a neo-lamarckian view of molluscan evolution - researchgate

Reprinted from:The Veliger 41(3):227-238 (July 1, 1998)

© The California Malacozoological Society

William Healey Dall:

A Neo-Lamarckian View of Molluscan Evolutionby

DAVID R. LINDBERG

Department of Integrative Biology & Museum of Paleontology

University of California, Berkeley, CA 94720-4780, USA

([email protected])

Abstract. Throughout his career William H. Dall attempted to reflect evolutionary relationships in hismolluscan classifications. From 1865 to 1877 Dall’s evolutionary scenarios were built almostexclusively around heterochronic processes (primarily peramorphosis). Biogeographic congruence andnatural selection were also invoked. The patterns Dall saw and the processes he inferred were probablyderived from the training he received from L. Agassiz and others at the Museum of ComparativeZoology, Harvard University. By 1882 Dall had formalized his heterochronic arguments in terms ofEdward Cope and Alpheus Hyatt’s patterns of acceleration and retardation. Variation and de novostructures appeared through the interaction of physical forces with the organism, and were past on toprogeny by the inheritance of acquired characters. By 1882 Dall was an active participant in the Neo-Lamarckian movement in America. Dall's evolutionary models determined how he evaluated characterstate polarities, transformations, and their import. In his monographs and revisions he ordered hisspecies and higher taxa from “primitive” to “derived,” reflecting his best interpretation of their "naturalorder." The recognition of Dall's intent and the rules by which he interpreted history requires us tocarefully consider the implications of using his classifications today.


INTRODUCTION

William Healey Dall (1845-1927) was one ofthe great, late 19th and early 20th centuryAmerican naturalists. Like many naturalists ofhis time his expertise spanned a broad array oftaxa, geologic epochs and biological thought. His contributions are to a variety of fields,including physical and cultural anthropology,oceanography, paleontology, and invertebrateand vertebrate zoology. He published over1600 papers, reviews and commentaries inmany of the most prestigious journals of hisday, such as Nature, Science, AmericanNaturalist, Proceedings of the NationalAcademy of Sciences, and various publicationseries of the Smithsonian Institution (Bartsch etal., 1946). His expedition and field workcentered in Alaska, but he also conducted fieldstudies in Nicaragua and along both the east andwest coasts of the United States. He was anelected member of numerous Americansocieties, including the American Associationfor the Advancement of Science, NationalAcademy of Sciences, National GeographicSociety, Philosophical Society of Washington,as well as numerous European societies withwhom he met during his travels abroad.

Although Dall was an expert in many areasof natural history, his greatest scientificcontributions were in the field of malacology. As a malacologist working on both fossil(Tertiary) and living mollusks, W. H. Dalldescribed over 5300 species (Boss et al., 1968). Many of his publications were short taxonomicpapers, but several were comprehensivemonographs, including anatomical descriptionsand phylogenies of the taxa under consideration. Unlike most other pioneer Americanmalacologists Dall was interested in theevolutionary relationships of the taxa withwhich he worked. In two papers on thephylogeny of Docoglossa (= Patellogastropoda)published in 1871 and 1876 we get a glimpse ofhis evolutionary thinking. Like many biologistsof his day, Dall accepted evolution but thoughtDarwin’s theory did not fully explain its causes.

In this early work he used terminal addition ofcharacters, combined with biogeographicalpatterns to construct evolutionary scenarios(Dall, 1876). My purpose is to examine Dall'sevolutionary thinking as demonstrated in hispublished papers, addresses, reviews, andpersonal correspondence. My interest wasstimulated by the fact that we both have workedon the same group of gastropods – namely thePatellogastropoda (Dall's Docoglossa). However, our respective hypotheses ofrelationships are diametrically opposed (Figure2). And although both of our approaches areevolutionary in intent and argument, thediscrepancy in our respective results begsexplanation. Moreover, insights into Dall'sevolutionary philosophy may help us evaluatehis other systematic work and taxonomicgroupings, many of which remain in use today.

W. H. DALL THE EVOLUTIONIST

In Dall's (1877a) first strictly evolutionary paperhe moved closer to fully embracing Darwin’stheory of natural selection than he did in hisearlier taxonomic papers mentioned above. Hebegan by proposing a hypothesis to account for"missing links in the chain of development," apattern that he regarded as the "chief weapon ofall opponents" of natural selection (Dall,1877a:1). This defense of a theory that he hadregarded as "plausible but highlyunsatisfactory…" only six years earlier marksDall’s closest encounter with pure Darwinianevolution. Dall, aware of the absence ofintermediate types in the fossil record, had beenseeking a mechanism that would produce"leaps, gaps, saltations…for some years…” Hetermed his new mode of evolution "saltatoryevolution."

Dall began with a paradox outlined byEdward Cope (1868) in his paper “On theOrigin of Genera.” Cope had distinguished twodistinct evolutionary engines. The laws ofacceleration and retardation (see Gould,1977:85) guided the origin of genera, while the


origin of species was determined by naturalselection. These engines operatedindependently of one another. Thus, in Cope’sview it was possible “that at times the change ofgeneric type has taken place more rapidly thanthat of specific, and that one and the samespecies … has, in the natural succession,existed in more than one genus” (Cope,1868:272). This rapid change or leap wouldleave no intermediate forms and this is whatDall sought to explain and he concluded thatsaltations were “perfectly in accordance withthe view that all change is by minute differencesgradually accumulated in response to theenvironment…” (pp. 2). This is in markedcontrast to Cope’s assertion that themechanisms that would produce such leaps(acceleration and retardation) were independentof natural selection. In today's idiom, Dallsought a model to explain a macroevolutionarypattern that did not negate microevolutionaryprocesses.

Dall’s paper also contained some otherseemingly modern components. For example,Dall recognized aspects of stasis in the fossilrecord and the rapidity in which characterchange would take place, aspects of evolutionthat would much later fall under the rubric ofpunctuated equilibrium (Eldredge & Gould,1972). He also began his hypothesis with aclearly stated species concept, "... similarindividual organisms in which for the time beingthe majority of characters are in a condition ofmore or less stable equilibrium; and which havethe power to transmit these characters to theirprogeny with a tendency to maintain thisequilibrium.” (Dall, 1877a: 136).

Dall’s hypothesis required this tendency tomaintain equilibrium be strong enough to resistgradual changes in the environment until a pointwhere a critical threshold was achieved andthere was a massive reorganization within theanimal followed again by stasis. Dall likenedthis phenomenon to the damming of waterbehind debris in a gutter that ultimately wouldbreak through the dam only to reform andrepeat the event behind additional debris farther

downstream. However, the dam was nevercompletely watertight and small continuoustrickles existed between these events.

This variation and differential transmissionof the tendency to maintain character stateswould produce a divergence within a species,one population accumulating character statechanges as it tracked the environment while theother remained relatively unchanged until apunctuated event. The populations that trackedthe environmental changes on themicroevolutionary level would be better adaptedand “able to persist" across this event. Whilethose populations in stasis undoubtedly had a"broader base" [i.e., less specialized] and were"less injuriously affected by adversecircumstances and consequently might stillendure” across the event as well. Intermediateindividuals would be the “least fitted to persist”and would be “rapidly eliminated.” Throughthis model Dall envisioned “a parallel series ofspecies in two or more genera, existingsimultaneously.” Dall closed his paper with acall for the study of stasis (“inherited tendencyto equilibrium”) pointing out that the “inheritedtendency to vary” was receiving all theattention.

It is likely that Dall first noted examples ofCope’s paradox while working on brachiopodsrather than mollusks. Dall (1877b) discussedbrachiopod species pairs that had identicalspecific characters, but belonged to two genera– Terebratella and Magasella. Dall noted thatthe similarity between these species pairs was“usually only remarkable when the young of thelatter is compared with the adult Magasella”(pp. 164). After discussing the taxa and theirdistributions Dall stated that three criteria mustbe met to confirm that “the relations of the oneto the other in development should be inharmony with the development of the group asa whole in geological time and organicdifferentiation.”

1. The distribution of any two species sorelated to each other should absolutelycoincide.


2. The young should all be Magasellae; theadults (barring dwarfs), all the “companiongenus”

3. Actual study of the embryology and youngstages should be able to trace theedentueous stage into the Magasellae stage,and that into the final “companion” stage.

Dall presented observations falsifying allthree criteria and thought that “anotherhypothesis will explain them, if not equally well,yet in greater harmony with the analogy of thecase, and … with greater probability ofaccuracy.” Dall concluded that this subjectwould provide the key to some importantgeneralizations. And although he thought hehad identified transformations through threegenera “in the life of one individual,” Dalldiscounted Cope and Hyatt’s progressiveevolution as the mechanism.

Dall’s first excursion into evolutionarythought generated an unfavorable responsefrom his friend and colleague Alpheus Hyatt atthe Boston Society of Natural History. Hyattand Dall had undoubtedly met when both werestudents of Louis Agassiz at the Museum ofComparative Zoology at Harvard University in1862 (see below). Hyatt (1877a) thoughtDall’s paper on saltatory evolution to “misquoteCope and entirely skipped your humble servantwho’s specialty happens to be and has been for16 years just the point you allude to.” Hyattwent on to accuse Dall of not reading his[Hyatt’s] “little pamphlets, which I so trustinglysend you from time to time…" and of notacknowledging Herbert Spencer. Hyatt closedhis letter with pleasantries, but still maintainedthat Dall had overstated his contribution.

It is difficult to understand Hyatt’s criticismof Dall’s hypothesis. Dall did not followCope’s reasoning for the origin of genera andspecies, and his reference to Cope’s paper islimited to proposing an alternative hypothesis toexplain Cope’s one species, two generaparadox. Moreover, Dall does not mention anyacceleration or retardation mechanism, and tothe contrary, argues that natural selection alone

is sufficient to produce the paradox. SinceHyatt’s “little pamphlets” also primarily dealtwith Hyatt’s insights into the role ofacceleration and retardation in evolution, it islikewise hard to understand how Hyatt’s workrelated to Dall’s hypothesis. Whatever thesource of Hyatt’s irritation with Dall’s saltatoryevolution it apparently was soon smoothed overby a letter from Dall to Hyatt, because in lessthan 9 days’ time Hyatt had written Dall asecond letter apologizing for his hastyconclusions and promising to re-read Dall’spaper with greater deliberation (Hyatt, 3theAmerican Association for the Advancement ofScience meeting in Montreal, Quebec, Dall(1882) used the opportunity to state his view ofevolution and the role of natural selection. Dallbegan by focusing on the state of malacology inAmerica. He paid homage to Cuvier and the"immortal Lamarck" who reformed the Linneanclassification and "created a science ofMalacology" (Dall, 1882:4). He also recalledthe resistance that he and other workersexperienced when they first began to proposeclassifications that reflected phylogeny – "Theearly students, seeking to know the relations ofthe animals which were huddled in a fewheterogeneous genera by Linné, were thesubject of no little opprobrium from theconchologists of that day, and were verygenerally looked upon as dangerous radicalsand unsafe guides.”1 Dall continued with asummary of the state-of-our-knowledge ofNorth American molluscan faunas by habitat,and a review of potential research programs inthe field. Highlighted study areas includedbiogeography, the deep-sea faunas, andmolluscan development and behavior (all stillworthy topics today). The last study area thatDall addressed was “the subject, of which themethods applied to other forms of animal lifehave occupied a very large portion of thethought and activity of the scientific world for

1 It is noteworthy that similar distrust of phylogeneticclassifications and the workers who advocate andproduce them still exists in the field of malacologytoday.


more than twenty years.” Dall was speaking of“modification of organic life” and in a curiousway acknowledged Darwin without evermentioning him by name. He did this byacknowledging that the results of those studies“have revolutionized science and justlyimmortalized the remarkable naturalist who ledthe way” (pp. 10).

In contrast to his earlier paper (1877a), andunlike his treatment of Darwin, Dallacknowledged the American Neo-Lamarckianleaders by name and clearly aligned himself withthem – “The labors of Cope, Hyatt, Ryder,Morse and others among us [emphasis added],are no less fruitful than suggestive in thesedirections” (pp. 11). Dall echoed Cope’s andHyatt’s arguments that the characteristics onwhich natural selection worked were producedby dynamical evolution and “the rhythm ofdevelopment as shown by periodic accelerationand retardation….” (pp. 11). Dall evenvenerated Herbert Spencer. Dall’s praiseexactly corresponds to Hyatt’s criticism ofDall’s earlier paper and its lack ofacknowledgments.

After these acknowledgements, Dallreturned to his earlier theme of uniformity ofcharacter states between taxa and expanded itto ask the question why there were so few basicbody plans, given the profusion of variation inthe natural world. For Dall (1877b:12), theanswer to this “mystery lies in the directphysical action of the environment, by ways andmethods few of which are yet understood….”

Dall returned to the molluscan message ofhis address and revisited a topic first broachedin 1871 where he noted that natural selectionapparently was important in the evolution ofplants, insects, and birds, but had no appreciableeffect in the evolution of the Mollusca. Whereas Cope had created a dichotomy wherenatural selection was relegated to acting only atthe species level, while the laws of accelerationand retardation worked at higher levels, Dallsuggested a dichotomy based on mental andphysical prowess.

Dall considered the actions of natural andespecially sexual selection, to be far morepronounced and their effects far more importantamong organisms of "high mental and physicalrank" interacting with each other or on "lower"organisms with which "higher forms" interact. As one example of this latter case he suggestedbees and wasps interacting with plants. Dallthought simple organisms were much lesssubject to the actions of natural selection. "It isonly when advanced to a comparatively highstage of differentiation that organisms can offer,as it were, a handle for natural selection to takehold of.” (pp. 11).

Dall viewed mollusks as an intermediategroup between higher organisms (where naturalselection is active) and lower animals (where itis inefficient) and therefore concluded thatmollusks would make excellent exemplars forevolutionary studies.

Within the mollusks natural selection wasstrongest in terrestrial snails because theyinteracted with higher organisms (smarterenemies) such as birds and mammals. Colorpatterns could be strongly selected by sightedpredators. In contrast, the struggle in the seawas less violent than on land owing to the moreuniform conditions of the sea, the moreabundant food sources, and the less intelligentpredators (mainly fishes and other mollusks). Because natural selection was not as stronghere marine species showed more variation inform, external sculpture and coloration thanterrestrial species. Protoconch sculpture andthe bright colors of tropical pulmonates wereunder the control of some unknownevolutionary force.

However, even in marine species naturalselection could still operate albeit in a secondaryrole to physical causes. Dall noted that Alaskanlittorine snails exposed to heavy surf weremodified with low spires, enlarged apertures,and reduced shell sculpture. Dall concludedthat individuals not so modified would beremoved by wave action, and thought thisexample “one of the most obvious instances Ihave observed of the action of selection among


marine mollusca.” (pp. 14). Dall concluded hisaddress with a discussion of carrier shells(Xenophoridae) that have the habit ofcementing bottom debris to their shells. Heconsidered their behavior to represent anunexplainable acquisition of a valuable habitthat was perpetuated by natural selection insome species, while in others it continued topersist although it was no longer useful.

This address clearly aligned William H. Dallwith the Neo-Lamarckians. His earlier attempt(Dall, 1877a) to attribute both large- and small-scale morphological change to natural selectionwas abandoned, and the Neo-Lamarckian duetof dynamic evolution and acceleration andretardation were prominent in his world view. Although the perplexing pattern ofmorphological uniformity, first noted in 1877,still concerned him, another earlier theme –different evolutionary processes for “lower” and“higher” animals – resurfaced here as well. Because of Dall’s international reputation in themalacological community, the influence of hisevolutionary ideas was not limited to Americaand a translated extract of his address appearedwithin two months in Germany (Anonymous,1882). In his last principal paper on evolution Dall(1890) laid out his view of dynamical evolutionand argued its primary role in evolution. Dallagain returned to the argument that naturalselection does not produce variation andcontends that the physical forces andmechanical stresses placed on the organism bythe environment are the sources of variation,and that these acquired characters are theninherited. Because no two individuals are everexposed to identical environmental conditions,variation is an inescapable outcome. Dall alsorevisited his correlation between intelligenceand the strength of the role of selection withnatural, and especially sexual, selection beingmore important and often more rapid in thoseorganisms with higher “mental qualities.” Asbefore he pointed out that only one of any pairof interacting organisms need “possessintelligence of a certain grade," but his

terrestrial-snail-being-eaten-by-birds-and-mammals example was replaced by aninsect/orchid example.

Dall next considered Weismann’s (1882)attack on the evidence in support of theinheritance of acquired characters. Dallattempted to negate one of Weismann’s pointsby arguing against the inheritance of mutilationsand pathological characters. He chose as hisexample bivalve mollusks that settled in theempty burrows of rock boring taxa such asLithophagus [=Lithophaga] and pholads. Hepointed out that although they grew to conformto the “antecedent borer," he predicted thattheir progeny “would probably exhibit no tracesof their parents’ deformity.” This position wascontrary to Hyatt’s view of the potential ofpathological characters to be inherited and forma “degradational series of individuals, speciesand genera” (Jackson, 1890b). Dall thendiscussed his earlier paper on the developmentof the bivalve hinge structure (Dall, 1889) and aforthcoming paper on the development of thecolumellar folds of gastropods (Dall, 1894),both of which he considered excellent examplesof the dynamic influences of the environmentsof organisms (see below).

In a note added after his paper was readbefore the Biological Society of Washington,Dall reported that the Darwinians (and strongcritics of dynamical evolution) Lankester andWeismann had recently suffered serioussetbacks in their championing of naturalselection over Neo-Lamarckism. Dall’ssatisfaction with this state of affairs is expressedin his addendum:

“In fact these and other signs indicatethat the most able of those who havethrough haste or conservatism beendisposed to ignore dynamical influencesin evolution, will before long join in theprocession, and lend their undoubtedabilities to the perfection and elaborationof the only theory yet propounded whichfully and efficiently supplements that ofNatural Selection and closes the too


obvious gaps which have hithertoexisted in the intellectual structure of themodern theory of organic evolution”(1890:10).

Osborne (1890) made the same argument in asimilar response to the apparent weakening ofWeismann’s position.

In a review of Dall’s paper Jackson (1890a)credited Dall with providing a new way tounderstand the relationship between dynamicinfluences and natural selection. Rather thanthere being two separate forces in evolution,natural selection acted “in harmony with, and asa natural outcome of dynamic influences.” According to Jackson, Dall had melded theengine of variation (dynamic influences) withnatural selection.

Dall published two other papers that dealtwith dynamical influences in molluscanevolution. In the first Dall (1889) addressed thehigher classification of the Pelecypoda(Bivalvia). He considered earlier attemptsunsuccessful because the characters on whichsuch work had been based were “notfundamental in the evolutionary history of theminor groups” (Dall, 1889:445). For Dall thecharacters of adductor muscles, gills andsiphons were too variable because they wereintimately associated with the “mechanics” ofthe group. Dall then provided examples toillustrate his point and included a discussion ofthe role that convergence would play inconfusing relationships. Dall regarded the thencurrent classification based on hinge structuresas suspect, but he felt it could be resolved ifinterpreted in the context of dynamicalinfluences as Cope and Ryder had done in theirstudies of the development of the mammalianfoot and tooth.

Dall’s “archetypal form of bivalve” wassmall, with symmetrical, equilateral valves, ashort, central ligament, and a smooth hingearea, and noted that this was the case in thelarval shells of many taxa. He argued for initialsmall size of bivalves based on the fossil record. Dall also allowed that this condition “in the

adult state” was likely due to “degeneration.” Thus, as long as the taxa remained small andsymmetrical there was no mechanical selectionon the hinge structure. However with sizeincrease and/or asymmetry, the forces were nolonger trivial and changes in the ligament andhinge plate structure would be compulsory tocompensate for the new mechanical conditions– “Nature, through natural selection andphysical stresses, has developed these cardinalprocesses which are known as teeth” (pp. 452).

Based on his understanding of the evolutionof the bivalve hinge structure Dall proposedthree orders. These were theAnomalodesmacea, Priondodesmacea, andTeleodesmacea, the last taxon having the“highest and evolutionarily the most perfecttype of hinge.” Moreover, “prionodont traces”remained in most members of this latter group –a clear indication of the direction of evolution inthe group. Dall also correlated the presence ofnacre with these tooth types showing itcommon in the Anomalodesmacea, but absent inthe Teleodesmacea. The remainder of the paperdiscussed groupings within these orders and thederivation of their hinge structures. As in hisdynamical influences paper (Dall, 1890), heused a supplementary note at the end to againdrive home the importance of physical forces inevolution and its implications for reconstructingmolluscan evolution. Citing unnamed workerswho considered the molluscan shell to benothing more than a secretion of the mantle,Dall conceded that the “original theoreticprotoconch” may have been so, but once itexisted it came under the influences of physicalforces that influenced the growth and structureof the viscera. Dall saw molluscan anatomymolded by the shell as much as the shell wassecreted by a portion of that anatomy. In thisview the physical factors that produced the shellacted through the shell to constrain theanatomy. Thus, it was Dall’s conclusion thatwhen “intelligently studied and properlyappreciated” the relationships of the Molluscaare discernible solely through shell characters. The idea that the shell mechanically constrained


the viscera was to be revisited in his secondpaper considering dynamical influences.

In this work Dall (1894) addressed themechanical causes of folds in gastropodapertures. Dall began with the observation thatamong fusiform rachiglossate taxa theattachment points for the adductor muscle liedeeper within the shell in those taxa withcolumellar folds than in those without folds. Hethen formulated a model in which the gastropodanimal consisted of a thin, loose, cone-shapedmantle epidermis in which the relatively solidbody cone resided. The adductor muscleattached this dual cone complex to the shellcolumella. Dall envisioned that when the animalretracted into its shell “the natural diameter” ofthe mantle cone would exceed the shell volumeand the mantle epidermis would thereforewrinkle longitudinally. The strongest foldswould be along the columella because “theattachment of the adductor prevents freedom inwrinkling, and the groove of the canal willmechanically induce the first fold in thatvicinity.” Repeated extension and contractionof the wrinkled surface over the shell wouldproduce plications on the columella and eitherlirae or teeth on the outer lip of the aperture.

Dall then returned to his earlier observationof the correlation that the attachment points forthe adductor muscle lie deeper within the shellin those taxa with columellar folds than in thosewithout folds. Dall explained that taxa with theadductor muscle closer to the aperture wouldexperience less compression of the bodycomplex and therefore fewer wrinkles of themantle would be produced. The deeper theadductor attachment point, the morecompression of the body and more wrinkling,thereby producing more plications. Dallconsidered this explanation to have “marvelousprecision with the results called for … based onthe dynamical status of the bodies concerned,their motions and secretions” (pp. 913). Moreover, the exceptions were readily clarified. For example, species with extensive mantlestypically had lirate apertures (e.g., Oliva spp.,Cypraea spp.). Those with extensive mantles

but no lirae do not entirely withdraw into theirshells (Harpa spp., Opistobranchia).

Unlike his earlier hinge structure paper, thisarticle made no reference to the usefulness ofthese characters in understanding theevolutionary history of the rachiglossate taxa inwhich they were expressed. Instead, Dallseemed to view them as constructional artifacts;features that are present only because of theinteraction between tissues and coiled shell. Itis interesting that nowhere in this paper doesDall use the term “natural selection.” In Dall’sevolutionary model natural selection acted “inharmony with, and as a natural outcome ofdynamic influences.” Although these particularcharacters were the products of dynamicinfluences, they remained neutral and were notselected for, most likely because they were toointimately associated with the “mechanics” ofthe group.

NEO-LAMARCKIANISM INMOLLUSCAN CLASSIFICATION

In 1871 Dall published his first “natural” (=evolutionary) classification of a molluscantaxon, treating the Docoglossa (i.e.,Patellogastropoda of Lindberg, 1986); theclassification had been read before the BostonSociety of Natural History on 19 October 1870.For the next 50 years this arrangement of taxawould remain virtually unchanged in Dall’spublications and serves as one of the bestexamples of Dall’s evolutionary reconstructions. Dall had not previously stated any evolutionaryphilosophy, so the arguments he marshaled infavor of his 1871 patellogastropod classification(and in subsequent papers in 1876 and 1893),combined with the three evolutionary articlesdiscussed above are used here to examine hisapproach to reconstructing molluscanrelationships during the second half of the 19th

century.In the "General Remarks" section, Dall

(1871) made several statements thatunderscored parts of his evolutionaryperspective at that time. He considered the


group to have a "peculiar persistency ofimmaturity, when compared with other groupsof gasteropods [sic]"; for him this trend wasespecially evident in the shell, radula, and gills. Dall (1871:233) also found "a certaingeographical agreement in regard to genericcharacters which favors the hypothesis of adevelopment of the various forms from a fewmore simple and more closely allied ancestors." That concept would be more fully developed in1876, and although Dall believed that thispattern was the result of evolution, he could notattribute it "to the very plausible but highlyunsatisfactory doctrine of 'natural selection.'”

Dall's (1876) second paper on docoglossanphylogeny began with a comment onLankester's (1867) mistaken identification of thepatellogastropod “wart organs” as gonopores. The anatomical observations that he made torefute Lankester, combined with his acquisitionof additional specimens, provided Dall with theopportunity to further resolve and expand uponhis earlier phylogeny.

Dall viewed the northwest coast of Americaas the center of origin of the Docoglossa. Fromthere they had migrated south and east wherethey "changed or added to their originalcharacters" (Dall, 1876: 40) (Figure 1). Thispattern required three components to support it:(1) the "maximum development of the lower orparent forms" in the North Pacific, (2) "a localabundance and radiating distribution of the nexthigher genera," and (3) the presence of the mostspecialized taxa in the nearest "favorable"region. The importance of the proximity of the"favorable" region was a suspected correlationof time with specialization. Thus, the soonerthe ancestral taxon could get to a new area, themore time there would be for subsequentspecialization to occur. In the Docoglossans“this is exactly the real state of the case.”

Dall considered radula, gills, sensorystructures, and body size to be key charactersfor reading this pattern, and all supported hismodel. The supposedly most primitivedocoglossans – the lepetids – are foundsubtidally in the Arctic and boreal North Pacific

and Atlantic oceans. They are small limpetswithout eyes, gills, and lateral teeth and are"sluggish in their motions." Given theirobviously inferior condition, Dall concludedthat they were "protected by the uniformconditions of their deep water station."

Dall suggested that the Acmaeidae evolvedfrom the lepetids by developing the radula(perhaps by "natural selection") and acquiringeyes and gills; a general size increase was alsopresent. “Strong in the possession of their neworgans" they invaded the intertidal zone(Collisella) although a "few smaller and weakerforms" remained in the subtidal. Travelingwestward from their North Pacific center theAcmaeidae reached Japan (Collisella) andmigrated down the western Pacific margin toAustralia (Collisellina). Conditions were lessfavorable eastward through the Bering Straitand over Arctic Canada, and this accounts forthe fact that only two species occur in northernEurope. Lottia, with its large size (>100 mm)and the addition of a secondary gill, representedthe next step in acmaeid evolution. Completionof the secondary gill along the anteriormostmantle margin in Scurria of South Americamarked the "highest stage of development" inthe family.

For Dall the next step in the development ofthe Docoglossa was the transition from theAcmaeidae to the Patellidae (Figure 1). Thiswas accomplished by: (1) loss of the gill fromthe nuchal cavity ("rejection of useless parts"),(2) development of the muzzle frill into tactilepapillae, (3) development of a "rhachidian [sic]tooth of properly proportioned size," and (4)development of the "abortive uncini of theAcmaeidae" into functional teeth. Moreover, itis in this last group that "the highestdevelopment of total bulk known to the order,is added to the greatest known specialization ofthe other characters."

For Dall there was complete agreement ofcharacter polarities and transformations in fourdistinct character groups of eleven taxa, as wellas complete biogeographic congruence betweentheir distributions and relationships as well as


aspects of their ecology. These latter twoaugmentations of character polarization wouldbe formalized as the criterion of “chronologicalprogression” (Hennig, 1966). Dall (1876:40)was so confident of his phylogeny that heargued, “In many cases their paths have becomedry land, and the track must be followed ratherby organic relations than contiguity indistribution.” Modern practitioners ofvicariance biogeography share Dall’s confidencein biological relationships as a guide toreconstructing earth history. Dall knew that“Greater knowledge would doubtless increasethe complications” for his phylogeny, but he stillallowed that “without verging greatly on thespeculative, we may construct a genealogicaltree, which cannot greatly differ from thefollowing scheme” (Figure 1).

Dall's first two papers on docoglossanphylogeny were published only 5 years apart,but it was 17 years until the third paperappeared. In the interim all three of Dall’sevolutionary theory papers appeared. Dall(1893) wrote the third phylogeny paper as aresponse to Thiele (1891) who Dall felt hadmisinterpreted his conclusions regarding themost primitive members of the Docoglossa. Dall’s arguments are similar to his earlier pointsand there are no obvious references todynamical evolution. The only element in thispaper that may reflect Dall’s acceptance ofNeo-Lamarckian principles is used as adisclaimer for the phylogeny he was defending. Dall (1893:285) confessed that he attached“little importance to speculations of this kind,which can only be placed on firm footing byextended embryological researches…”

After this caveat Dall stated that "we findtherefore in Lepetidae the greatest number ofarchaic characters (somewhat masked bydegeneration of other organs) which remain inany of the three groups..." (Dall, 1893:285). Tothe earlier characters he now added protoconchmorphology, and reiterated the patterns of the1876 phylogeny, starting in the cold northwhere the simple forms first appear andsubsequently migrate into the temperate and

ultimately tropical regions of the world wherethey become larger and more complex in theircharacter states.

The most interesting portion of this paper isDall’s (1893:287) cautionary remarks aboutconvergence in limpet-like shell morphologiesand a prediction about monoplacophoranaffinities. A series of discoveries of distinctradular types in deep-sea limpets with virtuallyidentical shells had impressed on Dall the strongconvergence that was possible in limpet-likespecies. If such convergence were possible inliving species, fossil taxa would likely be presentsimilar problems. Moreover, determinations inthe fossil record would be even more dubious,the deeper the time and the more unfamiliar thetaxa. He singled out the similarity of shells ofSilurian Tryblidium with Recent patellid taxaand warned that it was dangerous to concludethat Tryblidium anatomy would have beensimilar to living patellids – “it is almostinconceivable that the Silurian form shouldhave any closely allied recent representative.” Moreover, the symmetry of the adductor scarsof the monoplacophoran fossils suggested toDall “a peculiar disposition of the organs whichmight, indeed, have paralleled in someparticulars the organization of some of theChitons of that ancient time.” It would be 45years until the same argument was repeated byWenz (1938) (see Knight, 1952), and another19 years before the recovery of livingmonoplacophorans confirmed Dall’s insight intothe non-torted state of these animals (Knight &Yochelson, 1958).

In summary, the overall direction of Dall'sevolutionary trends in the patellogastropodswas the addition of characters; this resulted inan increase in both complexity and size indescendant taxa. Dall’s polarity determinationswere based on ingroup comparisons. However,by 1893 he thought that the ultimate test of hisphylogeny would be made by extendedembryological research.

Cladistic analysis (Lindberg & Hedgeaard,1996) (using many of the same characters thatDall used) produces a hypothesis of


relationships that reverses Dall’s evolutionarytrends and argues that the derived taxa exhibitmostly paedomorphic, not peramorphic,character transformations (Lindberg, 1988a,1988b) (cf. Figures 2a & b). The diametricallyopposed nature of our respective phylogeniesresults from our different assumptions regardingcharacter polarity and transformations. Dall'smodel assumed strictly progressive evolutiongoing from simple to complex forms by terminaladdition. In contrast, the alternative phylogenyof Lindberg & Hedegaard (1996) is based on aparsimony analysis, with the determination ofcharacter polarity and transformations based onoutgroup analysis.

Dall’s work on bivalve taxa in the late1890’s and early 1900’s also containsterminology and scenarios indicative of Neo-Lamarkian thought. Many of these scenarioscontain terms that make them appearmainstream from today’s perspective, butdynamic evolutionary thought is clearly present. Dall (1901) considered the shell sculpture ofthe Lucinacea, which showed virtually nochange from the Cretaceous to Recent, to be anexample of “neutral selection." Dall argued thatthe sculpture originally resulted from “triflingmutations of the armature of the mantleedge…” but were not “essentials in the lives ofthese animals…” Therefore, once they wereacquired “natural selection has little or noinfluence upon them, and therefore rarely setsup any tendency to change” (Dall, 1901:780).

Dall’s (1899) synopsis of the bivalve group“Leptonacea” (= Galeommatacea) wellillustrates his evolutionary views at the end ofthe 19th century. He saw in this group thegeneral effects of degeneration overlain bymodifications for specific habitats. Dallconsidered this group to have membersrepresentative of “teleodont” ancestors. However, this similarity was only superficialbecause groups that represented true startingpoints for taxa are “notable for their tendency tovary and interchange characters.” In theLeptonacea the evolution of commensalism andparasitism produced paedomorphic characters

“accompanied by a revival of atavistic primarycharacters” (Dall, 1899:873). Dental features ofthe hinge plates of the Leptonacea resulted fromdegeneration and had produced indistinct andamorphous dentition. Bernard (1897) had usedpositional information to argue homology ofbivalve hinge plate structures, but Dallcautioned that:

The dynamic reactions of the teeth uponeach other are, I am confident, of theutmost importance in the development ofthe hinge. As in the vertebrate skeleton,pressure and friction in localized areaswill produce directly a response in facetsand buttresses. In fact, to the eye trainedto take such matters into account, everyhinge [emphasis added] shows more orless evidence of the mutability of hingestructure and its responses to stress aswell as to inherited tendencies of form” (Dall, 1899:874).

Moreover, of all the bivalve groups Dallthought this mechanism was most obvious inthe Leptonacea. Thus, from a reduced andsimplified starting point “trifling modifications”resulting from dynamical evolution produced allstates seen in the taxon.” Although the overall pattern was from simpleto complex forms by the addition of structuresto the hinge at the pressure points, furtherdegeneration also could occur.

Five of the 17 characters used by Bieler &Mikkelsen (1992) in their phylogenetic analysisof the leptonacean taxon Galeommatidae werebased on hinge structures and all weresubsequently discovered to be synapomorphiesof clades. Like the patellogastropod examplediscussed above, most of the transformations inthese characters involved reduction or loss(lateral hinge teeth, cardinal teeth), not thesimple-to-complex pattern Dall saw in hisscheme. Bieler & Mikkelsen also concluded thathinge teeth states were difficult to interpret andscore. Unlike Dall, but in agreement withBernard, they suggested that ontogentic studies


would be required to resolve hinge teethhomologies. These and other examples suggestthat it was not Dall’s eye that was trained to seethe natural arrangement of the taxa he studied,it was an unqualified belief in Neo-Lamarckianprinciples that found its support in every bivalvehinge he examined.

DISCUSSION

William H. Dall’s early training in “naturalclassifications” as well as clandestine exposureto evolutionary theory began at the Museum ofComparative Zoology (MCZ), HarvardUniversity in 1862. Dall’s father, a graduate ofHarvard and Harvard Divinity School, took the17 year old William to meet Louis Agassiz in1862. Dall subsequently left high school in hisfinal year to begin studies with Agassiz. Although Dall always referred to himself as a“pupil of Agassiz”, there is little evidence toindicate that the feeling was mutual. Winsor(1991) does not list Dall as one of Agassiz’sstudents or associates nor does he appear onunpublished lists of students (Winsor, personalcommunication). Dall’s (1908) listing of hisfellow students at the MCZ includes J. A. Allen,H. Hagen, C. F. Hartt, F. W. Putnam, S. H.Scudder, and A. E. Verrill and corresponds wellwith Winsor’s student chronology with twonotable exceptions. The first is Dall’s omissionof A. Hyatt who was in residence at MCZ from1858-1864; the second is Dall’s listing of H.Hagen, who did not arrive at Harvard until1867, four years after Dall had left Harvard(Dall, 1908; Winsor, 1991). Dall did notreceive a doctorate degree until 1904 when theUniversity of Pennsylvania conferred anhonorary degree of Doctor of Science (Dall,1908).

The absence of W. H. Dall’s name from thestudent rosters likely resulted from theintroduction his father provided to Agassiz. The elder Dall was a Unitarian missionary toIndia and he had hoped to see the younger Dallenter the tea trade in Assam, India. Accordingto Bartsch, et al. (1946), Agassiz and his

colleagues recognized the potential of having aMCZ collector in India and gave the young Dallintensive training in collecting and naturalhistory. Thus, Dall may have had a differentcurriculum and status at MCZ than hiscontemporaries. Dall (1908) recounts that hisyear or so at the MCZ consisted of training inzoology under Agassiz, training in anatomy andmedicine under Wyman, and geology fromAgassiz’s lectures. It is also likely that Dall wasexposed to discussions of Darwinian evolutionwhich first began among Agassiz’s students(including Morse, Verrill and Hyatt) in 1860(Wayman, 1942; Winsor, 1991).

Further zoological training, and especiallyexposure to evolutionary thinking, wereprobably limited after Dall left Harvard and theMCZ in 1863. Upon leaving Harvard, Dall didgarrison duty at the Watertown Arsenal, thenworked on the India Wharf as an office boy forthe firm of Deshon & Yarrington (West AfricanTraders), and later that year went to Chicagowhere he found work in the land office of theIllinois Central Railroad (Dall, 1908). In early1864 Col. J. W. Foster aware of Dall’s trainingwith Agassiz, asked Dall to serve as hisassistant surveying iron deposits in northernMichigan during the summer of 1864. Upon hisreturn from the field Dall spent the fall andwinter preparing field reports and working onthe chemistry of iron and steel. In late 1864 andearly 1865 Dall volunteered evenings at theChicago Academy of Sciences (directed byRobert Kennicott) and studied anatomy andmedicine under the direction of Daniel Brainardand N. S. Davis (Dall, 1908).

In early 1865 Kennicott asked him to jointhe Alaska Survey Party for the Russian-American Telegraph Company. He left forAlaska in March 1865 and did not return to theEast Coast until October of 1868. Scientificinteractions during this time were limited to an8-month stay in San Francisco betweenNovember 1865 and July 1866.

Dall took up residence at the SmithsonianInstitution in December 1868 and beganworking on his collections from Alaska. He had


completed his studies for the naturalclassification of the Patellogastropoda byOctober 1870. In July 1871 he was againsailing to Alaska, this time in the employment ofthe U. S. Coast Survey and charged withsurveying the Alaskan coastline; he returned tothe Smithsonian in the winter of 1874(Woodring, 1958).

After his return he may have discussed someaspects of evolutionary theory with A. Hyatt. In a letter to Dall dated 21 October 1873, Hyattwrote of the “little successes” Hyatt hadexperienced on his recent trip to Europe. Hyattconfided to Dall that his “theoretical views withregard to the evolution of forms etc. mustundergo great changes but that in the main theyare correct.” Hyatt did not go into detail in hisletter but promised Dall “all sorts ofdiscussions” when he visited Hyatt inCambridge the following spring (Hyatt, 1873); there is no record of what they may havediscussed. Within three years of his return Dallpublished his paper on saltatory evolution.

The above chronology suggests that Dallhad few opportunities to discuss and interactwith colleagues engaged in evolutionary studiesafter he left Harvard until he returned to theSmithsonian in late 1874. Possible exceptionsinclude the time he spent at the CaliforniaAcademy of Sciences and the three years at theSmithsonian between 1868 and 1871.

The importance of Dall’s contributions toNeo-Lamarckian theory are difficult to gauge.Jackson (1890a) favorably reviewed Dall’spaper on dynamical influences in the AmericanNaturalist and cited his contributions tomolluscan evolution in his work on bivalvephylogeny (Jackson, 1890b). Hyatt (1894)acknowledged Dall only for loaning ammonitesto him in his1894 tome on the Phylogeny of anAcquired Characteristic. In contrast, the workand contributions of Cope, Jackson, andBeecher were widely cited by Hyatt. Cope(1896) listed Dall second in research featuringthe inheritance of mechanically acquiredcharacters in the Mollusca [Hyatt, Dall,Jackson, and Beecher] and he cited Dall’s work

a total of four times. Kellogg (1908) presentedDall’s (1877a) theory of sudden species changesin his chapter on “Other theories of species-forming.”

Pfeifer (1965), who considered Dall a lesserfigure in the American Neo-Lamarckian school,also cited Dall’s (1877a) paper, finding in it theNeo-Lamarckian disposition to view evolutionas a struggle between the forces of change andthose of equilibrium, but there are no otherclues here that Dall was writing from a Neo-Lamarckian perspective. To the contrary, heevoked only natural selection as a process, anddid not spare his praise of “Mr. Darwin, whomnothing escapes…” This paper contains noreference to the inheritance of acquiredcharacters or the source of variation. Instead heattempts to explain stasis in the fossil recordand argues the equal importance of the“inherited tendency to equilibrium” with the“inherited tendency to vary.”

Hyatt’s (1877a) accusatory letter that Dallhad failed to cite pertinent literature suggeststhat Dall was not fully immersed in the Neo-Lamarckian literature at that time, and there isevidence that Cope et al. did not consider himone of their own either. Cope’s (1896:528)“List of Papers by American Authors who haveContributed to the Evidence Used in this Book”lists Dall’s evolutionary papers beginning in1889. The only reference to an earlier paper isCope’s mention of Dall’s (1877b) brachiopodwork in which Dall rejected progressiveevolution as an evolutionary mechanism in theformation of species pairs, an uncharacteristicaction for a supposed Neo-Lamarckian. Lastly,Dall’s (1877a) own footnote states that he didnot have a copy of Cope’s (1868) paper andhad not read it since its publication. It had beenpublished 9 years earlier and most likely cameout during his 8 month association with theCalifornia Academy of Sciences betweenAlaskan cruises. This suggests Dall was notfully familiar with the literature on evolutionarytheory. However, by 1882 there is no doubt ofDall’s knowledge of, and allegiance to the Neo-Lamarckian school.


Dall’s account of his formal trainingcombined with his opportunity to interact withcolleagues in the Neo-Lamarckian movementand the above analyses of the evolutionaryscenarios in his papers, suggests two stages inDall’s evolutionary thinking. Before 1877Dall’s views were built exclusively aroundheterochronic processes and often incorporatedbiogeography into his patterns (e.g., Figure 1). While there were some gestures to the role ofnatural selection, they were never developedand no alternative evolutionary modes wereproposed or discussed. By 1882 Dall hadformalized his heterochronic arguments with thepatterns of acceleration and retardationespoused by Cope and Hyatt. This is also whenexamples and arguments in favor of theorigination of structures by physical forces andthe inheritance of acquired characters firstappear in his writings. Dall’s first stagerequired nothing more than the training hereceived from Agassiz or reading Agassiz’s(1857) “Essay on Classification” (see Winsor,1991 on the training of Agassiz’s students). While the influences for the second stage ofDall’s evolutionary views most likely came fromHyatt and Cope and developed after Dallreturned to the Smithsonian in the late 1870’s. Perhaps this was spurred, in part, by Hyatt’sreview of Dall’s (1877a) first evolutionarypaper. Interestingly, that paper is primarilyDarwinian and therefore anomalous to bothstages.

It is likely that Dall's role and involvement inthe American Neo-Lamarckian movement hasnot been widely recognized in malacologicalcircles because his prodigious publicationrecord has caused the few primarilyevolutionary articles to be lost among thehundreds of papers on other topics. Moreover,most of his biographers have been malacologistswho have focused on his contributions tomolluscan systematics rather than his views onevolution. For example, Woodring (1958) in abiography for the National Academy ofSciences listed Dall's "principal contributions toscience", but not a single publication on

evolution is listed. I think there is little doubtthat if dynamical evolution had not beenrejected as an evolutionary hypothesis, Dall’scontributions in this area would have beenprominently listed here. Dall bet on the wronghorse, and although his evolutionary philosophyhas tremendous implications for his systematicsand ultimately the classifications he produced, ithas been previously ignored because of aparadigm shift.

It is both unfair and inappropriate to judgeDall's evolutionary thinking in terms of today'stheories and assumptions of evolutionaryprocesses and models. For their time Dall'sevolutionary arguments are both plausible andinternally consistent. With the rediscovery ofMendel's work in the early 20th century and theemergence of a new model for the passing ofcharacters between generations and the originof variation, the Neo-Lamarckian model was nolonger viable and its advocates were soon quiet.

Although criticism of Dall's evolutionarytheories is untimely, the legacy of his immensecontribution to North American molluscanclassification based on those theories remainslike a skeleton in the closet. Because of thenomenclatural status of his work, and becausenomenclature and taxonomy are not decoupled,it cannot be swept away or ignored as a sillyidea of the past. Dall's evolutionary modeldetermined how he evaluated character statepolarities, transformations, and their import. Inhis monographs and revisions he ordered hisspecies and higher taxa from “primitive” to“derived” reflecting his best interpretation oftheir "natural order." The recognition of Dall'sintent and the rules by which he interpretedhistory requires us to carefully consider theimplications of following his classificationstoday. The necessity of using phylogenies inbiological or paleontological studies thatpurport to draw evolutionary conclusions iswell documented (e.g., Lauder, 1990; Brooks &McLennan, 1991; Wenzel, 1992; Padian et al.,1994). While criticizing Dall may beinappropriate, workers who continue to use hisclassifications in evolutionary studies without


first rigorously testing his phylogenies do notshare his exemption.

ACKNOWLEDGMENTS

I am indebted to D. Jacobs for discussions ofthe heterochronic world of Agassiz, Hyatt andCope. The late J. Houbrick and J. Harasewychprovided access to and assistance with the W.H. Dall reprint collection in the Mollusk sectionof the U. S. National Museum of NaturalHistory. E. Gerson, M. Winsor and J. Valentinewere helpful guides to the literature on theAmerican Neo-Lamarckians, and E. Yochelson,B. Roth and an anonymous reviewer providedhelpful criticism of the manuscript. This iscontribution number 1658 from the Universityof California Museum of Paleontology.

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Table 1Synonyms and equivalents of Dall’s (1871) taxa (Figure 1) used for cladogram

construction in Figure 2.Figure 1. Dall (1871) Figure 2. Lindberg (1988a, In press)Cryptobranchia Included in LepetaPilidium PropilidiumLepeta LepetaCollisella LottiaCollisellina PatelloidaAcmaea AcmaeaLottia LottiaScurria ScurriaPatella PatellaNacella NacellaPatinella NacellaPatina HelcionHelcion HelcionHelcioniscus CellanaAncistromesus Scutellastra


North

Lepetidae

LepetaCryptobranchia

Pilidium

Acmaeidae

AcmaeaCollisella

Collisellina

Scutellina?

Patellidae

Lottia

Scurria

Patella

Nacella

Patinella

HelcioniscusHelcion

Ancistromesus

South

EastWest

Patina

Figure 1“Genealogical tree” of the Patellogastropoda redrawn from Dall (1876). Note the

incorporation of biogeography into Dall’s scheme.


A

Lepeta

Propilidium

Lottia

Patelloida

Acmaea

Scurria

Patella

Nacella

Helcion

Cellana

Scutellastra

Lepetidae

Acmaeidae

Patellidae

Scutellastra

Cellana

Nacella

Patella

Helcion

Scurria

Acmaea

Lottia

Patelloida

Lepeta

Propilidium

B

Patellina

Nacelloidea

Acmaeoidea

Figure 2Phylogenetic relationships among the Patellogastropoda. A. Dall’s (1876) genealogical tree

(Figure 1) redrawn as a cladogram; stippled branches have 0 length. B. Cladogram based onparsimony analysis of the Patellogastropoda [redrawn from Lindberg & Hedegaard (1996)].

See Table 2 for synonyms and equivalent taxon names.

a neo-lamarckian view of molluscan evolution - researchgate

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