Alan D. Gishlick, National Center for Science Education ... of Darwin, Haeckel, and ... strongest class of facts” in favor of his theory. ... but his laws do not prohibit development

HAECKEL’S EMBRYOS

ERNST HAECKEL ANDCOMPARATIVE EMBRYOLOGY

Ernst Haeckel (1834–1919) is both a heroand a villain in the biological communi-ty. He was a prominent figure in the late

nineteenth-century comparative anatomy com-munity and is famous for his phylogenetictrees, anatomical illustrations, support for evo-lution, and strong personality. He is perhaps aswell known, and considerably misunderstood,for his studies in embryology and his dictumthat “ontogeny recapitulates phylogeny,”called the Biogenetic Law. Haeckel espousedthe view that evolution generally proceeds byplacing each innovation on top of a previousone, like adding layers on a cake. Therefore,the embryo of an “advanced” organism shouldpass through (“recapitulate”) the adult stagesof more “primitive” forms as it develops.However, repeated observations of develop-ment by other workers (e.g., Wilhelm His,Walter Garstang, Wilhelm Roux, AdamSedgwick, Gavin de Beer, and others; seeGilbert, 1991, or Gould, 1977 for a detailedhistory) clearly showed that embryos do not gothrough adult stages of lower forms; rather,they share many common features in develop-ment. No biologist has accepted the biogeneticlaw for many decades and it may have been acaricature of Haeckel’s actual views anyway.Much of Haeckel’s developmental work isnow considered invalid, and some historians ofscience have provided reasonable evidence tosuggest that he manipulated his drawings to fithis preconceived views about developmentand evolution. Haeckel’s views about the pro-gressive nature of evolution are no longeraccepted.

Regardless of Haeckel’s accuracy or precon-ceptions, comparative embryology continues

to be central to our understanding of evolution.Comparative embryology shows how differentadult structures of many animals have thesame embryonic precursors. These shareddevelopmental features suggest that many ani-mals have ancestors in common. Further com-parative embryology shows that closely relat-ed animals show a unity of developmental pat-tern, particularly in earlier stages, and havemore developmental features in common thando more distantly related organisms. The factthat certain incipient structures such as pha-ryngeal pouches or arches exist in all verte-brate embryos yet develop into very differentadult structures suggests that they all share acommon ancestor whose embryo had pharyn-geal pouches (at least at some stage in devel-opment). In this way, developmental similari-ties that are inherited from a common ancestorare homologous, just like the patterns of bonesin adult limbs.

DEVELOPING AN ARGUMENT

Wells’s entire chapter on embryologyamounts to little more than a mis-reading of Darwin, Haeckel, and

others, combined with a general failure toacknowledge recent work on Haeckel and hisembryos by Gould, Richardson, and others. Init, he conflates ideas in history of developmen-tal biology with ideas of contemporary devel-opmental biology. He also fails to recognizeclose to 60 years of work in developmentalbiology and thus completely omits any discus-sion of the real developmental evidence forevolution. It almost seems that Wells’s goal isto discredit the entire field of comparativeembryology by proxy, employing a bait-and-switch between Haeckel and Darwin. Wells’sploy is reminiscent of a child’s false logicproof. It goes like this: Darwin relied onHaeckel, Haeckel was a fraud, thereforeDarwin is a fraud.

Icons of Evolution? Why Much of What Jonathan Wells Writes about Evolution is WrongAlan D. Gishlick, National Center for Science Education

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The charge that Ernst Haeckel intentionally“faked” his drawings is irrelevant. Regardlessof his intent, the drawings that Haeckel madeare incorrect, especially in what he labeled asthe “first stage.” But it really does not matterwhat Haeckel thought or whether his drawingsare accurate: modern comparative embryologydoes not stand or fall on the accuracy ofHaeckel any more than modern physics standsor falls on the accuracy of Kepler or Newton.Historically, Wells actively ignores the accu-rate work of many of Haeckel’s predecessorsand contemporaries (such as William andJeffrey Parker, Hans Gadow, Hans Selenka,Heinrich Rathke, Virgil Leighton, HugoSchauinsland, and Alfred Voeltzkow, to namea few). Haeckel and von Baer were not theonly embryologists in nineteenth-century sci-ence, but you wouldn’t know that from readingWells. Worse, Wells speciously extends his cri-tique of Haeckel to the present day. Wellsimplies that textbooks misrepresent the studyof developmental programs as evidence forevolution by accusing them of using Haeckel’sinaccurate drawings, in effect accusing text-books that show any embryos of “mindlesslyrepeating” Haeckel. The important question iswhether textbooks, and more importantlydevelopmental biologists, still rely onHaeckel’s work. The answer is no, but thatdoesn’t stop Wells from acting as if they do.

Wells sets up a straw man in his bait-and-switch, starting with Darwin’s famous asser-tion that embryology represented the “singlestrongest class of facts” in favor of his theory.Here Wells misrepresents both early embryol-ogy and Darwin’s own words. When quotingboth Darwin and other historical figures, hequotes them out of context, leaves out impor-tant parts of quotes, and even changes theorder of their appearance, all to misrepresenttheir real meaning and intent. Wells also con-flates “recapitulation” — that is, that embryos

go through the adult stages of their ancestors— with the idea that shared features ofembryos give insight into their phylogeneticrelationships. Failing to distinguish theseallows Wells to avoid dealing with the actualevidence for shared developmental features invarious embryos and to dismiss the entire fieldas based on an outdated and outright refutedclaim, one that embryologists know to be falsebut cling to anyway because of an ideologicalcommitment to evolution. Wells should knowbetter, as the holder of a Ph.D. in cell anddevelopmental biology.

REWRITING HISTORY FORTHE GREATER GLORY OF

THE REV. MOON

In the introduction to Icons, Wells statesthat he first became aware of the problemsin evolutionary theory when he was “fin-

ishing his Ph.D. in cell and developmentalbiology” (Wells, 2000:xi). He claims that heknew that the drawings of embryos presentedin textbooks were false because he was adevelopmental biologist. Shortly thereafter, heclaims, his observation was confirmed byother scientists. Before that seminal event, hesays, “I believed almost everything I read inmy textbooks” (Wells, 2000:xi). This state-ment is inconsistent with other claims ofWells’s. According to statements made byWells in a sermon on a Unification Churchwebsite (http://www.tparents.org/library/unifi-cation/talks/wells/DARWIN.htm), he went tograduate school with the specific intent ofattacking evolution: “Father’s words, my stud-ies, and my prayers convinced me that I shoulddevote my life to destroying Darwinism” andhe believed that its weakest point was devel-opmental biology. “I was convinced thatembryology is the Achilles’ heel ofDarwinism; one cannot understand how organ-isms evolve unless one understands how they


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develop. In 1989, I entered a second Ph.D. pro-gram, this time in biology, at the University ofCalifornia at Berkeley. While there, I studiedembryology and evolution.” So it was not somuch a “revelation” as it was a plan. If Wellsis so revisionist about his own history, how canwe trust him with the history of science?

DEVELOPMENTAL ANATOMY, DARWIN, AND EVOLUTION

Wells opens the chapter by telling uswhat Darwin thought about devel-opment and evolution. Wells uses

about 5 different quotes from the Origin in anattempt to show that Darwin was advocatingrecapitulation in spite of what the data showed.To do this, he distorts the history. Wells tries toconnect Darwin to Haeckel so that he can usethat to dismiss Darwin. Wells says that Darwinwas not an embyrologist and thus he relied onHaeckel (Wells, 2000:81). Anyone familiarwith the history of biology knows that this isimpossible. Haeckel did not publish hisAnthropogenie until 1874 (where the much-maligned embryo drawings first appear), 15years after the publication of the Origin. (Itshould also be noted that the drawings referredto by Wells [2000] are not from Haeckel butredrawn from the first edition ofAnthropogenie in a textbook by Romanes[1892; see figure 10a]. In later editions ofAnthropogenie, Haeckel corrected some of theerrors of the first edition drawings [Richardsonand Keuck, 2002; personal observation].)Wells quotes Darwin’s praise of Haeckel in hissixth and final edition of the Origin in such away as to obscure the fact that Darwin laudsHaeckel for his phylogenies, not his embryol-ogy. The quote is not even from the embryolo-gy section of the book; rather it comes fromthe classification section, in the final sentenceof which Darwin praises Haeckel for usinghomologous features (including but not limit-

ed to developmental ones) to generate classifi-cations for organisms. Darwin is praising theapplication of his theory by Haeckel.

Although Darwin did not use Haeckel onembryology, he did use von Baer. RecognizingDarwin’s use of von Baer, Wells then accusesDarwin of “misusing” von Baer’s work, twist-ing the data to fit his views. But Darwin doesnot. Wells claims that von Baer’s embryologi-cal laws are incompatible with Darwin’s con-clusions, but they are not. Von Baer may havedisagreed with Darwin about his conclusions,but his laws do not prohibit development elu-cidating common ancestry. Darwin came to adifferent conclusion from the same body ofevidence — this is not “distorting” the evi-dence. Darwin was making a general inductiveargument and searched for data that could testthe general proposition of common descent; heargued that von Baer’s data could be reinter-preted in terms of common ancestry. This wasno more a “misuse” of von Baer than wasAlfred Wegener’s reinterpretations of the dataof geology in light of mobile continents. Newscientific theories always use previous data. IsWells implying that evolutionary biology can-not cite any research that predates 1859? IsWells implying that developmental sequencessuch as those illustrated by von Baer and oth-ers are not data?

That Darwin and all modern evolutionistsadvocate some form of the “Biogenetic Law”is the central falsehood of this chapter; in factthe entire “resurrecting recapitulation” sectiondoes nothing but assert this. But Wells fails toexplain fully what recapitulation means. Thereare a number of meanings for “recapitulation”that Wells conflates in order to tar the entirefield of embryology with a biogenetic brush.As he says in a footnote, a “plain reading” ofDarwin shows that Darwin was advocatingrecapitulation — but just what kind? (1) Anembryo of an “advanced” form goes through


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all the adult stages of all its ancestors. This is acaricature of Haeckelian recapitulation, whichis false, and few scientists ever believed it any-way. (2) Evolution proceeds as an “add-on”process so that there is a general progression ofembryological stages from “primitive” to“advanced” forms. This more traditional read-ing of recapitulation is also false and has notbeen accepted for nearly a century. (3) Allclosely related organisms go through all thesame stages of development and always looksimilar. This is vague: how closely related isclosely related? How are the stages individuat-ed? But however these questions are answered,this reading of recapitulation would generallybe agreed to make too sweeping a claim. (4)Some parts of developmental sequences (andsome specific characters of them) in closelyrelated animals share more specific similarities(in pattern, sequence, position, etc. of develop-mental features) with each other than withthose of more distantly related animals. That’sbasically true. All modern biologists recognizethat all stages of development are open tomodification. This is generally the type of“recapitulation” accepted by the post-Haeckelian embryologists (such as FrankLillie) cited by Wells, as well as by currentembryologists, but Wells treats it derisively asif it were exactly what Haeckel thought.Finally, a “plain reading” of Darwin showsthat he was suggesting something between (2)and (3); even though he was not an embryolo-gist, he had a more sophisticated notion ofembryology and development than does Wells.

Wells chides Darwin and nineteenth-centuryembryologists for saying that the “earliest”stages of development are similar when in factthey are not. However, “earliest” is Wells’sword, not Darwin’s. It does not appear in anyof the quotes that Wells uses. Indeed, in theentire section on embryology in the Origin, theword “earliest” only appears once, in a quota-

tion from von Baer. Does “earliest” reflectDarwin’s belief, or is he merely reporting vonBaer’s? This is important because numerousscholars have made the mistake of confusingDarwin’s reporting of what others thought withhis expression of his own views (Padian,1999). So apparently has Wells. But it reallydoes not matter what Darwin thought: just asmodern embryology does not rely on Haeckel,neither does modern evolutionary biologyslavishly follow Darwin’s beliefs.

It is also important to understand what nine-teenth-century scientific workers may havemeant by the use of “embryo” and “earlystage.” For many workers in the nineteenthcentury, developing organisms weren’t calledembryos until they reached the tailbud (phylo-typic) stage. During earlier stages, they werecalled “developing ovum” or “developing egg”(see Barry, 1839, or just about any embryolo-gy work from 1820 to 1900). What this meansis that Haeckel, von Baer, and others, have adifferent meaning for “early embryo.” YetWells interprets them using modern defini-tions.

Wells also criticizes the field of comparativeembryology for the way it chooses its data andfor its names for embryonic structures. First,Wells emphasizes the disparity of “earliest”developmental stages, accusing biologists of“choosing” taxa (animals) that look most sim-ilar for illustrations in textbooks and else-where. He criticizes Haeckel for not using ani-mals such as monotremes in his work. Butdevelopmental sequences for monotremeswere not available in 1874. Monotreme devel-opmental sequences were not known ordescribed until 1884 (Caldwell, 1887; Hughesand Hall, 1998), and it was the developmentalfeatures monotremes shared with marsupialsthat led Caldwell to conclude that monotremeswere indeed mammals (Caldwell, 1887). Wasthe sample of organisms available to Haeckel


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biased? Yes, but only in the sense that earlyembryologists worked with the animals thatwere available to them. Most specimens of“exotic” animals were shipped to researchersby explorers and received in varying states ofdecay (Caldwell, 1887). Most nineteenth-cen-tury embryologists loved to describe the devel-opment of any animal they could. And Haeckelwas continually updating and adding neworganisms to his embryonic series as theycame available. Contrary to what Wellsimplies, there was no attempt to limit the data,and the sample was not “chosen” for any par-ticular reason.

Today, embryologists work mainly with“model organisms,” which were largely cho-sen for practical reasons such as ready avail-ability, small body size, large litter size, rapid

sexual maturity, rapid reproduction, ability fordevelopment to occur in the laboratory, andability to live indoors for several generations(Bolker, 1995). They were not chosen to “sup-port evolution” as Wells implies. In fact, themodel organism that is the subject of Wells’sown dissertation, Xenopus, was not the origi-nal “model” amphibian. The discovery thatXenopus does not need a breeding season wasa boon to embryologists and led to itsserendipitous adoption as a model organism(Gurdon and Hopwood, 2000). How Wellsknows that “model organisms” were chosen tomislead is unclear, especially given his ownuse of model organisms later in his chapter.Wells doesn’t show developmental sequencesfor any of the organisms he complains othersdon’t show. Why not? Because there is no evi-


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Figure 8. Developmental sequences of various vertebrates shown in phylogenetic context. Notethe shared similarities of some closely related taxa, particularly the amniotes (modified fromRichardson et al. 1998).

dence for his insinuation that developmentalbiologists treat their data selectively in order tohide something. The fact that embryologiststend to present, at least in textbooks, develop-mental sequences for which there is good datadoes not refute the idea that closely relatedtaxa, should, and do, have more shared simi-larities in developmental programs than moredistantly related taxa (Figures 8, 9). Wells triesto support his claim by using a quote byDarwin in which he states that embryos of thesame “class” are most similar in their earlieststages. Wells then says that the quote is false,and cites how the different “classes” of verte-brates are very different in their “earliest”stages. This is merely a semantic sleight-of-hand, a bait-and-switch. Darwin is not talkingabout different “classes.” Wells leaves outimportant information, as usual.

In the figures of embryos (Wells, 2000:95,especially stage 4, “gastrulation”), Wells’sillustrator resorts to a number of graphic tricksin order to make the embryos appear more dif-ferent than they are. First, the embryos are notshown from the same rotational angles. Thechicken is shown in a different position thanthe other “Haeckel’s first stage” embryos.

Second, they are not all scaled the same. In thefigure showing the neural crest infolding, theturtle and chicken are shown at a large scale,neglecting the large yolk they sit on, while thehuman is shown as part of the whole develop-ing ovum, so that the germinal disc and primi-tive streak formation are shown differently,even though it is shared by all amniotes(Schaunislaund, 1903; Nelson, 1953; Cruz,1997; Schoenwolf, 1997; Figure 9). Also pic-tured is a frog embryo, despite its indirectdevelopment, which is very different from thatof the other vertebrates pictured. Many of thegeneral “differences” in early embryo develop-ment that Wells mentions are a result of organ-ization due to the yolk size rather than beingspecific differences in the basic body-plan ofthe embryo (Arendt and Nübler-Jung, 1999).

Embryos do reveal phylogenetic informa-tion in terms of specific shared features, sharedearly developmental features such as the for-mation of a germinal disc and primitive streakin all amniotes or the neural crest cells of allvertebrates. The presence, and sequence ofdevelopment, of eyes, ears, somites, limbs,guts, nerve cords, tails, organs, etc. are indi-vidual features that no one would deny are


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Figure 9. Embryos of various amniotes shown during somite stage. All amniotes go through thesame sequence of development: primitive streak–neural tube–somite formation.

present in vertebrates and not present in thesame way in other animals. These are individ-ual characters whose developmental featuresare treated as shared features in reconstructingvertebrate evolution; these features do notalways have to be in agreement, and some ani-mals can show unusual derived features earlyin development, such as the snake’s tail(Figure 8).

Wells’s treatment of comparative embryolo-gy is remarkably limited; for example, henever discusses invertebrate development. Yetthere are plenty of shared developmental pat-terns there as well. Despite the very differentappearance of echinoderm, hemichordate, andchordate embryos, they all share the deuteros-tome condition, in which the first cell openingbecomes the anus, before they diverge to theiradult body plans. Or what about the tro-chophore larvae of most protostomes and spi-ral cleavage shared by annelids, arthropods,mollusks (Nielsen, 1995; Fell, 1997)? Thenauplius larvae of crustaceans (Gilbert, 1997)or the verliger larvae and development of gas-tropods, which go through flexure, torsion, anddegeneration of muscles on one side of thebody, suggestive of their evolutionary history(Nielsen, 1995; Collier, 1997)? These are justa few of the specific similarities of the kindthat Wells implies do not exist. Similarities inembryonic sequences are data — characters bywhich we can discover shared similaritiesamong organisms that can be used to recon-struct their relationships. Using such data inphylogeny is not the same as using those char-acters in any “recapitulationist” way.

Finally, Wells concludes by attackingprominent biologists such as Gould andFutuyma for supposedly not knowing the truthabout Haeckel, saying that this is “a confessionof ignorance not likely to inspire confidence inthe quality of our biology textbooks” (Wells,2000:107). Wells’s own misrepresentations of

the letter and spirit of the concepts and authorshe presents do little to inspire confidence inwhat he says about Haeckel or embryology ingeneral. Even if Wells were right aboutHaeckel’s work and Darwin’s use of it, whatHaeckel and Darwin thought doesn’t matter;embryology has moved beyond them. Wellsneeds to show a lack of specific similarities tosupport his case. Is Wells actually claimingthat there are no shared features in develop-ment at all? That a chicken gets a planula whilethe duck gets a naupius? If so, he needs toshow it, but Wells never gets to specifics —apparently because the specifics aren’t there.Innuendo and accusations of fraud do not cut itin science.

WHAT TEXTBOOKS SAY

For any textbook to show Haeckel’sdrawings themselves as unqualifiedstatements of developmental anatomy or

to advocate “recapitulation” in a Haeckeliansense would be inexcusable, but none of thetextbooks reviewed by Wells appear to do so.Wells gleefully excoriates Futuyma for usingHaeckel’s drawings (Figure 10a), but appar-ently in his fit of righteous indignation, he for-


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Figure 10a. Romanes (1892) embryo draw-ings reproduced in Futuyma (1998:653).

got to read the text, in which the drawings arediscussed in a historical context — statingwhy Haeckel is wrong — and Futuyma has anentire chapter devoted to development andevolution. Guttman (Figure 10b) uses them inan explicitly historical context as well. Wellsstates that books use “Haeckel’s drawings, orredrawn versions of them” (Wells, 2000:255),but this is not true. Figures 10a–j showHaeckel’s drawings compared to the drawingsin the textbooks reviewed by Wells. It can beclearly seen that a majority of the drawings arenot “redrawn.” Some textbooks show more

accurate drawings (Miller and Levine,Johnson, Biggs, Kapicka and Lundgren;Figures 10f,g,h); some use photos (Campbell,Reese and Mitchell, Mader; Figures 10i,j);only Starr and Taggart (Figure 10c), Raven andJohnson in their development chapter alongwith accurate drawings and photos; (Figure10d), and Schraer and Stolze (but redrawn andcorrected; Figure 10e) use what could be con-sidered embryos “redrawn” from Haeckel. Notextbook discusses embryology in any way


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Figure 10b. Romanes (1892) embryosreproduced and placed in historical con-text in Guttman (1999:718)

Figure 10c. Romanes (1892) embryosredrawn in Starr and Taggart (1998:317).

Figure 10d. Embryos redrawn and some-what corrected in Raven and Johnson(1999:288).

Figure 10e. Embryos redrawn and correctedin Schraer and Stolze (1999:582)

that could be considered strongly “recapitula-tionist.” In most textbooks, embryology is pre-sented in just one or two paragraphs, making ithard to discuss all the complexities of devel-opment. At a high school level, the aim of thebook is to convey some basic concepts of biol-ogy, not to confuse students with the complex-ity of a subject.


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Figure 10f. Original embryo drawings inMiller and Levine (2000:283).

Figure 10g. Original embryo drawings inJohnson (1998:179).

Figure 10h. Embryo drawings in Biggs et al.(1998:433). Identical drawings appear in theevolution chapter (p.416) of Raven andJohnson (1999).

Figure 10i. Embryo photos in Campbell,Reese, and Mitchell (1999:424).

Figure 10j. Embryo photos in Mader(1998:298).

WELLS’S “WELL-DEVELOPED”GRADING SCHEME

The grading scheme employed by Wellsis designed for failure. This is becauseWells assumes all drawings to be

“redrawn” from Haeckel and gives any bookwith a drawing an F (Figure 11). Wells doesnot explain how one would determine whetherthey are simply redrawn from Haeckel; in anycase none of the books appear to contain mind-lessly redrawn figures (Figure 10a–j). Using

more accurate pictures only earns a book a D.In order to earn a C or higher, a book must notuse “misleading drawings or photos.” Thisamounts to complaining that textbooks should-n’t allow students to be misled by reality!Wells does not specify what kind of drawingsor photos would not be misleading. Thus Wellsapparently thinks that all visual presentationsof embryos are misleading, whether they areaccurate or not. Wasn’t Wells the one com-plaining about selective use of data? He actu-


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Figure 11. Wells’s grades for the embryology sections of textbooks.

ally attacks Mader and Campbell, Reese, andMitchell, for using “misleading photos”because they show embryos of a chick and ahuman, which he says “just happen” to have astronger resemblance than would embryosfrom any other “classes” of vertebrate. Wells iswrong: a chick embryo at that stage looksmuch more like an alligator embryo than amammal embryo (comparisons made fromNelson, 1953, Schaunisland, 1903, and Reese,1915). This is in accordance with the predic-tions of evolutionary theory, because an alliga-tor and a chicken share a more recent ancestorwith each other than they do with a mammal,and thus should have more similar a develop-mental program. Wells also chides Mader forsaying that embryos “have many features incommon” (Wells, 2000:103–104). Does Wellsassert that they have no features in common? Ifso, he should document it. Having failed to dothis, Wells merely labels anything he does notlike “misleading.” Wells also takes exceptionto the colloquial term “gill slits,” which is acommonly used non-technical term for pha-ryngeal pouches. Wells implies that by usingthis term, biologists and textbooks are sayingthat all animals’ embryos have gills. This ispatently false. No textbook reviewed evenimplies the presence of gills in embryos. Thequestion is what these structures are and whatthey become, not what they are called. Usingthe terms “gill slits” automatically results in aC even if the textbook contains no images, andregardless of its content. Campbell, Reese, andMitchell, and Guttman both contain entirechapters devoted to developmental biology inwhich they do discuss some of the “early stagedifferences” that Wells suggests they do not.They receive no credit for these extensivetreatments (Figure 11).

WHY WE SHOULD STILL TEACHCOMPARATIVE EMBRYOLOGY

Despite changes in how we view the roleof developmental programs as reflec-tions of evolutionary history, we can

still see how the same embryonic structuresdevelop into different adult structures. Weobserve the unity of developmental plan in allvertebrates. This is what we see, and noamount of wishful thinking on the part of evo-lution detractors can change that. There is noreason to let their baseless complaints andcharacter assassination dissuade biologyteachers from presenting the evidence to stu-dents.

HOW TEXTBOOKS COULD IMPROVETHEIR PRESENTATIONS OF

COMPARATIVE EMBRYOLOGY

Textbooks could largely improve the pre-sentations of embryology by lengthen-ing their discussions of it, and by using

photos rather than cartoonish drawings. Theycould also be more explicit about how embry-onic precursors develop into different adultstructures. Finally, adding discussions of Hoxgene complexes (master developmental con-trol genes) and evolutionary developmentalbiology would help bring the books up-to-datein their treatment of developmental biology.We are learning more about the evolutionaryhistory and underpinnings of developmentalprograms every day. We are learning howdevelopmental programs are the source ofmuch of the evolutionary novelty that naturalselection shaped. Wells ignores all this. To fol-low Wells’s advice would arrest the develop-ment of students’ knowledge.


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Documents

Alan D. Gishlick, National Center for Science Education ... of Darwin, Haeckel, and ... strongest class of facts” in favor of his theory. ... but his laws do not prohibit development