Yet another alien invasion show. Not that that's a bad thing (the show that is - alien invasion would be a bad thing). I am looking forward to the re-imagining of the 80's series. However, it got me to thinking again about the possible motivations for an alien species to invade the Earth, and the many difficulties involved with invading an already populated planet.
- Atmosphere: a sentient species will be evolved to their specific environment. Slight changes can prove to be very toxic. An alien invading Earth would need to be able to breathe our particular blend of gasses. That would be a rare alien. Ah, but what about spacesuits or masks? True, those would help, but then why take over a planet that you can not breathe unassisted on? I would think it be easier to terraform a barren, or nearly so, planet than to "terraform" one with an already fully developed ecosystem. Though as mentioned in previous posts, postbiologic / robotic sentience creatures probably can withstand a very wide range of atmospheres.
- Nutrition/Dietetics: a sentient species coming to Earth to use us as food would run the risk of finding us to be indigestible or even poisonous. Even if their genetics/physiology are somehow close to ours (that DNA is somehow a normal result of biochemical processes leading to life in the universe), there are many example on Earth where food that is nutritious to one creature, is not nutritious to another (and may even be poisonous). Of course, if the aliens find Earth life to be eatable, it stands to reason that Earth life would, in turn, find the aliens eatable as well, from mammalian predators to invertebrate parasites.
But it is more likely that our physiological makeup will be too different to be of any use dietetic use. The To Serve Man recipe book would not be a top seller for aliens. Although if Earth animals were heavily processed, the aliens possibly could get some food value from them - but a lot of work for little return. Why not find a suitable barren planet, terraform it, and raise food more suitable to their physiology? If the aliens are postbiologic, which many think aliens would probably be (a next natural step in evolution for sentient species), they probably do not need biological food anymore anyway.
- Disease/Immunity: I have read conflicting opinions on this matter. One opinion is that humans and disease have evolved side by side - it's a continual arms race as our immune systems evolve to better protect, and diseases evolve to defeat our systems. An alien system would be, well, alien. Diseases have evolved to attack other Earth creatures and are finely tuned to Earth creatures and thus would not be able to attack an alien creature. Others are of the opinion that an alien would be wide open to attack, since their defense systems have never seen Earth diseases and thus have no finely tuned defenses or mechanisms to block or fight them.
In addition to diseases, there are all manner of venomous arachnids, insects, snakes, toads and poisonous plants that an alien would have to contend with. Many would not care if the creature they are in contact with is from the Earth or not. How many of us have put a straw or stick into an ant hill and see the ants swarm and viciously attack the stick? Would the alien bodies be able to tolerate foreign venom or poison?
However, with advanced nanotechnology (or technology advanced beyond it), aliens may very well have postbiologic systems to help them deal with diseases, venomous creatures, and poisonous plants - such matters may be of no real threat or concern to them.
- Other environmental factors: we have evolved in a particular gravity well, in a particular magnetic field, with certain ranges of light and other radiation hitting our planet's surface, and a certain range of temperatures. Any invading alien would need to have come from a planet similar to ours if they have any plans for long term domination. Unless, of course, they are postbiotic creatures.
- Water: many alien invasion scenarios have aliens coming for our water. Yet we are discovering that water is rather common in the cosmos. There is water on the moon, Venus, Mars, many of the moons of our gas giants, in comets and meteors. Why mess with a populated planet when water is probably much closer to home?
- Overpopulation: some alien scenarios have aliens invading because their home planet is overpopulated. I guess their entire solar system would have to be too, for them to move out into the stars to expand. If they were postbiologic and still felt the need to increase their population, they could easily colonize barren systems first or large space stations (Dyson spheres?).
- Salvation I: several scenarios have dying aliens coming to Earth in order to do medical experiments to either create some vaccine or gene therapy that can restore the alien's health, or to create alien-human hybrids so that the aliens can continue to live on, albeit in a rather different form. Besides the difficulties of two species evolving on two planets being compatible enough to be of any use to the other medically, again it would seem logical that an interstellar space faring race would be able to evolve into postbiological forms and thus not need to invade another planet to save their species. Though Studying other biologies can help uncover any universal biology laws and principles and thus help a species understand itself better.
But let us say, for the sake of argument, that they cannot or are unwilling to go the postbiologic route and need to leave their star system (going nova?) and colonize another system (ours) and thus need to create hybrids to survive in our very alien environment (this scenario also assumes they cannot or do not have time to terraform another unpopulated world). A hybrid would feel and be different than the aliens - it would be a new species, experiencing the universe differently, and thus evolving away from the invading alien's culture and identity. How is that helping anything? They might as well just impart their knowledge to another race and consider the torch passed and not bother with the whole hybrid thing.
- Salvation II: ala The Day the Earth Stood Still, aliens may invade to save us from ourselves, baring any alien version of a Prime Directive, or to prevent us from being a danger to our space neighbors (not all of our space neighbors may be advanced enough to be safe from dangerous space faring races).
- Salvation III: alien missionaries come to convert us.
Overall, it seems that for the most part postbiologic creatures would have very little drive to invade another planet. At least for physical reasons. But they may have psychological or theological reasons. For instance they find the postbiologic evolutionary step incredibly repugnant or blasphemous. They may fear for their safety or for the safety of other less develop extraterrestrial species and decide to keep us restrained or contained until we, in their minds, have matured enough. Maybe they have long forgotten their own early sentience past and look upon our aggression with psychological or theological horror. They may look upon us as heathens and feel the need to forcibly spread their theology upon us. Now those are scary thoughts indeed.
Image credit: ABC