Evolutionary Progress?

Progress might have been all right once, but it has gone on too long. (Ogden Nash 1962, p. 11) That the history of life on Earth manifests some sort of progress has seemed obvious to many biologists. Once there were only the simplest sorts of living things—replicating molecules, perhaps. Now the world contains innumerable species displaying amazing adaptations fitting them for every conceivable niche in the economy of nature. How could anyone who accepts an evolutionary view of life deny that progress has occurred? Yet perhaps no other issue in evolutionary biology has inspired such passionate controversy. According to one prominent critic, Stephen Jay Gould, “Progress is a noxious, culturally embedded, untestable, nonoperational, intractable idea that must be replaced if we wish to understand the patterns of history” (Gould 1988, p. 319). Other critics, such as William Provine, are somewhat less contemptuous but equally dismissive of the idea of evolutionary progress, issuing the common complaint that “the problem is that there is no ultimate basis in the evolutionary process from which to judge true progress” (Provine 1988, p. 63). Undaunted by these attacks, however, contemporary friends of the concept of evolutionary progress have insisted on its centrality in a Darwinian view of life. According to Richard Dawkins, the most important features of evolution simply cannot be understood correctly without embracing the notion of evolutionary progress: “[A]daptive evolution is not just incidentally progressive, it is deeply, dyed-in-the-wool, indispensably progressive. It is fundamentally necessary that it should be progressive if Darwinian natural selection is to perform the explanatory role in our world view that we require of it, and that it alone can perform” (Dawkins 1997, p. 1017). In Ernst Mayr's view, progress in evolution is simply as obvious, and as undeniable, as the manifest progress in the development of the automobile (Mayr 1994). As these divergent viewpoints reveal, the notion of evolutionary progress remains a hotly contested idea in evolutionary biology (Gould 1996, 1997, Ruse 1996). A cursory examination of this issue might tempt one to conclude that it is inherently unresolvable (Ruse 1993). But as I will try to show, the question, “Is evolution progressive?” admits of the same sort of answer as other questions in evolutionary biology. The key lies in spelling out more carefully the meaning of the term evolutionary progress. But although being clear about the meaning(s) of this term is necessary, it is not sufficient for answering this question. Once the meaning(s) of the term evolutionary progress has been clarified, there remains the empirical and interpretive task of determining whether evolution is progressive in one or more of these senses. There are, then, two basic questions concerning evolutionary progress: First, what is meant by evolutionary progress? Second, is evolution, in fact, progressive? With regard to the first question, I will argue that the notion of evolutionary progress has both a core meaning as well as a set of clearly specifiable alternative interpretations, each of which needs to be carefully identified. In response to the second question, I will argue that if some conceptions of evolutionary progress are exemplified in the history of life, then evolution must be considered progressive, at least insofar as those conceptions are concerned. Indeed, given the range of legitimate interpretations of evolutionary progress, it will almost necessarily be the case that evolution is progressive according to one of these interpretations. The notion of evolutionary progress has accumulated a range of connotations. Con se quently, it is worthwhile to return to the core concept of evolutionary progress (i.e., those features of evolutionary progress that virtually everyone, despite their other differences, would agree to) to see what the basic concept requires. This can be done by imagining a hypothetical world in which there is no evolutionary progress and then adding elements to this picture one by one until progress emerges. The result will be the minimum set of ingredients necessary for evolutionary progress. Imagine a world of entities in which there is no change whatsoever. An observer visiting that world today would observe exactly the same things as she would have seen on a visit a hundred, a thousand, or a million years ago. Clearly, such a world would not be described as embodying progress in any form. Without change, there can be no progress. But mere change is not sufficient. Simply altering the relative positions of the entities in that world, for example, or modifying the individual entities themselves would entail change but not evolutionary progress, because evolutionary progress requires a change in the ensemble of the constituents of a world through addition to or replacement of its previous constituents. There must be a population of entities whose membership changes over time. Even this change is not sufficient, however, because one can imagine a world in which the membership in the set of entities populating that world changes over time, but because the replacements are qualitatively identical to those replaced there has been no evolutionary change. A visitor returning to such a world after a year's absence would not notice any difference. Evolutionary progress requires sequential change in the relative frequencies of the properties characterizing a population of entities, such that the frequency of any given property changes over time. Returning to our hypothetical world, suppose, next, that the sort of changes just described occur. Would such a world now necessarily embody “progress”? Clearly not, because the changes could be purely random:The relative frequencies of the properties characterizing a population of entities might change in a haphazard fashion, without any discernible pattern. Simply making the changes nonrandom would likewise be insufficient to produce evolutionary progress. If the properties of the entities of this hypothetical world were to change in a cyclical fashion, such that the same properties appeared, disappeared, and then reappeared with monotonous regularity (like waves crashing on the beach), then, even though a nonrandom pattern would be present, there would be no evolutionary progress. Evolutionary progress presupposes not only sequential change and patterns but also significant trends. There has to be some discernible direction to the changes taking place to make a claim for evolutionary progress even remotely plausible. But is directional change sufficient for evolutionary progress? No, because not every directional change can be properly described as evolutionary. If the properties of an object change abruptly, or if one thing is simply replaced by another, different thing, this would not be an evolutionary change. Evolution, by definition, is a step-by-step transformation. If I trade in my rusty old gas-guzzling jalopy for a new, fuel-efficient automobile, there has been a directional change but not an evolutionary change because no series of intermediates connects the two cars. On the other hand, if an automobile manufacturer introduces new features on the same model of car year after year, each time using the previous year's version as the starting point for the new design features, this would be a directional evolutionary change. Let the entities in the imaginary world undergo gradual directional change. Does this form of change constitute progress? The notion of progress is inherently in a that is If a set of over time, we might them as But it is for these to be this gradual directional change cannot be considered progress. we might of that it has to such a that would be the would of as progress. 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Evolutionary progress is if evolution is at least for some progressive. evolutionary progress is with both of in which no progress and of in which some to an form. 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Evolutionary are adaptations that a for the of at in the history of life are seen by of progress as embodying evolutionary progress in its most form. their however, are obvious of evolutionary A in the of a is no less an evolutionary the development of for be the result of the of gradual of evolutionary or of It is important to however, that evolutionary progress can the from in some property of an right to the changes with the of new and in the of evolutionary not the of evolutionary progress, although make it more A basic evolutionary biology is pattern and The to a of in the history of life or of a for as described in a The to the for this pattern. Clearly, that a pattern has is one this pattern by its is In the of evolutionary progress, two of are important as An evolutionary might be or 1994). A as its one in which some or the evolution of the in a An would be an evolutionary and As each at or the other is to for example, in for both (Dawkins and A is one in which no such is but a in a because that is the only evolutionary or because evolution in one direction is less in other example, there might be a not because is but just because if the in a as are more to in one direction the other The and is clear to most biologists. The these two of and evolutionary progress is less It is to progressive evolution with and to conclude that cannot or not manifest progress 1996). But a that this picture is too First, one can imagine a that is example, a population of both and and that are at a relative to As the of in the population are and every a population through the of natural be to such an is not it is if it would be considered progressive. Second, one can imagine a that is progressive. through a in the direction of to a to which the of that only after has been a would be both and progressive. Clearly, a not be for it to constitute an of evolutionary progress. The these hypothetical is that evolutionary progress the pattern of evolutionary change, not its as there is gradual directional change embodying there is evolutionary progress, of the of the change. progressive evolutionary are the basic of the of natural selection that most progressive in adaptations will be by natural selection on to that evolutionary progress is a necessary and of the of natural selection p. other it clear that in and necessary of in On the “the of natural selection or the of the that or individual of a to these will be but this will be only p. clearly although natural selection remains the for progressive evolutionary it not such are there any other evolutionary that would make evolutionary progress Indeed, from simply evolution as progressive, it is to see what could or the view that evolutionary progress is evolutionary progress as that as on the of the process is with the more of evolution (Gould now from the set of basic it is clear that there are positions to to whether evolution is evolutionary is progressive in any evolutionary is and and evolutionary is at least in properly described as How is each the of different conceptions of evolutionary progress, only the most obvious of which have been evolutionary is to be if for no other that there are many in which it could be If there is even one in which evolution manifests some sort of progress, then evolutionary is evolutionary is also to be but for an different that it is not even in a that evolution is and are as by their to to the as by the make a in in the form of in in species are just as to their as are to their in with in that It is such to the that to the history of life on Earth from the of in which to the basic the of in to are and a of the or its replacement by a more In evolutionary on the other hand, we are but we of some from the patterns we have to we cannot each that we that there will be of one sort or of the the of and biology in the of On the of in which the considered simply as on according to the of with the of life on in which most and most have and are p. If both evolutionary and evolutionary are inherently that evolutionary that there are many legitimate to the claim that evolution is progressive, it is that evolution at least and in some properly described as progressive. Even more in of the core idea of evolutionary progress the of whether evolution is progressive is just the of whether there have been any gradual directional changes in the history of life that embody relative to some Clearly there are of such have progressive evolution from to the of the (Dawkins 1996). have progressive evolutionary from the of to the of the of is an over the of and and 1994). is an over It is even an those the of the from the of to that is an that some well and that the sort of with has over evolutionary time, as by a directional in the of these or in any that every property of in every has over every of its evolutionary that evolution as a is progressive. are that can be only by the task of taking the range of these is that there is a and in which evolution is correctly described as progressive. Evolutionary progress is more in both and many of evolutionary progress in one form or another, has been of the evolutionary process from its and is to for as as the process about evolutionary progress of the sort that have of this issue from to the present, however, are about progress should be for about evolutionary progress: The about evolutionary progress might have been all right once, but it has gone on too long. It is time for the over evolutionary progress to the of whether evolution is progressive or not, to a more of the and of evolutionary progress. I would to the of the and the for both and I would also to for the for but