Alien life: it’s the lynchpin of sci-fi. No one wants to read a story about humans who travel to a dead rock where nothing happens. At the core of space travel lies the will to explore, and the greatest triumph of space exploration would be the discovery of life beyond our tiny world. But what would such life look like? Would it be similar to life on our planet, so much so as to seem familiar? Or could alien species be truly alien, to the point of challenging our definition of life itself?
The nature of alien life has been one of the burning questions of science fiction throughout the genre’s existence, dating back at least to Edgar Rice Burrow’s A Princess of Mars. Depictions have ranged from mundane to fanciful, developing over time to account for advances in science. But what does modern science tell us about alien life? And how should the modern science fiction writer deal with the subject?
Aliens in Science Fiction
It would take far more time than I have to even begin to delve into the breadth of depictions of alien life in sci-fi. At this point, safe to say it is ubiquitous. Perhaps it would be more productive to consider how much depictions of alien life vary from life on our planet.
From Star Trek to Star Wars, Stargate to Flight of the Navigator, science fiction has often leaned on extraordinary alien creatures as plot devices. After all, the best way to make an alien planet feel truly alien is to populate said planet with a diverse cast of creatures, clearly very different from our own. Some, like the sarlaac from Return of the Jedi and the strange creature that attacked Kirk in 2009’s Star Trek, are clearly designed to be both otherworldly and frightening. Yet others, like the muad’dib mouse from Dune or the tauntaun from The Empire Strikes Back, were at least conceived of as believable creatures adapted to their environment. And that’s something the modern sci-fi writer should take note of.
The Science of Aliens
Though we’re learning more every day, at this point we have a pretty clear picture of how life evolved on our planet. And, for better or for worse, right now our best hope for understanding life on other planets lies with our own evolutionary history.
Arguably the single most important fact about the evolution of life is that it takes time. The evolutionary history of our planet spans a little over four billion years, but evolution didn’t follow a clearly-demarcated path. There were starts and stops, setbacks and dramatic leaps forward. While the earliest evidence of single-celled life dates back over four billion years, it took almost two and a half billion more for the first multicellular life to arise. Plants have been around for less than a billion years. Mammals, at least in the modern sense, didn’t show up until the Triassic at the earliest. And our species, humans, have been around a paltry one million years or so.
And that’s only talking about life in the conventional sense. Over the past twenty years, science has repeatedly questioned the limitations of life. It could be said that our concept of life on alien planets is often limited by human conceit: the notion that life on other planets must be similar to life on our own, just as intelligent alien life must resemble humanity. But even on our own planet, we’ve begun to realize life has fewer limitations than we tend to believe.
Scientists have found microbes living in hot springs, in pockets of air frozen in arctic ice, even on the insides of nuclear reactors. We’ve found that tardigrades can survive extreme conditions by expelling the moisture of their bodies, encasing themselves in a protective shell similar to glass. Silver ants survive in the middle of the Sahara (albeit barely) thanks to reflective exoskeletons that block the sun’s harmful rays. And some cephalopods display almost human-level intelligence.
So what does this mean for the modern sci-fi writer? Well, there are several factors to consider.
The first is environment. As I often say in my novels, evolution is life responding to its environment. How an alien species might look depends largely on its native ecosystem. On that end, science has some good news for sci-fi writers who’ve long sought to depict alien life as being familiar to us. Based on our current knowledge, it stands to reason that complex life would be most likely to evolve on planets similar to our own: comfortably warm, rocky worlds with liquid water, orbiting long-lived yellow dwarf suns. And since life evolves to suit the conditions of its environment, it stands to reason that life on planets similar to our own would follow a similar progression.
The second is time. As I said, evolution is a slow process. As life likely takes billions of years just to evolve past single-celled organisms, planets around young, hot stars (like most of the stars closest to us) might never come to harbor life. Such powerful stars tend to live fast and die young, and will likely go supernova long before the first stirrings of life in their planetary systems. If we did happen to find life on exoplanets, the timeframe of evolution suggests any organisms there would likely be at a very different stage of evolution. We’d be more likely to find planets covered in forests of lycopods, populated by giant amphibians, than worlds with deciduous trees and mammals like our own. Most likely, populated exoplanets would be mostly barren rock and oceans, the waters tinted green by vast colonies of cyanobacteria (primitive photosynthetic life forms which dominated Earth’s biosphere for nearly one and a half billion years).
The third could be called “X-Factors”. Our fossil record is littered with cataclysms: sudden, extreme global events that led to mass extinctions. These events invariably triggered great leaps forward in evolution, but only after periods of severe die-offs, often threatening to end life on Earth altogether. The most recent of these is perhaps the best-known: the Chicxulub Impact. Roughly 66 million years ago, a ten-kilometer wide bolide struck Earth near the present-day Yucatan Peninsula. That event ultimately led to the rise of mammals as the dominant form of life on Earth. But it did so only after wiping out 75% of all life, including all non-avian dinosaurs. The dinosaurs had been the dominant form of life on Earth for 135 million years. Carl Sagan famously theorized that, had the Chicxulub Impact never occurred, dinosaurs would have eventually evolved intelligence, developing mathematics on a base-eight scale (owing to their eight digits, as opposed to our ten).
It’s safe to say that we still know far too little about the nature and origins of life on Earth. That limits our understanding of life elsewhere. But perhaps the most important fact we’ve learned about life is best summed up by Doctor Malcolm in Jurassic Park: “Life finds a way”. Where there is water, organic material, and energy, there exists the conditions for life to spring forth. All it needs is a little time. – MK
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