As a long time science-fiction fan, I've often speculated on what an intelligent extraterrestrial being would really be like (if they exist at all). Would they be similar to human beings "with warts" as many movie and TV shows such as Star Trek, Star Wars and Babylon 5 depict them? Or would they be completely different, perhaps big fat grubs like Jaba the Hut, have octopus heads such as the writer H. P. Lovecraft's stories pictured them or have long skinny humanoid bodies, big eyes and no nose as many UFOologists claim? In this blog I'd like to give my opinions based on the latest scientific information.
First let us consider all the diverse types of life that have existed on our own planet throughout the three billion years since life first appeared. In size, living things vary from the microscopic to such gargantuan forms as whales, mastodons and brontosaurus. Life is everywhere, in deserts, seas and forests, even in volcanic vents, arctic climates and underground; each form adapted to its environment. Also, as conditions changed, the forms changed. For example, some animals whose ancestors walked on solid ground have evolved into sea creatures. It would seem then that life on a planet with completely different parameters would evolve into completely different forms. Or would it? Under different conditions, similar types of creatures have appeared. One example is a one horned thick legged herbivore such as Rhinos and Triceratops, one being a mammal, the other a dinosaur.
But what are the chances of a creature evolving that would be as intelligent as us or perhaps even more intelligent? Animals such as dolphins and whales have larger brains and may be as intelligent. Nonetheless, they are not capable of producing technology and probably never will.
The question remains. Would aliens be animals, plants or have characteristics of both? Would they have arms and legs and walk upright as we do? Would they depend upon vision as their primary sense or use another way to gather information about their surroundings? Would they "breathe" oxygen or some other gas?
First let's take a look at how evolution by natural selection (Darwinism) actually works. The basic rules governing whether species arise, live, remain unchanged or become extinct are those of evolution by natural selection as proposed by Charles Darwin. According to Darwin's Theory of Evolution, similar organisms reproduce similar organisms -- a dog reproduces a dog, a dandelion reproduces dandelions and a fish reproduces a fish. Often, the number of offspring are overproduced such that the number that survive is fewer than the number reproduced. In any population, individuals vary with respect to any given trait, such as height, skin color, fur color or shape of beaks, and these variations can be passed on to the next generation. Some variations are favorable, in that they make those individuals best-suited to their environment, and some are not. Those organisms with favorable variations will survive and pass those traits on to their offspring; those individuals with unfavorable variations will die before producing new individuals. Hence they would not pass on their traits. This is natural selection. Given sufficient time, natural selection accumulate favorable or neutral traits so that a new species evolves.
Using what we have learned from life on Earth, what can we say about alien life? While it may be vastly different from life on Earth, it must follow certain universal guidelines dictated by the laws of physics and chemistry. It must consist mainly of some sort of solvent. On Earth, the solvent used by life forms is liquid water. Other chemicals, such as ammonia, methane, hydrogen sulfide or hydrogen fluoride, could be the solvent in an alien life form.
Living things require temperatures and pressures at which its solvent remains liquid and need energy to remain organized. Most things on earth are powered by sunlight either directly or indirectly. An alien world, in order to sustain life, must have a source of energy, whether it be sunlight or other energy source.
On Earth living things are made of complex, carbon-based molecules that carry out biochemical functions. DNA molecules contain genetic information and direct the formation of other molecules to allow life to reproduce and function. Alien life forms must also have some type of informational molecule. Carbon can form bonds with up to four other atoms, in many shapes, to make many types of molecules. Although silicon is not as versatile as carbon, it can also form up to four bonds with other atoms and has been proposed as a basis for molecules of alien life, if the environment were such that silicon was more abundant than carbon. Alien beings larger than microbes must be multicelled.
The physiological make-up of a multicelled alien must be suited to its environment. Internal systems would be adapted to environmental conditions such as temperature, moisture and gravity. The alien must bring solids, liquids and gases inside its body, distribute them to every cell and remove waste products.
The alien must have senses to obtain information from the environment and respond to stimuli. They must also have the equivalent of a brain and a nervous system to process information. They must also have a means of reproduction of their species.
Alien organisms would probably have similar ecological structures to life on Earth. Population sizes would be limited based on the amount and type of food, predators, disease and other environmental factors. Just as life on Earth, alien life forms would exist in food chains and food webs in their native environment. Life forms similar to plants will create food that other life forms such as herbivores and omnivores will eat. There may be carnivores that eat other animals. Life forms such as bacteria are needed to recycle dead organisms into the environment.
Life of any kind is intimately tied to its environment. The characteristics of the planet would be extremely important in determining the characteristics of the life forms that exist on it..
Now what about the life form we are most interested in, an ET intelligent enough to use and create a high-level of technology? In the long evolution of animal life on earth, some characteristic are universal and appear in many species, such as limbs and eyes. Other characteristics such as hair, hands with fingers, skin coloring, the mechanics of sex, and so forth are arbitrary and appears in some species and not others. One of these are brains with the capability to produce advanced technology. In three and half billion years of evolution, such intelligence has appeared in a species only a couple of million of years ago, a very short time in evolutionary terms.
The design of any animal is toward survival in its environment. These designs can be arrived at via different evolutionary routes. For instance, predators in the ocean have a survival advantage if they swim fast. Consequently many of them have a torpedo shape, simply because this streamlined form gives them a better chance at snagging a dinner or escape being eaten. Dolphins and barracudas look similar in silhouette, although they evolved from very different forebears. Their shapes are the result of convergent evolution.
Some biologists have suggested that the same may be true of humans and extraterrestrial life -- that the human body plan is a good design for an intelligent creature. We have arms terminated by little hands that are useful for writing and using tools. We have two eyes with overlapping vision, which provides three-dimensional views of the world. Such vision aids in the use of tools. The eyes are located high up, which allows us to peer over grass and brush to find a mate, a meal or an approaching enemy. There are many more such traits. Humans, in many ways, are a reasonably functional design for a technically sophisticated creature.
I cannot conclude that humans are the best design (although some people insist that we are not). An intelligent technologically advanced ET may resemble us, but not exactly. After all, an extra set of arms might be useful, as would an eye in the back of our heads. A double spine might allow faster and easier walking, and a few extra digits on each hand could make for better tool use or piano playing. Any technologically advanced ET would probably have some features in common with us (two eyes, instead of one, for instance). Intelligent extraterrestrials may look vaguely humanoid, but no more than vaguely. So, perhaps the TV show and movies have it right. ETs will probably resemble humans with warts.
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