Though life’s varieties are infinite, when it comes to advanced, intelligent life (what some call class-1 life) it is quite possible that the fundamental archetype across the cosmos is more similar to us than not, since it uses the same basic ingredients and would be derived from a similar evolutionary process.
Like us, other intelligent class-1 life is likely to be carbon, nitrogen, and phosphorous based, using oxygen to fuel the flame of life. Carbon is the fourth most abundant element in the universe, after hydrogen, helium, and oxygen. It is also the hardest of all elements, and has the highest sublimation point—meaning it rarely melts into a liquid, preferring instead to jump directly from solid to gas. But its greatest characteristic of all is the four electrons spinning in its outer-valence shell which tirelessly seek four more electrons to complete the octet ring. This gives carbon the ability to readily form strong tetrahedral, four-way bonds with other elements, including other carbon atoms, allowing it to build complex chains of compounds, which are the basic building-blocks of life.
Life, in turn, resourceful as it is, uses this atomistic trait of carbon to form increasingly-complex compounds by diligently adding infinitesimally-small modifications to the previous design in order to fashion a more sophisticated model—and it does this tirelessly for billions of years. In fact, carbon forms more unique compounds than any other element; theoretically hundreds of millions, some say potentially billions.
Carbon, like other fundamental elements used by life, is formed deep in the heart of a star. Virtually all stars fuel their combustible light by fusing two hydrogen atoms together to make one atom of helium (1H+1H=2He). After fusing hydrogen into helium for billions of years, stars eventually run low on hydrogen, while becoming helium rich. As the heavier helium-rich core contracts, it gets denser and hotter, until it is hot enough to fuse three atoms of helium together to make carbon (3*2He=6C), and four atoms of helium to make Oxygen (4*2He=8O). Then, as temperatures increase, carbon fuses with hydrogen to make nitrogen (6C+1H=7N); and eventually, at even higher temperatures still, Phosphorous (15P) is finally formed, giving us the elemental Spark of Life.
And so, from the stellar womb of this fiery furnace the genesis of life is born when, upon her deathbed, the dying star explodes and births forth into the universe immense blazing clouds of gas and water and dust, the elemental progeny from which we all descend. And when, in time, those elements cool and gather to form new stars and planets, on some of these nascent goldilocks planets—those appropriately distanced from their sun—a germinal chemical amalgam forms, fueled by the sun’s heat from above and stoked by volcanic eruptions from below, infusing the simmering ocean pot with gas and ash and minerals for billions of years, until that one propitious day, that one instant in time, when the electrons from one compound form a fortuitous bond with another, igniting a phosphorous match to spark life.
Then, after a billion years more of infinitesimally-small modifications, two stand-alone life-forms collude, make a team, and fashion a deviously radical design, commonly known as blue-green algae—arguably the most important, abundant, and varied life-form known. Once that happens, once blue-green algae blooms in the seas and grabs hold of that nascent world, the stage is now set for everything to change. Now, the fledgling planet is transformed by this little green life who patiently, diligently, tirelessly, for another billion years or more bobs about in the ocean using energy from the sun to strip the two hydrogen atoms off a water molecule (H2O), using the hydrogen to make food, and releasing as waste into the air trillions of tons of oxygen.
But oxygen is far too volatile to remain free-floating for long and quickly binds itself to other elements, like iron dissolved in the sea. For hundreds of millions of years, molecule by molecule, dot by dot, the oxidized iron settles onto the ocean floor as rust, laying a foundation of rich iron-ore with which advanced life will one day forge a civilization. Although iron is fairly abundant, being one of the fundamental elements formed in the blast-furnace of stars, it is generally sparsely diffused through a planet’s crust and so not until the oxygen from blue-green algae concentrates it onto the ocean floor is it made more easily available for use by emergent class-1 life.
One may reasonably affirm, therefore, that all of intelligent life’s primal tools, and the foundational girder that buttresses its earliest civilizations, is gifted to us by the noble, tireless efforts of tiny, slimy, pond scum. No monuments are erected. No thanks are ever given. But those are the facts just the same. Without blue-green algae, life as we know it would not be. We should all be eternally more grateful.
As iron and other elements become oxidized—saturated with oxygen atoms—more oxygen is free to infuse the air. But oxygen is toxic to the earliest forms of life who planted their flag on an oxygen-free world, and so unfortunately—from their point of view, at least—the rising oxygen-level in the atmosphere leads to a mass extinction on the planet that wipes out 90% of all pioneer life, in what is called—from the pioneer-life perspective—“The Great Oxygen Catastrophe.”
From our perspective, though, this “catastrophe” is anything but, because now carbon’s and oxygen’s inherent ability to form long, complex compounds will be leveraged by our ancestors over the millions of years to follow, until one day the fundamental archetype of all intelligent life, our great-great grandmother to the Nth degree, our venerable diminutive Granny, who was little more than a brave eager tadpole, wriggles herself out of the primordial sea.
Nothing in nature is superfluous. Life is the master mad scientist, optimizing everything through rigorous trial and error. And so, after learning the hard way that it’s pretty tough to crawl around with only one, or two, or even three appendages—and noting that five is more than is needed—the successors of our earliest tadpole-Grannies inevitably settle on four limbs as the ideal number suited for effective locomotion. Through a similar trial-and-error process of endless augmentation and elimination, later successors settle upon five digits on each of the four limbs as the optimal number needed for balance, and running and catching things.
And on and on it goes. Trying. Failing. Improving. And trying again. Life never gives up.
By and by, some creatures learn—again usually the hard way—that having two eyes at the front of the head works best, since the lack of stereoscopic vision and depth perception with having only one eye bolted in front proved disastrous for catching and running from things. Over time, others found that having two ears was pretty handy too, especially when something really nasty was sneaking up on you from behind, making it hard to see. And eventually it became abundantly clear to most that having the nose situated close to the mouth was helpful for facilitating the interrelated functions of taste and smell; while the disposal of waste was best undertaken when the ass was placed far to the rear.
Some creative life-forms experimented with extra ears and eyes and legs and so forth, under the misguided premise that if some was good, then more must be better, but everything has a cost. Nothing in life is free. And so with extra eyes or ears or whatever, comes additional expense and support, which requires more energy, which means more running and catching things. Life, like everything else, must manage a budget and learn to live within its means. Thus, all new features and functionality are weighed in terms of evolutionary gain, versus the cost of service and support, until the proper balance is found. Because, although no one wants to pay for something extra which they don’t need; they sure as hell don’t want to be caught out crawling around late at night with their pants down, lacking something they did.
Naturally, what is considered necessary, important, and advantageous changes often over time as environmental conditions alter, so the research and development into new enhancements and prototypes never ceases. Plus, everyone has to constantly keep a watchful eye out over their shoulder for some tricky new life-form, like that sneaky blue-green algae bastard, who suddenly brings to market—evolutionarily speaking—a revolutionary new design that kicks everyone else’s ass, forcing them to change their design as well, or die. Evolution is a lot like business, in that way, but without all the feigned pleasantries and nasty politics.
As life enhances the design into increasingly-sophisticated models, the similarities in the archetype for advanced, intelligent life are likely to become even more pronounced. For example, all class-1 life needs a minimal level of tactile dexterity in order to fashion tools, which inevitably means having at least one opposable digit, out of the five, for making and grasping these things. And the more dexterity they have, the more precisely they can fashion tools, so, at least in the case of dexterity, more really is better. Additionally, any aspiring-to-be intelligent life-form must be physically strong enough to compete with the largest predators on their planet, otherwise they’ll consistently find themselves on the short end of a stick, which is not where a class-1 life-form generally wants to be. They also must be physically large enough to manipulate the natural world around them; and lastly, they have to stand erect and perambulate on only two of their four limbs, in order to keep the other limbs free for wielding and fashioning the various tools they make.
So, when all these factors are considered, when all the necessary characteristics needed to build an advanced, intelligent class-1 life-form are incorporated into the design, the end product that is ultimately brought to the evolutionary market is probably a fairly standard archetype, since it follows the same basic laws.