On The Form of Extraterrestrial Visitation

Some particularly gruesome incarnations of the alien invasion scenario have flooded our movie theatres over the years.  Hollywood and, by extension, Western culture, has been obsessed with the subject of violent contact with extraterrestrials for decades.  Even before the advent of moving pictures on the silver screen, Orson Welles presented his listening audience with a fright they never forgot, in his adaptation of H.G. Wells’ classic novel The War of the Worlds.  One thing Hollywood has made clear is their caricature of humanity’s fear of visitation from another world.

You must be familiar with the story: after a miraculous arrival, wrapped in mystery and awe, one question teeters on the lips of every man, woman and child…what are their intentions?  Shortly after, an all-out war ensues, pitting mankind against an unknown and enigmatic foe whose technological reach far exceeds our own.  And with a great loss of life and an epic struggle worthy of Hollywood production, humanity ultimately prevails, whether by military might, universal cooperation, or by the mysteries of nature, either driving the alien marauders from our skies or bringing their hulking ships crashing onto our lands.

Even among those unable or unwilling to distinguish fiction from reality, many have speculated about what form such a visitation might take.  Ultimately, such speculation becomes a prediction (however unprovable) about not only the existence of, but the nature of extraterrestrial life in the universe.  The sciences of Astronomy and Cosmology and Theoretical Physics have given us glimpses of what may be elsewhere in the cosmos.  They speak of the probability of organic life being spread throughout our galaxy and beyond.  They speak of the likely development of such life and the best-case chances of it developing to some point that we might call it intelligent.  And in fact, learned people, such as Stephen Hawking, Carl Sagan, Brian Green, and Chris Impey, may be the best theoretical chance we have of defining exactly what or who we might face in the deep, dark void of space.

Science suggests that microbial life may indeed be abundant in the universe, and that the conditions needed for complex life – intelligent life – to evolve are much too stringent and fleeting to have yielded to many more than a small handful of races in the entire history of the universe.  This has been said to be a somewhat narrow view, with detractors pointing out that intelligent life need not even be recognizable to humans. But if we cannot recognize intelligent life when we encounter it, then its existence is, for all practical purposes, irrelevant to us. We might already be surrounded by it and remain entirely unaware. 

So, as can be seen, the field of speculation that surrounds the possibility of extraterrestrial life in the universe is somewhat muddy, and even still, most mainstream scientists refuse to discount the possibility that intelligent life might exist elsewhere, adding the caveat that the question is not simply of where, but of when.  But if we can agree that the possibility exists, can we speculate on the form of such life?

This is a highly complex subject indeed, far more so than any science fiction writer is able or willing to admit. So, for the sake of convenience, I will only be discussing a small portion of the nearly infinite number of variables in question.

On the question of what they would look like, we’re faced with a multi-faceted problem, for the form of the visitor will dictate much else about the nature of their visit. In the language of science, there are fundamental boundaries to what matter can do and how it can behave, and these are imposed by the laws of physics. The work of scientists such as Albert Einstein and Stephen Hawking has helped establish that these laws are universal: gravity operates according to the same fundamental principles throughout the universe, the speed of light imposes a fundamental limit on the transmission of information, and even the direction of time has a preferred orientation, as described by the second law of thermodynamics. 

More controversially, though, I would argue that some, if not many, of the natural processes that govern life on Earth should also apply to life elsewhere in the universe. In particular, I suspect that some form of evolutionary process is unavoidable. If an extraterrestrial organism reproduces, and its offspring inherit characteristics that vary from one generation to the next, then those characteristics will inevitably affect the organism’s ability to survive and reproduce. Over sufficient time, those differences should accumulate, producing adaptation and change. The precise mechanism need not be identical to that which produced life on Earth, but the underlying principle—that life changes in response to the conditions in which it exists—would seem difficult to escape.

This may seem obvious, but it is a more consequential assumption than it first appears. Evolutionary biology is not normally considered a universal law in the same sense as gravity or thermodynamics, and we have no extraterrestrial examples with which to test the proposition. Nevertheless, it seems reasonable to suppose that evolution, or some broader process incorporating the same fundamental principles, is a consequence of life itself rather than an accident peculiar to Earth. If this is the case, then extraterrestrial life will likewise be subject to the never-ending process of evolutionary change, and its present form will be the result of an evolutionary history potentially stretching back millions or, more likely, billions of years.

If we can reasonably assert the above, then there are some automatic assumptions that can be made about their form.  Chiefly, that they would be a corporeal entity, with mass and shape. And, less confidently, we might predict sensory organs, limbs of some kind and locomotive abilities. This, of course, does not speak to the value of such form – we could not hope to predict bipedalism (walking on two legs), or even quadrapedalism (four legs) or any variation thereof, since the specific result of the evolutionary process on any foreign entity would be entirely dependent on their own alien environment.  If the natural conditions of their world favoured the selection of octopedalism or even tripedalism, it would inevitably follow that our ET visitors would conform to that nature.  The same would apply to sense organs, and even the configuration of body parts – one could equally expect to find a tripedal alien with no head and a mouth on its elbow (if one could identify its elbow), just as readily as a bipedal visitor with a telescopic neck, whose belly glows and whose finger lights up whenever the plot requires it. 

Further, it is entirely conceivable that such alien visitors could have evolved biological mechanisms and processes for purposes that we would find truly alien. One can imagine many such mechanisms: something analogous to what we might call psychic abilities, extraordinary regenerative capacity, or even the production or emission of materials entirely unknown to terrestrial biology. The possibilities are limited, at least in principle, only by what the laws of physics and chemistry permit.

This does not mean, however, that such abilities would have evolved specifically to aid or hinder human beings. An alien organism could not have evolved an adaptation specifically suited to human physiology if humanity had played no part in its evolutionary history. Its adaptations might nevertheless have profound and entirely unforeseen effects upon us. A toxin, pathogen, or other biological mechanism need not have evolved for humans in order to affect us.

The underlying point is simply that Hollywood’s predictions have generally pandered to an anthropocentric notion of alien form: typically bipedal, or, in more recent cases, tripedal, and possessing a discernible psychology to boot. We have imagined extraterrestrials not merely as creatures that look vaguely like us, but as creatures that think, perceive and behave in ways that we can readily understand.

With all of that in mind, can we reasonably predict some basic characteristics of extraterrestrials? Let’s start with their size.

As an extension of the laws of gravitation, Earth’s gravity imposes a fundamental constraint on any organism that might visit our planet. A massive and hulking alien creature could not simply arrive on Earth and function as it does in Hollywood without having evolved a biology capable of supporting its considerable mass under terrestrial gravity. The problem is not that gravity increases exponentially with mass—it does not—but that as an organism increases in size, its mass increases more rapidly than the cross-sectional area of the structures supporting it. Bones, limbs and other load-bearing structures therefore face progressively greater stresses as an animal becomes larger.

There are, of course, ways in which evolution might produce organisms far larger than anything familiar to us. The history of life on Earth itself demonstrates that terrestrial gravity does not impose an absolute prohibition on enormous animals. But such an organism would require a body plan, structural anatomy and physiology adapted to its size and to Earth’s gravitational environment. It could not simply be a scaled-up version of a smaller creature.

This presents an interesting problem for the Hollywood extraterrestrial. To imagine an immense alien arriving on Earth without considering how its body could support itself under our gravity is to assume that alien biology is somehow exempt from the physical constraints that govern everything else on this planet. And that, ironically, is itself a rather anthropocentric assumption: we imagine an alien creature in whatever form is convenient to the story, while ignoring the very environmental conditions that would have shaped its evolution.

The result is that any extraterrestrial visitor who hopes to survive in our gravity must conform to Sir Isaac Newton’s theory of gravitation.  This is not necessarily to say that an alien creature of immense size cannot exist, since the variable gravity of its home-world may be less than our own, wherein such a creature could exist; it simply could not inhabit our planet without some radically different physiology.

Let’s next talk about feature orientation and alternative body plans. While we cannot predict with any degree of accuracy how our visiting friends would orient their features, we can reasonably predict something about the functions those features must perform.

Living organisms are open systems. They must continually exchange energy and matter with their environment in order to maintain themselves, grow and reproduce. The precise means by which they accomplish this can vary enormously. Humans, for example, obtain usable energy through the ingestion of food and the absorption of oxygen through respiration, while plants capture energy from sunlight and obtain the raw materials necessary for growth from their environment. But these are merely terrestrial solutions to a more fundamental biological problem. There is no reason to assume that extraterrestrial evolution would have arrived at anything resembling a mouth, a digestive system, or even the concept of ingestion as we understand it. An alien organism might acquire energy directly from radiation, chemical gradients, electrical phenomena, or through some mechanism for which we have no terrestrial analogue.

What we can reasonably predict, then, is not the presence of familiar organs, but the presence of necessary functions. An alien visitor capable of maintaining itself as a living organism would require some means of acquiring usable energy and materials from its environment, and some means of disposing of the products of its biological processes. The mechanisms by which it accomplished these tasks, however, might be utterly unlike anything found on Earth.

What’s important here is the idea that all biological organisms must acquire energy in some form. On Earth, the overwhelming majority of that energy ultimately derives from the Sun, either directly through photosynthesis or indirectly through organisms that consume those that have captured it. There are exceptions, most notably organisms that derive energy from chemical reactions through chemosynthesis, but even these demonstrate the larger point: life requires some mechanism for acquiring energy from its environment and converting it into a form that can be used to sustain biological processes.

In our case, this involves a remarkably complicated collection of structures. A human mouth breaks food into manageable pieces; the esophagus transports it into the digestive tract; and the digestive system processes it into usable nutrients. Meanwhile, the lungs, bronchi, alveoli and circulatory system allow oxygen to be absorbed and transported throughout the body, while carbon dioxide is returned to the lungs for expulsion. These are all necessary components of mammalian life as we know it, but they are emphatically not necessary components of life itself.

Consider the insects. Although they ingest food in ways that can appear superficially familiar to us, they do not breathe through lungs. Instead, their tracheal system distributes oxygen through a network of tubes that extends throughout the body, delivering it directly to tissues. Aquatic insects have evolved a variety of further adaptations that allow them to obtain oxygen while submerged, including gills, air stores and other specialized structures. Their biology therefore demonstrates something important: even on the same planet, under the same physical laws, evolution can arrive at radically different solutions to the same fundamental problem.

And this brings us back to the question of extraterrestrial form. To predict the orientation of features on an alien body, we would first have to predict how that organism acquires the energy and materials necessary to sustain itself. We can predict the requirement; we cannot reliably predict the solution. Earth provides us with photosynthesis, chemosynthesis, mammalian respiration, insect tracheae and countless other mechanisms, all of which accomplish related biological functions through radically different means. If evolution can produce such diversity on a single planet, the potential range of solutions elsewhere in the universe is almost impossible to imagine.

An extraterrestrial, however, could not necessarily be said to be sustained by light and its derivatives as we are.  Though if an alien did exist which did rely on solar radiation for survival, it would not necessarily follow that such an alien would be sustained by the specific type of radiation being expelled by our sun.

In addition to a means to ingest nutrient energy, such a creature would also require external sense organs of some variety to interact with its environment.  Insofar as we can only speculate to an extremely shallow depth on the conditions which might have selected for such organs in an alien species, we cannot confidently predict the actual form of such organs as they would relate to conditions on their planet, nor how they would interact with our planetary environment.  It seems reasonable to conclude that all multicellular life requires organs that sense fluctuations in light and in sound vibration, though we can already see examples of life on Earth that does not conform to this idea.

Once we make the leap from acknowledging that we do not know whether an extraterrestrial organism would require eyes or ears to assuming that it does, we can begin to predict with some confidence how such organs might be oriented. But that leap would itself be unfounded. An alien species might perceive its environment through mechanisms that are presently unfathomable to us, and the evolution of those mechanisms would be shaped by the environmental pressures of its native world. 

Indeed, even the distinction between “sense” and “organ” may be a peculiarly terrestrial way of thinking about the problem. 

If extraterrestrial life developed on a world that is analogous to our own, we might expect to see binocular vision, stereophonic auditory features, and even olfactory features, though, as has been pointed out, since there is no demand for our own noses, ears and eyes to be oriented in the manner we currently find, there would be no reason to expect extraterrestrial life to conform to the same conventions of facial structure.  In fact, there could be an argument to support the idea that alien “facial features” should be vastly different from our own.

Even among these assumptions, there are hidden pitfalls; visual acuity in humans is vastly different than that of other mammalian life on Earth, not to mention aquatic, amphibian, avian and insect life.  The basic premise of the eye remains the same across most species: an organ tasked with receiving light input from the environment and sending corresponding signals to the brain to be translated into useful sensory information by a cortex of some kind.  But what light inputs are received and what sensory information is useful depends entirely on the species at hand.

The visible light spectrum—the relatively narrow portion of the electromagnetic spectrum that can be detected by human vision—is only a small part of the electromagnetic radiation reaching Earth from the Sun. Even among mammals, let alone the myriad other forms of life on our planet, there is considerable variation in the wavelengths that different species are capable of detecting. Many nocturnal animals, for example, have visual systems adapted to make the most of very low levels of visible light, while numerous species of insects can detect ultraviolet wavelengths beyond the range of human vision.

Indeed, many flowering plants have evolved markings that are visible in ultraviolet wavelengths and can be detected by insects such as bees and butterflies. These markings can serve as visual guides to nectar and pollen, effectively advertising the flower to its pollinators in a portion of the spectrum that we cannot see. Here again, the relationship between organism and environment has produced sensory adaptations that would be entirely unfamiliar to a creature limited to human perception.

From an admittedly anthropocentric position, it seems reasonable to claim that extraterrestrials might have eyes of some sort, though this is far from certain.  If their environment is predominantly without light, we might find species that are kinetically sensitive to electromagnetic fluctuations in their immediate environment, much like many types of fish on Earth, including sharks.  Or we might find that ET is visually able to detect light energy in a much larger band, say from low-frequency radio waves or gamma-ray radiation.

A similar argument can be presented for olfactory senses, wherein the vast diversity of olfactory capabilities found in animal life on Earth is already staggering, as this is the product of the large but finite collection of environments available on the planet.  Introducing other, more alien environments serves to introduce even more possibilities for the form and orientation of extraterrestrial features.

And so now that we’ve thoroughly confused the issue, it bears repeating.  While we are not able to predict the form of life outside of our small solar system, we can predict certain qualities of such form, though still with a margin of error which leaves much to the imagination.  Extraterrestrials must only conform to the laws of physics as they apply to their particular environment.  Should life evolve elsewhere, say on a planet considered analogous to our own, it is conceivable that such life might bear certain resemblances to life on Earth, though this should not be thought of as a universal rule.  For out of the infinite selection variables that have shaped life on Earth, we might have turned out quite different had the conditions of our own evolution varied even slightly.

Mankind sits atop his golden throne, but for a small cup of chance, and the argument rages on. We are not the creation of some grand vision of intelligence and superiority; we are simply the product of a particular evolutionary history, shaped by countless genetic variations and the relentless filtering of natural selection. Bipedal locomotion, opposable digits, binocular vision and the extraordinary expansion of the human brain are all products of that history. They are features that happened to confer advantages in the environments in which our ancestors lived, not milestones toward which evolution was somehow progressing.

Evolution did not favour us. It does not favour us. It has no preference for humanity, intelligence, consciousness or any other particular outcome. There is therefore no reason to assume that the same process would have produced the same, or even remotely similar, evolutionary solutions elsewhere in the universe. The circumstances that produced us were contingent upon an almost incomprehensibly complex combination of environmental conditions, genetic variation and historical accident. Change any sufficiently important part of that history, and there is no particular reason to expect anything resembling humanity to emerge at the other end.

Does that make us unique?  Most definitely.  Does that make us special?  Perhaps.  Does that make our form the inevitable outcome for all biological development in the universe?  Absolutely not.