Evolutionary trends in flowering plants

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Chaos and Evolution Beyond Natural Selection by Robert Wesson, The MIT Press, 1997. $29.95/f24.95 hbk (xv + 353 pages) ISBN 0 262 23161 1 Newton is to Einstein as Darwin is Unfortunately, we cannot fill to _. in the blank because the Einstein of biology lies in our future. What will this biology Einstein do? If I have interpreted Wesson correctly, in his highly readable book Beyond Natural Selection, the awaited Einstein will synthesize a geometric theory that unifies the phylogeny of species and the ontogeny of organisms, much as Albert Einstein synthesized a geometric theory that unifies time and space. Wesson provides us with little idea of what the needed theory may look like, otherthan identifying fractal geometries, which arise in chaotic dynamical systems, as lying at the heart of the theory. Wesson’s book is mainly an account of the extraordinary variety of life forms and life histories that have evolved on earth. He touches on all the areas that one would expect to see in a popular book on evolutionary theory (the saltational fossil record, the role of sex, the existence of altruism, the evolution of the mind) and then some (self-organizing systems, anthropic principles, the moral meaning of evolution). Consequently the book is much broader than it is deep. This is both its strength and weakness: it contains more fascinating biological information than any other book in its genre, but it contains errors that cause experts in the field to recoil in horror. Beyond Natural For example, Selection was severely lashed by Maynard Smith who recently reviewed the book for Nature’. Maynard Smith identified lacunas in Wesson’s discussion on the question of sex (namely, the possible role of parasites in the evolution of sex and in sexual selection) and errors in Wesson’s interpretation of Hamilton’s ideas on inclusive fitness. Wesson’s lack of rigorous population biology training is painfully apparent in the section entitled ‘The Theory of Altruism’. Also, Wesson makes factual errors at several points. For example, his statement that ‘the nervous systems of insects [have] up to 100,000 neurons’ is an underestimate by a factor of almost ten in the case of honeybees. Although such lapses cannot be entirely forgiven, I think that Beyond NaturalSelectionalso deserves much praise. Unfettered by neodarwinian life dogma (Wesson began academic as a political scientist and has written books on very different topics, e.g. 206

Ref. 21, Wesson bravely waves the heretical flag that natural selection plays a much smaller role in evolution than is generally accepted by the biological community. Many of today’s evolutionary biologists, mesmerized by notions of populations occupying adaptive peaks in Wrightian landscapes, have not yet begun to embrace chaos as a major player, let alone a title-role actor on the stage of evolution. Throughout the book, Wesson doggedly develops the case that fractal geometries associated with potentially chaotic morphogenetic, behavioral and sociological processes could be responsible for much of the structural richness of life on earth. As Wesson puts it, ‘There is no reason to suppose that there exists any particular utility for a myriad of very different shapes and configurations of leaves, or tree bark, or the shape of stems fulfilling the same functions in the same environment’. Referring to the 25000 species of the’ orchid family, Wesson matter-of-factly explains their ability to hybridize with little evidence of inbreeding depression, while debunking any ideas of coevolution, by the notion that ‘in the orchid family the [chaotic] attractor governing flower shape is unstable, and as variegated blossoms proved attractive to certain pollinators, there was a feedback rewarding and strengthening traits attractive to those particular wasps or flies or beetles’. Wesson is not out to prove that Darwin was wrong. Early in the book,

he concedes that ‘The core of the neo-Darwinist synthesis will remain valid.’ We still have much to learn about processes governing the emergence of structure in the biological world. Recent studies on the development of neurons in the human brain lend strong support to the idea (to use an analogy attributed to Sidney Brenner) that the development of neurons proceeds bythe American ratherthan the British plan: the fate of neurons is more likely to be determined by neighborhood than ancestry. Just as the connection between the extraordinarily beautiful Mandelbrot set and its simple generating equation is only revealed when we fully embrace the chaotic dynamics underlying such equations, so will the connection between the structure of organisms and ontogenetic processes be revealed by embracing their chaotic nature. Wesson’s entreaty that natural selection on its own is woefully inadequate to explain existing biological forms deserves our serious attention. A good place to start is by reading his book.

Wayne M. Gett Dept of EntomologicalSciences,Universityof California,Berkeley,CA 94720, USA References 1 Maynard Smith, J. (1991) Nature 352, 206 2 Wesson, R. (1980) State Systems: lntemational Pluralism, Politics and Culture, Free Press

FloweringPlant Evolution Evolutionary Trends in Flowering Plants by Armen Takhtajan, Columbia University Press, 1991. $51.00 hbk (x + 241 pages) ISBN 0 231 07328 3 The recent report’ of the UK House of Lords Select Committee on systematics has shown how what the layman might imagine biologists have as a major concern - biodiversity - has in fact been getting shorter and shorter shrift in the universities and other institutions in this country. Academics are not entirely to blame, of course, but the pressure for scientific ‘respectability’ has pushed university botanists, for example, from the forest and herbarium, field-kit and hand-lens, to jostle with the established test-tube shakers, as second-class citizens decked in labcoats and surrounded with all the

paraphernalia of the modern ‘plant sciences’ department. Teaching has followed suit with the consequences so lamented by their Lordships. To root for what is the very essence of biology in this shiny world is to question the wisdom of the trendsetters, whom the cynic could see as perpetuating their own (expensive) researches at the highest levels: the study of whole organisms inevitably crosses the boundaries of the increasingly canalized empires carved out of the original, yet to transgress such is to be ‘unfashionable’, ‘unpopular’ or ‘highly unlikely to attract funding’. The paradox in a real world awake to green issues is obvious: as the biosphere is destroyed, the establishment fiddles away and Everyman may well ask why*. After all, he is paying. It is refreshing, then, to turn to a

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book that is unashamedly ‘glad to be trad’. Armen Takhtajan is in his 82nd year: for well over half his life, he has been producing influential evolution, texts on angiosperm beginning in 1948 with his Morphological Evolution of the Angiosperms (in Russian); best known to English-speaking workers is his Flowering Plants: Origin and DisperSal3 in Charles Jeffrey’s translation. His new book concentrates on ‘those characters that are of special systematic and evolutionary significance’; he deliberately restricts his discussion to a number of theories and hypotheses and does not touch on trends in biochemical evolution -evolution of karyotype or sieve-tube plastids, for instance - because of ‘both the limitations and the scarcity of the knowledge and the capacities of the author’. Trends but not trendy. Takhtajan’s great achievements in his writings include not only the synthesis of a vast amount of literature, much of it in Russian - and therefore generally neglected in ‘the West’ - but also the championing of two key ideas in the evolution of angiosperms (and indeed other plants): neoteny, particularly with reference to the formation of the gametophytes, and heterobathmy. The spurious ‘character correlations’ put forward by others, notably the late Kenneth Sporne in his ‘advancement indices’ - attempts at mathematical respectability - have led to a number of dangerous suppositions latched onto by many botanists (including the more biochemically inclined ones). In those analyses, based on family descriptions (what do these mean in terms of living plants and their phylogeny?), it was found that certain character-states (what are these, and are they comparable across all angiosperms?) were correlated at statistically significant levels. Many of these were functional correlates4 and Takhtajan now elegantly points out how the general thought behind such analyses is misguided anyway. For, as early as 1893, Dollo discussed ‘chevauchement des specialisations’ and, in botany, Arber and Parkin came to similar views in 1807. The concept of heterobathmy derives from the observation that organs or, perhaps, functionally correlated character complexes, evolve at different rates, so that, for example, the flowers of some Nymphaeaceae are similar to those of fossil angiosperms - suited to pollination mechanisms still successful today - but are now associated with an aquatic habit, a highly specialized life form. It is perhaps

somewhat unfortunate that, with his last chapter devoted to this fundamental concept, Takhtajan still advocates the worn-out theory506 of the aquatic origin of the monocotyledons, a theory largely developed from correlation principles, in his first. What he does point out is that heterobathmy is less significant in animal evolution in that motile organisms with more determinate development and integrated organization are less likely to retain suites of primitive traits. Moreover, he notes that with increasing evolutionary specialization in plants the degree of heterobathmy is less marked, so that, for example, the ‘Sympetalae’ have almost all ‘advanced’ features. It would have been good to see this extended as an explanation for the clearcut nature of a family such as Compositae, and a discussion of what this ‘canalization’ of form might mean in terms of developmental sequences, when compared with the Nymphaeaceae’, where characters deemed invaluable at very high taxonomic levels in families such as Compositae vary greatly between (or within) closely allied taxa. Much of the evolutionary plasticity of form in angiosperms is due to intercalary growth, so that hardly anything of, say, a dandelion is strictly homologous with anything in a buttercup growing next to it in a meadow. It would have been good to see more attention paid to the fundamental, and crucial, study of meristems and their products, the rearrangements of form possible through ‘transference of function’, which can permit major breakthroughs in angiosperm evolution5. Much of the book, by contrast, is concerned with providing classifications for the mature organs - notably venation patterns in leaves

and types of fruits for example. And, finally, to Takhtajan’sopening remarks. Introductions rarely excite: but Takhtajan’s does, in that there is plenty to make so-called empiricists shake (objectively of course) with fury, for he argues, and persuasively, ‘the myth is prevalent that a true scientist proceeds from the observation of facts without any preliminary concepts and hypotheses. In the philosophical literature this myth has been called the “Fallacy of tabula rasa”. As is well known, however, the description of facts without preliminary ideas and concepts is logically impossible .. . Placing facts above ideas, which is characteristic of extreme empiricism, has an injurious influence on the development of plant morphology . .. as Darwin wrote many years ago in one of his letters “all observations must be for or against some view”...’ Try that in your next grant application. David Mabberley Deptof PlantSciences, University of Oxford, South Parks Road, Oxford, UK OX1 3RA

References 1 Select

Committee

on Science

and

Technology (1991) Systematic Biology Research I - Report, HMSO 2 Mabberley, D..l. (1991) Regnum Veaetabile 123, 123-l 32 3 Takhtajan, A..(1969) Flowering Plants: Origin and Dispersal, Oliver & Boyd 4 Wood, D. (1970) New Phytol. 69, 113-115 5 Corner,

E.J.H. (1980) in P.E.P. Deraniyagala Commemoration Volume (Gunawardana, T.T.P. et a/., eds), pp. 116122, Lake House 6 Hay, A. and Mabberley,

D.J. (1991)

Bat. Jahrb. Syst. 113, 339-428 7 Mabberley, D.J. (1990) The P/ant-book kz;;cted

edn),

Cambridge

University

Ecological Classics Foundations of Ecology: Classic Papers with Commentaries edited by Leslie A. Real and James H. Brown, University of Chicago Press, 1997. $68.95 hbk, $24.95 pbk (1000 pages) ISBN 0 226 70593 5 This book, sponsored by the Ecological Society of America, is a collection of 40 classic papers that have made a substantial contribution to our understanding of ecological processes. It is based on the decisions of an editorial board of eight mem-

bers with wide-ranging ecological interests, and I would judge from comments in the Preface that it is an outcome of vigorous debate among them that continued right up to the time of publication. Perhaps this is not surprising; no two ecologists are going to agree in their choice of the classics, and my own choice would also have been different. Foundations of Ecology consists of 28 papers published by people working in the USA, six papers from the UK, three from Australia, one from Canada, one from Italy and one from 207