If intelligent extraterrestrial life exists, what physical appearance is it likely to have?

There can be little doubt that one of the most important factors that will determine the manner in which our society reacts should contact ever be established with intelligent extraterrestrial (ET) life forms will be the physical appearance,or morphology, of the alien. All the prejudices, the fears, the mistrust and the bigotry that exists amongst the races that make up mankind will be focused into this reaction. Thus, speculating on the morphology of an intelligent alien is important for the future of space exploration.

Serious efforts are now being made around the world in the field known as Search for Extraterrestrial Intelligence (SETI) and the manner in which our society reacts to contact will depend to a great extent on the appearance of the alien. Anticipation of the possibilities now may reveal whether a shock for the world is likely. It is also useful to consider alien morphology in terms of gauging how likely the chances of intelligent aliens evolving really are.

An approach to the subject

The problem of trying to anticipate the physical appearance of the ET is at first sight ludicrously impossible. To start with, we don't even know if intelligent ET's exist, let alone what their planet of origin is like or what their morphology may be.

Our task is therefore limited to using what knowledge we have of the evolution of intelligent life on Earth, considering possible extraterrestrial planetary environments and making a series of reasonable assumptions. A combination of biology, zoology, and anthropology is required as well as the newer science of exobiology. Most important, the overriding thought when considering the subject should be "how would this imagined alien become intelligent?"

The two views

Conveniently, disagreement over the likely appearance of intelligent ET's divides itself into two opposing camps. On one side are those who take a rather anthropomorphic view of the ET and believe that it would basically be humanoid in shape with two ,arms, two legs, a head at the top of the body and the main sense organs located on the head. Opposing this view are those exobiologists who believe that the intelligent ET is bound to appear exotic because the creature would inevitably have taken a totally different evolutionary path from man and would have arisen in a very un-earthlike planetary environment.

This article will show, however, that the case put forward by the non-humanoid ET protagonists will not stand up to the example of the evolution of intelligent life on Earth, nor the necessities of morphology that a creature requires to become intelligent. It is therefore suggested here that any intelligent life across the galaxy will have evolved into a basically humanoid form.

Exotic biology

A possibility often suggested by more radical exobiologists is that extraterrestrial life might depend on a chemistry that does not require the carbon atom. Bracewell [1] has proposed that life could make use of the chemistry of the silicon atom rather than the carbon atom. Silicon based organisms would, for example, breathe out silicon dioxide (sand) instead of carbon dioxide. The rock eating creature has often been suggested as a product of this biological system. [An example of this can be seen in the STAR TREK episode about the Horta. AB]

The problem is that silicon polymers of the protein type are unlikely to from the compounds essential for for chemical evolution. Bieri [2] points out that the energy requirements for duplicating a living system are fulfilled only by carbon and the high energy phosphate bond.

It is very difficult to envisage any life other than that based on the carbon compounds forming in water. Unfortunately this limits the planetary considerations necessary for the evolution of larger sized organisms somewhat severely -- in fact it restricts planets that may have intelligent to those with broadly Earth-like surface temperatures and pressures. (It also restricts the type of star that may shine on life producing planets -- the DNA molecule is sensitive to high levels of radiation, particularly the ultraviolet.

What of possible creatures that could get by without requiring the availability of an Earth-like oxygen rich atmosphere? The conjectured 'balloon' creatures floating in the gas belts of Jupiter and using, instead of oxygen, a metabolism of hydrogen -- could they ever become intelligent ET's? And what is wrong with with Fred Hoyle's "Black Cloud," an intelligent gas cloud thousands of kilometers across? The answer lies in our prime question, "how could this creature become intelligent?" Intelligence, it is argued later, will probably only arise from astimulating predatory existence in a harsh but survivable physical environment.

Conceding defeat to the necessity for life to be based on carbon in a water medium, the exotic morphology ET supporters suggest that there are enormous variations open to chance evolution even under Earth-like conditions. Slight differences in surface pressure, temperature, gravity or solar radiation, they argue, will produce widely divergent evolutionary trends [3]. Steen[4] suggests that intelligent ET's might be insect like, bird like, fish like or even plant like. They may be spherical in shape, glutinous, jelly-like creatures, such as as "Quatermass" might meet, or possibly even a planet sized oceanic intelligence such as that in Stanislaw Lem's novel "Solaris".

For less bizarre (but still very exotic) alien creatures proposed for extraterrestrial life bearing planets, the exhibits on display at the National Air and Space Museum's "Life in the Universe" section in Washington, DC provides some good examples of exotic aliens [5]. Biologist Bonnie Dalzell has designed for a dry Earth-like world the "hexalope", a six legged antelope. For a high gravity planet, we are presented with the "bandersnatch", a monstrous herbivore with eight legs, a large mouth in its chest, two eyes on stalks and ears along the side of its body -- the creature weighs 30,000 lbs on its 3-G world! The intelligent ET that Dalzell presents us with is a six legged toad like creature.

Life on Earth shows us just how strange creatures can become in the chain of evolution. The giraffe is a good example of this. But it is highly unlikely that these creatures could ever become intelligent.

The anthropomorphic view

The problem ignored by exotic ET protagonists is that speculation on the morphology of the ET must take account of the lessons taught us by evolutionary development on Earth.

(The argument for humanoid ET's given here is based on the works of Robert Bieri [2], N.J. Berrill [6] and Robert Puccetti [7])

In the early period of the development of life on Earth, organic matter based on carbon compounds began in a water medium before the invasion of the land. The early sea bound creatures developed a critical characteristic that would decide the future form of land dwellers -- that of bilateral symmetry in the shape of the body. This shape reduced water resistance and turbulence to a minimum and became the characteristic of all the higher creatures of the sea. It can be seen that adoption of a predatory way of marine life has has developed has developed bilaterally symmetrical creatures as diverse as the squid, the penguin, the seal, the otter and the large fish. Radially symmetric ocean dwelling creatures all adopt a relatively stationary way of life, jelly fish, sea anenomae etc., having a loss of sensitivity and degeneration of the nervous system when compared to the more active predators.

Bieri points out that predatory animals with complex nervous systems and bilateral symmetry possess the largest and most important sensing and grasping organs close to the mouth. Also, digestion and excretion is most convenient with an anterior mouth and posterior anus for an active hunting animal. In order to reduce time for for nerve impulses to travel from the sensing organs, the brain is at the head.

Conceptualism and intelligence

Conceptualisation, it would seem, can arise only in a land animal. Birds cannot possess brains large enough for this due to the fact that they must be light in weight and have hollow bones to fly. A large intelligent brain requires a considerable amount of blood and therefore a heavy cardiovascular system -- both these factors would lead to an impossible power to weight ratio for an intelligent airborne creature. It is also difficult to imagine an intelligent ET evolving from gliding winged creatures such as the the flying squirrel (which glides from trees with the use of membranes under its front legs) -- it is too small to evolve intelligence. It is doubtful that even a gliding creature as large as the extinct Pterodactyl could ever develop a large enough brain.

The question of intelligence arising in sea animals is somewhat more complex due to the fact that the whale family happens to possess large brain capacity, a very advanced system of communication and displays remarkable feats of intelligence. However, conceptualisation, as Puccetti attempts to define it, seems to arise in conjunction with a social existence, speech and the use of tools. The development of tool usage undersea is extremely difficult due to the density and viscosity of water. Predatory sea animals rely on their natural hunting equipment -- teeth, streamlining, speed, etc. -- rather than weapons and tools. Only semi-land creatures, such as beavers a nd otters (both mammals) possess any sort of manipulating appending and these they use on the surface.

How the whale family came to develop such a large cerebral capacity tends to cast some doubt on the whole question of conceptualisation development. Here it is assumed that whales are clever, but do not conceptualise on their existence.

An encounter, therefore, with a race of intelligent aliens who are either aquatic, reptilian or are creatures capable of flight and who developed conceptualisation characteristics with a high level of technology, seems highly unlikely. Our intelligent ET's would have to be land dwellers.

The predatory supremacy

It should be emphasized that it seems most likely that all intelligent conceptualising creatures in the galaxy will have their own origins in predatory animals. Man's origins appear to stem from herbivore apes that, faced with climatic and vegetation changes, left the trees, became omnivorous and adapted to running on the savannah, hunting other animals in groups and using their ability to grasp and manipulate to develop weapons, tools and eventually a basic technology. It is difficult to imagine a animal bothering to use weapons and tools, firstly if it was a fully adapted herbivore and secondly if it was already a competent predator, such as the lion or tiger. Arthur C. Clarke describes this critical path that the early hunting apes had to take extremely well in 2001: A SPACE ODYSSEY (although of course he did not let his apes develop their technology purely on their own initiative.)

Man has remained the only creature with a technology on this planet because of his predatory hunting nature, despite the basic ingenuity of creatures such as the ant with its ingenious city like hills, chimpanzees which can fish out termites with sticks, and birds that can break shells with heavy stones and the sea otter that can break open shells by floating on its back and beating them against stones on its chest. These creatures have stretched their manipulative abilities to the limits.

Moving around

The development of legs, arms and grasping appendages is critical to our conceptual ET's road to intelligence. A primitive technology will require the ability to hold and manipulate, with some degree of sensitivity, basic tools and weapons such as clubs, spears, knives and twine. The intelligent ET must have this manipulative capability combined with speed of movement, otherwise it will remain in its comfortable environment (as did the dolphin) and we would certainly never meet it stepping out of a star ship.

As a method of movement, sliding, wriggling and rolling are all much too slow for the land predator. As Puccetti points out, walking is the only viable means of moving at high speeds and for long distances. The wheel was never used as a means of locomotion by nature except in some tiny bacteria. Although the reciprocating knee joint in the human leg can put up with large shock loads and the shoulder and hip joints can rotate through a considerable arc, it is difficult to imagine an organic bearing that could rotate through 360 degrees.

Insect like appendages are unlikely. Insects possess legs that are basically hollow cylinders with muscles and tendons inside the skeletal tube. The problem with this arrangement is that if the creature grows in size the tube will constrain the inner muscle size -- hence the Tarantula being the largest land insect left since prehistoric times. Hard levers and struts surrounded by muscles and tendons, as in land walking vertebrates, is a much more likely arrangement in the predator land dwelling alien.

The question of the number of legs is one of the most contentious when discussed by those speculating on the morphology of the intelligent ET. The four legs that we have are the product of genetic inheritance from our earliest mammal ancestors; but this inheritance allowed us great speed of movement and thus played a major factor in the development of intelligence. One leg is out of the question -- the creature could never get up if it ever fell over. Odd numbers are unlikely because of balance problems. More than four can only be found in insects. Galloping after prey with six legs is too complex for land predators (and herbivores, as we have established, are unlikely to become intelligent). Each leg has to swing through a wide arc for speed and with more than four this becomes very difficult.

Monkeys and apes can use their two legs for manipulation but have to run on both arms and legs together. Indeed the ape cannot use weapons to hunt whilst running on all fours. It is difficult to imagine the development of an intelligent hunting animal animal such as man running on two sensitive grasping appendages. Thus we have the evolutionary step of the conversion of one pair of legs to manipulating, pushing and pulling devices and the other pair to movement. In this way the creature optimises between high speed movement and delicate manipulation.

Sensory organs

So far we have formulated the picture of an intelligent ET with a body much like our own. Its sensory organs, however, show characteristics that are somewhat different, though not greatly.

Sense organs would largely depend on the characteristics of the aliens planetary environment and the illumination provided by the local sun.

More than two eyes is rare in land creatures -- the spider possesses multiple eyes, but they are of doubtful sensitivity, and would confuse a large hunting creature. Stereoscopic vision near to the brain and high on the body is the most suitable. Binaural hearing would seem the most logical. This is required for location bearing -- and thus the ET requires just two ears. Again these would be on the head. Only one mouth is needed with the smell sensor close to it and taste sensors inside it. The smell sensor can be used for breathing, whilst the mouth is occupied with eating and drinking.

Additional sensory devices such as bat like acoustic ranging systems or infra red sensors similar to those possessed by the rattlesnake, are possible. But as Bieri points out, the imply a corresponding reduction of vision in the normal sun illuminated spectrum. As we have established above that carbon life probably only develops on planets with suns much like our own we can assume that the visual spectrum would be similar to that on Earth for the alien ET.

Although, therefore, the sensors of the ET are similar to our own, the placement on the head and their form might be quite different. Odd shaped heads are likely, different ear shapes and sizes most probable and eye size and colour would be different.

The likely ET appearance

The argument presented above gives backing to the anthropomorphic view of the intelligent ET -- that is that the creature would be basically humanoid. But this only a starting point. What would the intelligent ET look like in detail?

This question is, of course, even more difficult to contemplate than speculating on the ET's likely basic form. However, here are a number of possible variables to consider:

1. SIZE AND BUILD -- The height and build of the alien has often been suggested as being related to the gravity on the creature's planet of origin. A planet slightly larger than Earth, with a subsequently higher gravity would result in the alien being squatter, with heavy bones and a powerful physique -- in other words, something like a gorilla. On the other hand, a lower gravity planet would result in taller, more spindly aliens. This argument is a little simplistic in its conclusion and does not explain the wide range in the sizes of Earth creatures -- for example, why is there such a large variation in the size and build of the apes, all of which are fairly clever animals?

It seems probable that one can draw parameters about the ET's size, the likely range being between the smallest of the human races (the pygmy) at about 4 1/2 feet tall and the upper limit being around 7 1/2 feet tall. If the alien is very much heavier than man, he would have problems with running for long distances in pursuit of prey in his early development as a land predator and would require a very large supply of readily available food to maintain himself.

One interesting point about man is that we appear to be getting taller due to our evolution, our bodies are losing their broader muscles and our heads changing shape. It is more than likely that the humanoid intelligent alien also experiences this form of slow morphological evolution due to changes in dietary nutrition and life style. There is, of course, no guarantee that the alien will meet man as we appear now. An intelligent alien basing his conception of what man looks like from previously discovered spacecraft message devices (such as those carried by Pioneers 10 and 11), or picked up TV images in, say, 50,000 years time, may be in for a surprise when he meets a hairless, chinless, towering egghead from Earth!

Equally interesting is the question of the differences between the male and the female of the intelligent aliens' species. Would the two be quite different morphologically as in the case of homo sapiens, or would the two be virtually indistinguishable as with some creatures on Earth?

2. SKIN COLOUR -- The wide variation in skin colour and tone with creatures on the Earth is enough to indicate the extreme range that could occur with the intelligent ET. Indeed, why would the ET have a smooth skin? It is possible that fur may cover the alien having been left behind after an evolution stemming from a bear like creature, for example. (indeed, it is interesting to wonder whether whiskers, or some sort of delicate sensory feelers may remain with an intelligent creature after it has begun to rely on its hands).

3. FACIAL ARRANGEMENT -- This, as already stated, is mainly constrained by the smell and taste sensors being close to the mouth and by the need for stereo vision and binaural hearing. Beyond this the facial arrangement possibilities would be reasonably wide.

4. NUMBER OF FINGERS/TOES -- Again, variations could be wide although beyond ten fingers or toes on each hand or leg would seem excessive and difficult for the brain to coordinate. Less than four fingers on the hand would make basic technology difficult to manipulate.

5. INTERNAL CHARACTERISTICS -- The internal digestive, cardiovascular and pulmonary systems inside the intelligent ET would most likely be quite different and it is not possible to list all the variations within the confines of this article.