Did any of you watch the summer TV series FALLING SKIES, about a resistance group in the aftermath of an alien invasion? I don’t think we’ve been told yet exactly why the aliens wanted to conquer Earth. They enslave human children by means of “harnesses” that provide mind control. Again, I don’t think the ETs’ motive for bothering with native captives has been made clear, although maybe more secrets will be revealed next season.
Many stories of alien invasion have problems in this area. The classic prototype, H. G. Wells’s WAR OF THE WORLDS, postulates that Mars, a dying planet, no longer has enough water to support its population, so they try to take over the nearest habitable world. Reasonable enough. Most invading aliens, however, come from outside the solar system. It’s hard to come up with a plausible reason why entities who can cross interstellar space would need anything Earth can supply. Don’t they have the technology to manufacture what they need? Or, if it’s raw materials they’re after, a galaxy full of uninhabited planets to choose from?
A lovely story by Zenna Henderson has the aliens invading Earth for salt because they’re sterile without salt in their diet. The character interaction is wonderful, but the premise doesn’t hold up under close examination. Sodium chloride couldn’t be so uncommon in the galaxy, and anyway, couldn’t a culture capable of traveling between stars synthesize such a simple compound? The same argument holds for just about any material resource, unless the author comes up with a substance so rare it can’t easily be found anywhere but here. Slaves? If the conquerors can invent FTL spaceships, surely they have advanced robotic technology, more efficient and reliable than live workers.
“Mars needs women”? Maybe, like the insectoid ETs in Octavia Butler’s “Bloodchild,” they require host creatures in whose bodies they lay their eggs. But why travel such a vast distance to find a new host species? (In Butler’s story, a small human colony has settled on the alien planet, not vice versa.) They want to eat us or drink our blood? The problem of biological incompatibility arises. Do they live on life energy, so any sapient prey would do? Still, again we have to ask why they’d make an interstellar voyage for that purpose. One way to get around these difficulties might be to make your aliens a band of refugees who settle on Earth and plunder it for whatever they need because they have nowhere else to go.
Another plausible standby is the “strategic location” premise. Earth sits at an interstellar crossroads. Or maybe there’s a wormhole portal hovering nearby that the aliens want to exploit. Worst plight for us, we might find ourselves in disputed territory fought over by two galactic empires that regard us as primitives whose welfare doesn’t matter.
I prefer to imagine aliens coming here for more limited, less hostile purposes. Trade or tourism, maybe. Our “primitive” artifacts might attract collectors of odd curios. Eco-tourism? Visiting a planet with tracts of what look to them like "unspoiled nature"?
“To Serve Man” was an entertaining TV episode, but I doubt it represents the typical motivation of a space-traveling culture.
Margaret L. CarterCarter's Crypt