Friday, January 27, 2017

The Aliens of Halo

The aliens of the Halo universe are, for the most part, a departure from the sort of humanoid, "rubber forehead" aliens we usually see in Hollywood SF. While most of them are tetrapod-like (bilaterally symmetrical and four-limbed) only two are very humanoid, with one being the unfortunate result of a low-budget, live-action series. The aliens of Halo feel a bit closer to what one would find in a science fiction novel and perhaps a bit closer to what might actually be out there. Since they're a step above the typical Hollywood movie alien, I've decided to review their plausibility and offer alternatives where their design falls short in that regard.

Plausibility Grades:

A:  The design is sufficiently alien to be considered a genuinely believable extraterrestrial organism. Such designs are impossible to confuse with any phyla found on Earth and may have a bizarre physiology or chemical composition. The Heptapods of Arrival are one of the few examples of this level of realism in a film.

B:  A plausible design but one that relies on a high degree of convergent evolution to justify its appearance. It must be a plausible example of convergent evolution, one that uses characters we can reasonably expect to evolve more than once under common selective pressures. I would give the Prawns from District 9 this grade.

C:  A somewhat plausible design, but one that suffers from misconceptions about biology, is lacking in scientific rigor, or takes convergent evolution a bit too far. If the mistakes were fixed, the design would be an A or a B. A "bad biology" example would be the xenomorphs from Alien. Many aspects of the creature are believably alien: the creature uses an acid instead of water as a solvent, its life cycle is unique, and it has a silicon-based exoskeleton. However, it also grows far too fast, the acid blood is absurdly strong for an organism, and its ability to "steal" genes despite its alien chemistry is simply impossible. The Predator is example of an otherwise good alien design that's a bit too humanoid to be convincing. If the Predator weren't obviously supported by a human skeleton, it would be an easy B.

D:  These may be plausible organisms, but they're not plausible aliens. They're most often aliens that are humanoid versions of Earth animals, e.g. humanoid cats. Such designs would require an extremely unlikely series of evolutionary coincidences. These aliens would make more sense as products of genetic engineering.

F:  These are either humans with some rubber glued to their head, humans with one small difference, or aliens that make no biological sense at all.

Huragok (Facticius indoles)

The Huragok, or Engineers, are one my favorite Halo alien designs. They're certainly one of the most plausible in that they couldn't be mistaken for any known animal phylum. They have a unique physiology and method of reproduction as well. They're described as biological supercomputers and as artificial constructs lacking true tissues and organs. I'm not quite sure what is meant by this. They must have connective tissues to hold their bodies together, something like a nervous system to process information, and muscles to move their bodies. Confusingly, it's also said they have structures that are virtually indistinguishable from tissues and organ systems. My interpretation is that they are a non-cellular form of life: They're composed entirely of organic nanomachines that are arranged into tissue and organ analogs. This is reinforced by the fact that they do not produce gametes that grow into adults. Instead, they replicate by working with one or more Huragoks to literally build a new individual with its parents' combined memories serving as heritable information.

At first glance, one would think their relatively few tentacles would be woefully inadequate for their purpose as dedicated engineers, but the Halo novels explain that each tentacle can split into thousands of cilia, allowing them to manipulate objects on a microscopic scale. The only potential problem I can see with their design is that they use lighter-than-air gasses to float about, which would make lifting heavy objects impossible—something that seems problematic for a creature that repairs machines. Their Forerunner creators had compact antigravity devices that the Engineers could have used to lift heavy objects, so this isn't really a problem within the context of the Halo universe.

Plausibility Grade: A

San'Shyuum (Perfidia vermis)

The San'Shyuum, or Prophets, were the leaders of the Covenant throughout the original Halo trilogy. They're a physically feeble species with a relatively small population and low fecundity. Their physical weakness is due to them originating on planet with relatively low gravity. This is further compounded by a sedentary lifestyle and a genetic bottleneck that occurred when they fled their homeworld. Judging by their hooked toes and vaguely primatoid body plan, an arboreal ancestry would be a plausible evolutionary background for this species.

There's nothing too particularly alien about the Prophets beyond the fact that their "ears" are located on the back of their heads. This is a bit strange, because they would have difficulty determining the direction of a particular sound. The ideal configuration would be laterally positioned and vertically offset ears. They have red respiratory pigment, implying something iron-based, like hemoglobin. They could be mistaken for a mammal if their weird ears were ignored. However, they do not have an overly humanoid body plan or a man-in-a-suit look, so they're somewhat plausible.

Plausibility Grade: C-

Sangheili (Macto cognatus)

I think the Sangheili are one of the best alien designs in the Halo universe and one of the better video game or movie aliens in general. While their body plan is definitely tetrapod-like, it differs in detail enough to be justified as an example of convergent evolution. Other tetrapod characters, such as jaws that evolved from gill struts, are absent. Jaws have evolved multiple times within Metazoa (animals), and never exactly the same way. For example, though cephalopods (octopuses, squids etc.) have rather parrot-like beaks, they overlap in the reverse orientation, have a different muscle arrangement, are made of chitin rather than keratin, and house a radula instead of a tongue. Sangheili jaws aren't exactly like those of any animal on Earth, and that goes a long way in keeping this species from being "lizard men". Their hands are rather human-like, but this is mitigated to a small degree by the inclusion of a second thumb. 

Their physiology is also believably alien, with purple blood and two hearts. In the animal kingdom, respiratory pigments span the entire rainbow. For example, the purple blood of the Sangheili could be due to having a respiratory pigment similar to hemerythrin, which is iron-based and turns violet-pink when oxygenated. Some animal lineages also have multiple "hearts" (cephalopods have three; oligochaetes have five). Sci-fi writers shouldn't use this as a justification for greater durability however. Animal's such as cephalopods may have more than one heart, but they cannot survive the loss of one any more than a human can survive the loss of a major artery.

Sangheili society appears heavily based on the Samurai, complete with a Bushido-like code of honor. One gets the impression that their entire race is composed of warriors, which raises the question as to what a Sangheili math professor is like, or a plumber. Halo sidesteps this problem to a degree, and even directly addresses it later in the series, by showing that non-warrior roles are largely filled by other species, resulting in a sort of species-based caste system. This problem is explored later in the series following the collapse of the Covenant when the lack of diversity in Sangheili society proves nearly disastrous.

It's implied that the Sangheili are sexually dimorphic and that the females remain on their homeworld to fulfill non-military roles. Most males are said to be monogamous, while the most proficient warriors are polygynous and have an "alpha male" status involving preferential access to mates. Based on this, and following the principles of anisogamy, one could expect the males of the Sangheili to be considerably larger, competitive, and risk-prone, as the stakes for mating are so high. This leaves only half of their population to fill non-military roles; consequently, they would probably need a creche system to raise their young, which seems to be the case based on the source material. Overall, their society isn't too particularly alien, but it does have enough nonhuman elements to feel plausible.

Plausibility Grade: B

Unggoy (Monachus frigus)  

The fan wikis, and perhaps the source material, describe the Unggoy in a somewhat biologically unsound way. Firstly, there seems to be some uncertainty as to whether they are arthropods or vertebrates. They would be neither—these are aliens we're talking about. A vertebrate is a member of the subphylum Vertebrata, which in modern phylogenetics comprises a clade defined by evolutionary relationships. Thus, while the Unggoy may have an endoskeleton, this doesn't make them vertebrates. It's possible for an organism to have an endoskeleton yet lack vertebrae, as is the case with echinoderms such as sea urchins. They wouldn't be arthropods either for the same basic reason. The best way to describe them is to say they are bilaterally symmetrical, tetrapodal, metameric, animal-grade organisms, with both an endoskeleton and an exoskeleton. That's a mouthful, so we could say they belong to the clade Monachata and call them monachates, not vertebrates.

Secondly, it's said in the source material that they "breathe" methane, which is plausible, but it would not be analogous to breathing oxygen. The correct term is "methanotroph". The methane would be a source of carbon and energy that would need to be oxidized into something metabolically useful, such as formaldehyde. This means the Unggoy would breathe methane and oxygen, and methane would be a sort of food for them. Since methane is lost in the atmosphere as a result of photochemical reactions, which is why 90 percent of atmospheric methane on Earth is biotic in origin, the methane of the Unggoy homeworld would probably have a biotic origin as well. This is implied in the source material by their swampy homeworld.

Unggoy blood is a bioluminescent blue. Since their mouths and eyes are not constantly glowing, it can be inferred that this only occurs when they are injured. Glowing blood would probably attract the attention of predators, which is actually what some dinoflagellates (a type of single-celled protist) do: They draw attention to animals that threaten them. I doubt this would translate well at higher trophic levels however, since whatever predator might eat a smaller predator would probably eat the Unggoy too. Instead, the Unggoy's blood could be a way to alert other members of their social group to danger visually rather than vocally. Their blood appears to be blue even while not glowing as well; this could be the result of a copper-based respiratory pigment, like hemocyanin, which reinforces the idea that they actually breathe oxygen along with methane.

The available material suggests the Unggoy reproductive strategy is r-selection, i.e. they produce large clutches of low-cost offspring. This makes them useful cannon fodder but also makes it difficult for their masters to control their population. The r-selection strategy is somewhat at odds with the strong bonds they feel for their offspring. While this may help make their exploitation by the dominant Covenant species more tragic, it doesn't make much sense if their young are abundant and easily replaced. This could be reconciled by having the bond Unggoy parents feel somewhat proportional to amount of energy invested into a particular child. For example, Unggoy parents may not feel too upset at the death of newborns, but may be devastated by the loss of a child who had nearly reached adulthood.

Plausibility Grade: B-

Yanme'e (Turpis rex)

Image from
I love eusocial insects, so I'm always happy when a space opera setting has a species based on them, provided they're designed well of course. The Yanme'e aren't bad; however, their biology could use a little more fleshing out. It's conceivable that a vermiform alien lineage could have undergone arthopodization, the evolution of the suite of characters that comprise the arthropod body plan. That being said, we should not expect an arthropodoid alien to have exactly the same type of body segmentation as arthropods on Earth.

An example of the variety of ways arthropods body segments have combined into tagma (Source:
The Yanme'e soldier shown in the image above this article is the most plausible version I've found. Unlike insects, which have three tagma (combined segments with a shared function), the Yanme'e have five: a head, neck, thorax, pelvis, and abdomen. The thorax, pelvis, and abdomen each have a set of legs. Yanme'e workers and soldiers also have six wings mounted on the thorax, with the anteriormost pair hardened into beetle-like elytra. Some of the designs have three pairs of compound eyes rather than one. The non-insectoid segmentation, the presence of six wings instead of four, and the six compound eyes help communicate that these are aliens, not insects. 343 Industries should take this further and add that they have lungs rather than a tracheal system (they're too big for that) and a closed circulatory system similar to those of annelids (worms). Their green blood could be a result of a respiratory pigment similar to chlorocruorin, which is found in some annelids.

Being eusocial, the Yanme'e have a queen, reproductive males, and various classes of workers. I'm not sure if it's clear that the workers consist of non-reproductive females like ants or males and females like termites. Eusociality occurring in an alien species is fairly plausible, given that it has evolved in wide variety of animals on Earth including hymenopterans (ants, bees, wasps), termites, thrips, aphids, beetles, shrimp, two species of mammal, and even a species of flatworm. Their social organization isn't a simple cut-and-paste version of a bee colony either: The queen is immobile and bloated with eggs much like a termite queen, and the males are wingless and actually care for and transport her. Wingless males that remain near the queen suggest that they might exhibit a high degree of inbreeding like thrips and unlike ants and bees. Another possibility is that the males shed their wings after a nuptial flight.

I'm glad to see that while the Yanme'e soldiers are fearless, more coordinated than human soldiers, and obey orders without question, they're not mindless and appear to function well without a queen. They even appear to have ranks, perhaps based on maturity, that imply some sort of chain of command. Too often the queen of a fictional eusocial species is presented as the "brain" of the colony, when in reality, she's closer to being its gonads. There's even some room for emotion among the soldiers, such as jealously, and there are a few "unmutuals" who refuse to cooperate with the rest of the colony. The workers and soldiers are described as being highly intelligent with an unusually strong grasp of engineering, mathematics, and science. In terms of society and behavior, they're one of the better portrayals of a eusocial alien species I've seen.

The person Bungie hired to write the background material on the Yanme'e homeworld, Palamok, screwed up: For some reason they decided that the likely homeworld of a giant, flying insect analog should be a planet twice the size of Earth with 2.2 times the surface gravity... why? Arthropods are generally small animals for a reason. To make things worse, the Yanme'e fly... and do so with antigravity devices attached to their exoskeleton. If they need antigravity devices to fly in 1g of gravity, how could they have evolved flight on a world with 2.2 times Earth's surface gravity? These two things do not make sense together. 343, if someone from your staff is reading this, there is an easy way to fix it: Make Palamok the name of a double planetary system, one with a larger body that is twice the size of Earth and another closer in size to Mars. Say that the Yanme'e's ancestors evolved on the larger world as small, insect-like organisms, but were somehow transplanted onto the smaller moon where they evolved to be much larger.

I'll ignore the homeworld issue, since it seems to be in contradiction with how they're described elsewhere in the canon, such as how they rely on antigravity devices to fly. It's also something that could be fixed fairly easily. Overall they're pretty good "bug men", but they could stand to be a little more alien in design. A very non-humanoid appearance could have made them creepier, more unnerving, as well as more realistic. 

Plausibility Grade: C

Lekgolo (Ophis congregatio)

The Lekgolo are an excellent example of how to make an alien genuinely alien. Despite the humanoid appearance seen above, the Lekgolo are actually colonial, lithotrophic, vermiform (worm-like) organisms that form highly motile, strong, sapient colonies. Individually, they're unintelligent, but they can link together to form a progressively larger and intelligent neural network, essentially an enormous composite "brain". As a colonial mass of muscular worms, the Lekgolo can take a variety of shapes, ranging from humanoid soldiers to massive spider-like tanks, by attaching themselves to a makeshift skeleton. 

Based on the available background material, the Lekgolo seem to be at least partly lithotrophic, meaning they use an inorganic mineral substrate, such as iron or sulfur, as a source of electrons and energy. This isn't a very efficient means of energy production, and on Earth, this occurs only in Bacteria and Archaea, so the Lekgolo could be mixotrophic, meaning they use a variety of energy sources, not just inorganic substrate. Their mineral diet was substantial enough, however, to allow them to eat technological artifacts left by the Forerunners, which triggered a war with the Covenant early in its history. Their blood is yellowish or orange. This suggests their blood contains high amounts vanabins, which are vanadium-binding metalloproteins. Vanadium is a rare element found in several alloys, so this fits with their artifact-eating habits. We don't really know why some real-world species concentrate large amounts of vanadium in their blood. Oxygen-carrying doesn't seem to be the reason, though it could be in an alien species.

Plausibility Grade: A+

Kig-yar (Perosus latrunculus)

I love these guys, but they're not realistic aliens as presented; there may be ways to fix that however. A few things for the wiki writers first: If they're aliens, they're not birds or reptiles. Furthermore, birds are dinosaurs, so it's probably more accurate to say they're dinosauroid (meaning dinosaur-like) in morphology, which they very much are. Many non-avian dinosaurs possessed feathers and beaks, so discussing the Kig-Yar in terms of being more avian versus reptilian isn't really accurate. The Kig-Yar are feathered, scaled, bipedal, have tridactyl hands, some have beaks, they're oviparous, they brood their young, and they have hollow bones - all characteristics of dinosaurs. Their young even have downy feathers! The only thing that suggests an alien origin is their purple blood. 

There are three Kig-Yar subspecies shown above going left to right: Ruutian, T'vaoan, and Ibie'shan. The Ibie'shan should be considered members of a separate family at a minimum, because their head morphology, which is more crocodilian in appearance, is considerably different from the other two. All three are so dinosaurian that I just cannot view them as aliens. One solution that would be quite interesting in my opinion, and "lore friendly", would be to posit that they are not aliens at all, but are rather a lineage of theropod dinosaurs that were translocated, or uplifted, over 66 million years ago by the Precursors, who were active in the Galaxy for billions of years, seeding planets with life. This is reinforced by the fact their homeworld, despite being a moon orbiting an ice giant, even resembles a Mesozoic Earth and is only 40 light years from our solar system. The only problem is their purple blood, but this could be explained away as being a result of genetic engineering, perhaps to adapt them to the atmosphere of Covenant ships.  

Plausibility Grade: D (if they're true aliens)

Jiralhanae (Servus ferox)

The Jiralhanae, or Brutes, are clearly very mammalian in appearance. I think it's unfortunate that in many works of science fiction, the furry, brutish species is so often modeled after cats, bears, or apes, while saurian species are always scaly. In reality, many dinosaurs were fuzzy, even some of the big carnivores, and some mammal ancestors may have been scaly. In some of the Halo games, shaved portions of the Brutes appear scaly, and I think it would be a good idea for 343 to incorporate this in future designs.

I like the fact that they come from a high-gravity homeworld. There is growing evidence that "super Earths" may be more common than worlds the size of our planet, so at least some alien species should originate on such worlds in works that involve many aliens. Unlike the Yanme'e, the Brutes actually look like they could support their weight on such a planet. 

Their social structure is a fairly unoriginal pack hunter culture. The detail about pheromones communicating emotions is something that could be expanded upon to make them a little more interesting however. Another issue is that I can't find any information about Brute reproduction or sexes, which I think presents another opportunity for the writers. Let's consider what we do know: They possess a pack hunter culture in which "alphas" dominate the pack, and a subordinate can only displace the alpha with a duel to the death. Mature Brutes eventually stop broadcasting their emotional state to their pack members, suggesting some physiological change as they age. Female Brutes seem to be absent. With all this in mind, I would make them protogynous sequential hermaphrodites, meaning they are born female and become males shortly before or after they achieve alpha status. The alpha's pheromones, along with those of the other pack members, could have regulatory function in controlling the sex of pack members. By combining reproductive behavior more commonly observed in fish with a creature that looks mammalian, it would help communicate that these are aliens and not simply beast men. One potential problem with this is the fact that, if I remember correctly, they refer to each other as "brothers" and generally use male pronouns. Since their speech is being translated, this could be because their language is mostly gender neutral while English is not, so a term like "pack sibling" becomes "brother" when translated. 

Plausibility Grade: D

Sharquoi (Drinol)

Virtually nothing about this species has been revealed, so I can only comment on their appearance. While they have a rather humanoid body plan, their head is convincingly alien, with a single, large compound eye reminiscent of those of copepods, and a unique jaw morphology.

Plausibility Grade: B


The Forerunners are the creators of the Halo rings and many other megastructures, including Dyson spheres and shell worlds. They were wiped out by the Flood 100 thousand years ago, and passed down the "Mantle", a role of galactic stewardship, to Humanity. While the Forerunners come in a variety of higher "mutant" forms, in their most basal state, they appear very human, with the only real difference being found in their ear and nose morphology. If they're intended to be aliens, I would give them an F; they're little different from Star Trek rubber forehead aliens. However, within the canon, it's suggested that the Forerunners are genetically related to humans in some way. This strongly implies a common ancestry. It's also said that they were seeded on their homeworld by a much more advanced species, the imaginatively named Precursors, 15 million years before humans evolved. If they're related to humans, the simplest explanation is that they're descended from early hominids, making them more distantly related to humans than orangutans but more closely related than gibbons. This is a semi-plausible way to have hominid "aliens" in a science fiction setting. It makes far more sense to have the humanoid aliens who evolved from Earth hominids, but were translocated somehow, than to say humans descended from aliens. Basically, the writers of the Halo canon avoided the biggest biological error in the film Prometheus. Humans are demonstrably related to other primates here on Earth. We did not come from space. 

Plausibility Grade: N/A (not true aliens)

The Flood (Inferi redivivus)

The Flood is a difficult one for me to grade. On one hand, the species is a convincingly alien superorganism with a complex life cycle reminiscent of some real-world parasites, the life cycles of some parasites such as malaria and liver flukes being examples. Some parasitoid wasps even employ viruses to alter the behavior of their host, effectively turning them into "zombies". On the other hand, the Flood is a sci-fi "omniparasite", one that can infect a plethora of unrelated species. Real parasites co-evolve with their hosts over millions of years and are often limited to one or two them. The fact that it's difficult for real parasites to infect new species that, compared to an alien, are virtually identical in terms of chemical composition, makes it hard to believe any such super parasites could exist somewhere in the Galaxy. The Halo canon includes something of a handwave to explain this: Flood super cells. Supposedly, the Flood have cells that can break down virtually any cell they contact, analyze them, and then mimic them, thus consuming their contents as food while simultaneously acquiring the information stored in the host's nervous system. I guess this would be the biological equivalent of "uploading" a mind by incrementally replacing and replicating the function of each neuron. The Flood would be fairly plausible if it were limited to one or two related species, but the "omniparasite" aspect bumps it down from an A to a B. 

Plausibility Grade: B


They're just humans in makeup - 343 Industries, why would you do this?

Plausibility Grade: F

Primary Halo references for information and images

Saturday, January 21, 2017

Worldbuilding Review: The Doom Universe

The Doom universe is a bit unusual in the world of Aliens-inspired intellectual properties. Unlike Aliens, Halo, Dead Space, Mass Effect etc. the monsters aren't eldritch abominations from space, they're literal demons from Hell. Conceptually, the game is Evil Dead meets Aliens. 

According to Gallup polls, somewhere between 60 and 70 percent of Americans believe Hell is real, and some believe it's an actual place that one can go, not a state of being or a metaphor. Of course, the game Doom runs with the idea that Hell is an actual place, complete with fire, brimstone, and bloody viscera in another "dimension" that one can reach—ideally with a double-barrel shotgun.

Spoilers for both Doom 3 and Doom 2016. 

The Premise:

In the 22nd Century, humanity has colonized the Solar System, and the ruins of an ancient civilization were found on Mars. The United Aerospace Corporation—a Weyland-Yutani analog—reverse-engineered some of the Martian technology and deciphered some their theoretical physics, leading to new forms of energy production, teleportation, and methods of faster-than-light travel. Doom 2016 expanded on this further with the UAC discovering a spacetime "tear" in a Martian trench that provides a fount of exotic energy called "Argent plasma". Unfortunately, the UAC ignored the many warnings the Martians left, and they soon learned that the teleporters open wormholes to Hell (called hellholes in the game), thereby letting demons invade the UAC facilities and eventually Earth, unless of course the player—a nameless tough-as-nails space Marine—can stop them first.

There is actually some theoretical basis for "higher dimensions" and parallel universes, such as brane cosmology. Our 3-dimensional universe may be restricted to a "membrane" that exists within a "bulk", a higher-dimensional space often called hyperspace or subspace in science fiction. However, the term "dimension" is usually misused in science fiction games like Doom. The higher dimension (probably 5th in this case, the 4th being time) isn't an alternate universe, it's how one would get there. For example, if we removed a dimension so that 3-dimensional space were reduced to the 2-dimensional surface of a sphere (the "brane" we live on), the "higher dimension", or bulk, would be the 3-dimensional volume within the sphere. Doom's teleporters would work by creating a shortcut through the sphere from one side to the other, like a wormhole through an apple, hence the name. Doom's Hell could be a void—imagined in Doom as a sort of spacetime prison for demons—that the teleporter shortcut runs into, allowing the monsters it contains to escape like liquid from a punctured container. Coincidentally, this resembles Dante's medieval conception of Hell which was believed to consist of concentric circles beneath the surface of the Earth. id could run with this dimensional analogy and even include the Nine Rings of Hell (alluded to in-game) by making them a series of nested, concentric "spheres" within hyperspace. The most recent game has "realms" of Hell that can only be accessed through portals, so the basic elements are already there for the developers to expand upon. Some of the architecture in Doom 3 seems to incorporate higher dimensions, as the player will often enter buildings that are much larger on the inside than on the outside, or pass through portals that teleport the player instantly from one point to another within the same building. If id borrowed some of these concepts from cosmology, it might give the series a degree of verisimilitude. Though, if the 2016 entry in the series is any indication, id seems to be moving away from the serious, "realistic" tone of Doom 3 and in a self-aware, deliberately cheesy direction. 

The rings of Dante's Inferno (image from Wikipedia)
The demons of Doom are mostly corporeal, biological entities. In the more recent games, you can explore labs where you'll learn demons are not only carbon-based organisms, they also have DNA with the same nitrogenous bases as our own and recognizable internal organs. In the recent 2016 reboot, id takes things even further, going so far as to discuss demonic embryogenesis, parasitism, evolution, and histology, making the demons practically extradimensional aliens (which is why they're being discussed on my blog). This is a fun approach in my opinion. Rather than saying science can't explain it and invoking magic, id did the opposite by having the UAC not only come up with a new branch of quantum physics to explain Hell's seemingly magical powers, but also ways to harness them for industrial applications and energy production!
This guy would probably pass as an alien in another sci-fi setting (image from the Doom Wiki)
Even Heaven and its angels seem to get a science fictional, quasi-naturalistic explanation. While Hell in the Doom series is presented as the medieval Christian sort, complete with hoofed demons, the Nine Circles, pentagrams, and upside down crosses, God and his angles are conspicuously absent. There is a singular mention of "Seraphim", the highest order of angels, in the most recent game's codex, but it's implied they are actually potentially dangerous, quasi-insectoid, Lovecraftian entities native to another "realm" or planet. There are no priests banishing demons with crucifixes, only marines shooting horned demons in the face with assault rifles.

In place of a Garden of Eden origin for humanity, we find that anatomically modern humans are at least partly descended from an extinct Martian civilization, which is a backstory rather reminiscent of Halo, Alien, Battlestar Galactica and other "ancient aliens" stories. I find the "ancient astronauts" trope annoying, personally; it's rooted in the myth that human origins are still a great mystery, when it's rather obvious that humans are primates who evolved on Earth. However, I find it a little more tolerable when the same fictional universe has what appears to be the Biblical Hell within it—it would make less sense if there wasn't some sci-fi connection to angels and gods too. Evolution and these ancient aliens ideas aren't incompatible, as Halo showed. Our species is much older than many realize, at least 200 thousand years old. There's more than enough time for some "uplift" scenario to produce a prehistoric human civilization on another world. Applied to a film like Prometheus, this would mean the Engineers came from us rather than the other way around.

Doom 16 expands on this ancient astronauts idea further by revealing the apparent fate of the Martian Civilization shown in Doom 3. While originally announced as a reboot, Doom 2016 appears to be a "stealth sequel", or soft reboot, as player's can find artifacts, relics, and tablets that allude to the fallen Martians of the prior game. In Doom 2016 the player character, known as the "Doom Slayer" by the forces of Hell (the game tries to be Metal af), seems to be an ancient astronaut, or in this case, and ancient space marine. It's implied that he was a Martian warrior who migrated to a world called "Argent D'Nur", a world that was later conquered and assimilated into Hell. Some fans speculate—based on the appearance and markings on his armor—that he is the Marine from the original game who has been either universe jumping or time traveling like Ash from the Evil Dead films. Which actually seems rather fitting given Evil Dead along with Aliens was the original game developer's source of inspiration.

Image result for Doom slayer doom wiki
Doom Slayer on an ancient demon wood carving battling alongside his space knight comrades (image from Doom 2016) 
With the success of Doom 2016, id can expand the Doom universe further. I hope they realize they can explore other places in the Solar System before jumping to Earth. There are the asteroid-like moons of Mars, Phobos and Deimos, the settings of the original game. Jupiter's volcanic moon, Io, which was one of the locations in Final Doom, would be awesome rendered with modern graphics. There is also an exoplanet in the series called Tei-Tenga that could be depicted as the real world, X-ray-blasted, tidally locked, red-dwarf-orbiting, Proxima Centauri b, a planet "only" 4.22 light years away. A portal linking Sol to Proxima Centauri could be another source of an invasion. Is Hell only associated with Earth, Mars, and this mysterious "Argent" world? Does each galaxy have its own Hell? The Universe? Multiple universes? What if the plethora of different demon forms were originally alien species that were conquered? Over time id could expand the scope of Doom to be on par with Halo while still retaining its unique premise.

—For an accessible and enjoyable book that explores bulk beings, travel through higher dimensions, and wormholes, I recommend Kip Thorne's The Science of Interstellar.