ctuated Equilibrium:The Missing Link in Education

BrianJ. Alters WilliamF. McComas

Accordingto the theoryof naturalselection an interminable ogy, geology and history of science at Harvard, numberof intermediateforms must have existed, linking formulated the theory of . In togetherall speciesin eachgroup by gradations as fineas our existingvarieties . . . (Darwin 1975,p. 182). their now classic article, "Punctuated Equilibria:An Alternative to Phyletic Gradualism," Eldredge and WhenSteven Stanley, professor of paleontologywas asked: Gould (1972) define punctuated equilibrium as evo- "If you couldgo backin time and sit down with Charles lutionary lineages that are characterized by brief Darwin, . . . what do you think would be important to tell Downloaded from http://online.ucpress.edu/abt/article-pdf/56/6/334/46818/4449848.pdf by guest on 27 September 2021 him about what's happenedto his theory?"Stanley an- episodes of rapid separated by long inter- swered: ". . . I'd like to tell him about the punctuational vals of stasis of the species thus produced (Avers scheme.. ." (Campbell1986, p. 727). 1989). In 1977, the two refined their earlierpaper and responded to criticismsof the new concept (Gould & T nHE scheme referredto by Stanley has been called punctuated equilibriumby its developers Eldredge1977). Myriadjournal papers, news articles, Niles Eldredge and . The and even books were written about punctuated equi- idea has astonished the scientificcommunity in much librium, primarilyin response to these two papers. the same way that Darwin did a century earlierwhen In 1980, a conference on macroevolutiontook place he proposed natural selection as the mechanism to at Chicago's Field Museum of Natural History. Due explain how living organisms have evolved through to the considerationgiven to punctuated equilibrium, an unbroken chain extending back to the first primor- many scientists at the conference suggested that the dial cells. Central to Darwin's theory of evolution by meeting was a turning point in the history of evolu- natural selection is the view that evolution is both tionary theory and was the most important confer- smooth and gradual. What Eldredge and Gould ence on evolutionary in 30 years (Lewin (1972) proposed is the revolutionary view that or- 1980). The majority of the world's top paleontolo- ganic evolution is not steady and regular, but epi- gists, anatomists, evolutionarygeneticists, and devel- sodic and jerky with long periods of minute change opmental biologists present at the meeting supported interspersed with rapid bursts of large-scaletransfor- some form of punctuated equilibrium(Adler & Carey mation of species. Bakker (1991), himself a revolu- 1980) as the most accurate view of the record tionary by championing the notion of "hot blooded" and hence of the history of life itself. dinosaurs, considers punctuated equilibriumthe big- Punctuated equilibrium does not overturn the es- gest bomb in evolutionary biology dropped this cen- sential notions of organic evolution, despite such tury (Bakker1991). Asimov (1989) listed punctuated claims by creationists, but rather provides a more equilibrium as one of the seven most significant accurateview of the history of life. Natural selection, events of world science for the year in which it was put forward by Darwin, is still the primary mecha- proposed, and both evolutionary biologists, Scully nism for the development of the new species. Only (1987) and Futuyma (1985) have stated that no other the rate and pattern of such speciation has been concept in modern evolutionary theory has drawn reformulated by punctuated equilibrium. What El- more attention in both scientific journals and the dredge and Gould have done is to bring the debate mass media. regardingthe tempo and mode of evolution to a new In 1971, Niles Eldredge, Chairmanand Curatorof generation of scientists. Even Darwin's staunchest Invertebrates at the American Museum of Natural contemporarysupporter, T. H. Huxley, criticizedhim History, and Stephen Jay Gould, who teaches biol- for insisting on a gradualistic pattern for evolution despite the lack of fossil evidence. The words spoken by Huxley (1900, p. 27), "You have loaded yourself BrianJ. Altersis a Ph.D.candidate in science education at the Universityof SouthernCalifornia. He can be reached at 3419Via with an unnecessary difficultyin adopting naturanon Lido,Newport Beach, CA 92663. WilliamF. McComas, Ph.D.,is facit saltum [nature makes no leaps], so unreserv- Directorof Science EducationPrograms and AssistantProfessor edly," could serve as the credo for today's punctua- at the Universityof SouthernCalifornia, School of EducationWPH 1001E,Los Angeles, CA 90089-0031. tionalists. Despite the importance of punctuated equilibrium

334 THEAMERICAN BIOLOGY TEACHER, VOLUME 56, NO. 6, SEPTEMBER1994 A comparison of the tenets of phyletic gradualism and punctuated equilibrium. Name:Phyletic Gradualism Name:Punctuated Equilibrium PrincipalProponent: Darwin PrincipalProponents: Eldredge and Gould * New species develop gradually and slowly with little * New species develop rapidly and then experience long evidence of stasis (no significant change). periods of stasis. * The fossil record should contain numerous * The fossil record should contain few transitionalforms transitionalforms within the lineage of any one type with the maintenanceof given forms for long periods of organism. of time. * New species arise via the transformationof an 0 New species arise as lineages are split. ancestralpopulation. * The entire ancestral form usually transformsinto the 0 A small subpopulation of the ancestralform gives rise new species. to the new species. * Speciation usually involves the entire geographic 0 The subpopulation is in an isolated area at the range of the species (called sympatry). periphery of the range (called allopatry). Adapted from Eldredge 1989;Futuyma 1986;Rhodes 1983;and Gould & Eldredge 1977. Downloaded from http://online.ucpress.edu/abt/article-pdf/56/6/334/46818/4449848.pdf by guest on 27 September 2021 to evolution, biology and science in general, it has not answer may lie in the confusion engendered in the yet been given appropriatespace in textbooks, if it is debate between those who support phyletic gradual- mentioned at all. This is unfortunate, since students ism and those who support punctuated equilibrium. of all ages should be provided with a complete understanding of modern evolutionary thought and should be given an opportunity to discuss its impor- What Is Punctuated Equilibrium? tance. In addition, punctuated equilibriumhas great value in its use as a tool for generating higher-order To understand punctuated equilibrium, one must thinking skills. examine it point by point with the Darwinianview of A survey of punctuated equilibrium'streatment in phyletic gradualism.Table 1 compares the two views a variety of middle and high school life science and of the evolution of life. biology texts (24 books, 9 publishers, published from The debate between proponents of phyletic gradu- 1990-1993) revealed that only 67% contained any alism and punctuated equilibriumis one of the most mention of punctuated equilibrium (Alters 1993). Of spirited in modern evolutionary thought. First, phy- those texts mentioning punctuated equilibrium, the letic gradualists contend that most evolution occurs average number of paragraphs was approximately within established species (Stanley 1982). Speciation 3.5. These paragraphs contained conflicting classifi- occurs via the conversion of an ancestral population cations, misnomers concerning the name "punctuat- into its modified descendents (Rhodes 1983) (see ed equilibrium,"incorrect definitions, and many mis- Figure 1). In contrast, proponents of punctuated leading and/or incorrectstatements. Such spotty and equilibriumhold that most speciation does not occur incomplete treatment is unfortunate in resources via the conversion of entire ancestralpopulations but upon which teachers rely to present the latest con- instead by cladogenesis (branching of a lineage into cepts of biology as a new foundation (or cofounda- two populations) (Gould 1991b) (see Figure 2). tion) for interpreting life's history. Kurten (1981 in Levinton 1982) takes issue with this It is interesting, as Gould (1991a) himself pointed punctuational cladogenic idea, specifically concern- out in an articleunrelated to punctuated equilibrium, ing mammals, stating that, within the last 3 million that virtually every life biology text in print contains years, muskrats constitute an evolving lineage with a detailed discussions of the long-discredited ideas of smooth transition from one genus-level taxon to the Lamarck's inheritance of acquired characteristics. next. Conversely, Stanley feels that there is no way to While the historicalperspective provided by a discus- explain the evolution of the age of mammals without sion of Lamarck'sideas is somewhat useful, should punctuated equilibrium. "I don't see any way that such notions be included at the expense of other, one can explain how entire species [without punctu- more cutting edge, ideas in biology? After all, there ated equilibrium]could become wholly transformed are only so many pages available in a textbook. So so rapidly . . ." (Campbell 1986, p. 725). perhaps it is time to dispense with the old traditions Second, speciation in a gradualistic model is in biology text writing in favor of materialthat reveals thought to occur over all or most of the ancestral the dynamic rate of the science to students. species' geographic range. However, in punctuated If, as the experts assert, punctuated equilibriumis equilibrium, a small subpopulation of an ancestral of major importance, why has it not been given form, in an isolated area at the periphery of the appropriate space or treatment in textbooks? The range, gives rise to a new species (Rhodes 1983;

PUNCTUATEDEQUIUBRIUM 335 HowSlow Is Slow? More important than the semantics of the name "punctuatedequilibrium" is the considerablecontro- versy with respect to terminology, such as "stasis" and "rapid." Succinct definitions of these words are indispensable to an understanding of punctuated equilibrium. "Stasis," the empirical cornerstone of punctuated equilibrium(Eldredge & Gould 1988),has been defined as being everything from zero change T and not evolving at all to no substantial change and homeostaticequilibrium. The originatorsof the punctuated equilibriumcon- I cept did not intend either of the former definitions of M zero change or not evolving at all. The idea of total stasis is clearly invalid (Mayr 1992). Gould (1992) was so E \Iu /"'

frustratedby the flood of erroneous definitions that Downloaded from http://online.ucpress.edu/abt/article-pdf/56/6/334/46818/4449848.pdf by guest on 27 September 2021 he wrote, "Unless we are all monumental fools, these cannot be the definitions that have fueled this de- N / bate" (p. 71). Beardsley (1990) wrote that, "Once a species has evolved, they [Eldredge & Gould] ar- L~~~~~i' gued, it enters a period of stasis, remainingunchanged [emphasis added] for possibly millions of years" (p. 37). But in 1988, just two years prior, Eldredge and Gould wrote, MORPHOLOGY Theimplication seems to be thatstasis necessarily entails no or even Figure1. Phyletic within-population, geographicallybased among- gradualism:Time vs. morphology. populationvariation; such a caricatureof our conceptionof stasisfurther implies a rigidlymonolithic straight-jacketed lackof variationthrough the entireduration of a species- Stanley 1979). The punctuational idea that most evo- lineage.Yet we havealways acknowledged that such varia- lution occurs rapidly in localized populations does tion existsat any one timein a species'history. The failure not require novel genetic mechanisms to explain the to convertthis variationinto substantialanagenetic change occurrence (Eldredge 1989; Stanley 1982). New spe- [directionalevolution of a feature]is centralto punctuated equilibria(p. 211). cies are formed by standard processes of isolation, natural selection and genetic drift (Futuyma 1985) as Some empirical examples of stasis are found in in the gradualistic description. However, after this mammal and invertebrate species lasting approxi- new species is formed, it may reenter the parent mately 2 million years (varying greatly from group to species' area and be better adapted to the conditions group) and diatom floras that last about 20 million there. Therefore, a trend would result of replacing years (Campbell1986). A typicallineage of eukaryotic old species with new ones in an appropriate direc- animals or plants that has survived for 105 to 107 tion. This mechanism has been named "species se- generations has undergone little change in form lection" (Stanley 1981). Species selection is defined as (Stanley 1982). These rates of are criticalto "the differentialmultiplication and extinction of spe- a long-term understanding of biological evolution cies as a result of differences in certain traits pos- (Raup 1986). sessed by the organisms belonging to the various species, and causing a spread of the favoring traits through the fauna or flora as a whole" (Wilson 1992, How Fast Is Fast? p. 406). "Rapid change" is perhaps even more difficult to Third, phyletic gradualism contends that evolu- define than is stasis. The following synonyms are a tionary trends are the products of slow, directional few that have been used in print without accompa- conversions, while punctuated equilibriumcontends nying numerical definition: instant, accelerated,fast, that most species change little morphologically, if at quantum leap, very quickly, abrupt, and brief periods. all, without apparent direction (stasis) and, when More specifically, the time ranges from a very few speciation occurs, it is very rapid (Gould & Eldredge years to within 50,000 years to hundreds to thousands of 1977; Gould 1991b). It is this rapid speciation that years. The point is that "rapid" is a blink of an eye makes up the "punctuated"and the stasis that makes in comparison to that species' stasis and would vary up the "equilibrium." for different taxa of organisms. In punctuated

336 THEAMERICAN BIOLOGY TEACHER, VOLUME 56, NO. 6, SEPTEMBER1994 equilibrium, there is not one unifying rate of specia- Gould 1972). This punctuational pattern of morpho- tion that all organisms must undergo. However, this logical change, seen as real by the developers of the rapidity of speciation does not require a new genetic concept, demanded the origin of punctuated equili- mechanism. A study of butterfly mimicry concluded brium. that punctuational change is fully compatible with Gould and Eldredge (1977)contend that: "Phyletic what is known of the genetics of populations (Turner gradualismwas an a prioriassertion from the start-it 1988). was never 'seen' in the rocks;it expressed the culture Some confusion among geneticists and paleontol- and politicalbias of 19th century liberalism"(p. 115). ogists has occurred because of the term "rapid." By the same token, while many feel that punctuated What is rapid to geologists may represent to geneti- equilibriumpostulates how speciation occurs, its oc- cists tens or hundreds of generations by traditional currence is not based on empirical evidence but on evolutionary mechanisms such as selection, mutation the apparent lack of evidence-gaps in the fossil and genetic drift (Scully 1987). Artificial speciation record (Hoffman 1992; Gingerich 1984). It is ironic has been achieved faster than intervals in the order of that the incomplete nature of the fossil record is as 100 years, with founder effects, genetic drift, and much a part of the argument of the punctuational shifting influence or regulatory genes all playing camp as it is of the gradualists(Mayr 1992). However, significant roles (Stanley 1992). many believe that various degrees of gradualismand Downloaded from http://online.ucpress.edu/abt/article-pdf/56/6/334/46818/4449848.pdf by guest on 27 September 2021 punctuationalism can be observed (Volkenstein for Punctuated Equilibrium 1987). For example, studies that yield support for The Evidence punctuated equilibrium have been conducted con- The evidence that provided the impetus for stasis cerning the following: hominids, horses, Ordovician and rapidity comes from the gaps in the fossil record. , Pennsylvanian gastropods, Mesozoic and Phyletic gradualism would predict the presence of Cenozoic mollusks, radiolarians,bryozoans, brachio- transitionalstages in the fossil record since change is pods, clams, pollen, butterfly mimicry, relationships gradual and continuous. Darwin (1975), a gradualist, of frogs, and patterns of behavior (Gould 1991b; thought that the fossil recordwould, in time, provide Rhodes 1984). One of the most shocking studies the transitional forms important to his view of evo- concerned a molecularbasis for constraints on devel- lution. But more than 130 years have passed without opment and evolution via a domain model for eu- many examples of the intermediate forms so anx- karyotic DNA organization. Bodnar, Jones and Ellis iously anticipated by Darwin. Clearly, one would (1989)suggested that one would not see intermediate have expected a wide range of transitional forms in forms in simple eukaryotes in the fossil record be- over a century of searching. Gould, himself a paleon- cause there are no intermediate forms. A single tologist, states: "Paleontologistshave paid an exorbi- mutation in a regulatory gene caused the change in tant price for Darwin's argument. We fancy ourselves one leap of evolutionary development. as the only true students of life's history, yet to preserve our favored account of evolution by natural Punctuated Equilibrium& the Biology selection, we view our data as so bad that we never Curriculum see the very process we profess to study" (Gould 1977, p. 14). Not only is punctuated equilibrium good science, Only 10%of geologic time is availablein sedimen- but its inclusion in the high school biology curriculum tary layers (Van Andel 1981) and, hence, the record is a necessity. First, an explorationof the evidence for itself is imperfect and the dearth of transitionalforms punctuated equilibriumand the related scientific de- in the intact sedimentary layers is troubling. There- bate promotes higher-orderthinking. Resnick (1987), fore, phyletic gradualists, as did Darwin in the last for example, has developed nine criteriafor higher- century, explain the lack of evidence for transitional order thinking, and punctuated equilibriumfulfills all stages by the fragmentarynature of the fossil record nine. The path of action is not fully specified in (Scully 1987). In contrast, proponents of punctuated advance; it is complex and yields multiple solutions; equilibrium state that the imperfections cannot ex- and it involves nuanced judgment and interpretation, plain all discontinuity and certainly cannot encom- applicationof multiple criteriawhich sometimes con- pass stasis. Punctuated equilibrium thus holds that flict with one another, uncertainty, self-regulationof the gaps in the record of the rocks are real and not the thinking process, finding structure in apparent simply artifacts of a poor fossil record. Gradual disorder; and it is effortful with considerable mental change is not the normal state of species develop- work involved. ment. The record in the rocks is clear; the vast Second, biology should be represented as ".1... a majority of species appear fully formed and then dynamic, experimentalscience rather than a body of remain in stasis during their later existence (Gould facts and terms which are to remain unquestioned 1980, 1991b; Gould & Eldredge 1977; Eldredge & and unchanged" (Penick & Leonard 1993, p. 17).

PUNCTUATEDEQUILIBRIUM 337 Clearly, the debate of phyletic gradualism versus tion, punctuated equilibrium is not listed in the punctuated equilibrium demonstrates well the dy- Libraryof Congress'Subject Headings (1992), Brennan's namic nature of biology and should be brought into Dictionaryof ScientificLiteracy (1992), nor McGraw- the classroom. The students should be shown that Hill's (1992)or Van Nostrand's (1983) scientific ency- the century-old view of phyletic gradualismis now in clopedia indexes. question. Such questioning is the hallmarkof science The name punctuated equilibrium (or equilibria, itself, as expressed by 72 Nobel Laureatesin a recent both are considered correct by the developers) was court brief: coined by Gould in 1972 (Gould 1991b). Punctuated Justas childrenshould understand and appreciate the scien- equilibriumwas named this for its descriptivenature, tifictheories that offer robust and reliablenaturalistic expla- yet, in the texts we surveyed, the authors of those nationsof theuniverse, children should also understandand texts termed it punctuationalism,rapid evolution, and appreciatethe essentiallytentative nature of science.In an punctuationalmodel. One of the most interesting mis- ideal world, every sciencecourse would includerepeated nomers was that of Asimov's. In The remindersthat each theory presented to explainour observa- his text, Chro- tionsof the universecarries this qualification:"as far as we nology of Scienceand Discovery(a text that science now know, from examiningthe evidenceavailable to us teachers might reference), he states, "In 1972 this today"(Amicus curiae brief 1986, p. 24). view [of phyletic gradualism]was challenged by the One way this understanding can be fostered is by American paleontologists Stephen Jay Gould and Downloaded from http://online.ucpress.edu/abt/article-pdf/56/6/334/46818/4449848.pdf by guest on 27 September 2021 having the students debate the merits of phyletic Niles Eldredge, who suggested what they called gradualism and punctuated equilibrium. Given the punctuatedevolution" (emphasis ours) (1989, p. 629). same data set, students could be asked to take posi- In addition, the classification of punctuated equi- tions and develop differing interpretations of the librium, from a philosophy of science perspective, is evidence. Or the teacher might give the students a problem. For example, the newer school textbooks differing data to interpret in a class debate. classified punctuated equilibriumas a "theory"38%, Third, as Eldredge (1989) states, the development "model" 19%, "view" 19%, "hypothesis" 12%, or of the theory of punctuated equilibrium is utterly "idea" 6% (Alters 1993). One text masterfully nego- symptomatic of a general upsurge of criticalanalysis tiated four paragraphswithout ever mentioning any going on in virtually every corner of biology. Since classification!One cannot blame the school textbook such analysis within biology has increased over the publishers for the array of classifications, as the last several years, this alone would make the phyletic scientificjournals themselves are guilty of using all of gradualism/punctuated equilibrium controversy a the above terms and more. It would benefit teachers valuable addition to the biology curriculum. if punctuated equilibriumcould be uniformly classi- Fourth, the context environment is one of true fied. The originators of punctuated equilibrium be- scientific accomplishment and one in which the stu- lieve that the classification of "theory" is most suit- dents would know that this is a real-lifeproblem, that able since it explains the fossil record (S. J. Gould, the instructor is not holding some "right" answer personal communication, January 29, 1994). Other that he/she must determine how to obtain. The authorities consider "law," or "principle," most ap- process of having the student "do" science is far propriate if it is used as a generalization or descrip- more important than the student's product. tion of the fossil record. In summary, the debate between phyletic gradual- Moreover, a wide variety of misleading and/or ism and punctuated equilibriumlends itself very well incorrect statements are associated with punctuated to higher-orderthinking and criticalreasoning skills, equilibriumin texts. For example, one middle school is current (and will be for some time), is a real (not book states, "Some scientists believe that evolution is contrived) science problem, and works well with a a gradualprocess while others think evolution occurs variety of teaching methods. in a series of rapid changes" (Villee et al. 1989). This is certainlynot incorrect,but it misleads readers into Overcoming the Obstacles to Punctuated thinking that only a dichotomy exists or that belief is Equilibriumin the Classroom the central tenet of the methods of science. As discussed earlier, an important point in punc- The major obstacle to the teaching of punctuated tuated equilibriumis how "rapid"is the punctuation? equilibrium lies in reference materials. An accurate School textbooks do not make the idea of speed any characterizationof punctuated equilibriumis a rarity less ambiguous than the various science journals among evolutionarybiologists (N. Eldredge, personal cited earlier in this article. The following are quotes communication, May 5, 1993). As noted previously, from the surveyed middle and high school texts: there are nomenclature problems with respect to hundredsof thousands;even millions of years; 100,000 punctuated equilibrium in the scientific journals years or less; 50,000 years or less; tens of thousandsof themselves, thus confusing the teacher who might years;fewt thousand or even tens of thousandsof years; like to conduct some background research. In addi- thousandsof years;1,000 to 10,000;and a fewhundred to

338 THEAMERICAN BIOLOGY TEACHER, VOLUME 56, NO. 6, SEPTEMBER1994 [. *6 9** **0 1 .1 "'0 ' 00 00 0

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B I~~~~~~~~~~~~ Downloaded from http://online.ucpress.edu/abt/article-pdf/56/6/334/46818/4449848.pdf by guest on 27 September 2021 time MORPHOLOGY Figure2. Punctuated equilibrium(paleontologists' empha- MORPHOLOGY sis): Time vs. morphology. MORPHOLOGY a few thousandyears. So, we have a range of a few Figure 3. Punctuated equilibrium (biologists' emphasis): hundredyears to millionsof years.While the time range Time vs. morphology. is reasonable, the variation and lack of agreement from one text to another could serve to weaken the the informationpresented in this article should help confidence of both educators and students. clarify many of the potential complexities. Finally, some school texts use a tree resembling Dobzhansky (1973) once argued that, "nothing in Figure 2 to illustrate punctuated equilibrium, while biology makes sense except in the light of evolution" other school texts use a tree resembling Figure 3. The (p. 125). We would add that nothing in evolution style chosen by a given journal author seems to education makes sense except in the light of punctu- depend upon whether that author is primarily a ated equilibrium. The biology curriculum will be biologist or paleontologist. For example, Figure 2, incomplete until punctuated equilibrium takes its with its horizontal branching, is used in journal place along side the work of Darwin in a truly articlesby Gould and Eldredge (1977)and by Stanley modern evolutionary synthesis. (1989), all paleontologists. Figure 3, with its non- horizontal branching, is used in journal articles by Acknowledgment Futuyma (1985)and by Scully (1987),both population and evolutionary biologists. The authors wish to thank Stephen Jay Gould and Both trees are correct. The biologists tend to illus- Niles Eldredge for their enthusiastic reviews of the trate that there is significant change in time occurring manuscript. during the punctuation period. This would help the biologists explain the punctuation period using more References conventional genetic mechanisms. Most paleontolo- Adler, J. & Carey, J. (1980). Is man a subtle accident? gists agree with Figure 3, but illustrate the punctua- Newsweek,11(3), 95-96. tion period as being more abrupt, as viewed in a Alters, B.J. (1993). An analysisof the treatmentof the topicof geological time frame, in the fossil record, as seen in punctuatedequilibria in middleand secondarylife-science and Figure 2. Each graphic representation of punctuated biologytextbooks. Los Angeles, CA: The University of Southern Califomnia,School of Education. Unpublished equilibrium has certain advantages, so armed with manuscript. the distinctions made here, the biology teacherwould Amicuscuriae brief of 72 Nobel laureates, 17 state academies be advised to use both. of science, and 7 other scientific organizations, in sup- The four cases discussed above, along with many port of appellees; submitted to the Supreme Court of the others, present significant challenges to the educator United States, OctoberTerm, 1986, as EdwinW. Edwards, in his officialcapacity as Governorof Louisianaet al., Appel- who wishes to conduct personal researchon the topic lants v. Don Aguillardet al., Appellees. and incorporate this powerful idea of punctuated Asimov, I. (1989).Asimov's chronology of science& discovery. equilibriuminto classroom discourse. We believe that New York:Harper & Row.

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TheNCational Alssociation of tdiology teachers thanks its caffiliateorgacnizaztions for their support, andfor their efforts to further biology cwl life science edMccation. BiologyAssociation of TeachersSt. Louis KansasAssociation of BiologyTeachers CaliforniaBiology Education Association LouisianaAssociation of BiologyEducators ClevelandRegional Association of Biologists MarylandAssociation of BiologyTeachers ColoradoBiology Teachers Association EmpireState Associationof Two-YearCollege Biologists MichiganAssociation of BiologyTeachers IllinoisAssociation of BiologyTeachers New YorkBiology Teachers Association IllinoisAssociation of CommunityCollege Biologists South CarolinaAssociation of BiologyTeachers IndianaAssociation of BiologyTeachers Texas Associationof BiologyTeachers

340 THEAMERICAN BIOLOGY TEACHER, VOLUME 56, NO. 6, SEPTEMBER1994