Reviews

Syst. Zool., 27(1), 1978, pp. 125-130

Ontogeny and Phylogeny.—Stephen Jay Gould.1977. Harvard University Press, Cambridge, ix+ 501 pp. $18.50."Why don't you, my dear peer, think instead of

but compiling?" —Leon Croizat (1962 [1964]: 673[slightly paraphrased]).

"Words, words, words"—William Shakespeare,Hamlet, Act II, Scene II.

Stephen Gould has written this book (1) for prac-tice "before embarking on [his] magnum opus aboutmacroevolution" (p. viii) and (2) to show that, inspite of the collapse of Haeckel's biogenetic law,the subject of parallels between ontogenesis andphylogenesis is still of importance to biology.

Nobody can contest the first purpose, but the sec-ond one is more dubious. The reason for this is tobe found in the review of Holmes (1944), in whichthe validity of the biogenetic law is refuted, exceptfor those cases where evolution occurs through ter-minal addition. Gould realizes that non-terminalmodifications may take place, and that recapitula-tion presupposes terminal addition (and condensa-tion), so his stand is the same as the opinion pre-vailing half a century ago. What news can Gouldhave to report?

The first part of the book is a survey of the historyof "recapitulation," the basic concept in Haeckel'slaw; the second part outlines those domains of bi-ology where the phenomenon of recapitulation (asrepresented by heterochrony and paedomorphosis)is observable. This part contains two original con-tributions, a clock model of heterochrony and anattempt to explain the occurrence of heterochronywith reference to ecology. The last chapter dealswith neoteny in man.

From my sparse knowledge of Gould's scientificproduction I had formed a very favorable impres-sion of him; he writes well on many different sub-jects. Since I have devoted much time to the prob-lem of the link between ontogenesis andphylogenesis, I was happily surprised to learn thatGould had written a book on this subject, and anx-iously looked forward to meeting some new andfresh views.

Gould's book is a great disappointment. First ofall, not in my wildest dreams did I anticipate thatthe theme was Haeckelian recapitulation. But Hae-ckel's law and the phenomenon of recapitulationmay of course be of historical interest, for, as Gouldwrites: recapitulation "served as the organizingidea for generations of work in comparative em-bryology, physiology, and morphology. . . . In . . .paleontology, . . . it governed most studies inphyletic reconstruction from Haeckel's day rightthrough the 1930s" (p. 116). It would certainly be

of great interest to know about the outcome of theseendeavors. We are told nothing about this, osten-sibly because it "would need another volume evento begin an adequate treatment of how biologistsused recapitulation in their daily work" (pp. 115-116), and that volume, which would require originalresearch, has yet to be written. And since such atask apparently would be incompatible withGould's pace of publication, he leaves the subject.And although the historical sections report certainfacts previously unknown to me, this lack of infor-mation on the biologically central issue is the sec-ond source of disappointment with Gould's book.

But still, Gould is generous; we are not left withempty hands. And if there is a dearth of literatureon recapitulation and the history of biology, thereare fortunately authors who have discussed the in-fluence of the theory of recapitulation on criminalanthropology, racism, child development, primaryeducation, and psychoanalysis!!! I wonder whowould go to a book entitled "Ontogeny and Phy-logeny" to be enlightened on these topics. Gouldshould have considered that "lengthy expositions"need not be four hundred pages; three hundredmight have done.

The third reason for disappointment is that thesubject is evidently too enormous for Gould; eitherhe did not spend the time necessary to penetrate itor else it is beyond his reach. Gould lives in hisown world of abstractions. His closest contacts withthe world of living things are shells and antlers ofextinct animals; otherwise biology to him is a jug-gling of words and numbers. And his book dealswith words, concepts, and their history. Gould canindeed handle abstract concepts more easily thanmost biologists, but apparently he does not masterthem. I once wrote to Gould that he is a scholar,and so he thinks himself (p. 1). After having strug-gled with his book for some weeks, I must withdrawmy judgment; the breadth is there, but the depth iswanting. Gould is a compiler (of words), not a schol-ar; but this conclusion cannot come as a surprise tohim, for he admits this himself on p. vii.

But let us take a look at some details. Regrettablyenough, "recapitulation" has come to mean not justthat, but "recapitulation of adult characters." Ac-cording to Holmes (1944), this idea of recapitulationmay be traced back to a statement by Kielmeyer in1793, but it is usually credited to Meckel andSerres, whose law says: "The development of theindividual organism obeys the same laws as the de-velopment of whole animal series; that is to say, thehigher animal, in its gradual development, essen-tially passes through the permanent organic stagesthat lie below it" (p. 37).

This law of recapitulation was rejected by von

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Baer (p. 52 ff.) who, on the basis of his comprehen-sive and outstanding studies of comparative em-bryology, claimed that (adult) recapitulation is im-possible and that all we can observe in the embryois a repetition of embryonic stages.

It is unlikely that the views of von Baer's pre-decessors would have survived if Haeckel, underthe impact of Darwinism, had not revived themwhen formulating his biogenetic law: "Ontogeny isthe short and rapid recapitulation of phylogeny" (p.76). This law implies that all evolution occursthrough terminal addition, and Haeckel knew thatvon Baer had shown this not to be the case. There-fore, it was necessary to introduce the concepts"palingenesis" and "cenogenesis"; the former rep-resents ontogenesis through terminal, the latterthrough non-terminal addition. It is typical of Hae-ckel's way of thinking that the occurrence of ceno-genesis was considered a falsification of the "pre-vious phyletic history," but not of his law (p. 82).It is surprising that biologists in general (there weresome opponents) did not see that the concept of"cenogenesis" was an ad hoc hypothesis serving toprotect the biogenetic law from falsification.

Gould discusses the common (?) notion that Hae-ckel's theory collapsed under the ever-increasingweight of accumulated exceptions, and writes:"Natural history does not refute its theories by cat-aloguing empirical exceptions . . . With millions ofpotential examples . . . how can a catalogue ofcounter cases ever refute a theory?" (p. 167). I read-ily admit that certain biological phenomena, for in-stance phylogenetic evolution, involve stochasticelements to the extent that single isolated eventsmay not be predictable. But does this imply that allbiological occurrences are of this kind? Are therenone which follow "laws," and hence are predict-able, and the "laws" consequently falsifiable?

Gould really places us in a difficult position, forif biological theories are not falsifiable by eitherenumeration or failure of prediction, what criteriado we then have to ensure progress? In Gould'sopinion the biogenetic law did not fall becauseeverybody with eyes in his head could by studyingthe development of almost any embryo convincehimself that von Baer was right and Haeckel wrong,but because "it became unfashionable in approach(due to the rise of experimental embryology) andfinally untenable in theory (when the establishmentof Mendelian genetics converted previous excep-tions into new expectations)" (p. 168; if Gould hadnot italicized, I would have). Where has all epis-temology gone? For me it has been hard enough toaccept the Kuhnian version, but the Gouldian oneis too strong. "Theoretical untenability" sounds allright, almost Popperian, but "unfashionableness?"That is too much to swallow.

I shall not discuss the objections raised by theexperimental embryologists and the geneticists, butI must comment on one point. Gould writes that"Mendelism . . . disproved the two 'laws' of evo-lution that recapitulation required for its generaloccurrence—terminal addition and condensation"

(p. 202). I believe Mendelism is a theory of geneticswhich makes predictions about gene frequencies,not about epigenetic phenomena like terminal ad-dition and condensation. For this reason aloneMendelism could not disprove Haeckel's biogenet-ic law, but there is another reason too: the law wasnot all wrong.

As we have seen, Haeckel's law is valid onlywhen terminal additions are involved, in caseswhere a new form arises by passing through andbeyond the ontogenetic stages of its predecessor.This case, called hypermorphosis, is usually asso-ciated with allometry of various kinds, and is wellknown from many studies on both extinct and extantforms. To emphasize, this is the only case wherethe phenomenon of adult recapitulation can ever beobserved.

One may, of course, include in this context thephenomenon of terminal subtraction, which un-questionably has been involved in certain instancesof phylogenetic evolution. This leads to paedomor-phosis by truncation. It would seem natural to em-ploy the name hypomorphosis in this context, butGould uses "progenesis." This choice is unfortu-nate, for "progenesis" implies opposition to epi-genesis, when in fact it designates a shortened pro-cess of epigenesis.

To go beyond the phenomena discussed hereGould evokes the phenomenon (or should we sayconcept) of "heterochrony." In fact, he writes:"Despite its baroque excrescences and digressions,this book is primarily a long argument for the evo-lutionary importance of heterochrony—changes inthe relative time of appearance and rate of devel-opment for characters already present in ancestors"(p. 2).

Let us first observe that in the phenomena of hy-pomorphosis and hypermorphosis it makes littlesense to apply the concept of heterochrony, as ap-pears from a glance at the clock model (pp. 257 and258). For the character for which the relative timeof appearance is changed in these cases is sexualmaturation, a phenomenon which always occurs to-wards the end of somatic development and, indeed,is usually causally involved in the arrest of the lat-ter.

So among the four categories of heterochrony list-ed by Gould I believe that only two really deservethis name, viz. (1) acceleration of somatic features,purportedly leading to recapitulation and (2) retar-dation of somatic features, leading to paedomor-phosis. The latter case is exemplified by, and ac-tually called, "neoteny."

Evidently these cases are not too different fromhypermorphosis and hypomorphosis; actually Ifound it necessary to look at the clock models tounderstand exactly what they imply. It thus appearsthat the mature descendant animals have the sameage and size as their ancestors, but they have beeneither accelerated or retarded with respect to their"shape."

As discussed above, the phenomenon of hyper-morphosis is well known, and I believe that even

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hypomorphosis has been documented in some in-stances. It would therefore be reasonable to assumethat these are the most common cases of "hetero-chrony." Gould is not of this opinion; he believesthat acceleration and retardation are much morecommon than prolongation and truncation.

This stand is supported by two arguments and byreference to empirical observations. The argumentsare: (1) "The paradox of infinite length. . . . Any or-ganism has thousands of ancestors in its lineage;if phytogeny proceeds by simple addition, ontogenywould grow inconceivably long" (p. 216). But no-body except Gould believes any longer that "phy-logeny proceeds by simple addition." And to savehis own argument he does not shrink from high-handed rejection of an authority like Severtsov. (2)The second reason advanced for preferring the phe-nomena of acceleration and retardation is that "mostcases of prolonged or truncated ontogeny arecaused by the acceleration or retardation of matu-ration (p. 220, my italics). A moment's reflection willshow that Gould here uses "acceleration" and "re-tardation" in senses which are quite different fromthose defined above.

Gould's arguments are not very convincing: Thefirst one in particular is naive, being of the sameclass as the paradox of Achilles and the turtle; there-fore it is of particular importance to see the actualobservations of the phenomena on which Gouldplaces so much importance.

Let us begin with neoteny, which is the best sub-stantiated phenomenon. This is exemplified mainlyby two instances, perennibranchiate urodelans andman. We shall deal with the latter case presently;about the former it is in my opinion wrong to talkof retardation, since we are here dealing with arrestof development, caused in the simplest situation byan insufficient production of thyroxin. It is no ex-cuse for Gould that his predecessors (for instance,de Beer) are responsible for this blunder, for a per-son with a revisionist's zeal like Gould should atleast be able to think clearly for himself. The worstthing about neoteny being used as an instance ofretardation is, of course, the implication that thelarva represents an ancestral stage.

As far as acceleration is concerned, the only ex-ample I have been able to find in the book, apartfrom numerous speculations, deals with sutures inammonites. If this was the last time accelerationoccurred, it surely cannot be of great importance inphylogenetic evolution.

Much discussion has centered around the phe-nomenon of paedomorphosis, which by many form-analytic evolutionists has been regarded as thepanacea which can bridge the abyss between thevarious animal phyla or other higher taxa. That pae-domorphosis has played a role in evolution is verylikely, but this hardly warrants the fantastic pro-posals which have been submitted in the course oftime, for instance, that the vertebrates have theirorigin in a tunicate larva!!!

But what must be objected to particularly as con-cerns this reliance on heterochrony is that nothing

really new is created. If, as suggested, the onlyprobable cases are hypermorphosis and hypomor-phosis, then their results are mostly slightly modi-fied animals, larger or smaller as the case may be.Paedomorphosis concerning larval forms does notlead anywhere unless it is associated with innova-tions, and radical ones to boot. Even if the tunicatelarva theory were correct, its assertion does not ex-plain how this puny creature could aquire the thou-sands of features required to make an adult verte-brate.

The most original feature of Gould's book is hisattempt to unite the theories of heterochrony andr-K selection. The r-K selection theory predicts thatorganisms living under at least periodically plenti-ful conditions must strive towards maximization ofr, the intrinsic rate of natural increase, a goal whichmay be arrived at through early maturation, highfecundity, etc. Contrariwise, organisms living in asatiated environment, with strong competition,would aim at maximizing K, the carrying capacityof the environment. The latter may be achieved bythe production of few offspring of high competitiveability, coupled perhaps with parental care.

If we now make a logical approach to the unifi-cation of these two theories, the reader will easilysee that r selection must be combined with hypo-morphosis (progenesis), since this phenomenon in-volves an acceleration of maturation. Likewise, Kselection should be combined with hypermorpho-sis, which is associated with a retardation of matu-ration. This choice would have the advantage that itopted for the most likely instances of "hetero-chrony." But for some inexplicable reason Gouldthinks that K selection should be associated withneoteny, supposed to involve a retardation of so-matic features and possibly, but not necessarily, ac-companied by delayed maturation.

This theory is tested on the neoteny observed incertain amphibians, notably the axolotl. In thosecases where this feature is facultative, it can be ex-plained in a very simple way. It has been shownthat low temperature suppresses metamorphosis,and also that animals living in cold Rocky Mountainponds are more often neotenous than those in low-land habitats. Thus it might simply be assumed thatthose individuals that happened to colonize themountain ponds had to pay for their survival bynever "growing up." But isn't this a modest priceto pay for survival? And, of course, this modifica-tion, which forces them to remain aquatic, wouldbe of special advantage if, as is wont in mountains,the terrestrial environment is harsh.

This explanation is not satisfactory to Gould. Hewants to know whether "any adaptive significancecan be ascribed to consistent patterns in the fre-quency of paedomorphosis" (p. 319). Thus he sug-gests that paedomorphosis is more common inmountain ponds "because they are more permanentand free from predaceous fish than lowland ponds"(p. 319). Thus we face two explanations, a physio-logical one, known and corroborated in fair detailthrough empirical observations, and an ecological

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one which, to say the least, has not been corrobo-rated. Which shall we choose, or must we acceptthem both?

"All this clearly points to K selection for the morepaedomorphic populations" (p. 320). But stop now;what is the expected strategy of K organisms? Yes,"low reproductive effort with late maturation, long-er life, and a tendency to invest a great deal of pa-rental care in small broods of late maturing off-spring" (p. 291). But neoteny does not imply latematuration (in fact metamorphosed and neotenoussalamanders mature at the same age; cf. p. 321) norany of the other features, and my own experiencewith axolotls has not convinced me of either theirsmall broods or parental care.

The correlation between hypomorphosis and rselection is illustrated by the life histories of var-ious insect species. These data may possibly sup-port Gould's theory, but when it is further testedwe read: "I find a remarkable correlation betweenprogenesis and r selective habitats (except in caseswhere selection works primarily for small size it-self). I do not know of any instance in which juven-ilized morphology per se is clearly the major deter-minant of progenesis. Rapid maturation or smallbody size are the primary objects of selection; ju-venile morphology is often an incidental (thoughnot inadaptive) by-product" (p. 324). But isn't thetypical feature of progenesis that shape and size arechanged at the same time?

But the discussion on the association betweenecology and heterochrony, especially paedomor-phosis, is, of course, a side issue aimed at showingthat these forms have a survival value as such, arequirement for their coming into existence in thefirst place. But their importance for the main themeof the book is that hypomorphic animals to someextent may be equated with those generalizedforms which so many evolutionists have invoked tobridge phylogenetic gaps. Gould believes that onextremely rare occasions—"but extreme raritythrives on the immensity of geological time" (p.340)—these hypomorphic creatures may have givenrise to some new major design of organism. I fail tosee how one can advocate more or less crippledjuveniles as a potential source of evolutionary in-novation while rejecting Goldschmidt's hopefulmonsters (p. 341).

The last chapter deals with human ontogenesisand phylogenesis. Man exhibits many similaritiesto the other primates, especially their juveniles, andyet there are some conspicuous differences. Someof the most important ones are birth weight, lifespan, certain features concerning the ossification,particularly of the skull and the lower extremities,size of the brain, and reduction or lack of body hair.

To a convinced Darwinian these and all other rel-evant features should have developed indepen-dently, more or less, and in small steps. But manyauthors have claimed that several traits in the hu-man adult can be explained on the assumption thatin man the development of shape, if not of size, hasbeen stopped at a stage corresponding to a juvenileprimate.

Man may thus represent an instance of paedo-morphosis (neoteny), and the possibility exists thatthese various characters are epigenetically con-nected, having their origin in changes in some su-perior controlling agent. Before we discuss thisquestion we may deal with the first point, birthweight, and the last point, body hair. As far as theprenatal growth rate is concerned, the human em-bryo is not retarded, but accelerated, the birthweight being twice that found in the large primates(Portmann, 1941). And although it is true that pon-gid embryos, if not juveniles, are hairless, the sit-uation in man cannot be explained as a conse-quence of neoteny. The growth of hair is a typicalnon-epigenetic character, the occurrence of whichis independent of other ontogenetic processes, asdemonstrated by the fact that animal hairiness maybe restituted by a single gene mutation (cf. Ohno,1970).

The most comprehensive argumentation for anepigenetic explanation of the origin of man is foundin Louis Bolk's foetalization theory (1926). Bolk wasof the opinion that the various features distinguish-ing man represent two different phenomena, retar-dation of development and retention of ancestraljuvenile proportions, but that the latter is causally(i.e., epigenetically) dependent upon the former. Inother words, once upon a time the rate of devel-opment of some ape-like primate was substantiallyretarded, and as a consequence there arose a man-like primate.

Above I have observed that the notion of "retar-dation" is questionable in connection with the ex-emplar instance of neoteny, the perennibranchiateurodelans. Is it better in the present case? FromTable 9 (p. 368) in Gould's book one may see thatlife span and several other parameters in man (firstand second dentition, growing period, female sex-ual maturity) are close to twice the correspondingvalue in the other primates. The only deviationfrom this rule is the period of gestation, which isapproximately the same.

The anticipated consequence, that the humanbaby is much more helpless than the pongid one,is a well-known fact. Indeed, Portmann (1941) hascalculated the theoretical gestation period for manto be 21 months, and he argues that it is so, too.This view is based on the fact that in man, in con-trast to all other mammals, the growth rate duringthe first year after birth is not subject to the reduc-tion typical of post-natal life, but remains at the fetallevels.1 If we accept this interpretation, it follows

1 I have here presented Portmann's interpreta-tion. It is a noteworthy fact that a closer analysis ofPortmann's data does not support his own claims.The human baby weighs twice as much as any ofthe non-human primate babies, but it grows rela-tively less than any of these during the first year.Here it is certainly not warranted to consider thegrowth rate of the former as typically embryonic inany sense. And furthermore, it is true that thegrowth rate in the child is considerably reduced

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that all phases of human life have been doubled intime, a phenomenon which may be called "retar-dation," although surely "prolongation" would bemore justified.

According to Darwinian orthodoxy this "retarda-tion" should occur in many small steps, a month orso at a time, and this was also Bolk's answer (p.360). There can be no doubt that the life span ofeach organism is controlled by some inheritedmechanism. We have no idea of how it operates,but I believe one should consider the possibilitythat it does not work in small installments, but insteps representing a geometrical series of base 2.Some pathological observations on the life span ofcertain human beings could be accounted for onthis assumption.

As regards the mechanism of this prolongationBolk submitted that it was determined by "the en-docrine system of the organism . . . In controllingthe intensity of the metabolism these hormones caninhibit or promote the growth" (pp. 360-361).

But the assumption that controlling factors are atwork in evolution immediately raises the possibilitythat a relatively small change in such agents maycause large-scale changes (macromutations) on low-er levels. As a good Darwinian, Gould is on hisguard here: "If internal factors2 direct evolution,then adaptive significance plays no essential role inthe assessment of evolutionary change" (p. 362).This statement unfortunately shows that Gould hasnot grasped the implication of Bolk's theory, that"adaptive significance" plays no role in the creationof evolutionary change, but which does not excludethe requirement that every change be selectivelyassessed with respect to its "adaptive significance."Because of this lack of understanding, Gould sensesthat Bolk threatens his scientific creed, and there-fore he hits out with the worst imaginable (in thiscontext) epithet: "In short, Bolk was not a Darwin-ian. He believed that inner factors controlled thedirection of evolution by transforming entire organ-isms along harmonious and definite paths of vital-istic determination" (pp. 361-362, my italics).Could Gould uphold this claim if "inner factors"were replaced by "hormones"? And does not almostevery organism develop harmoniously?

However this may be, human life was prolongedand the rate of development of shape retarded; canthis fact explain the anatomical features referred toabove as well as the size of the brain? Bolk was ofthe opinion that "our ancestor already possessedall primary specific characteristics of contemporaryman, but only during a short phase of its individual

during the second year, but in the other primatesit increases or at least remains constant. These datashow the uniqueness of the human pattern, to beexpected if from a higher starting point we have toreach the same end value, but it is difficult to acceptthe terms in which it is interpreted by Portmann.

2 Bolk called his endocrine agents "internal fac-tors." Although logically impeccable, this choicewas rather unfortunate, as we shall see presently.

development" (p. 360). How fatal the choice of con-cepts may be at times! If Bolk had thought of "pro-longation" rather than "retardation," he would havenot forced himself into this impossible situation.Bolk tried to circumvent this position by distin-guishing between what approximately amounts toepigenetic and non-epigenetic characters, but thisdoes not help; many adult features are epigeneticconsequences of embryonic ones. Thus Bolk, theepigeneticist, became sort of a preformationist, forhis notion implies that man arose by enlargement(i.e., growth), but not differential growth, of a stagein early primate ontogenesis.

Surely, human ontogenesis is associated with dif-ferential growth away from the embryonic state, astate which is common to the human and the pongidembryo. Once this point has been reached, theroads diverge as a consequence of various differ-ences, for instance, in the values of the allometriccoefficients. Typical of human development is thatthese values are smaller as far as growth of the faceis concerned, and larger for the growth of the legs.

Is man neotenous? As defined, neoteny impliesthe retardation of the shape such that it remains atan ancestral stage. As I see it, if man is neotenousthis should have two implications. First, if it werepossible to continue our somatic development, weshould come to resemble apes. Second, the com-mon ancestor of Homo and the pongids must bemore man than ape. Gould does not say this direct-ly, but to uphold the theory that man is neotenic hewrites: "We did not evolve from any primate bear-ing much resemblance to the adult forms of chimpsand gorillas," rather, "the best prototype among liv-ing forms is the human fetus or juvenile itself (p.384). I have thought this statement over manytimes, and can only come to the conclusion that ac-cording to Gould the ancestor of man was an adultresembling the human fetus. If this is wrong, wheredo I make the logical mistake which leads to thisridiculous outcome?

Gould writes: "the human brain is paedomorphicbecause it has increased by prolonging to latertimes and larger body size (even past birth) thecharacteristic positive allometry generally confinedto fetal stages in primates and other mammals" (p.365). If this is true, as I believe, then this is a vin-dication of Bolk's general tenet, a fact which is alsoacknowledged by Gould.

But if an essential number of the "paedomorphic"features of man can be explained as consequencesof the retardation of ontogenesis, then this wouldseem to pave the way for accepting even Bolk'sepigenetic theory of evolution. At some placesGould comes perilously close to this stand. Thus hewrites: "I share D'Arcy Thompson's conviction thatcomplex organic pattern can usually be reduced tofewer and simpler generating factors" (p. 395). Al-though this conviction helped D'Arcy Thompson toreject Darwinism, Gould bravely sticks to the tra-ditional arguments.

Darwin wrote: "False facts are highly injuriousto the progress of science, for they often endurelong; but false views, if supported by some evi-

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dence, do little harm, for everyone takes a salutarypleasure in proving their falseness" (1906, p. 926).The history of biology proves Darwin wrong; the-ories which with a minimum of logic can be refuted,have often been preserved if just "supported bysome evidence." The worst thing about this state ofaffairs is that work based on or dealing with wrongtheories represents a terrible waste of effort andtime, and blocks further progress.

Haeckel's biogenetic law is such a case, but for-tunately this was realized half a century ago, whenmost biologists acknowledged its validity only in avery restricted domain. It would therefore seemcompletely unnecessary to reopen the discussionagain unless some really new insight had beengained. Nothing of the kind is to be found inGould's book; rather it seems to be a demonstrationthat a person with a flair for easy writing and dis-posing of "bulging files" can produce a "lengthyexposition" which contributes little of importanceto the advancement of biology.—S0ren L0vtrup,Department ofZoophysiology, University ofUmed,S-901 87 Umed, Sweden.

REFERENCES

BOLK, L. 1926. Das Problem der Menschwerdung.Gustav Fisher, Jena.

CROIZAT, L. 1962 [1964]. Space, time, form: Thebiological synthesis. Published by the author,Caracas.

DARWIN, C. 1906. The descent of man and selec-tion in relation to sex (2nd ed.). John Murray,London.

HOLMES, S. J. 1944. Recapitulation and its sup-posed causes. Quart. Rev. Biol. 18:319-331.

OHNO, S. 1970. Evolution by gene duplication.Springer, Berlin.

PORTMANN, A. 1941. Die Tragzeiten der Primatenund die Dauer der Schwangerschaft beimMenchen: ein Problem der vergleichenden Biol-ogie. Rev. Suisse Zool. 48:511-518.

Syst. Zool., 27(1), 1978, pp. 130-132

EVOLUTION: TAXIC ORTRANSFORMATIONAL?

Evolution.—Theodosius Dobzhansky, Francisco J.Ayala, G. Ledyard Stebbins, and James W. Val-entine. 1977. W. H. Freeman and Co., San Fran-cisco, xiv + 572 pp. $15.95.

Organismic Evolution.—Verne Grant. 1977. W. H.Freeman and Co., San Francisco, xiii + 418 pp.$15.95.

Genetic Evolution.—Chen Kang Chai. 1976. TheUniversity of Chicago Press, xviii + 341 pp.$20.00.There are two aspects, conventionally, to organic

evolution: that of process and that of history. Sys-tematists interested in evolution are pre-eminentlyinterested in history, and formulate hypotheses ofphylogenetic relationship among taxa. In addition,

systematists tend to be interested in evolution as aprocess for at least two, not mutually exclusive, rea-sons. Some systematists feel a need to adopt an apriori set of beliefs about the nature of the evolu-tionary process as a rationale for adopting a partic-ular methodology of phylogenetic reconstruction.Others prefer to view the connection between evo-lutionary process and phylogenetic history the oth-er way around—that hypotheses of process can onlybe tested when predicted patterns are comparedwith "actual" (albeit hypothesized) phylogeneticpatterns. In this latter view, phylogenetic recon-struction precedes investigation into evolutionaryprocess. A relatively smaller number of systematistsconsider the entire notion of evolution as at best acomplementary concept in systematics—one that,if not necessarily false, is at least irrelevant to thetask of ordering the elements of the biota. However,most systematists think there is some sort of con-nection between the two aspects of evolution.

The books by Dobzhansky et al., and by Grantare advanced texts; each is primarily concernedwith evolution as a process. As more-or-less ortho-dox statements of the neo-Darwinian paradigm, bothbooks are fundamentally good. Considered as ad-vanced-level texts, the book by Dobzhansky et al.,delivers more depth and perhaps also breadth,whereas that of Grant is perhaps better organizedand the brief chapters, though at times giving shortshrift to a given topic, are at least concise. Grant'sbook also contains far less of the historical aspectof evolution than appears in the Dobzhansky et al.,book, and Grant is more successful in his attemptsto integrate historical interpretation with notions ofprocess. I shall not dwell further on the attempts ineither book to grapple with phylogenetics (whethertheory, method, or results)—neither book was writ-ten primarily for this purpose, and neither is espe-cially good in this respect.

The books are especially to be compared andevaluated as contemporary statements of neo-Dar-winism. Neo-Darwinism is a complex and ratherheterogeneous array of propositions, not all ofwhich are mutually compatible. Two major themescan be detected within this paradigm: (1) the notionthat evolution is fundamentally a matter of changein gene content and frequency within populations;among-population phenomena are explained basi-cally as extrapolations from theoretical, experimen-tal, and field investigations of populations. Perhapsthe central theme of this "transformational" ap-proach is adaptation via natural selection; one ofthe outcomes of such evolutionary changes is theorigin of new species. The contrasting theme (2)holds that evolution is quintessentially a matter ofthe origin of species. Within-population changes ingene content and frequency assume significanceprimarily in the context of speciation, and evolu-tionary phenomena above the species level are tobe understood in terms of interspecific interactionsand differential species survival. Thus the "originand differential survival" of species becomes themore encompassing, integrative definition of evo-

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