Chance in Evolution

Grant Ramsey, Charles H. Pence, Grant Ramsey, Charles H. Pence

• Publisher: University of Chicago Press
• Year: 2016
• ISBN:
  9780226401911
• Topic: Biological Sciences
• Subtopic: Science General
• Index: Biological Sciences

Humans, however much we would care to think otherwise, do not represent the fated pinnacle of ape evolution. The diversity of life, from single-celled organisms to multicellular animals and plants, is the result of a long, complex, and highly chancy history. But how profoundly has chance shaped life on earth? And what, precisely, do we mean by chance? Bringing together biologists, philosophers of science, and historians of science, Chance in Evolution is the first book to untangle the far-reaching effects of chance, contingency, and randomness on the evolution of life.The book begins by placing chance in historical context, starting with the ancients and moving through Darwin and his contemporaries, documenting how the understanding of chance changed as Darwin's theory of evolution by natural selection developed into the modern synthesis, and how the acceptance of chance in Darwinian theory affected theological resistance to it. Subsequent chapters detail the role of chance in contemporary evolutionary theory—in particular, in connection with the concepts of genetic drift, mutation, and parallel evolution—as well as recent empirical work in the experimental evolution of microbes and in paleobiology. By engaging in collaboration across biology, history, philosophy, and theology, this book offers a comprehensive and synthetic overview both of the history of chance in evolution and of our current best understanding of the impact of chance on life on earth.

* 1 *

The Historical Development and Implications of Chance in Evolution

CHAPTER 1

Contingency, Chance, and Randomness in Ancient, Medieval, and Modern Biology

David J. Depew

Toward a More Complicated History of Biology

In an oft-republished speech commemorating the centenary of Darwin’s birth and the fiftieth anniversary of the publication of the Origin of Species, the philosopher John Dewey claimed that Darwin came close to completing the scientific revolution by undermining the “Greek” or “classic” assumption of Plato and Aristotle that species of animals and plants are immutably fixed natural kinds, each defined by an unchanging set of necessary and sufficient conditions for class membership (Dewey 1910, 1–4, 9–10). I say “came close” because Dewey saw evidence of the incompleteness of, and active resistance to, the Darwinian revolution in “the recrudescence of absolutistic philosophies” that pay lip service to Darwinian evolution by turning on its side the Great Chain of Being, with its hierarchically ordered ranks of essentially defined types ranging from monad to man, and watching it unfold in time.1 This reactionary impulse can be pushed back, Dewey concluded, only if psychology and philosophy are quickly transformed into “Darwinian genetic and experimental logic” (18). He was alluding to his own “instrumentalist” view that ideas are tools for changing social and natural environments rather than pictures of an unchanging stability lying behind shifting appearances.

Fifty years later, the Nobel Prize–winning geneticist Hermann Muller took advantage of the Origin’s centenary and of Darwin’s 150th birthday to proclaim, albeit without Dewey’s plug for evolutionary psychology and pragmatic epistemology, that “One Hundred Years without Darwinism Are Enough” (Muller 1959). Two years later, as neocreationists were girding their loins to prevent school boards from taking Muller’s advice and incorporating evolution by natural selection into high school biology classes, the paleontologist George Gaylord Simpson used Muller’s title to say much the same thing (Simpson 1961). By then, the avian systematist Ernst Mayr was congratulating himself and other founding fathers of the modern evolutionary synthesis, including Simpson, for at last putting Darwinian natural selection onto genetic foundations solidly scientific enough to block regression from “population thinking” to Plato’s “typological essentialism” (Mayr 1963). Not to be outdone, the philosopher of biology David Hull argued that the effect of Aristotelian essentialism on taxonomic theory and practice was “two thousand years of stasis” (Hull 1965). Aristotle was more at fault than Plato because, unlike his mentor, he was a biologist—and a bad one.

Binaries this categorical are usually poor guides to history. Their rhetorical function is to simplify the past in order to induce an intended audience to take this fork in the road rather than that fork at an uncertain moment. If one thinks, however, that nothing is better calculated to advance knowledge than accurate history, one will soon come to agree with Polly Winsor (2006), Ron Amundson (2005), John Wilkins (2009), Richard Richards (2010), and Phillip Sloan (2013) that the “essentialism story” told by Mayr, Hull, and their predecessors is a myth.2 By the same token, we can also agree with Jonathan Hodge and Gregory Radick that “complications . . . make wholly unacceptable any version, no matter however qualified, of the Deweyan thesis about Darwin’s place in the intellectual long run” (M. J. S. Hodge and Radick 2009, 247). Premodern biology, they report, was not nearly as typologically essentialist as Dewey alleged, and Darwin, who arose in the midst of a transition to evolution already under way, did not initiate as great a break with the biological philosophy of the past as Dewey believed.

For Hodge and Radick, greater continuity becomes visible when the influence on modern biology of ancient philosophers other than Plato and Aristotle, notably Epicurus and Lucretius, is taken into account, and when the subject of reproduction, which twentieth-century Darwinians screened off from evolutionary biology when they shifted to what Mayr called “population thinking,” is restored to its crucial role in the history of evolutionary thought.3 In this chapter, I will develop these points by tracing a series of shifting alignments since antiquity among the closely related, overlapping, but distinguishable concepts of contingency, chance, and randomness. These alignments affect how biological teleology—the ascription of functions, end-directedness, and adaptedness—is conceived and how it relates to natural selection. I will make six main points:

1. The history of biological contingency is much older than Darwin. There are elements of contingency even in Aristotle’s theory of generation and, since contingency is the opposite of necessity, in his seemingly catachrestic concept of hypothetical necessity (Lennox 2000, 138–40). Although reproduction accurate enough to maintain species lineages is too regular and too end-directed to be due to chance, Aristotle held that species are reproductive lineages, not types. Although it is natural for each organism faithfully to reproduce the form of its male parent, he acknowledged that particular parent-offspring links in such chains vary and might not have occurred at all. “It is not necessary,” Aristotle writes, “that if your father came to be you must have come to be. But if you came to be it is necessary that he did too” (Generation and Corruption [GC] II.11.338b10–11).4 The element of contingency in Aristotle’s theory of reproduction was defended by Galen in late antiquity (129–217 CE) and, through Galen’s lasting influence on medical education, was revived in early modernity by William Harvey (1578–1657).5 Harvey coined the term epigenesis to name the Aristotelian approach. After the embryological discoveries of Caspar Friedrich Wolff (1735–1794), epigenesis entered into the ferment surrounding the emergence of a unified discipline of biology a few decades before Darwin. Dewey and Co.’s contrast between ancient fixism and the contingency of species, I conclude, is overdrawn.

2. Species fixism of the sort that figures in Dewey’s, Mayr’s, and Hull’s story did exist, but it isn’t nearly as ancient as they imply. It arose in the late seventeenth century (Wilkins 2009, 96). Before then, naturalists, especially botanists, were comfortable with the mutability they observed in hybrids. What changed was the superimposition of the logical category of species onto biological classification and closely related efforts to involve God in fixing species boundaries (89). To maintain these boundaries, preformationists, who opposed epigenesis, hypothesized that God encapsulated into the germinal material of the first, directly created instance of each species the germs of all subsequent members of that kind. There ensued a long in-house debate among preformationists about whether he placed this information into the egg or the sperm. Strange as it may seem to us, anti-Aristotelian advocates of the mechanical philosophy were among the most ardent preformationists. They realized that the functional and goal-oriented characteristics of organisms are inconsistent on their face with modern physics, so they placed these teleological properties into the divinely created prototype of each species and let them mechanically come rolling out, true to type, generation after generation (Richards 1992; Arthur 2006, 172). A strong dose of necessitarianism, marked stress on the language of natural forces, and a correspondingly diminished role for contingency and chance characterized this period in biology’s history, or, to be more accurate, prehistory. Species fixism and typological essentialism, I conclude, are comparatively recent phenomena.

3. The idea that chance is the origin of the natural world has been around since Empedocles (c. 490–c. 430 BCE), Epicurus (341–270 BCE), and the Roman scientist-poet Lucretius (c. 99–c. 55 BCE) (M. J. S. Hodge and Radick 2009, 248). Chance adds to contingency, whose opposite is necessity, an element of indeterminacy that, whether it is located in the nature of things or only in our ignorance, defies explanation, especially explanation in terms of purposes. Roman materialists, to relieve people’s fear of death, promoted the idea that we are accidental confluences of atoms that will dissipate when we die. As late as the fourth century CE, St. Augustine acknowledged at an especially discouraged moment in his youthful quest for wisdom that he “would have awarded the prize to Epicurus” if he had been able to rid himself of his “belief that the soul lives on after death to account for its acts” (Augustine 1992, sec. VI.16). Since fear of death is for Christians the beginning of wisdom and is best cured by trusting in Providence, the idea that chance accounts for biological order served later thinkers mostly as the butt of reductio ad absurdum arguments in which natural theologians, preformationists, and epigeneticists alike reaffirmed the functional and goal-oriented characteristics of organisms that partisans of chance, supposed or real, denied.6 Appeals to chance in biology are tolerant of species mutability. Accordingly, anyone who was perceived as advocating transmutation in the early nineteenth century was likely to be accused of being a materialist and a partisan of chance. That happened to Darwin.

4. There was genuine novelty in Darwin’s anti-Lamarckian stipulation that the causes of variation are independent of its subsequent utility in coping with environments. When variants first arise, they only happen to be useful. But if they are heritable, they can gradually evolve into adaptations by the enhanced reproductive success of the organisms that have them. Darwin uses “chance” to signify the causal independence of variation’s origin from subsequent biological adaptedness (Beatty 2013, 147). But he also used “chance” in other, closely related ways. There is a chance that variations that would prove useful in a certain environment will not be available. There is also a chance that useful variations, even if available, will not be passed on. There is a chance, too, that a useful and heritable variation might not spread through a population (C. Darwin 1859, 126–27; M. J. S. Hodge 1987; Hodge, this volume, chap. 2; Beatty 2013). It is no wonder, then, that Darwin had to fend off accusations that he was a friend of chance. Far from being a theory of chance in the way Empedocles’s, Epicurus’s, or Lucretius’s ideas were, however, Darwin’s view was that natural selection working selectively on chance variation in the ways I have briefly described has the power, amid much failure, to evolve traits that are as genuinely functional as Aristotle’s, Galen’s, or the great comparative anatomist Georges Cuvier’s. In Darwinism, contingency and chance combine with environmental determinism to evolve natural purposiveness. Adapted traits exist to perform certain functions. Accordingly, there is a certain unexpected affinity between Aristotelian functionalism and Darwinian adaptationism (Lennox 1993, 1994; Depew 2008, 2015). The price for embracing this affinity, however, is to admit that by making adaptedness depend on local environmental conditions and on the contingent availability of useful variations, Darwin further undermined the already vulnerable Great Chain of Being that placed humans at the top of the well-ordered, thoroughly purposeful biological continuum. It was an implication that made Darwin’s mentor, friend, and supporter Charles Lyell queasy. It also troubled Asa Gray, a trusted correspondent with whom Darwin thought aloud about these issues. Darwin opposed both friends. Nonetheless, he assured himself that a temporalized version of systematics in which less advanced kinds are succeeded by more advanced followed as an ex post facto consequence of his theory.7 In the long run, however, this may be among the least enduring elements of Darwin’s response to the conceptual currents swirling around him.8

5. Darwinians were able to undercut the long-standing dichotomy between chance and purposiveness because Darwin’s theorizing stood on the edge of the “probability revolution” that, by mathematically “taming” them, gave chance and chances for the first time a key role in law-governed explanations of natural phenomena (Porter 1986; Krüger, Daston, and Heidelberger 1987; Krüger, Gigerenzer, and Morgan 1987; Gigerenzer et al. 1989; Hacking 1990; Gayon 1998). There are statistical regularities. In fact, the basic laws of physics are statistical. The rise of Darwinism as the dominant research tradition in evolutionary biology is inseparable from the fact that Darwin’s successors not only took advantage of the explanatory resources of the probability revolution to develop what Mayr called “population thinking,” but were also leading contributors to this revolution on its mathematical side. A factor in the continuing resistance of populist religious and political culture to Darwinism, I surmise, is the lagging uptake of the probability revolution into common sense.

6. The discovery that the ultimate source of heritable variation is spontaneous mutation in DNA has amply justified Darwinism’s postulate that variation arises independently of its subsequent adaptive utility.9 But this discovery has also resulted in an assimilation of chance to randomness conceived as inherent unpredictability. Twentieth-century physics tells us that even if statistical regularities and patterns can be found at higher levels of resolution, there may be a pervasive indeterminacy at the level of individual events. It is even possible that indeterminacy of this sort plays a large role in evolutionary change (McShea and Brandon 2010). This possibility goes beyond Darwin’s assumption that what we call chance events are as caused as any other occurrences, even if their causes are so tangled that they will forever elude our grasp (Beatty 2013, 147). But it also weakens the long-standing conception of chance as good (or bad) effects accidentally caused, a conception shared by figures as different as Empedocles, Aristotle, Epicurus, and Darwin. It is increasingly likely that randomness does affect the course of evolution, though just how much is a disputed question. For Stephen Jay Gould it dominates macroevolution, the larger history of life (Gould 1989; Blount, this volume, chap. 10; Erwin, this volume, chap. 12). In the form of genetic drift, it is a wild card in microevolution, evolution at or below the species level (Millstein, Skipper, and Dietrich 2009; Strevens, this volume, chap. 6). Nonetheless, any interpretation of natural selection in which sheer randomness is allowed to color what Darwin meant by the chance relationship between the adaptive utility of variation and the causal origin of that variation misconstrues his most basic and most fertile idea.

In this chapter, I will focus on the historically more remote of these theses. They set the context for a volume that contains detailed explorations of the more recent ones. If the history recounted in this chapter, sketchy as it is, lends some clarity to the sixth point, it will have proved its worth. For it is on the relationships among the concepts of randomness, chance, natural selection, and adaptation, I think, that most of the seemingly intractable deficiencies in contemporary public discourse about Darwinism turn.

Contingency, Chance, and Teleology in Aristotle’s Epigenetic Biology

In a seminal chapter in his Physics, Aristotle divides chance into two sorts. The first is luck (tuché), a species of chance that because of its importance in our lives gives its name to the genus. Luck is chance in matters typically under the sway of choice, such as chancing to run into an acquaintance who owes you money you had been meaning to recover (Physics [Ph.] II.5.197a5–6). The other species is spontaneity (to automatou), the analogue of luck in matters under the sway of natural tendencies and impulses (Ph. II.6.197a36–b15). In discussing the latter, Aristotle reports at length the views of Empedocles, who assigned greater objectivity to the functional and goal-directed appearances presented by living things than did Democritus, who was a more determinist and necessitarian materialist, at least according to Aristotle, and who in consequence believed that the appearance of purposiveness in organisms was just that: appearance (Ph. II.8.198a15–16). Genuinely good results, said Empedocles, happen in nature as they do in human affairs. Organic kinds originated in a way not unlike the way you happened to run across your debtor in the marketplace (Ph. II.8.198b15, 199a8).

Here is how Empedocles thinks it works. Biochemical compounding of the four elements, he admits, is necessitated. In an era when the cosmos was under the sway of Love, these compounds were more likely to form parts that self-assemble into organisms than we see today. Even during the reign of Love, most of these aggregations didn’t last, because their components didn’t reliably stick together. They stick together even less often in our own Strife-ridden times. Still, Aristotle reports Empedocles writing in his poem about cosmogony, “Whenever all the parts did coalesce together (sumbanei) as if they had come to be for the sake of something, these animals were preserved (esothê), having been aptly (epitedeios) constituted spontaneously (ap tou automatous). Those of which this is not the case perished and continue to perish, as Empedocles says of ‘human-faced oxen’” (Aristotle, Ph. II.8.198b27–33, my italics; see also Ph. II.4.196a24).

For Empedocles, organisms persist because their parts happened to be physically stable in relation to each other even when, as in our own age, the cosmic cycle is too strife-ridden to form new combinations that endure. What sticks together and doesn’t is necessitated. But insofar as the effects of such affinities are life preserving, and so, from the perspective of the living beings that survive, are good, their cause is nothing like that of a well-planned and well-executed series of intentional actions. What links the happy outcome with its causal antecedents are not means put to ends. It is spontaneity (to automatou), the natural counterpart of luck.

Empedocles realized that the continued existence of oxen or humans or any other stable kind requires a mechanism by which they replicate themselves. In an early but not unprecedented version of pangenesis—the theory of inheritance favored...

Table of contents

• Cover
• Title Page
• Copyright Page
• Contents
• Acknowledgments
• Introduction: Chance in Evolution from Darwin to Contemporary Biology
• PART 1  The Historical Development and Implications of Chance in Evolution
• PART 2  Chance in the Processes of Evolution
• PART 3  Chance and Contingency in the History of Life
• References
• Contributors
• Index