“Look here brother who you jiving with that cosmik debris?” Frank Zappa, Apostrophe’, 1973.
Consider the following three pairs of statements
1. “I don’t like to say bad things about palaeontologists, but they’re really not very good scientists. They’re more like stamp collectors” a Nobel laureate infamously remarked in an interview in the New York Times in 1988. In the same year at a meeting of the Society for the Study of Evolution a prominent biologist asked a younger colleague “How can someone who is able to solve integral equations, like you, waste his time on such non-sense as homology?” The first case elicited an international wave of indignation among palaeontologists, and before the year ended the perpetrator of this heinous statement was dead (no causal relation assumed here). In the second case, the biologist who posed the rude question lived on for another 26 years, and the question merely precipitated a bemused thought in the young biologist’s brain: “Needless to say, I took this as a compliment.” It is of course well known that Luis Alvarez uttered the first remark. In the second case, it was John Maynard Smith who asked Günther Wagner the impolite question (Wagner, 2006).
2. In 1990 Simon Conway Morris described a “bizarre metazoan” from the Carboniferous Bear Gulch Limestone of Central Montana (my own first publication was on stem group mantis shrimp from the same deposits) that he called Typhloesus wellsi. The name referred to its possession of a voluminous but blind gut with ample contents (from the Greek typhlo, for blind, and oesus, for glutton). This hallmark characteristic poses a serious challenge to the interpretation of the biology of Typhloesus because its general body shape and external anatomy suggest the animal was an active swimming predator or scavenger with a smooth streamlined body and a posterior fin presumably used for propulsion. Blind ending guts are typically restricted to either diploblasts, such as cnidarians, or sessile or low-activity bilaterians such as platyhelminths and articulate brachiopods. In speculating on the phylogenetic affinities of Typhloesus, Conway Morris (1990: 618) considered the “failure to identify any of the expected features such as a notochord, gills slits or myotomes” as ground for a “refutation that Typhloesus is a chordate.” In 1999 Geoffrey Fryer wrote a review of Conway Morris’ book The crucible of creation. In his review Fryer takes issue with several phylogenetic hypotheses of Cambrian metazoans reported in Conway Morris’ book. For example, Fryer deems the conclusion that Anomalocaris is “some kind of arthropod” to be severely compromised because “no indisputable arthropod has anything remotely like its circular jaw apparatus” (Fryer, 1999: 2).
3. In his important book The evolution of developmental pathways, Adam Wilkins concludes that new discoveries in molecular developmental biology necessitate “some changes in the ways in which we view, and use, the term ‘homology.’ The basic concept of shared possession of a trait through common descent remains intact, but the idea that the ‘same’ trait in two different organisms may actually exhibit more points of visible difference that of discernable identity seems counterintuitive, to put it mildly” (Wilkins, 2002: 167). In a paper published the next year, fellow newsletter correspondent Brian Hall devised a new classification for homological and homoplastic correspondences. Hall (2003: 409) concluded that “joint examination of nearness of relationship and degree of shared development reveals a continuum with an expanded category of homology, extending from homology → reversals → rudiments → vestiges → atavisms → parallelism, with convergence as the only class of homoplasy,” thus “seeing reversals, rudiments, vestiges, atavisms and parallelism as closer to homology than to homoplasy” (Hall, 2003: 426).
I expect that most readers will not immediately sense a uniting thread of logic that could bind these three pairs of statements into a coherent whole. Similarly, perhaps with the exception of the acrimonious statements by Alvarez and Maynard Smith, many readers may not identify anything obviously objectionable about the last two pairs of statements. In this essay I will show that all these statements are logically related to each other by continuing the metaphysical musings that I started in issue 60 of the newsletter. Specifically, I will present a brief ABC of the individuality thesis, which I believe is the logical foundation of the natural sciences and the conceptual key that is necessary for grasping the hidden bond between the above statements. Now, don’t be alarmed. What follows is not particularly difficult, but it is without question one of the most fundamental topics you can think about. I guarantee that getting familiar with the individuality thesis could really change your perspective on science. Personally it helped me a lot. At the very least I hope this little exercise will provide some flesh on the bones of vaguely articulated intuitions that you might already have, and that it will spur you on to read more deeply into the literature. A proper grasp of the individuality thesis can provide you with the most broadly applicable intellectual tool you can wish for. For me it was a real eye-opener.
Before going into details, I want to try to pre-empt a response that certain readers inevitably have. This is not merely an issue of semantics! What comes is neither simply the juggling of words or an act of semantic sanitation, nor is it merely the pasting of imaginary labels on abstract mental constructs. Even though an armchair is really the only tool we need here, this essay deals with nothing less than reality at its most fundamental level. This is the sense in which metaphysics should be understood here. Michael Ghiselin (1997) goes so far as to include metaphysics within science, rather than considering it as the necessary context for science. It emphatically does not refer to new age wish-wash or other pseudoscientific pap. It is sometimes said that science is, or at least ought to be, metaphysics neutral. I vehemently disagree. Some people dismiss difficult or personally uncomfortable conceptual problems as ‘mere metaphysics.’ At best this is an attempt to neutralize deeply conceptual issues by exiling them from the realm of scientific responsibility to the no man’s land of lawless speculation. At worst it is an act of intellectual cowardice. As we will see when we return to the statements posed above, turning a blind eye to metaphysics can only lead to confusion. Metaphysical commitments set the inescapable boundaries within which all scientific work attains its meaning, and it is irrelevant whether the commitment is conscious or not. By explicitly addressing metaphysics one can at least ensure that the elements of one’s work exhibit logical coherence, as well as external consistency with the evidence and ideas of one’s discipline outside of one’s own personal research programme.
Most fundamentally and least controversially, scientific materialism is the metaphysical commitment that underpins all natural sciences. As discussed in the previous essay, it was his radical materialism that worried Charles Darwin greatly because it broke so sharply with tradition. In Ghiselin’s (2005: 127) words “much as Copernicus had moved the sun to the center of the physical world, Darwin moved concrete particular things to the center of the metaphysical world.” Materialism, or naturalism as it is also sometimes called, comes in two basic flavours. Methodological materialism (or naturalism) is a commitment to viewing the world as being governed by natural causes, and the scientific approach to obtaining knowledge can only address the materialist aspects of the world. It does not deny that the supernatural may exist, only that science is impotent in informing us about it. Metaphysical materialists (or naturalists) on the other hand commit to the view that the world is basically as we ‘see’ it. According to this perspective science is the only way to obtain knowledge about the world, with no place for the supernatural. Not surprisingly metaphysical materialists are typically atheists. Religious fundamentalists, including proponents of intelligent design, deny the validity of both methodological and metaphysical materialism (see Ruse, 2005a for an example). If you do not accept at least methodological materialism I respectfully say goodbye to you at this point. Our views of the world are so different that I cannot presume to be able to understand you, and vice versa. For the remaining readers, here is a very succinct summary of the core of individualism.
I consider the individuality thesis (IT hereafter) to be a logical corollary of materialism, which confers a particular shape or flavour upon it. This is what it tastes like. (The following is heavily indebted to the work of Michael Ghiselin, in particular his book Metaphysics and the origin of species. This is simply the most insightful book written by a biologist that I have read in many years, and its message is absolutely indispensable for any self-respecting biologist and palaeontologist).
The distinction between classes and individuals is the most fundamental ontological dichotomy within IT. Anything you can think of is either a class or an individual. The following distinctions are important:
1. Individuals are concrete and spatio-temporally restricted. Classes (including natural kinds) are abstract concepts outside of time and space.
2. Individuals, by virtue of being concrete, can partake in natural processes, while classes cannot.
3. The ontology of individuals is the part/whole relation, wherein high-level individuals are composed of low-level parts. Consequently, ontologically, the whole body of a multicellular organism versus its comprising parts (e.g. organs, cells) exhibit the same part/whole relation as a high-level monophyletic taxon versus its subclades or species. In contrast, the ontology of classes is the membership relation. As a result, and in contrast to individuals, classes can have members, examples, and instances.
4. Individuals do not have defining properties. They can undergo an indefinite amount of change, and still remain the same individual. A class has defining properties and can therefore not change indefinitely without becoming a different class.
5. Natural laws don’t refer to any particular individuals. Laws can only be formulated for classes, of which individuals may be members.
These five stipulations leave no doubt: species and other monophyletic taxa are individuals. So are organisms, and the parts or characters that they are composed of. For me this understanding provided a hugely efficient broom that could sweep up the conceptual debris that had accumulated in the corners of my mind.
Before we take a look at how the logical implications of IT can help clean up the conceptual debris that contaminates the three pairs of statements posed at the beginning of this essay, you may find yourself still in doubt about IT. This would not be too surprising. Although the concepts of IT are not particularly difficult, they do deal with ultimate reality or at least with the ultimate insights about the world that science at its best can provide. Consequently it may take some time before you convince yourself about the compelling logic of IT. Please delve into the literature. Use the work of Michael Ghiselin and David Hull as starting points, and try to include some of the recent writings of Olivier Rieppel for a contrasting view. The issue is too important not to deal with explicitly at least once in your professional career. Yet, such an exercise may still not convince you. Although I think that the majority of biologists and palaeontologists accept IT, either implicitly or explicitly, there is no absolute consensus. Philosopher Michael Ruse, for example, labelled IT as “a good idea…that just did not work” (Ruse, 1998: 286). In the 1980s Ruse told Ernst Mayr in a discussion group at Harvard that he thought that the idea that species are individuals was nonsense. This triggered Mayr to cross the room towards Ruse, waving his finger, and yelling (Ruse, 2005b). After all, Ruse is a philosopher, not a biologist, so what does he know about species, right?
In my initial excitement about IT, I wrote a paper on the logical implications of embracing IT for current thinking in the field of evolutionary developmental biology or evo-devo (Jenner, 2006). The summarizing statement of one of the reviewer’s reports gave me a taste of my own medicine (I recently found out that several of my colleagues have awarded me the dubious honour of making my name a verb. To ‘Jennerize’ has apparently come to mean to ‘severely criticize’…): “this is a hopelessly lost treatment of an old problem, that does not appear to contribute anything useful to evo-devo thinking.” Luckily the other reviewer and the editors did not agree. See for yourself what IT can do for you.
Specifically, IT brings into plain view previously hidden traces of typological thinking that remain surprisingly prevalent in the literature. A hallmark of typological thinking is to consider taxa as classes rather than individuals, but surely modern biologists are not typologists? In the annual address of the Systematics Association in 2001 Norman Platnick said the following: “Now one thing I’ve learned from 30 years of watching biologists is that whenever you find one systematist calling another one an essentialist or a typologist, you can be 100% sure that the name-caller is purely, simply, and entirely, wrong, and is just creating a smokescreen to cover his or her tracks.” Two remarks are necessary here. First, Platnick is wrong. As I will show below and document in Jenner (2006), typological thinking is still prevalent, but its manifestations are more hidden than what you might expect from a cardboard 19th century pre-Darwinian. Which leads to the second remark: Platnick is right, but perhaps not in the way he intended. In his insightful book The changing role of the embryo in evolutionary thought Ron Amundson takes a critical look at the traditional historiography of evolutionary biology. He makes the critical observation that the widespread idea that many pre-Darwinian typologists were religiously deluded idealists, is based on the uncritical acceptance of what he calls Synthesis Historiography, of which Ernst Mayr was a major architect. What is wrong with this interpretation of history is that no distinction was made between metaphysical typologists, who really interpreted real species as mere manifestations of eternal non-material types, and those who invoked typology more as a methodological precept, akin to methodological materialism among materialists as discussed above. Amundson’s revised interpretation reveals that history is riddled with far fewer boneheaded metaphysical typologists than previously thought. Surely Platnick is right that today people so inclined are virtually non-existent among serious scientists. Yet, a typological undercurrent can still be diagnosed in the current literature, as we will see now when we turn to the three pairs of statements with which I began this essay.
The problems with the three pairs of statements become clear when we realise what implications the recognition of individuals can have for conclusions at different levels of generality. Pairs two and three are intuitively the easiest to grasp, and they can be united by the following aphorism: differences don’t matter. IT stipulates that individuals can change indefinitely without compromising the identity of the individual. This may be counterintuitive, as the vernacular understanding of individuals hinges on their uniqueness. For example, Gould (2002: 602) wrote that “an individual may undergo some, even substantial, change during its lifetime, but not so much either to become unrecognisable or to encourage redefinition as a different thing.” This is particularly ironic because throughout his career Gould explicitly endorsed IT for it constitutes the conceptual foundation for punctuated equilibrium. Yet, spatio-temporal continuity is all that an individual needs to stay the same individual, and nothing else. No change in the intrinsic characters or parts of an individual can negate individuality. Charles Darwin said as much for taxa as individuals without having explicitly worked out IT: “Let two forms have not a single character in common, yet if these extreme forms are connected together by a chain of intermediate groups, we may at once infer their community of descent” (Darwin 1859: 409). This reveals the error in thinking by Conway Morris and Fryers in the second pair of statements. The fact that Typhloesus seemingly does not possess “expected features” of chordates is no “refutation that Typhloesus is a chordate.” Differences are impotent with respect to phylogenetic conclusions. Without going into character study, Typhloesus could in principle well be a chordate, which has lost many plesiomorphies. Differences are agnostic with respect to phylogenetic relatedness because evolution is “descent with modification” and no amount of modification can therefore erase common descent. Moreover, all that monophyletic taxa that are part of a higher-level individual (more encompassing clade) need to share is common ancestry. Just because a given taxon is related to another does not allow us to expect that they share particular traits. That is merely a matter of historical contingency, dependent on whether change has in fact occurred or not. Similarly, Fryer’s conclusion that the possession of a distinctive autapomorphic circular jaw apparatus in Anomalocaris negates arthropodan affinities is flawed. These conclusions would only make sense if taxa are classes with particular definitions, by virtue of which one can extrapolate across members of the class based on the traits stipulated by the definition. In that case if a member does not possess a certain character required by the class’ definition, such as a notochord or appendages as mouthparts, that member no longer fulfils the necessary membership criteria of the class and therefore is excluded from it. Applying such thinking to taxa is perniciously typological. The resolution provided by IT shows that no matter how much a part of an individual may change, in this case a species as part of a larger clade, this does not falsify it as a part of the higher-level whole. In other words, no degree of modification can negate a conclusion of common descent.
The same reasoning shows the problems with the third pair of statements. Homology is nothing more than a correspondence relation between homologues, based on shared common ancestry. Consequently, even if homologues change through time, no matter how much, they do not become less homologous. Fundamentally, it is a metaphysical impossibility for intrinsic properties (similarity) to influence decisions about relational properties (homology). The extraordinarily modified middle ear bones of extant mammals are not less homologous to the jawbones of their non-mammalian ancestors than those of the earliest mammals. Character similarity is merely a tool to help diagnose possible homologues, nothing more. The fact that Wilkins (2002) feels this is “counterintuitive, to put it mildly” shows that our intuition is a tool much too blunt to cut through conceptual Gordian knots. It scarcely provides a robust rationale for accepting partial homology, as advocated by Wilkins. A similar problem is inherent in the thinking of several other evo-devologists, including Brian Hall (2003), who attempt to mingle the mere diagnostic criterion of similarity of possible homologues with their proper definition as being simply a result of common descent. For the definition of homology an uninterrupted continuum of shared history is all that counts. I do appreciate the motivation for Hall’s attempted new classification of homology and homoplasy. He wants to express the important fact that even in cases of phenotypic homoplasy, conserved developmental mechanisms may be implicated. However, by arguing that reversals and atavism are “closer to homology than to homoplasy” Hall is likely to sow more confusion than enlightenment. Homology is an either/or issue. Homology does not come in shades or degrees. If corresponding parts and wholes are properly recognized, homology is either fact or fiction. Evolutionary retention of developmental mechanisms that later become active in the development of an atavism, for example, simply indicate non-homology of the phenotypic product with previous plesiomorphies and homology of continuously retained developmental mechanisms (see Jenner, 2006 for additional discussion).
The first pair of statements addresses the old issue of the status ranking of scientific disciplines. Even at this very general level IT can illuminate the problem. The snide remarks by Alvarez and Maynard Smith are unsurprising given a long history of classifying the sciences based on perceived worth along some scale of vague description. Without exception physics is placed triumphantly at the top of academic prestige, while the humanities, historical, and social sciences are frequently not even labelled as ‘science.’ I believe such conclusions at the same time represent the acme of academic arrogance, and a blatant display of metaphysical ignorance. A non-arbitrary classification of science distinguishes between the nomothetic, or law propounding, disciplines, and the idiographic disciplines that describe and explain contingent events. IT teaches us that laws of nature do not apply to particular individuals, and can only be formulated for classes, of which individuals may be members. Consequently, the nomothetic sciences are never concerned with investigating the properties or history of just single individuals, but always have a broader focus on a class that contains at least several individuals. Moreover, the nomothetic sciences are not concerned with the vicissitudes of contingent events, but with the predictable outcomes of natural laws. This means that any science that concerns itself with single individuals is idiographic, and therefore resides squarely in the domain of historical contingency. Such disciplines naturally lack in predictive ability, which is typically associated with the operation of natural laws that produce predictable regularities. It is important to note that the arrow of arrogance in the sciences unfailingly soars straight from the nomothetic arena to impale innocent idiographers. This is sad and ironic, because a full understanding of the natural world is absolutely dependent upon the integrated efforts of both nomothetic and idiographic disciplines, and nomothetic sciences are incapacitated without idiographic data. Without a richly documented fossil record Luis Alvarez would never have been able to make his important contribution to our understanding of mass extinctions. And without the central role that homology has played in establishing the fact of evolution, and in providing the cornerstone of comparative biology, an aircraft engineer named John Maynard Smith would perhaps have never escaped his hangar.
Yet I think that the nomothetic sciences will always be considered as somehow superior to the idiographic. The prestige of precise predictions, the ideal of quantification, and the appeal of smooth extrapolation have a very strong attraction. Even such a staunch campaigner for disciplines with a strong idiographic tradition, including natural history and palaeontology, such as the late Stephen Jay Gould, could not entirely escape the beguiling glare of nomothetics. From his early days as a professor at Harvard, and most vociferously in the 1970s and 1980s, Gould laboured mightily at the cradle of palaeobiology (Sepkoski, 2005). Gould explicitly envisioned palaeobiology to be the nomothetic brethren to traditional idiographical palaeontology, and Paleobiology was to become the primary outlet for nomothetic approaches to the history of life. Nevertheless, I think that the message that Gould himself impressed most firmly in the minds of both lay and professional readers is that contingency rules the history of life. In contrast, it was Simon Conway Morris who effectively took advantage of the nomothetic realm in his last two books to present a view of the history of life that stands in almost complete opposition to Gould’s view of life. Especially in Life’s solution, Conway Morris catalogues an impressive array of examples of convergent and parallel evolution. Considering certain expected, perhaps universal boundary conditions, a broad predictability may characterise the history of life on Earth and possibly elsewhere. To be sure, the predictions will be very broad, but given the rules of competition for limited resources (economics in a very broad sense), and the physical rules that govern gas exchange and locomotion, for example, one may be led to expect certain characteristics. Similarly, closely related and similar organisms may repeatedly evolve the same adaptations or analogues based on constraints in their construction and faced with similar environmental challenges. Ultimately, we need both idiographics and nomothetics, individuals and classes, chance and necessity, contingency and law.
Before we conclude I want to return briefly to the question that I posed at the end of the previous essay. I agree with Ghiselin that IT is the proper conceptual basis of modern evolutionary biology. I think that accepting a Darwinian view of life logically engenders it, and that it is the core of the Darwinian revolution in thinking. Yet, the revolution has not yet been completed. Why could that be? I suspect the answer is not very ennobling. I believe that the individuality thesis, which was brought to general attention with Ghiselin’s 1974 paper titled “A radical solution to the species problem,” has simply suffered from scotoma born out of apathy. Less than two years ago I was not at all interested in metaphysics. This lack of interest was a simple result of ignorance. Even during my PhD training as a systematic biologist I cannot remember any serious attention being paid to IT. Maybe this is a result of the fact that in the Netherlands we don’t have to take many courses, but the ones I have taken remained silent on this fundamental topic. I think that for many people IT simply doesn’t pop up on their radar. Depending on your discipline, you may not have much daily use for it. If you are engaged in experimental work in developmental biology, you may never have seriously to consider IT to be able to be successful. It is a very different matter in comparative and evolutionary disciplines. The extent to which one can extrapolate findings from one taxon to another, the value of similarities and differences for phylogenetics, and the relation of nomothetic and idiographic aspects in evolutionary biology, are all informed by IT. Ignore it at your peril.
Metaphysics is not a semantic sanitizer. Instead it is a most potent conceptual caustic soda that is able to dissolve through the most caked conceptual debris we may find before us. A substantial amount of this residue we find scattered in the literature is the conceptual contamination deposited by many decades of uncritical and outdated typological thinking. IT is a conceptual fractal that can shed equally illuminating light on thinking in evo-devo, palaeontology, and evolutionary biology. I leave it to you to diagnose and disinfect the remaining conceptual debris you may find on your way. Trust me, there is enough for everyone...
Ronald Jenner
Department of Biology and Biochemistry, University of Bath, UK.
REFERENCES
AMUNDSON, R. 2005. The changing role of the embryo in evolutionary thought. Cambridge University Press, Cambridge.
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CONWAY MORRIS, S. 2003. Life’s solution: Inevitable humans in a lonely universe. Cambridge University Press, Cambridge.
FRYER, G. 1999. Cambrian animals: evolutionary curiosities or the crucible of creation? Hydrobiologia 403: 1–11.
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