There are theories that they have long been among us, and has even infiltrated into the ranks of state structures. Maybe this is not so, but how to determine this stranger?
All of the following 11 suggestions are based on scientific evidence:
One of the main differences between homo sapiens from the other body is aggressive behavior towards less developed forms of life.
It is in the struggle for survival, we have become the most successful animal species on their planet.
Newcomers, too, will consider themselves the dominant race and treat us only as a resource, that is the same as we treat, such as draft animals.
According to a document recently published by the University of Missouri, aliens, likely will face a much higher level of development. To explore the possibilities and the level of human development, they need aggressive offensive policy.
But she will not necessarily take the form of an armed invasion.
2. Research interest
Any alien life form, which reached Earth, by definition, must have some research curiosity.
Interest intelligent beings from other planets to Earth would be similar to the one that led Christopher Columbus, Vasco da Gama, Marco Polo and other great travelers and explorers of the earth.
According to physicist Stephen Hawking, the aliens are not likely to destroy the planet, they will try to use it for their own subsistence.
For humanity, it can turn into trouble, for all underdeveloped native tribes of colonization.
3. Immunity to earthly diseases
In science fiction books and motion pictures quite common assumption that aliens could never take over Earth, because their immune system will be extremely vulnerable to any terrestrial bacteria and viruses.
Of course, in the case of Indian civilization and conquistadors what happened - the Spaniards found themselves defenseless against syphilis and other diseases of the Americas, that has caused epidemics that caused considerable damage to the population of Europe.
But, according to Seth Shostak, an employee of the project «SETI», terrestrial viruses are unlikely to cause harm to aliens.
Germs and bacteria dangerous to mankind evolved millions of years to adapt to life in the person.
Terrestrial bacteria and even viruses rarely affect various species of animals (e.g., influenza virus is absolutely not dangerous for dogs), and the device of alien organisms is likely to be fundamentally different from the structure of the human body.
The bacteria simply do not "understand" how to survive in aliens.
4. Aliens are unlikely to devour men
Mankind for thousands of years, eats the other inhabitants of the planet, and even specially bred animals intended "for slaughter". The idea that aliens can do with people is the same, inspires fear and the desire to resist the alien invasion to the last drop of blood.
However, it is unlikely that human flesh will please discerning palates alien taste.
Rather, aliens, going on a long journey, it necessary to provide a supply of food and the possibility of their production, so that prey on people they do not have to.
In addition, protein foods from the Earth is unlikely to be compatible with the digestive system visitors from another planet - is another argument in favor of the travelers seize all the food with them.
The development of civilization has always come to the fact that hunting and livestock - are not the most effective means of production of food, so the steaks from human flesh on the tables at the alien will not be gluttons.
5. Newcomers - passionless killer
You've found in their home of cockroaches, ants or flies?
Further events are difficult to predict, first you violently exterminated defenseless and, by and large, harmless insects, and then put the special traps everywhere and process chemicals apartment.
This terrible fate may befall us: from the point of view of the aliens, people may well be something of these parasites, insects.
The new owners of the world may hold a large-scale purge, and then will safely dispose of the earth's resources.
To rid the world of parasites, people will most likely be applied bacteriological, climatological, or some other, unknown to mankind weapons.
6. Insects - no!
Writers of horror films and science fiction writers sometimes imagine alien invaders in the form of huge insectoid creatures.
Newcomers like giant beetles and wasps, probably one of the most terrible and disgusting creatures of the human mind.
However, from a scientific point of view, this assumption is unsubstantiated.
Rather, in such representations reflected people's fear of a purely terrestrial insect carriers of deadly diseases.
Due to the specific structure of the body of insects range of comfortable living conditions for them is rather narrow.
In insects, there is no blood, so they can not get sufficient amounts of oxygen from the atmosphere - this is explained by their small size.
Many millions of years ago, when the concentration of oxygen in the air was much higher, the size of some species of insects have reached one meter, but these giants died out pretty quickly, giving way to a more sophisticated and unpretentious animals.
You probably noticed that almost all the cinematic and literary aliens have Overmind.
This is logical - otherwise they would be able to carry out a space flight, but still try to capture the alien planet?
However, aggression and bloodlust, which is usually attributed to the aliens, somehow not really fit in with the image of supramental beings.
If an alien civilization is at a high level of socio-political, scientific and technological development, it is hardly settled on its representatives pashas banal world war - it may bring more problems than benefits.
Mission aliens likely will not be a military operation, and an invitation to dialogue.
Politicians from the ground and guide the newcomers will have to compromise and develop options for mutually beneficial cooperation, while preventing bloodshed.
8. inhuman beauty looks
No matter how violent and sophisticated was not fancy people, fictional appearance of newcomers often broadly resembles the human body.
Cinematographer it allows much more colorful and more convincingly depict scenes of communication between people and aliens: if the "green man" at least somewhat similar to the Earthman, it is forcing sympathize with him more than, for example, creatures, looking like bowling balls (this image aliens found in one of the books Clifford Simak).
However, something Simak was right: the aliens will surely be strikingly different from the animal world of the Earth.
The structure of any living being depends primarily on the environment and the climate inhabited planets of other galaxies almost unknown, so if contact with their residents still take place, the exterior guests will surprise humanity.
9. Skills speech
The development of civilization is largely determined by the development of forms of communication.
Technical, social and social progress of the last decades has allowed to raise the exchange of information between people at a completely different level - the information became the main value, and every year the volume of data transmitted grow.
Every day, people have to solve a lot of problems related to language barriers and ways of thinking in different countries, but in general any Earthman can somehow be explained with the neighbor country or continent, such as through gestures or drawings.
If aliens visited Earth, first of all, to establish relationships with people, they (and we) need to take care of the process of transmission of information - accessible, acceptable and understandable for all participants interplanetary dialogue.
Everything is complicated by the fact that we do not know how the aliens talk to each other, because they can use to communicate electromagnetic waves, if not to use telepathy.
10. Do not wait to visit alien "bodybuilders»
Numerous fans of movies and books about aliens will surely be disappointed that the burly, strong and devilishly clever alien monsters, which they say writers and creators of the films most likely does not exist.
When a civilization reaches a high level of technological development, physical development of its representatives is gradually slowing down, and may begin degradation.
For example, when our ancestors to survive, were forced to have strong muscles and agility, many people today prefer not too torture yourself physically demanding, because to have lunch, do not need to catch a mammoth, and clothing can easily buy without stripping the skin with the tiger .
With increasing energy the body has been steadily declining amount of muscle that at the same time compensated by the development of the brain.
This, in particular, mentions HG Wells (Herbert Wells) in his famous "War of the Worlds" - his Martians brain highly developed, but the body adapted mainly to using the buttons and levers to control a variety of mechanisms such as described in novel martial tripods.
11. Functional limbs
Despite the fact that the aliens are expected will not possess the significant physical strength, they still probably be one or more limbs, their functionality is similar to the human hand.
In order to achieve certain heights in science and technology, intelligent creatures should surely manipulate tools and equipment, and for this they need a truly golden hands, then there are certainly capable of being precise and carefully planned movement.
Tools are constantly being improved, simplified management, and at the same time expanding opportunities, but it does not always lead to a loss of skills fine manipulation of objects. For example, spears and swords as weapons is now hardly used, giving way to nuclear warheads and drones, but any adult, even if not perfectly, but he knows how to handle them.
Incidentally, these characteristics also apply to us.
When we will travel between the stars and arrival on another inhabited planet, we will be that way.