Soon after the publication of Origin of Species, Charles Darwin wrote the following in a letter to Hugh Falconer:
“You were very antagonistic to my views on species. I well knew this would be the case. I must freely confess, the difficulties and objections are terrific; but I cannot believe that a false theory would explain, as it seems to me it does explain, so many classes of facts.”[1]
The purpose of this paper will be to place this significant statement within its proper context so as to fully appreciate Darwin’s reasons to holding to his theory in the face of “terrific difficulties and objections.” In order to do this I will describe the intellectual climate in which Darwin presented his theory, specifically as it pertained to the philosophy of science. I will then proceed to demonstrate how Darwin’s argument in Origin of Species is a direct product of such an environment. In conclusion I will make explicit the relations which Darwin’s intellectual context had to the statement quoted above as well as note how a proper understanding of Darwin’s arguments can clarify the debate which has followed in the wake of Origin of Species.
Isaac Newton and Vera Causa
Throughout the 19th century, and especially throughout the British Isles, the paradigm case of how science should be practiced was that of Isaac Newton. While it would take us well beyond the scope of this paper to fully articulate the extent to which this was the case, it suffices to say that scientists strove to make their reasoning and theories more “Newtonian”, for it was the less-Newtonian of two theories which was treated as the disposable one. The philosophy of science at the time can thus be seen as an attempt to establish what it was, exactly, which made Newton’s science so great. In virtue of what had Newton’s thinking accomplished what none had before him?
The answer which had emerged triumphant was that Newton’s science had been a vera causa argument. By this, it was meant that Newton explained physical phenomena by tracking their true causes. To explain something scientifically, is to provide a hypothetico-deductive model such that when one knew the initial conditions of some system, given the relevant forces and (true) causes which the explanation posits, one could predict how the system would behave. Furthermore, it was precisely because such explanations appeal to the true causes that they were seen as being counter-factually robust, meaning that they could describe what the system in question would have done had the initial conditions been different.
What the scientist was aimed at, then, was discovering the true causes which governed any system which they were studying. What the philosophers of science were aimed at, on the other hand, was discovering how the scientist could know whether they had discovered the true causes underlying the system in question or not. Within this intellectual context, Darwin was presented with essentially two distinct, though not incompatible answers to the philosopher’s question. One of these vera causa arguments, that of John Herschel, was largely empiricist in nature while the other, that of William Whewell, was largely rationalist in nature.
Before we consider each of these arguments, let us first grasp what kinds of explanations the vera causa arguments were intended to exclude. Vera causa arguments of both the empiricist and rationalist flavors are aimed primarily at avoiding ad hoc explanations in science. Very roughly, an ad hoc explanation is one which does not describe the true causes at work in a system. As such, ad hoc explanation are not counter-factually robust in the appropriate way. While an ad hoc explanation may give an explanation of sorts regarding why some system behaves the way it does, if it says anything at all about how the system would have behaved under different conditions, it is usually wrong. In other words, ad hoc explanations tend to be more like descriptions rather than the hypothetico-deductive explanations such as Newton provided in the case of physics.
An example of the ad hoc explanations which Newton replaced would be those of Aristotle. The answer to why objects fell to the earth and why the planets move as they do was based in the natural tendencies of the objects in question. Matter, in some sense, “belongs” on the earth and therefore falls to it when released. Similarly, it is, in some sense, “natural” for the planets to move as they do. Of course many discoveries had been made regarding the nature of terrestrial (Galileo, Descartes) and celestial (Kepler, Brahe) motion prior to Newton, but these explanations differed from those of Newton. None of these prior theories had gotten at the true causes or forces which were the underpinning of their mathematical models. There was no reason why Galileo’s and Kepler’s particular mathematical relations should hold rather than some others. In other words, their models were, to some extent, not counter-factually robust.
According to Herschel, the safest way to avoid ad hoc explanations is, whenever possible, to only appeal to and generalize from forces and causes which one already knows to exist. A clear illustration of such a method can be seen in Isaac Newton’s theory of universal gravity. We know that in the case of terrestrial objects gravity acts as a force which causes a certain amount of motion. From this, Newton can thus be seen as proceeding by way of analogy from the causal explanations, which we know work in the case of terrestrial objects, to using those same causal explanations in the case of celestial objects. Accordingly, Herschel’s vera causa method amounts to an admonition for scientists to extract their causal explanations from past experience, since that is the most reliable source of true causes which they have available to them. The closer the analogy between the domain from which the scientist is trying to extract their causal explanation and the domain to which they are trying to project such an explanation, the more reasonable it is to suppose that the causal explanation used in the former accurately depicts the causal relations which actually exist in the case of the latter.
“If the analogy of two phenomena be very close and striking, while, at the same time, the cause of one is very obvious, it becomes scarcely possible to refuse to admit the action of an analogous cause in the other, though not so obvious in itself.”[2]
Whewell’s version of the vera causa argument differs from that of Herschel in a number of important respects. Whereas in the case of the latter, the scientist avoids ad hoc arguments by drawing their explanations from experience, in the case of the former the scientist avoids ad hoc explanations by projecting their explanations onto experience. More specifically, we have reason to believe that an explanation is not ad hoc when it successfully provides information regarding questions which the explanation was not aimed at answering. The more surprising the accurate information is in the case of his explanation, the more sure the scientist can be that his explanation is not ad hoc in nature. Whewell calls this “jumping together” of scientific domains the “Consilience of Inductions”:
“[The consilience of inductions] is exemplified principally in some of the greatest discoveries. Thus it was found by Newton that the doctrine of attraction of the sun varying according to the inverse square of the distance, which explained Kepler’s third law of proportionality of the cubes of the distances to the squares of the periodic times of the planets, explained also his first and second laws of the elliptical motion of each planet; although no connection of these laws had been visible before…
“The theory of universal gravitation, and of the undulatory theory of light, are, indeed, full of examples of this Consilience of Inductions… The history of the undulatory theory was a succession of felicities. And it is precisely the unexpected coincidences of results drawn from distant parts of the subject which are properly described.”[3]
In the case of Newtonian physics, the theory explained not only the motion of terrestrial bodies, but also provided significant information about the motion of celestial bodies as well. It is significant that whereas in the case of Herschel’s vera causa argument one in limited in the direction of application, for one must reason by analogy from the obvious to the unknown. In the case of Whewell’s account, however, there is no such limitation. One could just as easily reverse the situation described above with the same effect: Newtonian mechanics explained not only the motion of celestial bodies, which it was aimed at explaining, but also provided significant information about the motion of terrestrial bodies as well.
With respect to rationalist version of the vera causa argument, it does not matter which of these two accounts of Newtonian mechanics was actually the case, historically speaking. What matters was that Newton’s theory allowed the motion of terrestrial bodies and celestial bodies to be brought together in a way which had never been anticipated prior to him. In other words, the confidence which the scientist could have in Newton’s theory was not in how well it predicted terrestrial movement, for Galileo and Descartes had already made significant strides in this domain. Nor was it due to how well the theory predicted celestial movement, for Kepler and Brahe had already done quite well in this regard as well. The confidence which Newton theory merited was not even due to the combination of the two. Rather, the greatest achievement in Newton’s work, according to Whewell’s reasoning, was the unification of the terrestrial with the celestial, something which no theory prior to Newton’s would have led one to expect. Whereas in the case of Herschel the confidence which could be placed in an explanation was proportional to how close it remained to past experience, for Whewell it is proportional to the degree that the explanation successfully moves beyond past experience.
“The evidence in favor of our induction is of a much higher and more forcible character when it enables us to explain and determine cases of a kind different from those which were contemplated in the formation of our hypothesis. The instances in which this has occurred, indeed, impress us with a conviction that the truth of our hypothesis is certain. No accident could give rise to such an extraordinary coincidence. No false supposition could, after being adjusted to one class of phenomena, so exactly represent a different class, when the agreement was unforeseen and uncontemplated. That rules springing from remote and unconnected quarters should thus leap to the same point, can only arise from that being the point where truth resides.”[4]
Charles Darwin and Vera Causa
Whereas Charles Darwin famously described his Origin of Species as one long argument, it is possible to somewhat isolate three relatively distinct arguments at play within the text which contribute to the work as a whole.[5] The first is a deductive argument for natural selection inspired largely by Malthus: IF there is variation within a population, and IF there is heredity, and IF there is a struggle for life, THEN the more fit and adapted will survive while the less fit and maladapted will not.[6] This is an argument for the existence of natural selection. A second argument which plays a significant role in Darwin’s work is an empiricist vera causa argument from analogy: artificial selection has created many different forms and kinds in domesticated life, therefore the many forms and kind of life found in nature can be explained by natural selection. This is an argument for the capacity of natural selection to produce the changes and differences within populations. The final argument which can be discerned in Origin is a rationalist vera causa argument from the consilience of inductions: natural selection unifies the facts from many domains which would otherwise remain isolated from each other absent natural selection. This is used as an argument to establish the claim that not only is natural selection capable of producing changes and differences within populations, but that it actually has been responsible for such things. It should be noted how the rationalist vera causa is more encompassing in its conclusion than is the empiricist vera causa argument, just as the latter is in turn more encompassing in its conclusion than the Malthusian argument from deduction is.
Let us consider how Darwin implements each of the vera causa arguments within the text of Origin of Species. In order to do this it will serve us well to first consider the rather ad hoc explanation which Darwin took himself to be overthrowing: special creation. In the case of the geographical distribution of biological taxa and relative similarities and differences between species, special creation is, according to Darwin, an entirely ad hoc explanation. To some degree, the theory answers the questions at hand, but it provides absolutely no information beyond this very specific question. In the case of Aristotelian physics it was unclear whether things fell to the ground because they “belong” there or we simply say that things “belong” on the ground because they fall. In other words, the scientist is left with no reason to suppose that the “belonging” is a true cause or not. Similarly, it is unclear whether biological taxa are distributed as they are because the Creator wanted them distributed thusly, or whether we simply say that the Creator wanted biological taxa distributed as they are because they are so distributed. The biologist has no reason to believe that the desires (or even the existence!) of the Creator is actually a true cause. This is the explanation which Darwin attempts to replace with his theory of natural selection.
Within the text of Origin of Species one can scarcely miss Darwin’s strong appeal to the analogy between artificial selection in breeding and natural selection in the wild. This strategy makes perfect sense when interpreted as an implementation of Herschel’s empiricist version of the vera causa argument. Darwin demonstrates how artificial selection is the obvious cause of change and variety in the case domesticated breeding. He then proceeds to draw as strong of a parallel between selection as it operates in the domesticated context and how it operates in nature. It is possible that species with all their variety and differences were created by a Creator just as it is possible that they were produced by natural selection. The conclusion which should thus be drawn, by Herschel’s account, is that natural selection should be favored over special creation since we already know that selection both exists and is capable of creation whereas the same cannot be said for a special creator.
The entire second half of Darwin’s work is an appeal to the rationalist vera causa argument. He makes this all but explicit in his notebook from which the work was eventually drawn: “Absolute knowledge that species die and other replace them. – Two hypotheses: fresh creation is mere assumption, it explains nothing further; points gained if any facts are connected.”[7] In the Origin of Species Darwin argues that natural selection, which he has already shown, by way of deductive argument, to exist and, by way of analogy with artificial selection, to be a competent force of nature, that this force actually is responsible for the variety within and among species. To establish this he makes an appeal, breathtaking in it scope, to the consilience of inductions. With natural selection in place, not only can we explain the origin of different species, but we can also explain the geological and geographical distribution of taxa as well as the mutual affinities, morphology, embryology and rudimentary organs across species. The immense scope of this consilience should not be lost on us: while the consilience wrought by Newton unified the terrestrial with the Celestial, that wrought by Darwin unified more than half a dozen theretofore distinct domains.
Charles Darwin and Hugh Falconer
Let us now return to the passage with which we began this paper:
“You were very antagonistic to my views on species. I well knew this would be the case. I must freely confess, the difficulties and objections are terrific; but I cannot believe that a false theory would explain, as it seems to me it does explain, so many classes of facts.”
There are two points which I find striking about this passage. The first has to do with the structure of the debate between Darwin and his critics after the publication of Origin of Species. Most critics aimed their criticisms at the empiricist vera causa argument by attempting to demonstrate that the analogy between artificial selection and natural selection was not very close: the latter is directed and has produced limited change and variety while the latter is not directed and is supposed to have created vast amounts of change and variety. Accordingly, so the argument goes, natural selection cannot have been responsible for producing the data in question since it is not capable of having done so. Darwin, on the other hand, argues that considering the vast amount of consilience. Accordingly, so the argument goes, natural selection must have been capable of producing the data in question since it is actually responsible for the data in question. The two parties are arguing from relatively distinct premises.
The second and final point which I wish to make is that the debate surrounding evolution by natural selection and special creation has, to this day, largely followed the same structure. All anti-Darwinian criticisms, if not nearly so, are aimed at the competency claim which Darwin argued for in the first half of his book by way of his empiricist vera causa argument. While many of the Darwinian counter-replies to these points are also aimed at the competency claim as well, these counter-replies are almost universally motivated by the overwhelming consilience wrought by Darwin and his theory. Indeed, the very reason why it is so difficult for the evolutionary biologist to imagine natural selection being overthrown is precisely because it is so difficult to imagine some other theory which could possibly unify so many different domains as natural selection has done.
[1] Darwin, F. 1887. The Life and Letters of Charles Darwin, Including an Autobiographical Chapter, I:455
[2] Herschel, J. 1831. Preliminary Discourse on the Study of Natural Philosophy, 149
[3] Whewell, W. Novum Organon Renovatum: Being the Second Part of the Philosophy of the Inductive Sciences, 88-99
[4] Whewell, W. Novum Organon Renovatum: Being the Second Part of the Philosophy of the Inductive Sciences 87-88.
[5] Ruse, M. 1979. The Darwinian Revolution: Science Red in Tooth and Claw, 198.
[6] Darwin, C. 1859. On The Origin of Species by Means of Natural Selection, 127.
[7] De Beer, G. 1960-76. Darwin’s Notebooks on Transmutation of Species, P. 104
YOU ARE A COPY CAT!
Comment by Ashley — March 23, 2007 @ 3:59 am