Metaphysics and the Origin of Species Purchased

Michael Ghiselin is well aware of the average reaction of scientists to the simple mentioning of metaphysics: ‘Although things are changing, “metaphysics” has tended to be a term of opprobrium.’ (p. 19). It is quite easy to agree with his diagnosis, that one main reason has been the popularity of what is called ‘positivism’, the praise of the fact as such. Less easy would probably be for most practising scientists to follow Ghiselin when he strongly advocates a reversal of the trend, while contending that ‘there is no way in which one can divorce science from metaphysics altogether: to deny metaphysics is itself a metaphysical thesis. [..] The only choice is that between good metaphysics and bad metaphysics, good science and bad science.’ His arguments, at any rate, are very strong and convincing, and also phrased in a language devoid of empty sophistry and useless technicalities, which probably matters much to the average scientist.

Of course, this is not a book to be browsed through: ‘The reader who follows the common practice of reading just parts of books had better not waste such time on this one.’ (Preface, p. X).

To begin with, Ghiselin explains why and how he will treat metaphysics not as a branch of philosophy, but as one of the natural sciences. To be sure, these first few chapters will require more than cursory attention from readers not accustomed to some degree of abstraction, but the exercise will be rewarding.

Within a few pages, the author brings us well into his major issue, that of species‐as‐individual, a notion already defended by Ghiselin in his first book ( Ghiselin, 1969 ) and even earlier ( Ghiselin, 1966), although it definitely came to the attention of the scientific community only through his 1974 paper published in Systematic Zoology under the provocative title ‘A radical solution to the species problem’.

This is not the right place to summarize the concept, or to review the main consequences of its acceptance from the point of view of evolutionary biology. On the one hand, I think that many readers of this journal are already familiar with it; on the other, Ghiselin’s new book will rapidly sweep off most of the previous literature on the topic, thus providing the best introduction by far to this problem area. Rather, I will explain why I think that an evolutionary biologist should pay serious attention to this book.

It might be true that species are mainly the business of systematists – roughly speaking, of people whose primary job is to classify. The fact is, however, that ‘Classification, contrary to what its etymology suggests, is not just the making of classes, or the product of that process. Rather it is the organization of knowledge. Therefore the revolution that is going on in systematic biology has profound implications for our understanding of everything that is known and is knowable, especially of knowledge itself.’ (p. 17).

The definition of species provided by the author (p. 99) is as follows: ‘Biological species are populations within which there is, but between which there is not, sufficient cohesive capacity to preclude indefinite divergence.’ One might notice here some change in wording in respect to previous definitions provided by the same author, or by others. At any rate, we are clearly, and firmly, within the range of possible definitions of what we are accustomed to call the biological species. Of course, it could not be otherwise, if species (species taxa, not the species category!) are considered to be individuals, rather than classes.

It is challenging, and perhaps a bit ironic, that Ghiselin’s work appears on my working desk only few weeks after the book edited by Claridge et al. (1997 ), entitled Species: The Units of Biodiversity, where two dozen systematists explain why they do, or do not, recognize biological species, rather than ‘morphospecies’, or other things, in the groups of animals, plants and bacteria they specialize in. As one might probably expect, the approaches presented in that book are much more diverse than somebody might wish to have, including Michael Ghiselin, Michael Claridge and myself.

The fact is, as Ghiselin explains, that ‘the critics of the biological species concept often argue that it is not broad enough to suit their needs. Their point is not that they object to drawing the line in one place or another. Rather, they want a species concept so broad that every organism is an element of a species. And of course this precludes asexual clones and the like. The real justification for this claim is the supposed advantages that we would gain from being able to refer to each and every organism by a specific epithet, and to do so in what seems, at least, to be a straight‐forward manner. We lose, however, the advantage of having the most basic unit in systematics coincide with one of the most basic units in theories of evolutionary processes’ (p. 103). However, ‘when it is asked how many species there are in the world, the question is not what somebody might want to call species, but how many units of a given kind do in fact exist. A pluralistic species concept renders such an effort altogether worthless. Imagine what would happen if the United States Bureau of the Census attempted to do its job with a “pluralistic” conception of “inhabitant” and instead of everybody collecting the data counting heads, one census taker were to count heads, another legs, another digits, another perhaps hairs’ (p. 120).

A critical issue is that of uniparentally reproducing organisms, where the biological species concept cannot be applied, by definition. I agree with Ghiselin in regarding these organisms as being outside that part of natural economy which is organized in species. That will not please others, however, for instance specialists of Rubus or Taraxacum, notoriously ready to christen with Linnaean binomens any recognizable clone they might come across. To be sure, I am not underestimating the interests of these organisms, and of their reproductive behaviour, for biology in general and evolutionary biology in particular, but I am not ready to subscribe to the species concept favoured by taraxacologists or to use the ‘species’ names they use for their clones. No less than 235 ‘species’ of dandelions, for example, are described in a recent monograph dealing only with the flora of Great Britain and Ireland ( Dudman & Richards, 1977) – an interesting book, whose section on the nature of dandelion species is, however, unconvincing. As Ghiselin puts it (p. 105), ‘if a species should give off a clone, we should, in principle, be able to refer to it by naming the species from which it arose, and giving a name (or number, or other symbol) that distinguishes it from other clones.’

Beside the species, one of the most controversial topics discussed by Ghiselin in his new book is macroevolution. The author’s point is easily summarized in one sentence, namely, that ‘above the species level, taxa of the same rank have nothing scientifically interesting in common’ (p. 270).

This leads to a short but pithy walk through the major branches of the animal kingdom, summing up to the following overall result (pp. 276–7): ‘what I think people are trying to do when they rank taxa is to equilibrate on the basis of some criterion of degree of generality, but the procedure is anything but rigorous. The entities in question are “more or less general” in so many diverse, incommensurable, and often purely subjective ways that ranking them in that manner had little if any scientific value. This in addition to the point that the properties in question are largely a matter of tradition, artifacts of extinction, and how much information we happen to possess about one group or another.’

Therefore, ‘if we are to achieve progress in this area [the study of macroevolution], our classifications need to be based upon something other than tradition, ignorance, and bad metaphysics. Whatever phyla are, they are not, as Gould (1989) puts it, “designs for living” [..] Phyla at best are lineages, i.e., descendants of a common ancestor, that some people for any number of reasons happen to have ranked between the class and the kingdom in a Linnaean hierarchy. [..] If we want to understand the history of life on earth and explain it properly, we need something other than generalizations about classes of genera, families, orders, classes, phyla, and the like. We need an explicit history of the lineages themselves, a kind of scenario that tells us what really happened to real organisms, and real populations thereof, in real environments’ (pp. 281–2).

It is difficult not to agree with Ghiselin on a final point, namely, that major shortcomings of the current state of evolutionary biology are due to the inadequate level of education, hence of scholarship: ‘Much of what gets presented to students at all educational levels is mere vocabulary, and the way in which we learn words is apt to prejudice us with respect to how we learn everything else. This is especially the case with taxonomy, one of the main functions of which is to provide us with a language. [..] When one identifies a specimen, one decides which group it belongs to. [..] For purposes of identification one wants characters that are conspicuous [..] and easily made out. Identification manuals naturally emphasize such characters. [..] Even if one does not get the impression from such an exercise that the characters so used are “defining” of the taxa, one still is apt to get the impression that classification is “based upon” such characters. [..] If people who teach systematics and write the text books are confused about such fundamental matters, one might wonder about everybody else’ (p. 180). ‘[We need to go] back to the source of our knowledge, including of course reinvestigating the organisms that interest us with new techniques both physical and intellectual, but also taking a hard and critical look at the sources through which we are deriving our tradition. It would be all well and good, were we simply able to check up the observations, but the labels that we put on our drawings are theory‐laden in the extreme. To interpret the texts we need to know the assumptions, especially the tacit assumptions, and this means knowing a lot of context and background’ (p. 297).

You might broadly agree with Ghiselin’s theses, as I do, or disagree. But you will find reading his book a profitable exercise anyway, because, beginning with the first pages, you will feel obliged to take a stance, to explain, to yourself at least, where and why you agree with him, or not. Whatever your former, or future, metaphysical mind, your critical attitude towards comparative and evolutionary biology will much likely come out improved.

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Author notes