Alien Biochemistry: The Story Behind the Science

by Jay Werkheiser

Science fiction is packed full of alien life. Strange new worlds and all that. There are plenty of exotic planets with dinosaurian reptiles stalking our heroes through alien forests. What makes the forests so alien? Well, um, the trees are shaped oddly, and the leaves are strange colors. And the grass, uh, it writhes and wriggles, grasping at the hero’s feet as he runs from the ravenous pseudo-velociraptor. Alien worlds always seem to evolve some sort of earthly analog—felinoid predators, reptilian monsters, cute bunnyoids, humanoid villains. That kind of thing always bothered me. Why would trees and grasses, earthly life forms, evolve on an alien planet? Why are there always things that look like scary dinosaurs? I mean, Earth has come up with more alien things than that! (Self-serving side note: look for my story that explores the alien intelligence of octopuses in the next issue.)

And don’t get me started on those humanoid aliens who can somehow interbreed with humans. That’s mainly a TV and movie trope, but jeez, didn’t anyone in Hollywood read Larry Niven’s “Man of Steel, Woman of Kleenex”? And we SF writers aren’t off the hook, either. Science fiction stories and novels are full of aliens that look and act conveniently like some earthly animal. I get it; aliens can be metaphors, a comment on the human condition, and so on. Many writers chose to focus on the metaphors and the alien biology is mostly an afterthought. But I don’t have to like it.

In my fact articles I talk about carbon chauvinism, the conceit that all life in the universe must be carbon-based like us. But most science fiction goes well beyond that to taxonomic chauvinism. Yes, I just made that up. It means that the alien life we imagine fits neatly into the biological taxonomy of Earth. Descriptions of alien trees make it clear they’re deciduous. Alien animals fit neatly into the mammal, reptile, arthropod, or other category. Linnaeus himself would have had little trouble fitting them into his taxonomy.

I want to imagine life that is truly alien, things that could have evolved on a different world. Natural selection is environment-driven, of course, so there’s no escaping the literal world-building that hard SF writers so often do. Life that evolved on a low-gravity world with a thin methane atmosphere will be tailored to that environment. But to get life that is really alien, look beyond that. The molecular landscape of life shapes evolution at least as much as the macroscopic environment. And that’s something I wanted to explore in my fiction.

Which brings us to alien biochemistry. My degree is in chemistry, so exploring this topic seemed a natural fit given the whole write-what-you-know thing. Still, the last formal biochem course I took was more years ago than I’d like to admit. Things change, new ideas emerge, our understanding improves. Well, if you want to write hard SF, you’re going to have to be the kind of person who enjoys doing research anyway. I wanted to pursue the idea of making one or more changes to the biomolecules on an alien world and see what evolves, so I dove deep into the messy details of biochemistry. For fun.

Layered on top of the biochemistry is the physical environment of the planet, which drives natural selection in particular ways. Several stories evolved from this basic framework. “Thanksgiving Day” (Analog, November 2009) looked at life that used quirky polysaccharide bonding (1,6-glycosidic bonds as opposed to the usual 1,4 found commonly on Earth, for you biochemistry nerds out there). “Ambidextrose” (Analog, October 2012) used reverse chirality biomolecules along with frequent asteroid impacts to drive one of my favorite evolutionary schemes. (Incidentally, for those who like the aliens-as-metaphor thing, I used biochemical chirality as a metaphor for the cultural conflict occurring in the story, so you can have the literary stuff and still keep the scientific rigor.) “Kepler’s Law” (Analog, May/June 2017) deals with life built using pyranosyl RNA on a nitrogen-deficient world. I explore that world in greater detail in a novel that I’m currently shopping around. “Retrograde” (under contract for an anthology to be revealed later) explores a world orbiting a red dwarf with frequent intense flares, which leads to life that has to be both photosynthetic and ambulatory.

“It’s not that difficult to take a known working chemical system and tweak it. It’s a whole other thing to build a new system from scratch. There’s a reason silicon-based life is the most popular non-carbon-based type of alien out there. Silicon falls right below carbon on the periodic table and therefore follows similar chemical rules. But even as a kid watching the Horta dissolve redshirts, I wondered how accurate it was to have a silicon-based creature breathing the same air as the human miners.”

By playing with biochemistry and evolution, I found that I could create convincing ecosystems that felt truly alien yet seemed plausible. No tree-oids with blue leaves for me! It occurred to me that I had tons of information on alien biochemistry stored in my research folder. As all writers know, much of that research never made it into the stories. But it was fascinating stuff, and I wanted to tell everyone about it. I’m a teacher; it’s what I do. Thus was born my first fact article, “Alien Biochemistry: Embracing the Carbon Chauvinist” (Analog, September/October 2018).

A carbon chauvinist is one who believes that, since life on Earth is carbon-based, life elsewhere must also be. In writing the article, it occurred to me that I had been guilty, however unknowingly, of carbon chauvinism. Why? Because write what you know, that’s why. It’s not that difficult to take a known working chemical system and tweak it. It’s a whole other thing to build a new system from scratch. There’s a reason silicon-based life is the most popular non-carbon-based type of alien out there. Silicon falls right below carbon on the periodic table and therefore follows similar chemical rules. But even as a kid watching the Horta dissolve redshirts, I wondered how accurate it was to have a silicon-based creature breathing the same air as the human miners. (Yes, I was a strange kid.)

Clearly you can see how I had no choice but to write a second fact article, “Alien Biochemistry: Rejecting the Carbon Chauvinist” (you can read it in this month’s issue) [on sale now]. I did a little poking around to see if Analog had published anything on the topic. The most recent article I could find was called “Xenobiology,” published in the March 1981 issue (it’s available online here). A lot of science has happened since 1981, so I figured it was time for an update. Since I’d already done some extensive research into biochemical systems built from various combinations of boron, nitrogen, and phosphorus for the aliens in “Briz” (January/February 2017), I already had a good head start on the article.

For me, science fiction is as much about exploring the limits of science as it is about exploring the limits of the human condition. I once read (I don’t remember where) that Poul Anderson’s Tau Zero reads like a textbook with characters. I don’t know if that was supposed to be a negative review, but it immediately put the book on my to-read list. Perhaps I’m a bit of a hard-SF extremist, but if there’s any group of people who can at least tolerate all the gory biochemical details (as well as the nerdy dad jokes), it’s Analog’s readers.

Jay Werkheiser has been writing science fiction since he was old enough to hold a crayon. He began writing professionally in 2009, when Stan Schmidt bought his story “Thanksgiving Day” for Analog. He is now closing in on thirty published stories, most appearing in Analog. When he’s not writing, you can usually find him talking about chemistry. As a teacher that’s his job, but he’s never let that stop him from rambling on about nerdy science stuff outside the classroom as well. You can find him online, mostly posting inconsequential nonsense, on Facebook, MeWe, Twitter, and a million other social media platforms.