Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization

First Edition

© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm


13.6  Alien Senses

We are far from having exhausted all of the sensory possibilities. Man himself has many others -- the vestibular senses relating to body position and accelerations, pain, time (circadian rhythms), blood sugar level monitoring, thirst and hunger, internal temperature, and so forth. Most organisms, including jellyfish, shrimps, octopuses, and virtually all vertebrates are able to sense gravity to some degree. Even most of the higher plants have gee-sensors to keep them growing upright.*

The water scorpion Nepa uses a fathometer sensitive to hydrostatic pressure gradients to keep itself informed of the depth to which it has dived,2358 and the alciopid worm Torrea has an unusual double-retina eyeball which may serve as an accurate depth gauge.2482 Honeybees and a species of fire ant (Solenopsis) can detect changes in the concentration of carbon dioxide in the air. Other organisms have humidity sensors, brightness sensors, salinity sensors, and so forth. Any of these could be quite useful in combination with the more important modalities discussed earlier.

One possible extraterrestrial sense that is often overlooked is the ability to detect radioactivity. Such a sense could be much in demand on a world with highly concentrated radionuclide ores near the surface, or on a planet in the throes of recovering from a global nuclear holocaust. Biological Geiger counters would give warning to steer clear of large tracts of radioactive hazards.

The ability to respond to radioactivity has been artificially bestowed on a small group of experimental animals. Several cats were outfitted with portable Geiger counters which telemetered impulses directly to the "fear centers" of the feline brains. When confronted with a pile of radioactive materials in one corner of their cages, each cat shied away.92

We could also imagine a sophisticated meteorological sensorium, especially useful for ETs native to a world with highly volatile, perpetually inclement weather. Barometric (like the pigeon’s) and humidity sensors would be helpful, as would an anemometer to measure wind velocity (like the blowfly’s). It’s also well-known that atmospheric turbidity, which is closely related to developing weather patterns, greatly influences the degree of skylight polarization. A sensor responsive to the intensity and distribution of polarized light might permit its owner to seek shelter from the elements before disaster struck.

The ability of many animals to "sense" an earthquake or tornado before it strikes is documented fact. The phenomenon is thought by some to relate to the perception of very low frequency infrasonics or minute electrical field variations which immediately precede the event. And elephants are said to be able to sense water located a meter or so underground, as in a dry river bed. Although this allegation remains unproven, biological "dowsers" would be far more likely to survive on a drought-stricken planet.

Two unrelated points should be made in closing.

First, it is not necessary for an alien’s primary sensory modalities to be located near the brain or even on the head. There are many lifeforms on Earth which disobey this seemingly essential rule. Some animals carry their ears on their stomach (grasshoppers) or on the knee-joints of their front legs (crickets), or which hear through antennae (mosquitoes) or their whole body (cicadas). Still others smell and taste with the soles of their feet (flies), the tips of their tentacles (octopuses) or their antennae (bees). Then there is the scallop, a headless mollusc with hundreds of eyes distributed around its perimeter.

The argument is often heard that senses should be located close to the brain in order to minimize neural response times, facilitate navigation, and maximize safety. But it must always be borne in mind that these are only broad generalizations and not the holy grail. Nature may see fit to violate them if there are good enough reasons.

Second point: The role of the brain must not be neglected when we consider the kind of world an alien sees. The mechanisms and patterns of perception may depend on sociocultural factors as much as on biophysical ones.

An interesting example of this is the phenomenon in humans known as "color hearing." This is not just a matter of vaguely associating sounds with colors, which many people do, but rather of rigidly linking specific musical tones to specific colors. Sir Isaac Newton supposedly associated middle-C with red, D with orange, E with yellow, etc. The composer Alexander Nicholaevich Scriabin is said to have experienced the piano keyboard as a sequence of particular colors. Indeed, such is often interpreted as a symptom of mental disorder, in which a patient is literally incapable of distinguishing whether a given color stimulus is a sensation of sound or of light.79

The explanation seems to be that as infants we make little distinction between the various forms of sensory input -- the sounds, sights, and smells of the world around us. In our culture we are taught this demarcation at an early age. Yet anthropologists have reported the discovery of whole cultures in which the young are not taught to differentiate between audio and visual data. Their native languages reflect this fact.

Learning alters perception. Other worlds mean, not just other senses, but other ways of dealing with sensation. In the English language, smell and taste are closely linked; in other societies, seeing and hearing are allied instead. What peculiar patterns and combinations of information might alien cultures put together? If so many different senses are available, are not the permutations and synergistic blends almost uncountable?


* In the absence of nervous systems, sensors remain uncomplicated. A few "vegetable sense organs" have been discovered. The sensitive pea has scarlet beads at the base of its stalks. When this tropical plant is stimulated with heat, light, or various chemical substances, the beads can control the drooping of the leaves.90 Venus flytraps are pressure-sensitive, and plants are known to grow in the direction of an increasing gradient of moisture or light. But this, apparently, is the best that nonsentient leafy lifeforms can do.


Last updated on 6 December 2008