Tuesday, August 28, 2012

Alien Plausibility Review: Xenomorph from the Alien Franchise

Image lifted shamelessly from wikipedia.org
The aliens of the Alien Franchise are formidable, intense and frightening organisms. They are extremely territorial, intelligent and uncontrollable. And they are very popular. Thus far there have been 7 movies about them, along with various comic books, novelizations and video games. Film makers went to some lengths to create a creature based on the general rules of biology. Indeed, the alien appears to be a biological creation through and through where as movie and television aliens from yesteryear usually ignore principles of biology, as well as the laws of physics and the periodic table of elements. But just how plausible an organism is this alien, which is referred to as the Xenomorph for lack of a better name? Is it possible for a creature like this to exist somewhere in the galaxy or universe? Let's examine the issue using the Alien Plausibility Review, or APR. There are 8 categories for an APR: Evolution, Originality, Chemistry, Physics, Biology, Behavior, Intelligence, and Presentation. Each category is worth up to 1.00 point and can be scored in quarter units (like 0.25, 0.50, and 0.75). A total score of 8.00 is possible, which indicates that the alien is a perfectly plausible organism. In addition to AstroExo's score, which is explained in the post, you have a chance to contribute to a CrowdScore. If you disagree with some aspect of the scoring, then leave your own scores and reasoning in the comments section. After a time, an average score will be calculated from all of the scores offered from the crowd and will be posted in the article. Now, about the Xenomorph...

Evolution: How plausible is the evolutionary path of this creature? In this section, we try to determine the evolutionary significance of the Xenomorph's features. Firstly, let's take a look at its body plan. While it does generally rock the standard quadruped body plan, it can switch to an upright posture in much the same way a chimpanzee might. It can be argued that this feature is too close to that of Earth-life. What does "too close to earth-life" mean? It means that no two evolutionary lineages will ever be the same (however, there is some overlap, called Convergent Evolution). Despite this concern (or perhaps because of it), the film's creators have given the Xenomorph a certain mimicry ability where it takes in some of the characteristics of the host (the Xenomorphs are parasitic in that they incubate their young in other organisms). This ability can be seen several times throughout the franchise and is selective in nature (we don't know if this sort of thing is AS selective here on Earth, but it does happen). Due to this mimicry ability, the Xenomorph body plan can change from one generation to the next, depending on its host organism. At best guess, we figure this to be a hyper form of Horizontal Gene Transfer

The Xenomorph famously has acid blood and can spit an acidic solution at victims. Several organisms on Earth can spit at targets for various reasons, most famously the spitting cobra, which is where the Xenomorph's ability was probably lifted. The acid blood, however is much harder to explain and represents the most 'alien' quality of the Xenomorph. Acid blood, theorized as hydrosulfuric acid, is not a quality seen in biology on Earth. However, while it is not specifically mentioned anywhere in the Alien franchise, it is possible the acid might not be the blood of the organism, but instead a protective feature to ensure that the Xenomorph does not become someone else's prey. For example, ladybugs and poison frogs evolved bad taste and poison to deter predators from eating them, which is a feature called Aposematism. Having evolved this feature with hydrosulfuric acid instead of a bio-toxin, the acidic solution would be kept and maintained in specialized organs and transport vessels in the Xenomorph's body and wouldn't hurt the creature the same way that stomach acid - HCl, KCl, & NaCl - doesn't kill you because of your specialized stomach lining. 

Other qualities, such as the tail and the exoskeleton, are clearly lifted from examples on Earth, but since the Xenomorph has an accelerated, selective version of Horizontal Gene Transfer, it is hard to say that many of these features are permanent. Overall, the creativity of this alien is apparent and uses a thoughtful, and terrifying, mix of known biological features than can be found in a variety of carbon-based Earth-life, leading one to conclude a plausible evolution. Score:
AstroExo: 1.00    CrowdScore: -.--

Originality: Among the fictional aliens of the world, the Xenomorph stands out as one of the first to embrace the rules of biology, as opposed to kinds of aliens that are telepathic or endowed with superpowers. While many features of the organism are found in nature, they are combined in an interesting way to form a wholly unique animal. Especially considering the acid blood, a possible version of Aposematism and the hyper-Horizontal Gene Transfer, the Xenomorph is a very original creation in light of previous Hollywood aliens. As a kind of testament to its originality, it has been copied countless times in film and television. Score:
AstroExo: 1.00   CrowdScore: -.--

Chemistry: The movies of the Alien franchise do not delve too deeply into the scientific reality of the Xenomorph, despite building the Xenomorph on some biologically-endowed grounding. There is nothing obviously wrong with the organism's chemistry...it seems as if it is a carbon-based lifeform that behaves according to known biology. There is nothing wrong apart from the acid blood, that is. It is never mentioned in the movies exactly what the blood is made of, only that it is highly acidic. Once, in the DVD extras of one of the movies, the blood was theorized as a kind of hydrosulfuric acid, which is a relatively weak acid yet toxic for most earth-based life. However, can it eat through a metal bulkhead quickly? Hard to say. Other acids can react with metals of various sorts (here is an example of Hydrochloric acid eating an aluminum pull-tab) as well as non-metal materials (here is an example of Sulfuric acid eating through a sponge). It is more likely that the movie makers felt the idea of acid blood was terrifying and implemented  this condition without considering just what kind of chemistry is involved. Since there is some possibility of a potent-enough acid, some score is possible. However, down a quarter for being cloudy on this one bit of chemistry. Score:
AstroExo: 0.75   CrowdScore: -.--

Physics: Does the alien violate the laws of physics? The alien violates no known law of physics. There are no telepathic powers, no time travel (we are on to you, Doctor Who), no known laser beams or other energy discharges. There does seem to be an innate awareness that the Xenomorphs have of each other, especially regarding the Queen. While this does seem improbably telepathic, it is best explained by the possibility of pheromones. Additionally, the Xenomorph doesn't mysteriously fly like Superman might (Superman = terrible alien BTW). The alien behaves according to the basic principles of biology and chemistry, apart from the acid blood thing, both of which can only be possible through normal physics. It has life cycles, growth rates, and sensory perception on par with many Earth organisms. It can be killed in a manner consistent with its known biology and abilities. Score:
AstroExo: 1.00   CrowdScore: -.--

Biology: Many different concepts of biology make their way into the construction of the Xenomorph. Exoskeletons are a normal feature of most of the earth's multi-cellular organisms. The body plan, while certainly practical, seems too close to that of Earth's evolutionary heritage. However, the producers explain away this issue, probably by accident, by indirectly evoking a very cool and exotic feature known as Horizontal Gene Transfer, which occurs right here on Earth. The acid blood, even though the chemistry is questionable, could possibly be a form of Aposematism. Major consideration is given to these biological features. HOWEVER...the degree to which Horizontal Gene Transfer exceeds anything that is found on Earth. And most importantly, those organisms that are capable of this type of gene exchange evolved the ability in concert with very specific target species. Raflessia arnoldii, the world's largest flower, is an organism capable of Horizontal Gene Transfer...but it can only take genes from one particular species of vine that with which the Raflessia forms a parasitic relationship. That relationship undoubtedly took quite a while to cultivate, on the order of thousands to possibly millions of years. So, while HGT is a cool, exotic alien-style concept, it is highly unlikely that the Xenomorph will be capable of such a high degree of HGT (or any degree at all) in the short, episodic span of time it has experienced with its human hosts. To say nothing of the compatibility of the human and Xenomorph DNA!! The DNA of both organisms (human and Xenomorph) would have to have shared an evolutionary heritage in order to be compatible. We don't even know that the Xenomorph is sporting a DNA encoding mechanism. So, down a quarter because of too much and too quick HGT-like capabilities and down another quarter to reflect the fact that the human and Xenomorph DNA shouldn't even be capable of interaction. Score: 
AstroExo: 0.50   CrowdScore: -.--

Behavior: The Xenomorph's behavior is territorial and aggressive, which can be compared to many kinds of Earth-based organisms, such as predatory cats. A lone mountain lion or grizzly bear can present as much a threat against an unarmed target, all other things being equal. The Xenomorphs also engage in some kind of collective society, in much the same way that ants or bees do. This collective behavior is probably arranged for the purposes of reproduction, and involves a division of labor (most notably with the Queen Xenomorph), which is also familiar territory for ants and bees. And, much like ants colonies, the Xenomorphs appear able to sense each other. This is likely the work of pheremones or pheromone-like systems, which ants utilize greatly. In addition to these behavioral qualities, the Xenomorph's reproductive cycle involves a parasitic stage, where the facehugger implants an egg or larvae into another living organism - which will later hatch, horrifically. Many organisms on Earth go through staged development, such as caterpillars and butterflies. Not rare among the Earth organisms are those that must get inside another organism in order to perpetuate themselves. The Zombie Ant Fungus not only hatches from inside and kills a target host organism, but it alters the host organism's behavior in order to maximize reproduction. Score: 
AstroExo: 1.00   CrowdScore: -.--

Intelligence:  The Xenomorphs display a level of learning and problem-solving that is probably on par with primates of Earth. In various movies, the aliens appear to learn about their environment and alter that environment to meet certain objectives, such as gain access to human prey. In Alien Resurrection, some of the Xenomorphs display a learning style based on experience when some captive Xenomorphs immediately cease a threatening display when their human handler threatens to retaliate with an unpleasant punishment. While intelligence among aliens, generally, is difficult to guess, the level of intelligence displayed by the Xenomorphs is more suited to the collective, hive-like existence they seem to be used to. This style of intelligence is also something we see on Earth in various species, including dolphins, dogs, primates...but definately not on a level of human. This level of intelligence is fairly consistent throughout the franchise. Score: 
AstroExo: 1.00   CrowdScore: -.--

Presentation: The overall presentation of the Xenomorph is generally excellent. While the movies of the Alien Franchise are intended to be suspenseful and frightening, from the viewer's point of view it does feel like simply being around a loose wild animal. Although many of us would not know what it is like to be stalked by a large predator, its probably strikingly similar to some of these movies. Take Alien 3, for example. It appears that only one Xenomorph is loose in the prison compound where Ripley's character has landed. The organism hides, evades, strikes only when it feels it has the upper hand...these are elements that any large mammalian predator would probably exhibit. Other considerations must include the acid blood and the mimicry ability (possible Horizontal Gene Transfer). The mimicry ability is almost beyond explanation, but is honestly muted during the course of the franchise (unless you get into Alien Resurrection and the Alien vs Predator films). So, it isn't an overwhelming power most of the time. The acid blood is quite an issue, and although it is chemically questionable, this ability seems to be an minor feature for the creature. The Xenomorph really wins against its assailants by being territorial and aggressive. Even if it had only teeth and speed, the movies' protagonists might not react too differently to the organism. Overall, this alien is thoughtful on the rules of biology and is one of the first of many Hollywood aliens to pay major tribute to the SCIENCE in science fiction. Score: 
AstroExo: 1.00   CrowdScore: -.--

Overall Score:


  1. Although this is already a pretty good score, my only comment would be to say that the universe is infinite. The very nature of an infinite universe is that all eventualities are realised. No matter how small the chance of something occurring, it WILL occur in an infinite universe. Therefore, all the sections above have a rating of 1 and the overall score must be 8.

    1. Hard to ignore this logic. I'm sure Douglas Adams might have a thing or two to add to this.

  2. At one point, I did read an article regarding the proposed biology of the xenomorph, and the way they explained inherited characteristics from the host orgainism was rather interesting. Basically, they were saying that the facehugger creates the embryo in the same way that a virus invades a cell - the facehugger is somehow able to alter the host's DNA so that the body creates the xenomorph embryo itself. That way, the body doesn't recognize the "antigen" until it's too late.
    I'm not a biology expert, but I thought that was a bit interesting - also, although they're not always considered "living," there are plenty of extremely adaptable viruses that can affect a wide variety of species - who's to say that the xenomorphs would not have evolved such that they could adapt their lifestyle to meet environmental change?

  3. I did enjoy this article, however the way you compared the xenomorph species to species sound on earth bothers me. First off they are not from earth, and second this makes me feel like you are narrow minded. Just because a species is nothing like that which we find on earth doesn't mean it can't exist. In this universe there is no way earth holds all forms of life; it only has all known forms, for now. And also I want to discredit your rating process one minute you say it resembles life of earth too much, so it can't exist, then you go on to compare it to earth life saying that's why it could exist. How can it not exist because its like life on earth, but exist for that same reason.

  4. However I do not want you to feel like you Dont have valid points because you do, and your rating process for the most part is a great one