At least the Thread and the native life forms have had some time to co-evolve. McCaffrey's colonists fan out from their initial base at Landing and spread seeds, spores, eggs and new species of megafauna all over the planet. They seem utterly unaware that this will cause massive displacement of species up and down the food chain, perturbing nearly every ecology in the world. They also seem unaware of the possibility that local life forms might be better adapted at some things, and might see them and their imports as food as well.

I raise this not to dump on McCaffrey (whose books are marvelous) but becauseDragonsDawn perfectly exhibits the conceptual blind spots that have gotten us into trouble on our own planet. Even more, however, DragonsDawn flags a giant blind spot among proponents of space colonization. This blind spot is the idea that the worlds we want to locate and colonize should be worlds like Earth.

The fact is, the last place we want to set up a human colony is a planet with a fully developed Earth-like ecosystem. Jared Diamond provides some of the reasons why in his excellent study of the European conquest of the Western hemisphere,Guns, Germs and Steel. European settlers didn't just come over and settle; the Vikings tried it and died out, and many early colonies in the Indies and America failed. Those settlements that were successful were the ones that had the benefit of knowledge earned through long experimentation in the micro-ecologies of the Azores, and the Canary Islands, and in Africa and Asia. More importantly, however, the successful colonies weren't bands of human beings--they were humans accompanied by the right mix of food animals, edible plants, and microorganisms. In other words, it wasn't European humans who colonized the Americas; it was European ecosystems. And the effect, both on the flora and fauna and on the humans already in the Americas, was apocalyptic.

A single species can't colonize another world; it takes a whole biosphere. Even your gut fauna have the potential to wreak havoc on a planet that's never encountered them before. You might think you could genetically engineer solutions to this whopping big problem, but the thing is, species-by-species interventions won't work. Most of the microorganisms in any randomly-selected drop of water are unknown to science, and you have thousands of species living inside you, all of which would need to be taken into account. Ditto for the new biosphere you're moving into; adaptation must be mutual.

So, these green, Earth-like worlds with their blue skies and oceans, warm breezes and waving, untouched forests--these aren't the worlds you're looking for. They're impossible to colonize without unforeseeable catastrophic results. We will want to look for them, to study them and admire them from afar, but we'd better not ever set foot there.

Instead, the worlds we will want to colonize (and I disagree here with Charlie's assessment that colonizing other worlds is impossible or impractical) are those that are fallow--Earth-analogues that could have developed life but never did. We might get luckiest on planets that do have life but where that life is stuck in the proterozoic stage, and has oxygenated their atmospheres but not yet colonized land. As long as we're willing to pave over that indigenous life entirely with our own, this might be the best way to go. Otherwise, however, for the purposes of eventual colonization, we should be searching for the Fallow Earths.

--Oh, hey, I just came up with a book title. Anybody want to pay me to write a novel around it?

Addendum: for the comment thread around this entry, head on over to Charlie's Blog.