Since the time of the Dover trial in 2005, I’ve made a hobby of debating Intelligent Design proponents on the Web, chiefly at the pro-ID website Uncommon Descent. During that time I’ve seen ID proponents make certain mistakes again and again. This is the first of a series of posts in which (as time permits) I’ll point out these common mistakes and the misconceptions that lie behind them.
I encourage IDers to read these posts and, if they disagree, to comment here at TSZ. Unfortunately, dissenters at Uncommon Descent are typically banned or have their comments censored, all for the ‘crime’ of criticizing ID or defending evolution effectively. Most commenters at TSZ, including our blog host Elizabeth Liddle and I, have been banned from UD. Far better to have the discussion here at TSZ where free and open debate is encouraged and comments are not censored.
The first misconception I’ll tackle is a big one: it’s the idea that the evidence for common descent is not a serious threat to ID. As it turns out, ID is not just threatened by the evidence for common descent — it’s literally trillions of times worse than unguided evolution at explaining the evidence. No exaggeration. If you’re skeptical, read on and I’ll explain.
Common Descent and ID
The ‘Big Tent’ of the ID movement shelters two groups. The ‘creationists’ believe that the ‘kinds’ of life were created separately, as the Biblical account suggests, and these folks therefore deny common descent. The ‘common descent IDers’ accept common descent but argue that natural processes, unassisted by intelligence, cannot account for the complexity and diversity of life we see on earth today. They therefore believe that evolution was guided by an Intelligence that either actively intervened at critical moments, or else influenced evolution via information that was ‘front-loaded’ into the genome at an earlier time.
Creationists see common descent as a direct threat. If modern lifeforms descended from a single common ancestor, as evolutionary biologists believe, then creationism is false. Creationists fight back in two ways. Some creationists argue that the evidence for common descent is poor, or that the methods used by evolutionary biologists to reconstruct the tree of life are unreliable. Other creationists concede that the evidence for common descent is solid, but they argue that it can be explained equally well by a hypothesis of common design — the idea that the Creator reused certain design motifs when creating different organisms. Any similarities between created ‘kinds’ are thus explained not by common descent, but by design reuse, or ‘common design’.
The ‘common descent IDers’ do not see common descent as a threat. They accept it, because they see it as being compatible with guided evolution. And while they agree with biologists that unguided evolution can account for small-scale changes in organisms, they deny that it is powerful enough to explain macroevolutionary change, as revealed by the large-scale structure of the tree of life. Thus guided evolution is necessary, in their view. Since common descent IDers accept the reality of common descent, you might be surprised that the evidence for common descent is a problem for them, but it is — and it’s a serious one. Read on for details.
The Problem(s) for ID
I’ve mentioned three groups of IDers so far: 1) creationists who dispute the evidence for common descent; 2) creationists who accept the evidence for common descent, but believe that it can be equally well explained by the hypothesis of common design; and 3) IDers who accept common descent but believe that unguided evolution can’t account for macroevolutionary change. Let’s look at these groups in turn, and at why the the evidence for common descent is a serious problem for each of them.
The creationists who dispute the evidence for common descent face a daunting task, simply because the evidence is so massive and so persuasive. I can do no better than to point readers to Douglas Theobald’s magnificent 29+ Evidences for Macroevolution for a summary of all the distinct lines of evidence that converge in support of the hypothesis of common descent. Because Theobald does such a thorough and convincing job, there’s no need for me to rehash the evidence here. If any IDers wish to challenge the evidence, or the methodologies used to interpret it, I encourage them to leave comments. The good news is that we have Joe Felsenstein as a commenter here at TSZ. Joe literally wrote the book on inferring phylogenies from the data, so if he is willing to respond to objections and questions from IDers, we’re in good shape.
I have yet to encounter a creationist who both understood the evidence and was able to cast serious doubt on common descent. Usually the objections are raised by those who do not fully understand the evidence and the arguments for common descent. For this reason, I emphasize the importance of reading Theobald’s essay. Think of it this way: if you’re a creationist who participates in Internet discussions, the points raised by Theobald are bound to come up in debate. You might as well know your enemy, the better to argue against him or her. And if you’re open-minded, who knows? You might actually find yourself persuaded by the evidence.
The evidence also presents a problem for our second group of creationists, but for a different reason. These are the folks who accept the evidence for common descent, but argue that it supports the hypothesis of common design equally well. In other words, they claim that separate creation by a Creator who reuses designs would produce the same pattern of evidence that we actually see in nature, and that common design is therefore on an equal footing with common descent. This is completely wrong. The options open to a Creator are enormous. Only a minuscule fraction of them give rise to an objective nested hierarchy of the kind that we see in nature. In the face of this fact, the only way for a creationist to argue for common design is to stipulate that the Creator must have chosen one of these scant few possibilities out of the (literally) trillions available. In other words, to make their case, they have to assume that the Creator either chose (or was somehow forced) to make it appear that common descent is true, even though there were trillions of ways to avoid this. Besides being theologically problematic for most creationists (since it implies either deception or impotence on the part of the Creator), this is a completely arbitrary assumption, introduced only to force common design to match the evidence. There’s no independent reason for the assumption. Common descent requires no such arbitrary assumptions. It matches the evidence without them, and is therefore a superior explanation. And because gradual common descent predicts a nested hierarchy of the kind we actually observe in nature, out of the trillions of alternatives available to a ‘common designer’, it is literally not just millions, or billions, but trillions of times better at explaining the evidence.
What about our third subset of IDers — those who accept the truth of common descent but believe that intelligent guidance is necessary to explain macroevolution? The evidence is a problem for them, too, despite the fact that they accept common descent. The following asymmetry explains why: the discovery of an objective nested hierarchy implies common descent, but the converse is not true; common descent does not imply that we will be able to discover an objective nested hierarchy. There are many choices available to a Designer who guides evolution. Only a tiny fraction of them lead to a inferable, objective nested hierarchy. The Designer would have to restrict himself to gradual changes and predominantly vertical inheritance of features in order to leave behind evidence of the kind we see.
In other words, our ‘common descent IDers’ face a dilemma like the one faced by the creationists. They can force guided evolution to match the evidence, but only by making a completely arbitrary assumption about the behavior of the Designer. They must stipulate, for no particular reason, that the Designer restricts himself to a tiny subset of the available options, and that this subset just happens to be the subset that creates a recoverable, objective, nested hierarchy of the kind that is predicted by unguided evolution. Unguided evolution doesn’t require any such arbitrary assumptions. It matches the evidence without them, and is therefore a superior explanation. And because unguided evolution predicts a nested hierarchy of the kind we actually observe in nature, out of the trillions of alternatives available to a Designer who guides evolution, it is literally trillions of times better than ID at explaining the evidence.
One final point. Most IDers concede that if the evidence supports unguided evolution, then there is no scientific reason to invoke a Creator or Designer. (It’s Occam’s Razor — why posit a superfluous Creator/Designer if the evidence can be explained without one?) It is therefore not enough for ID to succeed at explaining the evidence (which it fails to do, for the reasons given above); it’s also essential for unguided evolution to fail at explaining the evidence.
This is a big problem for IDers. They concede that unguided evolution can bring about microevolutionary changes, but they claim that it cannot be responsible for macroevolutionary changes. Yet they give no plausible reasons why microevolutionary changes, accumulating over a long period of time, should fail to produce macroevolutionary changes. All they can assert is that somehow there is a barrier that prevents microevolution from accumulating and turning into macroevolution.
Having invented a barrier, they must invent a Designer to surmount it. And having invented a Designer, they must arbitrarily constrain his behavior (as explained above) to match the data. Three wild, unsupported assumptions: 1) that a barrier exists; 2) that a Designer exists; and 3) that the Designer always acts in ways that mimic evolution. (We often hear that evolution is a designer mimic, so it’s amusing to ponder a Designer who is an evolution mimic.) Unguided evolution requires no such wild assumptions in order to explain the data. Since it doesn’t require these arbitrary assumptions, it is superior to ID as an explanation.
Here’s an analogy that may help. Imagine you live during the time of Newton. You hear that he’s got this crazy idea that gravity, the force that makes things fall on earth, is also responsible for the orbits of the moon around the earth and of the earth and the other planets around the sun. You scoff, because you’re convinced that there is an invisible, undetected barrier around the earth, outside of which gravity cannot operate. Because of this barrier, you are convinced of the need for angels to explain why the moon and the planets follow the paths they do. If they weren’t pushed by angels, they would go in straight lines. And because the moon and planets follow the paths they do, which are the same paths predicted by Newton on the basis of gravity, you assume that the angels always choose those paths, even though there are trillions of other paths available to them.
Instead of extrapolating from earthly gravity to cosmic gravity, you assume there is a mysterious barrier. Because of the barrier, you invent angels. And once you invent angels, you have to restrict their behavior so that planetary paths match what would have been produced by gravity. Your angels end up being gravity mimics. Laughable, isn’t it?
Yet the ‘logic’ of ID is exactly the same. Instead of extrapolating from microevolution to macroevolution, IDers assume that there is a mysterious barrier that prevents unguided macroevolution from happening. Then they invent a Designer to leap across the barrier. Then they restrict the Designer’s behavior to match the evidence, which just happens to be what we would expect to see if unguided macroevolution were operating. The Designer ends up being an unguided evolution mimic.
The problem is stark. ID is trillions of times worse than unguided evolution at explaining the evidence, and the only way to achieve parity is to tack wild and unsupported assumptions onto it.
If you are still an IDer after reading, understanding, and digesting all of this, then it is safe to say that you are an IDer despite the evidence, not because of it. Your position is a matter of faith and is therefore a religious stance, not a scientific one.