As scientific understanding progresses, it gives us a clearer perspective on many things. I really respect sci-fi authors who attempt to stick to the science as much as possible. Far from constraining, I think it gives stories new and interesting turns. Written science fiction has gotten much more believable to me over the years, but I still roll my eyes when I see movies and TV shows portraying alien-human affairs and even hybrid children. As a neurologist, maybe I’m more keenly aware of the ludicrousness of alien biology as it is popularly imagined. Here are a couple things that annoy me—things that are infinitely implausible.
- Aliens with DNA. All Earth lifeforms happen to rely on DNA and the related RNA as the molecule of heredity. It seems likely that many other molecules could be just as useful as the templates of life, so why wouldn’t they? Even if life on an alien planet evolved on DNA, the genomes of such creatures would we different, from the molecular machinery of their cells (assuming they have them) to the amino acids and sugars they are composed of (more on that below). Even if the aliens by some 1:10×10^52 chance have identical cellular mechanisms, they would be able to breed with humans only about as successfully as a drosophila fly or an amoeba. So unless your story is going to suggest that humans and an alien race have common ancestry somehow, don’t imply your aliens have DNA! A super-intelligent alien race might decide to engineer their minions after the human genome. What twisted intentions might they have by doing so?
- Humanoid aliens or aliens bearing resemblance to an Earth critter. They look just like us only their smaller, skinnier, and gray. Or they all have receding hairlines and funny bumps of different shapes on their foreheads. Or they are just big insects. Inconceivable! For multicellular organisms, embryonic development is like origami. Where folding is concerned symmetry is a property likely to be work on your side, so whatever appendages an alien life form might have, it will likely have a right and left side. More than two sides is possible, but the digestive tract and nervous system ‘construction procedures’ would get tricky for anything much smarter than a starfish. Think about the unique environment in which they evolved. Factors such as gravity, living in air vs liquid, diet, lifespan, reproduction, etc. Come up with something interesting.
- Humans dining on alien cuisine or otherwise subsisting on alien plants and animals. It would be very plausible to find water and oxygen on an alien world, but all forms of animal life on Earth require amino acids, sugars, and trace vitamins and minerals in their food. 20 ‘standard’ amino acids are used in accordance with our RNA templates to construct all the proteins that comprise our cells. Of those 20, we must obtain the nine in our diet and we can synthesize the other 11 from them. Would they be found on the alien planet? Unlikely (see above). It turns out it’s not even that simple. All but one of the standard amino acids has a mirror configuration, or enantiomer. (Glycine does not because its mirror is the same.) Nature chose on the the L configuration as the standard and all our enzymes evolved thusly. If you were to visit a parallel universe where Earth’s life evolved according to the D configuration, you would not even be able to digest the grilled chicken there. In fact, it would probably smell and taste like a toxic chemical (since your olfactory and gustatory receptors are also oriented to the L configuration). The same would go for all the plants. Oh, and sugars synthesized by lifeforms on Earth follow the D configuration, so we could have all sorts of fun with the permutations of parallel universes. The take-home message is that if a human is to subsist on an alien planet, they could do so only with technology that would synthesize food from the basic chemical elements. No feasting on the native flora and fauna. If you value your life, it would be best to bring your own lunch to the restaurant at the end of the universe.
In future posts I plan to discuss potential alien neurology, communication, and culture. Stay tuned. . .