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Evolutionary Theory
A Hierarchical Perspective
By Niles Eldredge, Telmo Pievani, Emanuele Serrelli, Ilya Tëmkin The University of Chicago Press
Copyright © 2016 The University of Chicago
All rights reserved.
ISBN: 978-0-226-42622-8
CHAPTER 1
Pattern versus Process and Hierarchies
Revisiting Eternal Metaphors in Macroevolutionary Theory
Bruce S. Lieberman
Introduction
Debates about the nature and value of certain types of research in the historical sciences, including paleontology, evolutionary biology, astronomy, and so on, are often marked by a tension or dichotomy that exists between approaches that emphasize simply documenting events that happened, or history, and approaches that emphasize discovering mechanisms, or ahistorical scientific processes and universal truths (Eldredge 1999). Stephen Jay Gould (1970) referred to these two approaches as, respectively, "idiographic" and "nomothetic," and a detailed definition of these terms was also provided in Raup et al. (1973). The idiographic approach later became largely subsumed under Gould's (1989) concept of contingency. This chapter focuses on elucidating these issues in the context of paleontological research in general and on the work of Stephen Jay Gould, Niles Eldredge, and Elisabeth Vrba, three of the principal paleontological architects of modern-day macroevolutionary theory, in particular. (Macroevolutionary theory focuses on the study of the patterns and processes pertaining to the birth, death, and persistence of species [Lieberman and Eldredge 2014].) Further, contributions of phylogeneticists and philosophers of science were also very important to macroevolutionary theory, and therefore relevant works of Ed Wiley (e.g., Wiley 1981, 1989) and others are also considered. Finally, the significance of punctuated equilibria (Eldredge 1971; Eldredge and Gould 1972) and the turnover pulse hypothesis (Vrba 1985, 1992) to the contingent versus nomothetic debate vis-à-vis the study of the tempo and mode of evolution will be considered, as will some scientific analyses germane to this topic.
Gould's views on this topic differed from those of Eldredge, Vrba, and Wiley. Especially noteworthy is that Eldredge, Vrba, and Wiley consistently saw what Gould generally considered to be intransigent dualities as the means for unifying perspectives. Thus considering the works of each of these authors in turn provides important illumination on the topic and can help resolve longstanding arguments in evolutionary biology.
Gould's Early Views on Contingent and Nomothetic Approaches
Early in his career, there were several indications that Gould already saw this as an important issue. Further, his early writings seemed to suggest that a nomothetic approach might be seen by some as scientifically more worthwhile, although an approach that emphasized the study of history was not without value and could even be transformed into a nomothetic approach (Gould 1968).
Gould (1970) also discussed the issue of contingent versus nomothetic approaches specifically in the context of Dollo's law. Absolute convergence in morphology was impossible to Dollo (and Gould) because organisms were so complex and history was a sequence of largely unique phenomena. Here, Gould drew on Simpson (1964), who essentially saw Dollo's law arising from the fact that history cannot repeat itself in a probabilistic sense. To Gould (1970), aspects of evolutionary biology were nomothetic — for instance, the operation of natural selection. However, he also specifically acknowledged the historical nature of evolutionary events and indeed suggested that it was paramount. Further, Gould (1970) concluded that this largely precluded the formulation of true evolutionary laws with one exception to the rule comprising Dollo's law: that law was valid because it demonstrated the importance of history. The distinction between contingent and nomothetic approaches is also emphasized in Gould (1980).
The MBL Group
Sepkoski (2012) described in detail the workings and history of a group of scientists who used the so-called marine biology laboratory (MBL) model. The MBL model was basically an attempt to simulate the random evolution of clades, and the results of these random iterations of simulated evolution could be compared to actual evolutionary events preserved in the fossil record.
One of the important premises of the MBL group was that until we know the "degree of apparent order that can arise within random systems, we have no basis for asserting that a pattern has a conventional cause" (Gould et al. 1977, 24) — that is, patterns must be compared against a null hypothesis, which should be some form of a random walk. Cornette and Lieberman (2004) also endorsed the value of applying an approach that compared actual diversity patterns in the history of life to those that could be generated by a random walk. They concluded that throughout the Phanerozoic, in terms of its overall diversity and patterns of origination and extinction, marine animal life was undergoing a random walk.
Raup et al. (1973) argued that one of the significant impediments to the success of paleontology as a scientific discipline was its focus on why any individual taxon went extinct at any given time period. Thus they were suggesting that the contingency-based approach to paleontology was antithetical to achieving scientific status for the discipline. Still, randomness in the history of life was useful because it enabled predictability (Gould 1981).
Another major conclusion of Raup et al. (1973, 534) was that the evolutionary histories of simulated groups operating under identical constraints can differ dramatically. This is significant because it basically reveals the importance of taking into account contingency when using the nomothetic approach to the study of the history of life. Simply by historical accident (or contingency), groups can show dramatic differences in their evolutionary patterns over time even if there are no differences in the evolutionary processes generating those patterns. This ties in with Kant's views on manifest biological complexity as distinguishing life from a Cartesian-Newtonian mechanical arrangement (Eldredge and Grene 1992). The existence of complexity is one of the reasons the reductionist approach held by those such as Dawkins (1976, 1982), Dennett (1995), and others fails. In fact, life is hierarchically organized, with processes operating at several different emergent levels including the gene, organism, population, and species (Eldredge and Salthe 1984; Vrba and Eldredge 1984; Eldredge 1985, 1986, 1989a). This indicates that processes operating at one specific level, especially a lower hierarchical level, cannot be extrapolated to explain patterns in higher-level entities like species.
Time's Arrow and Time's Cycle
One aspect of Gould's work that is quite relevant to the general debate about nomothetic versus contingent viewpoints that has not generally been considered was broached in Gould (1977). This represented an important attempt to unite the seemingly trenchant nomothetic and contingent approaches: "The task of history is to explain the contexts so clearly that they can be separated and subtracted, thus permitting us to see the unchanging themes" (Gould 1977, 4). Indeed, this is where the term contingency (Gould 1977, 9) first appeared in his writings. It is also where he introduced the category "time's arrow," a later harbinger of Gould (1987), where it was conjoined with "time's cycle." These should be viewed as broader metaphors relating to contingent and nomothetic, respectively. Time's arrow was a synonym to Gould (1977, 1987) for an approach predicated on seeing history as an irreversible sequence of unrepeatable events that further indicated directionality in the history of life. He argued that this perspective, when applied to geology, was most consonant with that of the catastrophists, who held that the earth was continually changing and had only a limited duration. The time's cycle frame of reference matched the perspectives of uniformitarians such as James Hutton and Charles Lyell (early in his career), who both held that all was constancy and the earth unchanging — with the earth's duration effectively infinite — and the same processes that operated today were operating in the distant past. In this standpoint, "events have no meaning as distinct episodes with causal impact upon a contingent history" (Gould 1987, 11).
One of the underlying purposes of Gould (1987) was to find a means of uniting these dichotomies vis-à-vis the study of evolution and geology. He argued lucidly that a time's arrow–only viewpoint makes the history of life (and Earth) unintelligible because nothing ever repeats and thus no scientific processes can be adduced. By contrast, a time's cycle viewpoint implies scientific processes that effectively operate outside of history such that the "history" of life can be viewed largely in an ahistorical context.
However, Gould's views did evolve. By the time Gould (1987) had been published, he was retreating from a singular focus on time's cycle. While praising the profound insights of Hutton that led to the discovery of deep time, he did somewhat chastise him for not grasping "the power, worth, and distinction of history" (Gould 1987, 97). In essence, Hutton strived to make geology like Newtonian physics, but it could and should never be like Newtonian physics (see also Eldredge and Grene 1992; for that matter, contemporary physics is not like Newtonian physics, either). Too much emphasis on time's cycle, to the detriment of time's arrow, could not give us an adequate theory of the earth (Gould 1987, 97) or of life, and "time's arrow and time's cycle both capture important aspects of reality" (Gould 1987, 178). Thus Gould (1987) implored accommodation for both views as equally valid and important.
Gould in "Wonderful Life" and Beyond
Gould's views on the importance of time's arrow and contingency for our understanding of evolution reached their apogee in Gould (1989), and they never receded from this high water mark until the very end of Gould (2002; discussed more fully below). It was important that Gould championed reinstating the importance of history or time's arrow into the history of life. He felt it might not lead to generalities, but Gould (1994, 3) argued that we "should treasure the intricate story of our planet and its life." He even asserted, "The discovery of timeless and universal laws and the prediction of all occurrences under their guidance cannot be an expectation or even a desideratum" (Gould 1994, 4). But one does wonder if Gould almost went too far in the realm of biological evolution, arguing that everything was about history and that there were no general unifying principles or mechanisms governing the history of life. Certainly in toto Gould did not believe this, as he continued to argue in various places and venues for the importance of punctuated equilibria (and thus also allopatric speciation) and the blanket power of mass extinctions, which do represent general unifying principles (e.g., Gould 2002, 1339–40). However, at least a certain aspect of Gould's (1989, 1994) work started to give up on such unifying principles and instead came to emphasize individualistic particulars. Part of his validation of contingency or time's arrow — to the exclusion of views that would have been more mechanistic and predictable — represented Gould's (1989, 35) reaction against "our hopes for a universe of intrinsic meaning defined in our terms."
This was codified in Gould's (1989) notion that if we were able to replay the tape of life again, we would witness a very different result. It had become paramount for Gould to demonstrate the appositeness of paleontology to evolutionary biology, and whereas earlier he might have drawn on other theoretical threads, here he accentuated that "historical science is not worse, more restricted, or less capable of achieving firm conclusions because experiment, prediction, and subsumption under invariant laws of nature do not represent its usual working methods. The sciences of history use a different mode of explanation, rooted in the comparative and observational richness of our data" (Gould 1989, 274).
Gould (2002, 1337) repeated these points, contending that "our increasing willingness to take narrative explanations seriously has sparked a great potential gain," but he (Gould 2002, 1337) did add that not "all conceivable evolutionary questions must invoke enough historical particulars to require a large contingent component in their full explanation" (emphasis in original). By the near concluding paragraphs of Gould (2002, 1338), contingency became the leftovers of what cannot be explained by general laws. Gould did contend that to him, and he did embrace the power of the nomothetic approach and dignified it as the one that most motivated him as a scientist.
Wiley and Brooks's (1982) and Brooks and Wiley's (1986) discussion of evolution as entropy also viewed macroevolution as firmly rooted, and best viewed, as a matter of contingency (although there was an overarching, mechanistic explanation for this: information transfer and entropy). In this case, information transmission is similar to energy transmission and must follow the Second Law of Thermodynamics. Therefore evolutionary change should be expected, and it is actually the conservation of information (or stasis) that requires special explanation (Brooks and Wiley 1986).
It is worth distinguishing between the accuracy of Gould's (e.g., 1989, 1994) vision of contingency when considered on the microevolutionary scale and on the macroevolutionary scale. The smaller the hierarchical level in the genealogical hierarchy considered (Eldredge and Salthe 1984; Vrba and Eldredge 1984; Eldredge 1985, 1986, 1989a; e.g., genes, cells, populations), and the shorter the evolutionary time scale involved, the more likely true episodes of actual convergence will be, the less important history and time's arrow will be, and the more dominant time's cycle will be. The longer the evolutionary time scale considered and the larger the hierarchical level in the genealogical level considered (e.g., species, clades), the more important history and time's arrow will be, and the less dominant time's cycle will be.
A key issue in the entire discussion about the importance of nomothetic versus contingent views of macroevolution has to do with the mode of speciation. The greater the predilection for speciation to occur via the allopatric mode (as predicted in Mayr [1963] and used in the punctuated equilibria model sensu Eldredge [1971] and Eldredge and Gould [1972]), the more important contingency will be in the history of life because it entails that speciation (and thus macroevolution) will be motivated by unique climatic or geologic factors that cause geographic isolation. By contrast, if speciation is usually sympatric and involves competition for various resources, it will be more predictable, and there will be a more muted role for chance and contingency. For now, allopatry seems to be the most common style of animal speciation (Brooks and McLennan 2002; Coyne and Orr 2009; Wiley and Lieberman 2011), suggesting that contingency must be factored into any treatment of macroevolution.
(Continues...)
Excerpted from Evolutionary Theory by Niles Eldredge, Telmo Pievani, Emanuele Serrelli, Ilya Tëmkin. Copyright © 2016 The University of Chicago. Excerpted by permission of The University of Chicago Press.
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