The Inevitability of Evolution (Part I)

PERHAPS THE SECOND-MOST IGNORANT of the common objections to the theory of evolution (after the ever-popular “Why are there still monkeys?”) involves some kind of objection based on the imagined “odds” against this or that biological feature appearing “completely at random.” The best known general form of this objection is presented by the Discovery Institute, a well-funded collection of creationists who pretend to offer scientific opposition to evolution.

In response to the question What is the theory of intelligent design? they offer this: “The theory of intelligent design holds that certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection.” Whatever the Discovery Institute may say about this, it’s nothing but a claim that evolution is far more improbable than their conjectured designer.

This kind of argument — which is essentially saying “I don’t believe it!” — could be employed against more than evolution. A creationist could look at the current totality of English history, or the biosphere, or whatever, and impulsively exclaim that it’s “impossible” for such to have occurred without outside guidance. But is it really?

If England is impossible, so of course is the rest of human history. So are you, because the innumerable events leading to your conception are vast beyond comprehension. Everything is impossible to such a mentality. At what point does reductio ad absurdum intervene to put an end to this nonsense? “Never,” replies the creationist. “Prove I’m wrong!” Thus it appears that we need this series of articles.

There are several variations of the argument that the odds are against evolution, all of them fallacious. Some formulations involve different fallacies, some involve them all. This series of articles will consider a few of them.

The first fallacy is “collapsing the continuum.” The usual application involves a computation of the supposed odds against the happening of some sequence of events. The fallacy consists of wrongly treating the entire sequence of events as if it were one single event.

For example, let us consider the odds against, say, tossing a coin 100 times and getting it to turn up “heads” every time. Of course, the chance of getting some string of results — any one at all — is 100%. But the chance of getting 100 heads in sequence, or any specific string of coin tosses involves an exponential computation — one chance in two for the first toss, then the same thing for the next, etc. At the end of the sequence, the likelihood of a specific outcome is so minuscule that it’s declared to be “virtually impossible.” [The actual odds against tossing 100 heads in sequence are 2¹⁰⁰, or approximately 1.27 times 10³⁰.]

However, at any step along the way the chance of getting heads on the next toss is one out of two, or 50%. So if you had already enjoyed an improbable sequence of tossing heads, the chance of success for the next toss is still 50-50. Confusing the odds for each step (which are always 50-50) with the odds for the entire sequence (1 in 1.27 times 10³⁰) involves the fallacy of collapsing the continuum.

Let’s make it more complicated than heads or tails. Consider a deck of cards. Each shuffle of a deck of cards has an outcome which is one in 52! (That’s 52 factorial, which is 8.06581752 times 10⁶⁷.) It’s a huge number, which can be a metaphor for the odds (quite unknown) against our presently-existing biosphere. For comparison, the estimated number of stars in the universe is “only” 10²¹. Source: this NASA webpage.

By comparing those exponents we can see that the odds against any particular card shuffle are truly beyond astronomical. Yet, if you go ahead and shuffle a deck … ta-da There it is. You’ve obtained a virtually impossible outcome.

The point of the card-shuffle example is not that our particular biosphere isn’t unlikely, because it is. It’s just that whatever biosphere gets produced will be equally unlikely. Ours is no more unlikely than any other. If you went back to 4 billion years ago and started the whole thing all over again, you’d probably end up with a totally different mix of species, none of them exactly like what we have now. But this particular shuffle of the cards is ours. We’re unique. Never to be repeated. Irreplaceable. Priceless. This is why — contrary to the endlessly repeated claims of the creationists — the evolutionary point of view places a far higher value on humanity than one where we could be wiped out and started up again on a whim.

One can, if so inclined, see the hand of Providence (excuse me, the Intelligent Designer) in the outcome. Or one may decline such speculations, because each step along the way is a natural event, and the outcome is therefore every bit as natural as its component events. There’s no scientific answer to such questions. But there’s always Occam’s Razor.

Similarly, the odds against the history of England being what it has been are probably even greater (I wouldn’t even guess at how to quantify that). It wouldn’t be repeated the same way, even if it could be started all over again. It happened, quite naturally, day by day. In retrospect, the sequence that occurred is improbable, sure, but no more than any other that might have resulted; and despite the “odds” against it, there’s nothing impossible or miraculous about any of it.

The biggest problem with these computations (coin tosses, card shuffles, English history, or the biosphere) is that if you take all the events that ever happened and then whomp up some kind of monster mathematical result by stringing all the steps together, then you miss the key point: each step along the way is mathematically on its own! It’s an error to assign the characteristics of the entire sequence to an individual step. For further insights, see the Gambler’s Fallacy.

So that’s the first fallacy: assuming the entire sequence is all one step, which we’ve named collapsing the continuum. All creationists’ arguments that involve this fallacy are worthless. Evolution works. You can bet on it.

In Part II of this series we will consider another fallacious “odds” argument used by creationists: thinking small, or failure to appreciate the scale of things.

Copyright © 2009. The Sensuous Curmudgeon. All rights reserved.

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