This list starts off making the presumption that Alien is equivalent to those who might come a vistin’, rather than life that we might discover through our own exploration of the Universe. Several of their ideas are misguided or just wrong, and we will tell you why.
What separates humans from other species on the planet in terms of evolution comes down to a simple principle: aggression. For any species to thrive within a given habitat it has to confront adversity and overcome it. These struggles drive evolutionary adaptation. The dominant life form on a planet (which aliens would almost certainly have to be) must have been able to master their environment.
A paper published by the University of Missouri suggests this means they would be aggressive—they would populate and conquer their surroundings in order to progress. If they are more intelligent than we are, they will likely see us as a resource, the way we view farm animals and their habitats.
This is just wrong. Humans did not survive due to aggressiveness. There are plenty of animals more aggressive, and better adapted to aggressive behavior than we are. What sets us apart is our ability to cooperate with each other, to overcome aggression by recognizing the common good, and this is, in some regards the opposite of aggression. An alien species would need to have learned to cooperate to travel to the stars. That is the true trait that should be listed here.
Any life form that reaches Earth will, by definition, be an explorer. Looking to our own culture for clues, we immediately see how unexplored territories are targeted for their resources. We wonder what lands might possess that can help further our causes. Look at Columbus and the Americas, Marco Polo and the East Indies, the Vikings and most of Europe.
According to Stephen Hawking, aliens are likely to seek out other planets in order to colonize them or mine them for resources. Aliens may not come to destroy our planet, but they will in all likelihood seek to exploit what they find to increase their race’s reach, as again this is the hallmark of a developed species.
Hardly even worth mentioning as it could be taken as a given. Though I cannot agree with Hawking in the idea that an alien race would need to find other planets for resources. Even we are looking at our own asteroid belt or mining comets for resources. They are there, in plenty, and in purer form than on a volcanic planet that tends to stir things up. It would take tens of thousands of years, probably more, to use up the resources of one solar system. If they have mined their entire system, unless we are the next nearer system they have nothing to gain by coming here.
Viral and Bacterial Immunity
It’s a common trope in Science Fiction that aliens, having never encountered Earth bacteria before, will succumb to simple diseases which they have no immunity to. Just look at the pilgrims and conquistadors, and the havoc smallpox and typhus wreaked on unexposed native populations. But conquistadors and Aztecs were both human. According to Seth Shostak, senior engineer from SETI, bacteria are limited to the life forms they are biochemically related to.
Our germs have evolved to survive on our unique DNA. Even viruses and bacterial infections that infect one species on our planet will only rarely spread to another. Dogs don’t routinely get the ‘flu, for example. Any alien life form that invaded earth will likely be immune to earthly diseases, so don’t expect a War of the Worlds solution.