Monday, February 9, 2009

Evolution and chance: to live, perchance two die

I recently came up with an allegory in a discussion over at on evolution that I'm a bit proud of. The question it seeks to address is: If God didn't create life on Earth, then how did it come about, given the minuscule chance of life evolving on its own?

For life as we know it to exist, you have to have the right mix of situations — a suitable solar system, a planet with liquid water, atoms that can form amino acids, amino acids that can self-replicate, etc. The chance of any one of these things happening is very small, and the chance of all of them happening in the same place is virtually nil. Only God, the argument goes, could have tipped the balance to create life here on Earth.

I should preface the allegory by stating that although I do believe in evolution (though I also believe it'll have to be amended, and possibly significantly, as any theory is), the following isn't a proof that God doesn't exist. As an agnostic, I don't believe such a proof exists. But I do treat this allegory as an illustration of the fallacy that God must exist for humans to have formed.

So, now: An allegory two die for

Imagine a simple game involving two players and a 100-sided die (hence the pun in the title, for which I apologize... kinda). The players each roll the die, and if one rolls higher than the other, the player with the higher number wins. Otherwise, they both lose.

Now consider a single-elimination tournament with a million players. At each round, you kill the losers and put the winners in the pool for the next round, randomly seeded. For simplicity, let's say that anyone who isn't matched in a given round (ie, the "odd man out") dies before the round starts. There's a minuscule chance that any one person will win the tournament, but a very high (99%) chance that somebody will win.

At the end of the tournament, you interview the remaining player, if there is one (if the last round was a draw, there's nobody left). Sure enough, that player says he's extremely lucky to be alive. There was less than a million-to-one chance he'd live, and it wasn't even guaranteed that there would be anyone alive at all. He's so lucky, in fact, that only the existence of God explains it.

In fact, God doesn't explain it. It's just that by the very nature of the game, you only get to interview the fortunate winner. God may exist and he may not, but the existence of a survivor isn't evidence one way or the other.

It's the same with us coming from evolution, except that the losers (those without suitable solar systems, or who didn't have water, or who didn't create amino acids, etc) didn't die — they never existed in the first place. We're left with us, the fortunate few survivors in a game of chance, who look at our situation and are fooled into thinking that the question was "will humans evolve on Earth" and not "will something evolve somewhere."

When people look out to the universe and ask, "if it's all just luck, how come we don't see any other life forms?" they're missing the point. The winner in our allegory could ask the same question, especially if he didn't understand the rules of the game he just played.

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