Evolutionary Progress? | BioScience | Oxford Academic
Ruse, a philosopher of bioethics and evolutionary biology at the University of Michael Ruse. Ubiquitous in Darwin's time, the idea of an unceasing improvement in life insinuated its way into evolutionary theory from the first. In interviews with today's major figures in evolutionary biology - including Stephen Jay Gould, Edward O. Monad to Man - The concept of progress in evolutionary biology Michael Ruse. Note moyenne. Donner le premier avis. Lire la suite. Retirer en librairie.
Monad to Man - The concept of progress in evolutionary biology
A renowned writer on evolutionary theory and its history, Ruse has long been sensitive to the fact that many people-and not simply religions enthusiasts-find something deeply troubling about much of what passes for science in evolutionary circles. What causes this tension, he finds in his search of evolutionism's year history, is the intimate relationship between evolution and the secular ideology of progress.
Ubiquitous in Darwin's time, the idea of an unceasing improvement in life insinuated its way into evolutionary theory from the first. It offers an unparalleled account of evolutionary theory, from popular books to museums to the most complex theorizing, at a time when its status as science is under greater scrutiny than ever before.
Monad to Man: The Concept of Progress in Evolutionary Biology
Date de parution. Harvard University Press. If there are fundamental particles the constituents of quarks, perhaps , then this is a fact about nature that is true independent of human observers, and it is conceivable that we will never discover these particles or their exact properties, either because of their nature or because of ours.
Similarly, suppose that evolutionary progress consists of an increase in some property of organisms, but that we are either ignorant of this fact or unable to accurately measure this property. In this case, there might be evolutionary progress, even though it is not possible to show that there is. Thus, unless one adopts an operationalist definition of progress, according to which the very meaning of progress is determined by the procedures that are used to measure it, it will always remain possible that evolutionary progress exists but eludes our ability to observe it.
This possibility is not nearly as odd as it might seem. After all, presumably it either is or is not the case that there is a series of five consecutive twos in the decimal expansion of pi, even though we may never know which of these possibilities is correct. Likewise, there either are or are not intelligent aliens inhabiting other worlds, even though we may never find out that there are or are not.
Such claims are merely applications of the philosophical view known as scientific realism: Nature exists independent of us and need not be coextensive with our abilities to know it. Reality, according to the realist, should not be conflated with knowability. In summary, being unable to identify or measure evolutionary progress does not mean that evolutionary progress is unreal, any more than being unable to identify or measure sub-quarkian fundamental particles shows that such particles are unreal.
To say that a standard is an artificial construct is, by contrast, to say that it is invented by us to pick out properties of things of interest to us. Although some objects were precisely X meters long for eons before humans arrived on the scene, and at least some of them will continue to be the same length long after humans as a species have departed, it is only by virtue of our interests and concerns that the fact of something being any number of meters long has any significance.
We did not invent all of the objects that we measure with the metric system, nor did we invent length—but we did invent the metric system itself, by which the length of objects is measured.
Is “improvement” a scientifically respectable concept?
It is worth stressing that the properties a constructed standard picks out may well be perfectly real. That is, a meter picks out a real property of objects, even though the unit of measurement itself is invented by humans for our purposes. A constructed standard can pick out imaginary properties of natural objects as well, although these will usually be of much less interest to those who wish to understand the natural world.
To say that a standard of evolutionary progress is an artificial construct is, thus, just to say that it has been invented to serve our concerns, our questions, or our quest for understanding, and that apart from us or other creatures capable of considering the issue there is no fact of the matter about whether evolution is or is not progressive. Notice that despite its invented character, a constructed standard of evolutionary progress might nonetheless pick out real properties of organisms or evolving lineages and thus tell us something both interesting and true about the evolutionary process.
There might, of course, be more than one constructed standard of evolutionary progress, with the consequence that specific aspects of the evolutionary process might be judged progressive according to one standard but not according to another. Surprisingly, evolutionary progress as measured by a constructed standard is in exactly the same epistemological boat as the notion of evolutionary progress as a natural fact. That is, it is possible that we are unable to know that evolution is progressive or to properly measure its progressiveness, even though we ourselves invented the standard of evolutionary progress.
This inability may seem paradoxical at first. As a conceptual invention, a constructed standard is known as soon as it is formulated. But knowing what the standard requires and knowing precisely how it applies in a given situation are two different issues. The constructed standard may be crystal clear, but its application in a particular instance might be completely murky. Consider an analogy: The nanometer as a unit of measurement is perfectly clear, but it might be impossible to determine how many nanometers in diameter a given object is because the object is too small, is too large, is constantly moving, or is hidden inside other structures.
Likewise, someone might propose increasing complexity as a standard of evolutionary progress and devise a rigorous definition of complexity, but be unable to accurately measure the complexity of a given biological entity. Consequently, even if a given standard of evolutionary progress is constructed, there is no guarantee that we can know whether evolution is progressive or not according to this standard. The foregoing distinctions and clarifications are essential to understanding as clearly as possible both the core idea of evolutionary progress and the different kinds of standards that can be used to measure evolutionary progress.
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To bring the issue of evolutionary progress into sharper focus, additional distinctions are necessary concerning the pervasiveness of evolutionary progress, the property or properties that might increase in evolution, and the identification of the entities that might undergo progressive evolutionary change. Each distinction centers on a controversial issue in contemporary discussions of evolutionary progress.
One of these issues is whether evolutionary progress, if it exists at all, is universal or merely episodic. Evolutionary progress is universal if evolution is everywhere and at all times manifesting progress. Evolutionary progress is episodic if evolution is at least sometimes, for some lineages, progressive. Episodic evolutionary progress is compatible with both periods of stasis, in which no progress occurs, and periods of regression, in which some lineages revert to an earlier form. Clearly, evolution might be episodically progressive without being universally progressive, but not the converse.
Few evolutionary biologists argue that evolution is always and everywhere progressive because, among other reasons, there appears to be no single standard according to which universal evolutionary progress may be judged to have occurred. For example, complexity, size, or perceptual abilities increase in some lineages and decrease in others and sometimes change direction even within a given lineage. Saying that evolution is episodically progressive, however, leaves open a number of distinct possibilities that range from saying that there is at least one instance of evolutionary progress—no matter how local and fleeting—in the history of life, to saying that evolution is occasionally progressive, to saying that evolution is often progressive, to saying that it is usually in a majority of lineages for most times progressive, to saying that evolution is almost always but not quite universally progressive.
Because the issues of what proportion of lineages manifest progress and of how long any given lineage manifests progress are distinct, the assertion that evolution is episodically progressive could result in a number of distinct theses. For example, evolution might be progressive in all lineages over all time periods i. Simply asserting or denying that evolution is progressive does not make clear which of these distinct theses is meant.
Being clear about the extent of the evolutionary progress one is considering is essential for answering the question, is evolution progressive? Clearly, these forms of progress are not mutually exclusive. If uniform progress occurs, then by definition so does net progress, although the converse is not necessarily true. Ayala's distinction is useful, but to understand the idea of evolutionary progress as clearly as possible it is necessary to make a further distinction. Imagine a case in which the evolutionary change in a given sequence has been nonuniform, such that even though later members of the sequence are not on the average better than earlier members, something has occurred that can reasonably be regarded as evolutionary progress.
For example, consider intelligence and suppose for the moment that this is a well-defined concept. In addition, suppose that it is possible to rank] organisms on a scale from 1 to 10 with regard to their intelligence, with organisms at level 1 being exceedingly stupid and organisms at higher levels being increasingly more intelligent.
Finally, suppose that at time T1 there are organisms at level 4 but no higher, whereas at some later time, T2, there are organisms at level 7. In this case, the upper level of intelligence would have increased. But this increase in the upper intelligence level could have occurred even if the average intelligence level dropped or if the sequence leading up to it changed in a nonuniform fashion.
For example, the organisms occupying lower levels of the intelligence scale might be far more numerous than those occupying the higher levels, or the number of individuals within species at the lower levels might far outnumber those occupying the higher levels, dragging the average level of intelligence down.
Conversely, the average level of intelligence could increase without a corresponding increase in the highest level of intelligence achieved e. Consequently, there are at least three alternative meanings to the claim that the history of life manifests progress. This claim might mean that with respect to some property, every individual later in a sequence is an improvement upon all those that preceded it uniform progress ; that later members of the sequence are, on average, better than those that came before net progress ; or that some but not necessarily every later member of the sequence is better than every earlier member of the sequence according to a certain feature apex progress.
It is, in fact, this last conception of evolutionary progress—namely, that higher levels of a certain property or characteristic appeared later in the history of life than lower levels—that generally first comes to mind when considering the idea that life has advanced from its simple beginnings. If one considers mammals to be higher than insects, and if mammals appeared later in the history of life than insects, then according to this conception evolution has manifested progress. Likewise, if there are currently organisms with greater intelligence than any that came before, then there has been evolutionary progress with regard to intelligence.
This conclusion would be valid even if, as seems to be the case, such intelligent organisms constitute only a minuscule fraction of all living things considered in terms of either species or number of individuals , now or in the past. Discussions of evolutionary progress are often marred by unclarity concerning the objects that are thought to manifest progress. One can speak of progress in the evolution of life taken as a whole , within an evolutionary lineage e. Clearly, it might be possible to find progress in one of the senses defined earlier in one or more of these objects but not in others.
For example, progress within the horse lineage does not entail progress in life as a whole or even within a given species of horse. That is, within the horse lineage there might, over the course of several million years, be an increase in running speed, even though there is no increase in running speed within a given horse species, the average or maximum running speed of its members remaining constant throughout its existence. Such possibilities will be ever present when dealing with objects consisting of constituent parts or members.
What is true of the whole need not be true of each part, and vice versa. In like manner, there is no reason why progress must include improvement in every aspect of the organism under consideration. Use of the terms higher and lower with respect to organisms often seems to imply that organisms are higher or lower as a whole, rather than with respect to some particular property or set of properties.
For example, the fossil record might reveal a long-term trend toward increased size and reduction in the number of toes within the horse lineage—changes that might be judged improvements for efficient terrestrial locomotion. However, there may have been no corresponding changes or improvements in dentition in the lineage.
Of course, although one organism may be judged as higher overall than another, especially within a given lineage, it may not always be possible to rank whole organisms in this fashion, especially when organisms in distinct lineages e. Consequently, disagreements about evolutionary progress can probably be minimized although not eliminated completely by specifying as precisely as possible the property or set of properties at issue and the relevant comparison class i. Ultimately, what is important is not trying to determine the true object of evolutionary progress but rather being clear about what, precisely, a given claim of evolutionary progress is asserting and then conducting whatever investigation is necessary to determine whether that particular claim is true.
In addition to the modalities of evolutionary progress, we can also consider, more briefly, its magnitude. Ruse locates the debate over evolutionary progress in two points: significant, new adaptations innovations and long-term trends. Evolutionary innovations are adaptive breakthroughs, adaptations that cross a functional threshold.
Although explanations for the prevalence of innovations at certain times in the history of life vary Nitecki , they are seen by proponents of progress as embodying evolutionary progress in its most dramatic form. Despite their striking character, however, innovations are merely especially obvious instances of evolutionary improvement. A slight increase in the running speed of a predator is no less an evolutionary improvement than the development of wings for flight. Long-term trends may be the result of the slow accumulation of gradual improvements, of relatively rapidly appearing evolutionary innovations, or of both.
It is important to recognize, however, that evolutionary progress can span the spectrum from slight, hardly noticeable improvements in some preexisting functional property of an organism right up to the dramatic changes associated with the appearance of entirely new structures and capacities. Differences in the magnitude of evolutionary improvement do not alter the essential nature of evolutionary progress, although they may make it more conspicuous.
A basic distinction within evolutionary biology is between pattern and process. The former refers to a sequence of events in the history of life or of a particular lineage, for example as described in a phylogenetic tree.
The latter refers to the events responsible for generating this pattern. Clearly, establishing that a particular pattern has occurred is one thing; explaining why this pattern exists by identifying its causes is another. In considering the causes of evolutionary progress, two additional sets of distinctions are important as well. An evolutionary trend might be either driven or passive McShea A driven trend is, as its name suggests, one in which some force drives or pushes the evolution of the lineage in a particular direction. As each side becomes better adapted at capturing or escaping capture, respectively, the other side is forced to develop counteradaptations, resulting in, for example, increases in maximum running speed for both lineages Dawkins and Krebs A passive trend is one in which no such force is operative but rather a lineage evolves in a certain direction, either because that is the only available evolutionary path or because evolution in one direction is less constrained than in other directions.
For example, there might be a passive trend toward increasing complexity, not because complexity is better but just because if the organisms in a lineage begin as very simple creatures, they are more likely to evolve in one direction e. The distinction between driven and passive trends is reasonably clear to most biologists. The relationship between these two kinds of trends and evolutionary progress is less so. It is tempting to associate progressive evolution with driven trends and to conclude that passive trends cannot or do not manifest progress e.
But a moment's reflection demonstrates that this neat picture is too simple. First, one can imagine a driven trend that is nonprogressive. For example, consider a population consisting of both altruistic e. As the proportion of selfish organisms in the population increases, resources are depleted and every organism's fitness decreases. Such a population could, through the operation of natural selection, be driven to extinction.
Although such an outcome is not inevitable, it is certainly possible and, if it occurred, would hardly be considered progressive.