I've been (re)reading Isaac Asimov's classic 'Foundation'  science fiction series.   It's the story of an galactic empire, which has collapsed under its' own weight, and a plan by scientist Hari Seldon, devised to create a second, more integrated and robust society.  The plan is formulated to bring about a new galactic empire within 1000 years of the first empire's demise, instead of the predicted 30,000 years of wars and internecine fighting should the plan not be implemented.  The entire series posits a galaxy populated by a single intelligent species, ostensibly homo sapiens.  As I've been reading the books, it's occurred to me that Asimov's notion of a galaxy populated solely by human beings seems rather quaint today.  Modern astronomy predicts an extremely large number of planets in our universe on which life could potentially emerge, and were intelligent life forms to evolve on those worlds it would almost certainly differ genetically and morphologically from ourselves.

Many authors and film makers depict such extraterrestrials as adversaries who would like to have us for lunch.  Literally.  This model of extraterrestrial behavior, I classify here as the  "Space Nazis Paradigm".  H. G. Wells' 'War of the Worlds' and Orson Scott Card's 'Ender' series are classic examples of the Space Nazi model.  Card invents an arthropod-like species of bipedal bugs with opposable digits that swarm through space in search of planets to sack like their r-selected distant cousins, the locusts.  This idea has been extrapolated in films like the 'Alien' series, in which futuristic weapons manufacturers try to harness "the perfect killing machine" in the form of an armored bipedal being, again with opposable digits, and blood that is so acidic it dissolves steel. The Space Nazi paradigm also embodies the underlying theses for blockbuster films like The Matrix and Independence Day.

Even the excellent comedy film, 'Men in Black' was based on an invasive space "bug".  Men in Black differs in one major respect in its' inclusion of intelligent extraterrestrial species which are amenable to living in harmony with humans.  The 'Star Wars' franchise mixed it up a bit as well, offering the comedic relief of the gargantuan muppet, Chewbacca, as well as the mildly offensive Jar-Jar Binks as well as some hostile morphologically divergent species.  Unlike Bukowski, Speilberg does barflies of the galaxy a great disservice in his depiction of the camaraderie of sharing a drink with your galactic mates at the risk of having your head blown off.

So there are myriad ways our popular culture assesses what these "close encounters of the third kind" might look like.  I'm going to try and factor into the predicted behavior of a technologically advanced alien species some of what I understand of the Fermi Paradox which defines the "apparent contradiction between high estimates of the probability of the existence of extraterrestrial civilizations and the lack of evidence for, or contact with, such civilizations".  Astronomer Frank Drake quantified in the so-called "Green Bank" or "Drake Equation" the uncertainty of the factors that determine the number of technologically advanced extraterrestrial civilizations.  From wiki:

"Drake suggested that a large number of extraterrestrial civilizations would form, but that the lack of evidence of such civilizations (the Fermi paradox) suggests that technological civilizations tend to destroy themselves rather quickly. This theory often stimulates an interest in identifying and publicizing ways in which humanity could destroy itself, and then counters with hopes of avoiding such destruction and eventually becoming a space-faring species."

Frederick Pohl's short story, "Fermi and Frost", directly explores this scenario that "cites the paradox as evidence for the short lifetime of technical civilizations -- that is, the possibility that once a civilization develops the power to destroy itself (perhaps by nuclear winter), it does."

Much of Drake's equation is conjecture, but we can see other issues than nuclear Armageddon, which might shorten the longevity of a technologically advanced society.  Issues such as green house gases which we pump into our atmosphere along with the resultant acidification of our oceans lend credibility to the concept that a technologically advanced species might be unable to reverse these environmental effects in time to save their planet and species from self-imposed limitations if not destruction. 

Given the long turnaround time of reversing these environmental effects and the concomitant extinction of  lifeforms associated with major habitat disruptions, an emerging technologically advanced culture must learn relatively quickly to live within an ecological balance on their home planet if their society is to endure long enough to develop the technology required to traverse the long distances of space necessary to colonize other planets.  If a civilization which hadn't achieved ecological homeostasis became capable of leaving their home planet before being overwhelmed by environmental catastrophe, they would likely do so as space refugees, incapable of waging war on an intelligent dominant species of the planet that they chose to migrate to.  If they were so lucky as to choose an uninhabited planet for colonization, there is a strong probability they would bring with them a profound cultural awareness of the pitfalls that technology inevitably presents to a developing world and would tend to orient their actions toward ecological stasis. Subsequent development of their technological abilities would likely include a predilection for balancing the stochastic equation of living in environmental harmony. 

A world in ecological balance would have one less reason to set off on a mission of galactic conquest having all ready solved the problem of an exponentially growing population and its' corollary, diminishing resources.  An extraterrestrial civilization capable of waging interstellar war would have all ready had to have passed a sort of self-selecting test by limiting their population growth to zero, while learning to live within their environmental constraints.  In doing so, they would likely have developed a decidedly gentler culture and utilization of resources than sacking their neighbors' planets. 

For these reasons I suspect that if technologically advanced extraterrestrials exist that are capable of interstellar travel, they are more likely to be in the "Fluffy Bunny" vein than the "Space Nazi" camp, although they may be curious enough about emerging civilizations to administer a few tests and experiments on the dominant species of such planets. 

Thinking on Asimov's books about a galactic empire of planets populated by human beings, I'm struck by his vision of an ever-expanding human population that colonizes world after world.  Perhaps once a species such as homo sapiens possesses the technology for interstellar travel we would continue "to go forth and multiply" upon initial colonization, but somehow I think that would not be a defining characteristic of a culture that has come to live in balance with their planetary environment.  I'm struck with how far we as a species and a global culture must progress before our descendants could ever hope to establish such an interstellar "empire".  In a sense, we must redefine "human nature" if we are ever going to prove Drake wrong. 

Even if we do survive ourselves, there is always the probable impact of a world changing asteroid, such as Chicxulub which makes it imperative if we hope to survive as a species that we get off this planet.  In order to have the time to develop the kind of technology interstellar travel requires, we need to attain an ecological balance that has eluded our species since our earliest migrations and the extinctions that have paralleled that migration.