Will Wright talks about design influences on Spore (from Seed magazine, which as far as I can tell gave me a one-year subscrtiption in hopes I'd renew):

The science in Spore can be seen as the offspring of two seminal ideas: Powers of Ten, a 1977 documentary film by Ray and Charles Earnes that first showed viewers the zooming perspective of the universe described above, and the Drake Equation, a controversial attempt by the astrobiologist Frank Drake to quantify the prevalence of intelligence in our galaxy.  "If you look at the terms of his equation," begins Wright, "he's trying to estimate how many intelligences there are out there — how many stars times how many planets times what proportion of those might have life, times what proportion of those might become intelligent — but those terms end up spanning all these different scales, from physics to chemistry and biology, all the way up to what we know as sociology and culture.  So in some ways, Drake's equation is a really interesting spine along which to attach all the other sciences."

I scarcely know where to start.  So instead of getting sidetracked into a discussion of the idea of sciences having some kind of orderable "scale", let alone being able to hang them all off the Drake equation, let's just look at the Drake equation.  But don't waste too much time looking at it too closely.  Because it's complete bullshit.

Oh, sure, the statement of the equation is basically sound, as far as it goes, if you accept its underlying assumptions.  But there's seven terms on the right-hand side of that equation, all multiplied together.  How many of those seven terms do we have hard data ... no, let me take that back — how many of those seven terms do we have a reasonably reliable estimate for?

One.

Yup.  The first term, the average rate of star formation in our galaxy, is the only term in the entire equation that we have an estimate for that is backed up by observational data in which we have some kind of confidence.  Even the second term, we didn't have a prayer of backing with actual data in 1960 when the equation was proposed, because we didn't have the capability in 1960 to detect extrasolar planets.¹  (Heck, it took us until 1930 to discover what we thought were all of our own, and we're still arguing about the exact number depending on how we define "planet".)  Every star in the galaxy could have planets, or ours could have been the only planetary system in the Galaxy, and there's no way we could have known.  And the remaining terms just get worse and more abstract.

So in other words, what we have here is an "equation" that yields us the product of one number in which we probably, by now, have some reasonable grounds for confidence, and six more that were partly or completely pulled out of someone's ass (or several different people's).  The Drake Equation can give you any result you want – just make up numbers and plug them in until you get the result you're looking for.

In short, the Drake Equation has no predictive or analytical power whatsoever.  And that makes it pure noise.  Any time you see an argument for the prevalence of extraterrestrial life (or extraterrestrial pretty much anything else, really) justified by reference to the Drake Equation, you're talking to somebody who doesn't actually know, but likes to pretend he does.

Poor Drake.  Astrobiology can scarcely even really be said to be a science.  At the moment, it's purely a debating club of "what if" and "just suppose" and "I wonder", and it'll remain so until we actually have some hard observational data to base any conclusions on.  Until then, astrobiology is like the possibly-apocryphal Greek philosophers sitting in a cafe expounding logical arguments about the number of teeth in a horse's mouth.²

In an ironic way, the Drake Equation winds up being an oddly apt metaphor for the development of Spore, as the article goes on to describe how, in the interest of maintaining "Spore's broader potential to teach scientific principles", almost all of the actual science got left out.  Science came up against cute, and cute won.

[1]  We're starting to be able to detect extrasolar planets possibly as much as a couple of hundred light-years out, now.  We think we may soon be able to detect Earthlike planets around the nearer stars within that range, and we believe ourselves to be on the edge of being able to detect known biological molecules in the atmospheres of [relatively] nearby extrasolar planets.  We still have no idea whether alternative biologies are possible, though, or what their "fingerprints" might be.  And the rest of the terms continue to be pure guesswork, based at best upon partial data with a sample size of one.

[2]  The big blind spot of the Greek philosophers was they were so convinced of the supremacy of pure reason that many of them refused to sully their hands with actual experimental data.  As the story goes, these philosophers were sitting around debating how many teeth a horse had, and were unable to come to a consensus, so they called in a random passer-by off the street to judge them.  The man, an Arab trader, sat and let them buy him wine while he patiently listened to all their arguments, then excused himself.  A few minutes later, he came back to the table and told them the correct answer, which happened to be a number that two of them had arrived at, although by different means, leaving the question still unresolved.

"But whose reasoning was correct?" they asked the Arab.  "Whose logic is the sounder?"

"Logic be damned," says he, "I've just been around the back to the stable and counted them."