Authors: Don Lincoln
Flying has evolved on Earth at least four times, with birds, pterosaurs, bats, and insects, suggesting that this is a fairly common locomotive adaption. A flying Alien is entirely plausible.
There is little reason to select any particular form of locomotion for our Aliens.
Speed
The speed of an animal is tied to many other things. For instance, a heavily armored animal is typically slower than one without armor. Predators tend to be fast. On the other hand, humans aren’t particularly fast in the Animal kingdom. There is little the animal world can tell us about Alien speed.
Color
The color of animals spans the rainbow. Aliens could have any color.
Defenses and Offenses
The natural defenses and offenses that Aliens could have are quite broad. Humans are actually rather unimpressive in their offensive and defensive skills, but make up for it in their ability to utilize weaponry to overcome their structural limitations. Any Alien capable of building a spaceship will have similar skill. However, there is no reason that the Aliens will not have other abilities. In nature, animals exploit a myriad of defensive and offensive strategies, from the camouflage of a leafy sea dragon, a tiger, or a cuttlefish to the venom of
a cobra, a scorpion, or a male platypus. Mammals tend to not be venomous, perhaps because they are quick enough to kill with tooth or claw, whereas venom takes time.
Shells, horns, and spines provide protection, for example the tortoise and the ankylosaur or the porcupine and the blowfish. And, of course, simply avoiding the conflict through a burst of speed is a wise defensive choice. Rabbits, the spine tailed swift, and the gazelle are able to move extremely rapidly.
Temperature Regulation
The internal temperature of an animal can be regulated by the body’s own metabolism (endothermic) or can depend on the environment, as is the case for insects, fish, and reptiles (ectothermic). In general, internal temperature regulation is a safer evolutionary choice, given that ectothermic species can be sluggish when the environmental conditions are colder. However, there is no reason to expect that the Aliens come from a planet as cold as Earth. Perhaps their planet is sufficiently warm that there is no need to evolve endothermy. Since metabolism depends on enzymes that tend to operate best in a fairly narrow temperature range, endothermic animals generally have a considerable advantage, but, in the right environment, the selection pressure may be small.
Blood
Blood is not necessary for all animals. Some insects use a fluid called hemolymph to transport oxygen to their tissues. However the higher animals use a substance that enhances the oxygen-carrying capacity of the liquid inside them. The most familiar type of blood contains a compound called “hemoglobin,” which contains iron and gives blood its red color. Each hemoglobin molecule can attach to up to four oxygen molecules and increases blood’s oxygen-carrying capacity to more than seventy times what it would be if the oxygen were just dissolved in water.
However, the iron-based hemoglobin molecule isn’t unique. There are other options. For instance, some insects have a copper-based blood, using a compound called hemocyanin. Hemocyanin transports oxygen about a quarter as efficiently as hemoglobin, so it is more suitable for creatures with lower metabolic requirements. Oxygenated blood containing hemocyanin is blue. And sea squirts and sea cucumbers carry a vanadium-based protein in their blood called hemovanadin. There is still some controversy on the role of this
protein in oxygen transportation. When oxygenated, it turns mustard yellow. It is pale green otherwise.
Diet
It is, of course, very difficult to know the diet of an Alien, but here on Earth, there are three options: carnivore, herbivore, and omnivore. Carnivores eat meat, herbivores eat plants, and omnivores eat both. There are pros and cons to all three. Herbivores have the greatest access to food, as plant life is ubiquitous. However, plant food tends to be lower in terms of calories available, leading to frequent eating. Carnivores have fewer food choices, as they must catch and eat other animals. This places constraints on their bodies, from the trapping of spiders, the “lurk and grab” of alligators, the “stalk and pounce” of cats, and the “communal attack” strategies of wolves. Carnivores get substantial nutrition influx with a successful attack, but they don’t have as reliable a food source as herbivores.
Omnivores (of which humans are a member) get the benefits of both food sources. It is hard to imagine an intelligent Alien that doesn’t have at least omnivorous capabilities, although it may opt to utilize one food source more often. We should also keep in mind that it is possible that the Aliens might need certain minerals or other substances, similar to Earth-life’s need for water and salt. It is therefore possible that the Aliens might need to ingest materials directly from the ground, like deer around a salt lick. Given that the Aliens will evolve in an ecosystem with a common biological heritage, it is likely that some of this mineral collection will be done by plants for subsequent ingestion by Aliens.
Respiration
Respiration is the intake of vital gases from the environment (oxygen in the case of most animal life on Earth) and the removal of waste gases (predominantly carbon dioxide). As we will discuss in the next chapter, Aliens might elect to use different molecules in their metabolic processes, but the mechanisms to exchange gases with the environment are likely to be similar, as the phenomenon must satisfy basic physical constraints. These constraints include collecting gases from the outside and dispersing them to the tissues of the body. The respiration system is likely to be internal; otherwise something could block the ability to breathe. (For instance, imagine if your lungs were on your outside and you somehow got splattered with mud.)
Small insects have the simplest respiratory system, by exploiting the diffusion of gases into and out of the circulatory system. Recent research has shown that insects have a diverse range of respiration techniques, with some using muscles to expand and contract their respiratory systems in ways that are not terribly different from higher animals.
Land animals usually use a lung system, with an intricate system of branching pathways. The inside of a higher animal’s lungs looks a little like a tree and for essentially the same reason. This design maximizes the area to exchange gases in the minimum volume. While birds, reptiles, and mammals differ in detail, the basic structure is similar.
Water-breathing animals, like fish and mollusks, use a gill system to extract oxygen from water. Extracting oxygen from water is a tricky business. Water contains about 3% the oxygen held by an equivalent volume of air. Consequently, fish have evolved highly efficient gills to extract approximately 80% of the oxygen from the water. (This can be contrasted with an approximate 25% extraction efficiency for mammals breathing air.) Still, this scarcity of oxygen might make it more difficult to evolve highly intelligent Aliens under water. Amphibians have a split system, breathing both through lungs and their skin. This ability to breathe through their skin is of great value when submerged in oxygenated water.
Environment
Does the Alien live on the ground, under the earth, under water, or in the air? This is one of the questions for which we can likely exclude some options. While animals exist in all of these environments, it is essentially impossible for our Alien to be purely a water breather. The reason is that we impose the need to have an ability to build a spaceship. While it is clear that intelligence can exist underwater (e.g., dolphins and octopi), building a spaceship requires technology, specifically manipulation of metal. It is very difficult to imagine an advanced technology that doesn’t shape metal. Forming metal requires heat, which means fire. Since fire is impossible under water, it seems that our Aliens cannot be (solely) water breathers. An underwater alien caveman is possible. An Alien in the sense we mean in this book is not.
Reproduction
The number of reproductive strategies employed by animals is astonishing. There is the sexual reproduction of higher animals and the asexual reproduction often seen in microscopic organisms. Some creatures can do both, that
is, reproduce sexually or asexually, depending on the environment. Asexual reproduction creates clones of the parent, which have the same susceptibility to disease or environmental change. Sexual reproduction ensures the genetic material is mixed. This results in a more diverse gene pool and is a guard against a change in the environment that might kill one individual but for which others might be better adapted. And, of course, for sexual reproduction there is external and internal fertilization, as well as egg-laying versus live birth.
Some species produce many offspring, knowing that many will not survive to reproduce themselves. An example might be frogs or rabbits. Other species produce fewer offspring but spend more time with them to ensure that they survive. This is the evolutionary tactic taken by humans.
For some species that have sexual reproduction, there are hermaphrodites, whereby a creature has the reproductive organs of both sexes and can both impregnate others and bear the young of their species. There are also species with tremendous sexual dimorphism, like the angler fish, in which the male fuses itself to the female and then atrophies away until he is nothing more than a sperm source.
An unusual adaptation in a few species actually has more sexes than the usual two. There are species in which individuals change from male to female and back again. There are species in which there are large “alpha” males with harems and smaller males of the same species with coloration that mimics the females. They hide in the harems and reproduce that way. There are insects in which a single dominant female lays the eggs and the other females are reproductively neuter. Even on Earth, sex can be complicated for a species. There is no reason to believe the male/female dichotomy will apply to Aliens.
Senses
What senses will our Alien have? It seems that a sense of touch is crucial to essentially all living organisms. Having a tactile awareness of your environment is important, whether you are predator or prey if, for no other reason than to know if something is biting you. Hearing is similar to touch, although there is a broad variation in how well species can hear. Taste or something similar allows organisms to decide if something is food or not. Vision is a very important sense and has evolved independently several times. Vertebrates, cephalopods (e.g., squids), and cnidarian (e.g., box jellies) have “camera-like” eyes, and each followed a separate developmental history.
There are at least ten different “eye technologies” that probably originated from a small spot of photoreceptive proteins on a unicellular common ancestor.
However the details vary, from the human-type eye, in which focus is accomplished by changing the shape of the lens, to another choice in which the lens doesn’t change, but the shape of the eye does. Then there are the multiple lenses of insects, the reflective eyes of scallops, and many other designs. Thus, while the details of the vision might be quite different, we can conclude that it is probable that our Alien will be able to see. It is simply too valuable an adaptation in a lighted environment to do without.
Of course, by “see” we don’t mean just “see what we can see.” Some snakes are able to detect infrared. Birds, reptiles, and bees can see some ultraviolet. So the possibilities of Alien vision are quite diverse.
It is important to recall that much of the vision of Earth creatures is optimized to see light where the sun is brightest. Aliens evolving on another planet would likely evolve the ability to see best using the brightest light available on their world. Thus it is possible that they could see the kind of light we do only poorly.
Senses that some Earth-life has that humans don’t include the echolocation of bats and dolphins (useful in low-light environments), the ability to sense electric fields like some fish and sharks, and the magnetic sense of many migratory species (e.g., some birds, tuna, salmon, sea turtles, and more). We can also imagine Aliens developing a sensitivity to radio waves.
Obviously it is not mandatory that Aliens will have all of the senses we do. For instance, a subterranean species would have no need to develop sight. Tactile and auditory senses seem like they would be universal, as they would be helpful in any environment. A sense of smell or taste provides a method of chemical analysis; for example, some poisons taste or smell bad. Both senses might not be crucial, but having one or something similar would probably provide an important survival advantage.
Communication
The communication between Aliens will be aligned to their senses. Here are some options that Aliens might exploit: motion, smell, light, sound, or radio. Imagine trying to talk to an Alien who uses scent to communicate. (Given how slowly smells travel and dissipate, this is an improbable scenario, but it helps one think about how difficult human-Alien communications might be.)
Life Span
This is difficult to generalize from Earth life. Mice live only a few years, while some tortoises might live to about 200 years. There appears to be no strong
correlation with metabolism rates on Earth. But, given the many factors that go into determining longevity, it is difficult to predict an Alien life span, except to state that an Alien must live long enough to learn the technology of previous generations.
Social Structure
Animals spend their time in many ways, from packs, to herds, to a solitary lifestyle. It is likely that Aliens will be social creatures in a way at least somewhat analogous to humans. The need for communication and retention of technical knowledge over the generations almost guarantees that the individuals will work together.
Wrap Up
These attributes of life are certainly not intended to be encyclopedic but rather to give a flavor of the kinds of variation possible should alien life evolve using carbon as the basic building block and with a biochemistry that is similar to our own. Of course, on a different planet, with different sunlight and chemistry, life might be quite different. Exploring some of these other options is the goal of the next chapter.