Some of the complaints I’ve often heard about Space Opera-style games/books/movies is there being too many species and too many humanoid species. I don’t necessarily agree with the first complaint, and I’ll explain why below, but the second complaint has merit. Humanoid aliens, and “forehead” aliens at that, are easy. Take a human, apply some strange or theoretical societal constructs to the beings, add some cranial ridges, and “eureka!” you have a new alien species. For TV and movies this is simply a matter of simplicity as it takes a lot more time and effort to create a believable non-humanoid alien than it does to apply make-up to an actor. However, I still see lots of humanoid aliens in literature as well, even when the hurdle of special effects are removed from the equation. I’m not calling authors lazy, but it is dramatically easier to imagine believable humanoid lifeforms than it is to imagine sentient oozes, crystals, etc. in a believable fashion.
I’ve said that I don’t agree that there are too many alien species, even in a universe as seemingly “crowded” as that of Star Wars or Star Trek. The setting I’m adapting to Stars Without Number is very much a “kitchen sink” setting. There are literally hundreds of alien species in my GM’s bullpen that I can call up to put against the players or allow the players to try out for themselves as a PC. So with the complaint of there being too many alien species (well, sentient aliens that is), I’ve come up with this justification: It is estimated that there are roughly 200 billion stars in the Milky Way. Most of those are believed to have planets, an average of 1.6 planets per star (though that number may very well increase as we discover more and more exo-planets). Now, the chance of there being a planet in the “Life Zone” of a star is pretty small, let’s say one half of a percent. That still leaves us with 1 billion stars that could support life. Out of those billion stars, maybe only 1% (these figures are obviously generous) of those have sentient life, leaving us with 10 million systems with sentient life. Even if the chances were still way smaller than that, there’s still that possibility that maybe the galaxy is more diverse than we ever thought. Plus, with this being a space opera setting, which borders on the fantastic as much as it does the scientific (even more so actually), grand cosmopolitan galactic societies appear a bit more plausible. These figures are also only taking into account that there are planets in the “goldilocks-zone” and therefore is at least in some way similar to life as we know it; not really taking into account lifeforms that may not require water or higher temperatures to thrive.
Even if we take a much more realistic view by using the equations devised by Duncan Forgan at the University of Edinburgh (source), by adding in 3 factors for how intelligent life can evolve on a planet (difficult to form but easy to evolve, easy to form but difficult to evolve, and being seeded by an extraterrestrial body) he comes up with a range of 361 to 37,964 different intelligent species in the galaxy. Those odds are nowhere as good, but both equations only think of life as we know it and don't factor in the possibility of silicon-based life or something other than carbon and water-based life (such as life here on Earth). Even then, with the possibility of anywhere from 361 to almost 38,000 intelligent species, I feel like I've got enough wiggle room to add in the species I want and still be within the confines of what could possibly be believable without straying too far into the realm of out-and-out fantasy.
My “justification” for the prevalence of humanoids in the setting isn’t really supported by any science. It’s tied more to the back-story and the mysteries of the setting. There are a lot of similar species, especially where humans are concerned, in the setting. Humans appear to be the “template” for life throughout the cosmos. There are many theories to why humanoid forms, and human forms at that, appear more than other bio-forms. These theories range from humanoid forms represent the most malleable and successful form brought forth through the trial and error of evolution to humans being the template for life selected by the “Precursor” species known as the Seeders or the Prometheans. Nobody know for certain, but with so many near-human species being found throughout the galaxy it is considered one of the great mysteries of science.
Speaking of Precursor species that will be one the next topics I cover in this series about my SWN setting…