Author: Sterling, Guest Writer Populating our fictional worlds with bizarre and wonderful creatures can be one of the most enjoyable aspects of world building. However, those who are not zoologically-inclined may struggle to find inspiration to design creatures that are truly compelling and unique. Despite the diversity of the animal kingdom here on Earth, creatures in popular culture are often built around the same basic template: vertebral, bilateral tetrapods with variations of fins, wings, scales, fur, and feathers. Though there is much fun and creativity to be derived from the four classes of tetrapods – mammals, birds, reptiles, and amphibians[1] – many creators might wish to branch out into less familiar territory. Where to look for inspiration? For inspiration, some look to invertebrates, which constitute the majority of the taxonomic tree yet are highly underappreciated. Invertebrates comprise all animal phyla except for the chordata, and even within chordata there are classes of invertebrates[2]. Non-animal lifeforms should not be overlooked either. Fungi, plants, protozoa, and bacteria are not as well-known to most people as animals are, but undergo many fascinating biological processes that can be incorporated into the ecology of your world. However, the fundamental properties of life itself do not change from one kingdom of creatures to another[3]. It helps for the zoological worldbuilder to understand these commonalities and why they are essential for all of life as we know it. These are the ‘rules’ of life, so to speak. Knowing the rules, writers and artists can follow or break them at their discretion. One may choose to design their fantasy creatures in accordance with the rules of life to make their world more grounded. Another might introduce world mechanics that disrupt the rules, leading to a new definition of life entirely. As we go through the seven properties of life, as agreed upon my most academic sources in biology, I will identify various opportunities for disruption or subversion of the rules. This will provide a starting point for getting used to the idea of breaking biology. However, with a little creativity, it should not be too hard to come up with biology-breaking concepts of your own. The Seven Properties of LifeOrder
Living things have some system of organization that allows them to function. Historically, the cell has been considered the smallest unit of life, but recently this definition has been challenged such that some non-cellular things are now considered living. Viruses are an example of non-cellular life[4]. A basic virus consists of genetic material surrounded by a protein capsid, which is not equivalent to a cell. Viruses also cannot reproduce on their own. They require cells of other organisms to replicate their genetic material and create new viruses, which is why viruses are pathogenic[5]. Nevertheless, a virus has a specific, organized structure made up of biomolecules.
Non-living things can have order as well, but they are excluded from the official definition of life by other criteria. A crystal, an enzyme, and a microchip all have organized components of varying complexity. If sentient AI is considered alive in your universe, then it would have order based on its hardware and software. Silicon, incidentally, is in the same group on the periodic table as Carbon[6]. If you have gods or other metaphysical beings in your world, then it is up to you decide what organizes them, or if they have organization at all. There could be a spirit whose very essence is disorder. Do spirits count as living things? That’s for the worldbuilder to decide. Response to Stimuli
This criterion encompasses a broad range of life processes. On the highly-responsive end of the spectrum, there are humans. We have responses to stimuli that aren’t even physical, like our worries about made-up scenarios, or reactions to things that may not have happened at all. At the other side, you get the most basic unicellular lifeforms reacting to the living conditions in their environment and to their own internal mechanisms. DNA replication complete? Commence cell division[7]. Foreign body attaches to cell membrane? Better form a vesicle around the object and fill it with digestive enzymes[7]. Plants respond to stimuli including temperature, light direction and intensity, the force of gravity, and changes from night to day at a pace that is too slow for us to see, but nevertheless occurs[7].
It is hard to imagine life that does not respond to stimuli in some way. A completely static lifeform that manages to fulfill all other criteria would provide a very interesting study of life. Perhaps that lifeform takes the form of a planet, which makes no attempt to increase its own survivability but nevertheless reproduces, grows, regulates itself, and consumes or produces food. A photosynthetic blob with no enemies could plausibly survive this way, but even so I find creatures more fun to write about when they are allowed to react to things around them. Reproduction
Not all individual lifeforms reproduce, but all life is initiated by reproduction. For organisms, which are cellular, reproduction consists of copying genetic material and passing it along to one’s offspring[7]. This process may or may not include recombination with the genetic material from another organism. We call it sexual reproduction if that happens, and asexual reproduction if it does not. Sexual reproduction typically requires two different sets of cells, known as gametes, that are complementary. In animals, the two gametes are sperm and eggs, and are generally allocated to male and female individuals, respectively[7]. Some species of animal are hermaphroditic, such as flatworms, which means individuals carry both gametes[2]. This changes the rules for reproductive engagement somewhat.
Non-life can also reproduce, if you broaden the definition somewhat: organic viruses, computer programs, machines, individual RNA strands. Non-life, particularly machines, can also alter the reproduction process in living things. Growth and Development
All species of organism have a life cycle. Some life cycles may seem to go on indefinitely, which is the case with some long-lived species of tree. Others are confined to a few years or even months. What happens in between is highly variable, and ripe for innovation by worldbuilders. Where immortal beings fit in with our various criteria for life is tricky. They may have all the behavioral properties of other lifeforms like humans. But, if something never dies, then on what basis do we consider it alive?
The growth and development of mammals is a fairly gradual process, where images of the adult form can be seen very early on in life. However, this is not a universal. In insects, the newly-hatched individual looks radically different from an adult, as seen with the butterfly and the caterpillar. Insects undergo metamorphosis between the larval and adult form[9]. The idea of metamorphosis was used in the novella of the same name by Franz Kafka, in which the protagonist metamorphizes into a beetle.
The life cycles of parasites are particularly fascinating, especially if they involve more than one host. If your worldbuilding includes elements of horror, a survey of parasitology is highly recommended. Parasitism can also be applied to non-physical lifeforms such as demons or spirits, who use their hosts’ bodies in a similar way. In the real world, parasites exist which can alter the behavior of their host in order to enable the transition from one host to the next[10]. This usually involves the first host getting eaten, so that the parasite is consumed as well. Two examples of parasites that do this are Leucochloridium paradoxicum[11], a flatworm, and Polymorphus, a genus of thorny-headed worms. Leucochloridium initially infects snails, and Polymorphus infects crustaceans[12]. Both induce behavior in their host with causes it to go to high ground where it is likely to get eaten. Regulation and Homeostasis
I grouped these two together because they are highly interrelated. Regulation refers to the processes a biological lifeform needs to keep itself alive. This includes nutrient transport, internal signaling, gene expression, and more[3]. Homeostasis is basically the regulation of an organism’s internal environment, which typically involves variables such as temperature, pH, and salinity[3]. Even robots need regulatory systems. A computer in real life needs power, software updates, occasional hardware upgrades, and cooling so it doesn’t overheat. Cooling is an application of homeostasis. Like animals, if the computer gets too hot, its internal components stop working. It can be interesting to think about the kinds of conditions required for survival in some extreme sci-fi and fantasy environments, such as deep space or the literal pits of hell. You don’t have to come up with an airtight explanation for these things, but thinking of something can enrich your world by adding neat new mechanics and limitations for your characters to work around.
Immortal beings may be considered exempt from regulation/homeostasis, as they cannot die and therefore don’t require anything for survival. However, some writers choose to have their spirits and deities be conditionally immortal, which means they cannot die by ordinary means but need something for survival such as offerings or worship. These beings can fade away if they don’t get what they need. Another kind of conditional immortality is the kind where something doesn’t die unless it is killed. This can create a system where the oldest beings are the most powerful and experienced, and the newest ones are small fish in a big ocean. However, any time you have immortal beings made of flesh and bone (or chitin, or cartilage...), it begs the question of how they replace dead tissue over time, something that every organism on Earth fails to do at some point. Metabolism
The processing of substances for energy. On Earth, there are two main strategies for metabolism: heterotrophy and autotrophy[7]. Autotrophs, or ‘producers’, metabolize their own food from non-organic sources. The classic example is photosynthesis, which plants, algae, and cyanobacteria use to convert energy from light into sugars. Sugars are then broken down by the cells for energy[7]. Heterotrophs, or ‘consumers’, also need sugars in order for their cells to function. They get sugars, as well as other biological macromolecules, by consuming other things, either autotrophs or other heterotrophs[7]. This is why the sun is seen as the beginning of the food chain on Earth, because it feeds the autotrophs, and they feed the heterotrophs.
However, there are places on Earth where life exists independently of sunlight. In hydrothermal vents, the food chain is supported is microbes that use the methane and sulfur released by the vents for energy[13]. There is even a bacterium that absorbs the geothermal radiation of the vents for use in photosynthesis[14]. Methane is also the primary source of energy in cold seeps, where mussels with endosymbiotic bacteria are abundant[15]. There are bacteria that survive by oxidizing Iron and Manganese in rocks[16]. These are known as chemoautotrophs, and they are types of autotrophs that may or may not use the sun for energy, which gives us another possibility for extraterrestrial life. Heterotrophy and photosynthesis are not mutually exclusive, either; a group of sea slugs known as sacoglossans take the chloroplasts from the algae they consume, and use them in their own cells, which may provide an additional energy source[17]. Conclusion As you can see, life breaks the boundaries and conventions that humans impose on it all the time. As a writer, you can do the same, and in subsequent articles, we may break biology further by going into more depth. I'm reminded of the famous quote from Jurassic Park, “Life breaks free. Life expands to new territories. Painfully, perhaps even dangerously. But life finds a way.” References:1 Comparative Anatomy of the Vertebrates (Ninth Edition); Kent & Carr. 2 Invertebrates (Second Edition); Brusca & Brusca. 3 General Biology (Boundless); LibreTexts. 4 “Are Viruses Alive?” Scientific American; Villarreal, 2008. 5 www.genome.gov/genetics-glossary/Virus 6 The Periodic Table 7 Biology: Science for Life with Physiology (Fourth Edition); Belk & Borden Meier. 8 House Plants: Simon & Schuster. 9 An Introduction to the Study of Insects (Sixth Edition): Borror, Triplehorn & Johnson. 10 “Behavior-Altering Parasite” on Wikipedia. 11 https://dailyparasite.blogspot.com/2016/12/leucochloridium-paradoxum-revisited.html 12 "Altered behavioral responses in intermediate hosts – an acanthoceptalan parasite strategy" The American Naturalist; Moore, 1984. 13 “Hydrothermal Vent Microbial Communities” on Wikipedia. 14 “An obligately photosynthetic bacterial anaerobe from a deep-sea hydrothermal vent” Proceedings of the National Academy of Sciences; Beatty et al. 2005. 15 “Gas-powered Circle of Life – Succession in a Deep-sea Ecosystem” NOAA Ocean Explorer; Hsing, 2010 16 “Dissimilatory metal-reducing microorganisms” on Wikipedia 17 “Functional chloroplasts in metazoan cells - a unique evolutionary strategy in animal life” Frontiers in Zoology; Handeler et al. 2009.
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