A vestigial structure is a functionless or rudimentary version of a body part that has an important function in other, closely allied species. (Freeman & Herron 2004, p39) Vestigial Organs and Structures Vestigial organs and structures (also called vestigia, rudiments, or remnants) are reduced body parts or organs, often without visible function in the derived bearers, that were fully developed and functioning in earlier members of that phylogenetic lineage. These structures, sometimes described as atrophied or degenerate, are usually small in comparison with their relative size in ancestral generations or in closely related species. ... vestigial structures may have acquired new, less obvious functions that differ from the original ones. Hence, a vestigium should not generally be considered without function, or only with respect to its ancestral, adult roles. (Encyclopedia of Evolution 2002, pp 1131-1133) vestigial Occuring in a rudimentary condition, as a result of evolutionary reduction from a more elaborated, functional character state in an ancestor. ( Futuyma 1998, from the Glossary) vestige noun 2: a bodily part or organ that is small and degenerate or imperfectly developed in comparison to one more fully developed in an earlier stage of the individual, in a past generation, or in closely related forms. ( Merriam-Webster Dictionary 2003) vestige, n . . . b (biol.) a rudimentary, degenerate survival of a former organ or structure vestigial, adj . . . (esp biol.) rudimentary, atrophied, degenerate (Wyld & Partridge 1963) vestige A degenerate anatomical structure or organ that remains from one more fully developed and functional in an earlier phylogenetic form of the individual. (Dictionary of Bioscience 1997) Even the etymology of "vestigial" signals that it does not mean "without function." "Vestige" and "vestigial" derive from the Latin word vestigium, which means "footprint, trace, mark, or track" and does not carry the meaning of "functionless, useless." It is significant that biologists chose the term "vestigial" over derivitaves of irritus, inutilis, inanis, or reiculus, which all carry the meaning of "functionless, useless."

Creationists on the web who cite Scadding (1981) ICR Impact 156: The Vanishing Case for Evolution AiG Feedback Response, 6/3/02: AiG misunderstands evolution? AiG: The non-evolution of horses TrueOrigins: A Critique of Douglas Theobald's "29 Evidences for Macroevolution" Harun Yahya: Yet Another Blow to the Myth of Vestigial Organs Pathlights: Scientists speak about vestiges Darwinism Refuted.com: The Myth of Vestigial Organs Creationscience.com: The Scientific Case for Creation Darwinisdead.com: Vestigial Organs Google Search: scadding (vestigial | vestige)

Introduction:

estigial organs and structures provide strong evidence for descent with modification. (See 29+ Evidences for Macroevolution (2.1): Anatomical vestiges.) As such, creationists frequently have used their bag of tricks in attempts to discredit the evolutionary evidence that vestiges provide. Quote-mining is a classic creationist technique where the views of some "authority" are misrepresented to make it sound as if they meant something they did not intend. In other instances, creationists simply cite people who were wrong and ignore the counter citations that demonstrate the error. One such example is the use of a 1981 paper written by developmental biologist, Steve Scadding, and published in the journal, Evolutionary Theory. In that paper, Scadding argued that vestigial organs offered no evidence for evolution other than the evidence they already provide as examples of homology.

An Irregular Journal:

Before we turn to the paper itself, we must make a note about the journal that published it. The irregular journal, Evolutionary Theory (more recently known as Evolutionary Theory and Review) was not your typical scientific journal. It specialized in presenting eclectic and unorthodox papers dealing with the evolutionary half of biology. Its peer review was not as stringent as other journals, as this description from the 1982 edition demonstrates.

This is an open journal. We welcome speculations and critical discussion of books, papers, or ideas. Short papers or even a few lines are appropriate, with no limit on maximum length. So are research suggestions or queries. We prefer a higher than usual probability of error to exclusion of new ideas, which are unorthodox by definition. Good taxonomic and other factual papers are welcome. Papers that disagree with the editors' views have a higher probability of acceptance than those that agree. Comments can be made on relevant papers in any journal at any time, or on more general questions. Comments and replies are reviewed like any other paper. (emphasis added)

The fact that Scadding (1981) appeared in such a journal definitely raises questions about any argument using it as the lone reference. This is not to say that Scadding was wrong because he published in Evolutionary Theory, but it does explain why it was published with its major flaws. It also explains why Scadding (1981) appears to be the only published scientific paper that creationists have found that questions in toto whether vestigial structuress are special evidence for evolution.

Scadding's Errors Were Corrected:

Scadding (1981) does not exist in a vacuum. Evolutionary Theory published a reply to it by Bruce Naylor the next year and a subsequent reply to Naylor by Scadding. If creationist scholarship was not already questionable enough, the failure to note that a subsequent paper raised objections demonstrates the poverty of their position. If they were not aware of Naylor's response, they are guilty of poor scholarship. On the other hand, if they were aware of it, then they are guilty of misrepresentation.

Scadding's Paper:

Creationists quote from two different parts of Scadding (1981). The first appears in the abstract:

An analysis of the difficulties in unambiguously identifying functionless structures and an analysis of the nature of the argument, leads to the conclusion that 'vestigial organs' provide no evidence for evolutionary theory. (Scadding 1981, p 173)

The second appears in the conclusion:

Since it is not possible to unambiguously identify useless structures, and since the structure of the argument used is not scientifically valid, I conclude that 'vestigial organs' provide no special evidence for the theory of evolution. (Scadding 1981, p 176)

Scadding Agrees that Vestiges Offer Evidence for Evolution:

Creationists who quote from the abstract are guilty of quote-mining because it does not accurately represent the view put forth by Scadding in the body of his paper. Scadding argued that vestigial structures do not offer any evidence for evolution beyond the fact that they are homologous. This is why Scadding uses the phrase "special evidence":

Vestigial organs represent simply a special case of homologous organs. . . . While homologies between animal species suggest a common origin, the argument . . . asserts that vestigial organs provide special additional evidence for evolution. (Scadding 1981, p 173) Naylor states that ... "[vestigial organs] would still provide powerful evidence for the theory of evolution." I agree with this, but I suggest that this evidence is due to the homologies these organs illustrate and not to their vestigiality. (Scadding 1982, p 172)

Anyone who cites Scadding (1981) as evidence that the appendix, coccyx, equine leg bones, or similar structures are not evidence for evolution is misrepresenting the paper. Scadding clearly recognizes that vestiges' homologies with structures in other lineages are evidence for common descent. However, Scadding was wrong to argue that vestigial structures offer no evidence beyond being homologous.

Naylor's Response:

Scadding bases his conclusion that vestigial structures do not offer any special evidence for evolution on two misconceptions. One is the meaning and importance of "vestigial" and the second is how "vestigial organs" are identified. Scadding (1981) argues against using "functionless" structures as special evidence for evolution, and makes some valid points. However, his mistake is to equate "functionless" structures with "vestigial" structures. This is an erroneous view of vestigial structures, since nothing in biology requires a structure to be without function in order to be vestigial (see first sidebar).

Several evolution deniers have falsely claimed that biologists changed the definition of vestigial and rudimentary structures when functions were found for many vestiges (see Bergman and Howe 1990 pp 2-3; Sarfati 2002). For example, creationist apologist Jonathan Sarfati, whose background is in physical chemistry and not biology, ironicly states:

Some evolutionists, like Dr Meiss, now want to re-define 'vestigial' to mean simply 'reduced or altered in function'. . . . AiG isn't going to let evolutionists change the rules at their whim when they are losing the argument.

(Sarfati 2002)

Regardless of popular misconception, from the beginning of modern evolutionary theory, a complete absence of function has not been a requirement for vestigiality (Crapo 1985; Culver et al. 1995; Darwin 1872, pp 601-609; Dodson 1960, p 44; Griffiths 1992; McCabe 1912, p 264; Merrell 1962, p 101; Moody 1962, p 40; Muller 2002; Strickberger 2000; Weismann 1886, pp. 8-9; Wiedersheim 1893, p 2, p 200, p 205).

Naylor (1982) made this very point in his response to Scadding (1981):

In considering what vestigial organs are, the proper use of words and their proper definitions are critical. My dictionary (Funk and Wagnalls Standard Dictionary, 1966 ed.) provides the following definitions:

1. Rudiment: "a part, organ, or other structure that has become aborted or stunted and will always be undeveloped; a vestige."
2. Atrophy: "a stoppage of growth and development."
3. Abort: "to fail of complete development."
4. Vestigial: (from vestigium, a footprint): "of, or of the nature of a vestige; surviving in small or degenerate form."

Darwin used the adjectival forms of the first three terms to refer to those organs that, today, we call vestigial. Therefore, it is not essential that a vestigial organ be totally without function. Although Darwin's (1979, p. 428) treatment largely concerns those organs "bearing the stamp of inutility," he also (pp. 431-432) writes "that an organ rendered, during changed habits of life, useless or injurious for one purpose, might easily be modified and used for another purpose. Or an organ might easily be retained for one alone of its former functions." This shows that, for Darwin, vestigial organs were largely, but not exclusively, useless to their possessors. It would seem evident that the human coccyx, that homolog and vestige of the pre-anthropoid tail, fits precisely into the concept embodied in this quotation. Certainly it is functional (Scadding, 1981), but just as certainly it is not functioning as an external tail for balance or grasping. It is a functional, vestigial organ (contra Scadding, 1981).

(Naylor 1982, pp 91 & 92)

It is definitely poor scholarship to ignore this rebuttal. For examples, see the sidebar with links to creationists who cite Scadding's paper.

Scadding's Response:

Scadding (1982) responded to this criticism by claiming that Naylor was the one redefining "vestigial." He attempted to support himself here by citing Darwin, Wiedersheim, and a medical dictionary.

Naylor begins his critique by redefining vestigial organs so as to include fully functional organs under his revised definition. This redefining of the term is unjustified. Darwin referred to "rudimentary, atrophied, or aborted organs" which have subsequently been called "vestigial organs", and he defines these as "organs or parts in this strange condition, bearing the stamp of inutility . . ." (Darwin, 1859, p. 450). Darwin goes on to say that "for the same reasoning power which tells us plainly that most parts and organs are exquisitely adapted for certain purposes, tells us with equal plainness that these rudimentary or atrophied organs, are imperfect and useless." (1859, p. 453). Wiedersheim (1895, p. 200) refers to "organs which may be rightly termed vestigial . . . having become wholly or in part functionless . . .". A lack of function in an organ having a functional homologue in ancestral species is the hallmark of vestigial organs. For a more recent definition, Dorland's Illustrated Medical Dictionary offers: vestige: "the remnant of a structure which functioned in a previous stage of species or individual development".

(Scadding 1982, p 171)

However, Scadding's support is very weak. For instance, a medical dictionary explains how physicians use terms, not necessarily how biologists use them, and thus is an improper resource here. Charles Darwin devoted an entire section in chapter 13 of The Origin of Species to " rudimentary, atrophied, or aborted organs." In it, Darwin makes it clear that vestigial structures can have some function. Wiedersheim also makes it clear that vestigial structures do not have to be functionless, as Scadding's own quote from him demonstrates.

Rudimentary organs sometimes retain their potentiality, and are merely not developed. . . .

( Darwin 1859, ch 13)

An organ serving for two purposes, may become rudimentary or utterly aborted for one, even the more important purpose, and remain perfectly efficient for the other. . . . [A]n organ may become rudimentary for its proper purpose, and be used for a distinct object. . . .

( Darwin 1859, ch 13)

Rudimentary organs, on the other hand, are either quite useless, such as teeth which never cut through the gums, or almost useless, such as the wings of an ostrich, which serve merely as sails.

( Darwin 1872, p 398)

Comparative morphology points not only to the essentially similar plan of organization of the bodies of all Vertebrates, . . . but also to the occurrence in them of certain organs, or parts of organs, now known as "vestigial." . . . By such organs are meant those which were formerly of greater physiological significance than at present.

(Wiedersheim 1893, p 2, emphasis added)

Retrogressively modified, the Organs having become wholly or in part functionless, some appearing in the Embryo alone, others present during Life constantly or inconstantly. For the greater part Organs which may be rightly termed Vestigial."

(Wiedersheim 1893, p 200, emphasis added)

. . . as was pointed out in the introduction, the term vestigial, is, as a rule, only applied to such organs as have lost their original physiological significance.

(Wiedersheim 1893, p 205)

Evidence of Inutility:

Scadding's second mistake is to think that there are no structures for which science has positive evidence to consider them functionless. Naylor (1982) provides a long list of such features covering many classes of animals, which Scadding (1982) does not address. Even though the conclusion may be negative ("structure X has no function"), the detection of biological functionality or lack thereof is based upon positive evidence, not negative evidence. In organismic biology, a function is a physical process performed by a structure that is necessary for the successful reproduction of the organism in a specific environment. Functions are measured in terms of reproduction and viability. A structure has no function in a given environment if the structure's presence has no statistically significant effect on reproductive success or viability. Both reproductive success and viability can be observed and measured quantitatively and are, thus, positive data.

Significance of Evidence:

Vestigial structures do offer evidence for evolution beyond the fact they are homologous. In the absence of evolutionary theory, there is no reason for wings to exist on flightless species or eyes to exist on blind species. The "proper" purpose (in Darwin's terms) of wings is for flight. The proper purpose of eyes is for sight. Rudimentary, flightless wings used for functions other than flight are vestigial, as are blind eyes used for something other than sight. Vestiges are truly functionless only with respect to their proper purposes. The coccyx may have many good functions, but as Naylor says, "certainly it is not functioning as an external tail for balance or grasping" (Naylor 1982, p 92). The human vermiform appendix may have a minor role in the development of the immune system, but it is not functioning as a cellulose-fermenting caecum. In contrast, fins and wings are homologous and are not vestigial organs, but the fins of a trout are functioning for their proper purpose, as are the wings of an eagle. That is the significant thing about vestiges — they are special, puzzling cases of homology, and evolution explains the puzzle in a testable, scientific manner.

In other words, the evolutionary concept of homology explains why similar underlying structures are used for different functions in different species. The evolutionary concept of vestigiality explains why structures specifically adapted for a certain function do not perform that function.

Conclusion:

In conclusion, creationists who use Scadding (1981) to support their contention that vestigial organs are not evidence for evolution are using a paper published in a minor, eclectic journal that was refuted soon after it initially came out. They cite someone who was wrong as "proof" that they are right. As such, it is another example of poor scholarship performed for the sake of pseudoscience.

References:

Acknowledgements:

RAC would like to thank the members of the Internet Infidels E/C forum for their valuable comments.

About the Authors:

RAC graduated cum laude, with honors from the University of Georgia with a B.S. in Genetics and an A.B. in Latin. He is currently a Ph.D. Candidate in (Population) Genetics at the same university. He can be found posting on Internet Infidels as RufusAtticus.

DLT earned a doctorate in Biochemistry from the University of Colorado at Boulder, where his thesis work involved using X-ray crystallography and thermodynamics to elucidate the molecular mechanisms of protein recognition of single-stranded DNA. He is currently an Assistant Professor of Biochemistry at Brandeis University, engaged in structural bioinformatic and molecular evolution research.