Some Thoughts on Evolutionary Theory
Scientific theories are usually not radically contested for more than about thirty years or so after they are first proposed. A small number will be debated for longer than that, but usually thirty years is enough for evidence to be collected and a decision made by society as a whole. Copernicus' theory, that the Sun is, in fact, the centre of our Solar System, was one of the few that was not immediately accepted or discredited. Evolutionary theory is in the same position today, and for mostly the same reasons.
In this essay, I wish to analyse the evolutionary theories of Natural Selection, Strict Creationism, and Intelligent Design, and evaluate each as a scientific theory. While issues of evidence are often taken to be sufficient to demonstrate Natural Selection's superiority to the other two, an adequate evaluation of such evidence would require an in-depth analysis and investigation of contemporary and historical scientific literature. Instead of taking this painstaking approach, we can evaluate these theories in other ways, and thus can push some of the issues related to evidence to one side. In this way, we need not give over our personal judgement on evolution to expert proponents of one or another theory.
It is often assumed that the principle of `verification' is sufficient to evaluate the scientific value of a given theory, ie, if a theory has a lot of evidence supporting it, then it must be better than a theory which doesn't. However, since the early part of the twentieth century, critics have pointed out that what qualifies as `evidence' is intimately connected with the attitudes of those investigating the theory. For example, suppose a scientist, in making calculations, arrives at a value which flatly contradicts the theory they are operating under They may take this as grounds to reject the theory, or believe that they made some error in their calculations, or chalk the problem up to `experimental error'. One position may be somewhat stronger than others (for example, if this is the first such contradiction to appear in the community of scientists working with this theory, an error in calculation or measurement may be claimed) but that does not mean that it is automatically `the right answer'. This is called the Duhem-Quine problem, after two well-known philosophers of science.
More generally, the evidence used to compare theories only makes sense when those theories can agree on what counts as evidence and how to interpret it; this remains quite controversial in comparing our three theories here. Thus, I offer instead of a purely empirical test the principle of `fecundity', which says that a given theory is better than an alternative if the given theory allows us to understand reality better, in terms of making predictions, making models, and interpreting sense-data. In a loose sense, a theory is more fecund if it gives scientists lots of interesting things to think about. Using this we can say, for instance, that because they are useful suppositions it is rational to at least pretend middle-sized durable physical objects (chairs) and electrons exist: we don't have to constantly worry about whether the thing we think we're about to sit on is really there, and we get transistors and other microelectronic devices.
Some definitions: By Natural Selection I refer to the theory of Darwin, and its intellectual descendants, including Punctuated Equilibrium. All life evolved from a common ancestor, and the features of organisms are the result of changes over time. The late Stephen Jay Gould exemplifies the advocate of Natural Selection, as does Richard Dawkins; we neglected the differences between these theorists here, because they're basically identical when compared with the other two theories. By Intelligent Design I refer to the theory which modifies Natural Selection by saying certain features of organisms (examples usually given are eyes, lungs, and blood clotting) are `irreducibly complex', could not have evolved in a gradual way, and thus were literally designed and implemented by some intelligent creator. William Dembski is an excellent prototype of an `Intelligent Design-er'. And by Strict Creationism I refer to the theory which says some demiurge brought forth all forms of life as they are today a few thousand years ago, in the spirit of a literal reading of Genesis, chapter one, and all sorts of Creationists whose names I don't know. Using these definitions and the principle of fecundity, we may now evaluate each theory by asking of each the question `How does this help us understand reality?'
Strict Creationism does this marginally at best. It allows us some sense of why organisms are the way they are, but it cannot explain this to any depth or offer us much beyond this. Strict Creationism gives us `Organisms are the way they are because God said so', but when pressed as to why God made organisms this way, Strict Creationism has no response, and indeed it is inappropriate within this theory to press further: God is ineffable, and it is inappropriate for mere humans to ponder God's motivations. Why do we have appendices and wisdom teeth? Because God said so. Why did God say so? No more questions, please. If we are to agree with Strict Creationism, we must adopt an epistemological wall immediately in front of our noses, and biology is reduced to descriptive physiology. Strict Creationism also offers no way to model or predict organic change: if every aspect of our physiology was established in a permanent form at creation, there is no reason to expect organic change (if it is even possible), unless God ineffably decides to introduce it. Any sort of bio-engineering, whether genetic engineering, pharmaceuticals, or even combating disease, as thus epistemologically impossible.
Intelligent Design does do a bit better: by accepting some degree of evolution it allows us to say, for instance, that humans have appendices because our ancestors had some use for them, as certain organisms that appear closely related to us by genetic evidence still do. But, ultimately, the theory posits another `black box' around the workings of biological systems, into which we cannot penetrate. We do enjoy more room to move about here than under Strict Creationism, but trying to bridge those irreducibly complex gaps is an impossibility: perhaps God introduced the irreducible features between generations, or established the original community of new species by fiat, but either way the process is not fully comprehensible by mortal minds. Hence, any attempt to accurately model biological history is, in this theory, necessarily incomplete. We also run into the same problem of ineffable divine intervention: God had to step in and implant these irreducibly complex components into our ancestry, and it is impossible for us to predict what may happen in the future so long as we posit divine intervention always, as it were, waiting in the wings for its next, unexpected walk-on. So while Intelligent Design theory is a great deal more fecund than Strict Creationism, is leaves us wanting.
Natural Selection does not have this problem. By not assuming any sort of irreducible complexity or other epistemological barrier, Natural Selection permits us to investigate and understand the evolution of the human eye, blood clotting, and whatever else we might be interested in. We also never have to postulate a necessary God: Natural Selection works whether you think it's a completely mechanical system, happening according to chance and quasi-economic principles or you think some deity is working things towards a conclusion by influencing what random variations occur to be selected for or against by the process itself. This freedom in choice of models gives Natural Selection considerable power for impressive feats of bio-engineering: we can, for example, model the evolution of HIV in a patient under certain programmes of medication with a good amount of accuracy.
We can get a better hold of the difference by considering a general scientific theory: a set of rules that models, if only probablistically and approximately, the workings of some part of the universe. For this theory to be fecund at all, it must be at least probablistically and approximately determinate; that is, the theory must allow us to make statements like `If the system is similar to x near time t, then the probability is close to p that it will be similar to y near time t+1'. But this means that while we can allow some leeway into our theory, for human error or other issues of uncertainty or randomness, we cannot permit our theory to include aspects that might occur at any time and have completely unpredictable effects.
Consider Quantum Mechanics, as it is normally understood. Many events that we consider impossible are merely extraordinarily unlikely, according to Quantum Mechanics: for example, there is a non-zero probability (so it is possible, even if extraordinarily unlikely) that I could appear in your living room as you're reading this sentence. There's even a non-zero probability that this could happen for every individual who reads these words. But Quantum Mechanics, for all its probabilistic weirdness, does not allow completely inexplicable causes and events, which would make prediction of even the roughest, most probabilistic and approximate sort completely impossible.
The God in Strict Creationism and Intelligent Design is precisely this sort of completely unaccountable cause, and divine intervention a correspondingly completely inexplicable event. Their theistic assumptions make these theories less fecund than the `weakly atheistic' (in the sense that it does not involve any divine intervention in the selection process itself) Natural Selection.
More broadly, Natural Selection has the same modelling strength and flexbility as Quantum Theory. Both of these theories are flexible enough to develop a wide variety of models, so we would expect both to be extremely fecund -- as they are. Quantum Theory is notable for its usefulness in all areas of modern technology; Natural Selection has been extremely useful in many areas of bio-engineering and medicine. Strict Creationism and Intelligent Design are not as flexible in their ability to create models, so we can conclude that they are less fecund than Natural Selection.
Hence, our analysis comes down in favour of Natural Selection: it gives us a more comprehensive, more interesting, and more useful way to model and interpret reality. It is therefore reasonable for us to conclude that Natural Selection is a better scientific theory than either Intelligent Design or Strict Creationism. The fact that the evidence gathered generally supports Natural Selection over the other two happily bolsters this conclusion.
Human history becomes more and more a race between education and catastrophe. --H.G. Wells, The Outline of History
Every child ought to be brought up more intelligent than [his or her] parents. --Clarence Darrow, Scope's "Monkey" Trial