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The Cladistics of DOOM

On 10 December 2__3, the UAC bases Phobos and Deimos were overrun by unidentified combatants. Footage of the events were captured by a Spacemarine operating the T.A.G.G.A.R.T. combat system, however, due to the several metric tonnes of weapons and munitions, there was only room for a 256 color 480×360 Steadicam. Despite the limited resolution, the bright, colorful graphics captured numerous remarkable morphological and behavioral traits of the “alien” or “demon” invaders. Type specimens were never collected from the now-abandoned bases, and as such, this footage, along with a few cultural depictions, remains the only evidence of the invaders.

55 morphological traits were recorded and included head/torso fusion, horn morphology, exposed brains, paired posterior sphincters, flight et cetera. There were 11 additional traits detailing behavior, 39 relating to sounds and 44 detailing toughness, size, reaction time and estimated mass. In all, there were 149 traits (32 multi-state) and 11 apparent taxa. The program MrBayes was used to analyze the Standard data and was run for 1,000,000 generation, finishing with an average stdev of split freq of 0.002921 and a TL PSRF of 1.000. The most parsimonious tree is as follows:


Perhaps the most surprising clade (bootstrap value of 100) is that consisting of the seemingly-disparate “Lost Soul”, “Cacodemon” and “Spiderdemon”. The latter two share the highly unusual trait of head/body fusion, whereas the “Soul” lacks any evidence of a body at all; its presence in the group could be the result of long-branch attraction. It is also notable that the “Spiderdemon” has extensive cybernetic modifications, so knowledge of its original state (if any) could significantly change its placement. One clade of horned, digitigrade “demons” (“Cyberdemon”, “Baron of Hell”, “Demon” and “Spectre”) receiving surprisingly low support (bootstrap value of 63) for unknown reasons. Also curious is that the most basal “demon”, the “Imp” is also the most humanoid, raising the question of what sort of relationship these aliens have with Homo sapiens.

A second incursion event occurred on 30 September 2––4, this time on various Earth locations. Steadicam footage was of similar quality to the first event and managed to record 7 additional taxa. The number of traits was expanded to 201, with 33 being multi-state. MrBayes was once again used to analyze the Standard data and run for 1,000,000 generations, ending with an average stdev of split freq of 0.006850 and TL PSRF of 1.000.


Interestingly, the position of the “Imps” is now closer to the horned, digitigrade “demons”, with two humanoid taxa (“Arch-Vile”, “Mancubus”) now occupying and unresolved position between the “former” humans and other demons. Interestingly, one taxa (“Revenant”) with some human-like traits (especially clothing and weapon use) is not a member of this polytomy. Also interesting is that the position of the “Lost Soul” is essentially unchanged and in fact more highly resolved with the additional taxa. The sister taxa of the “Cacodemon”, the “Pain Elemental”, is highly similar in being a volant, cyclopian entity with head/body fusion, although has “Spiderdemon”-like arms, “Cyberdemon”-like horns and bizarrely spits out “Lost Souls”; horizontal gene transfer seems like a likely explanation for this hodgepodge.

There are reports of a third incursion on a Mars base, however the high resolution footage is unfortunately far too dark to be of any use. There are projections that in a few years a fourth incursion will occur, so I advise future researchers to grab their double-barreled shotguns, strap a flashlight to the top, and bag some type specimens.

I’m not making these numbers up: here’s the data sheet. I can’t upload .nex files for some reason, but they can be easily recreated using that data. I should clarify that this isn’t phylogenetics — the study of evolutionary relationships — however, it is still cladistics — grouping based on shared, derived characteristics. I suppose ideas can evolve as designers swap and redesign ideas, and it does seem that cladistics can group them reasonably well. Of course, there could very well be some severe methodological flaws that I overlooked or a better method (phenetics?) but, eh, it’s April 1st.

This post owes a lot to the Doom Wiki, Spriters Resource, and of course the folks at id Software who made the games.