Exobiology is the scientific search for life-forms existing elsewhere in this universe, whereas exoevolution involves speculating on the adaptive histories of organisms on other worlds.
It is not generally known that, at least once in his life, Charles Darwin envisioned the existence of plants and animals on another world. In 1836, having returned to a Brazilian rain forest and being impressed with its luxurious life-forms, he thought how great it would be if it were possible to admire the scenery of another planet. Darwin recorded this speculation in Chapter 21 of his first book, The Voyage of the Beagle (1839).
Do life-forms exist on other worlds? Are there intelligent beings living among the galaxies? Have advanced civilizations emerged elsewhere in this universe? These questions were asked by a few major thinkers in antiquity, but now these same questions are being taken seriously by many distinguished scientists and philosophers. The answers will have a direct bearing on the place life itself and the human species occupy within dynamic nature.
In particular, is the human animal unique and alone in this material cosmos? Or is the human species just one of many similar sentient beings inhabiting unknown worlds throughout sidereal reality? The science of exobiology intensifies human curiosity and challenges the imagination, while the quest to find forms of life and intelligence beyond the Earth requires a multidisciplinary approach that involves scientific specialists in various fields, from astronomy and biochemistry to biology and engineering, as well as the latest advances in space technology.
If life emerged from matter on the Earth, then is it not possible that organisms have appeared elsewhere in this universe? From ancient speculations to modern hypotheses, some of the greatest minds in the history of philosophy and science have grappled with the idea of exobiology (the existence of life-forms beyond this planet), for example, Cusa, Leibniz, and Kant.
In antiquity, Anaxagoras and Lucretius maintained that life does exist beyond the Earth. During the Italian Renaissance, the daring philosopher Giordano Bruno (1548-1600) argued for an eternal, infinite, endlessly changing, and inhabited universe. He even held that intelligent beings, superior to the human species, exist on planets elsewhere in dynamic reality. Of course, his iconoclastic framework challenged the earthbound and human-centered worldview entrenched in Western philosophy and theology. In fact, Bruno was burned alive at the stake in Rome (near the Vatican) because of his unorthodox worldview.
In the 20th century, although a silenced evolutionist, the geopaleontologist and Jesuit priest Pierre Teilhard de Chardin (1881-1955) failed to take seriously the probability of life-forms and intelligent beings existing on planets elsewhere. Instead, he focused on this Earth and the human species. Actually, his cosmology is merely a planetology. In his major work, The Phenomenon of Man (1955), Teilhard believed that the final goal of human evolution is a spiritual Omega Point at which time the united human species will merge with a personal God at the end of Earth history in terms of a converging and involuting collective consciousness. It is not surprising that his mystical vision satisfied neither religious creationists nor scientific evolutionists, although the courageous Teilhard is to be greatly admired for his serious introduction of the fact of evolution into modern theology.
Going beyond the ideas of Galileo and Darwin, one may anticipate an exobiology revolution in scientific cosmology. The impact would be awesome for the human species. No longer would the Earth or the organisms on this planet, including humankind, be unique in this universe.
In the United States, astronomers Frank Drake and Carl Sagan took the emerging science of exobiology seriously. In 1961, Drake proposed a mathematical equation to determine the number of detectable civilizations in this universe. His calculations suggest that there may be thousands of civilizations similar to those of humankind in the Milky Way galaxy. And in his popular writings and television series, Sagan brought the exciting probabilities of exobiology to the general public. Modern technology now makes the search for life and intelligence elsewhere possible, particularly in terms of space probes and radio telescopes, for example, the Arecibo Observatory in Puerto Rico.
Concerning civilizations with advanced technologies, physicist Freeman Dyson speculates that superior beings could use planetary matter to build an energy-capturing sphere (“Dyson Sphere”) around their star.
In Russia, the scientists Nikolai S. Kardashev and Iosif Shklovskii have proposed the construction of several huge radio telescopes in the Earth’s solar system, in order to detect extrasolar planets. Actually, modern astronomers have already discovered over 60 planets existing in other solar systems. Kardashev has classified civilizations into three energy output types: Type 1 is planetary, Type 2 is solar, and Type 3 is galactic. Going beyond this scheme, one could even imagine a supercivilization utilizing the power output of a cluster of galaxies.
Considering the age and size of this expanding universe, with its billions of years and billions of nebulas, there has probably been all the time and space necessary for life (as now known) to have emerged more than once in nature. The general uniformity of both physical laws and chemical elements throughout reality increases the probability that life, that is, the RNA or DNA molecule, has appeared on other worlds. In fact, carbon and water are plentiful in this universe. Furthermore, organic molecules (amino acids) exist in comets, meteors, cosmic gas/dust clouds, and planetary atmospheres. Therefore, the conditions for the origin of life do exist elsewhere in reality. Surely, the discovery of the RNA or DNA molecule in the sidereal depths of outer space would give exobiology an empirical foundation it now lacks, and it would intensify further scientific investigation for conscious observers and intelligent machines elsewhere in this cosmos.
All living forms need not be restricted to only this planet. Because there are billions of galaxies, each with billions of stars, it seems reasonable to assume that there are millions of solar systems with planets similar to the Earth. No doubt, at least some of these planets would resemble the Earth in size, chemistry, temperature, and atmosphere. Thus, it is highly probable that zones with the necessary conditions for the origin of life exist elsewhere. Of course, extraterrestrial organisms need not be similar to those plants and animals that have inhabited and now exist on the Earth. As a result, alien forms of galactic life could be so different from known organisms that they may not be recognized by the human species or detected by its technology.
Is life a unique miracle or random accident or statistically inevitable, given enough time and the right situation? Actually, the origin of life on this planet was remarkably swift from the geological perspective. It appeared about 4 billion years ago, only 600 million years after the formation of the Earth. Surely, if the origin of life happened once, then it can happen again elsewhere under similar conditions; recall that the prebiotic chemistry for life pervades this universe.
Logic does not dictate that this planet or life on Earth or the human species must be unique in all reality (although religionists and theologians may still believe each of these claims to be true).
At this time, there is no direct empirical evidence to support exobiology. Because of the awesome cosmic distances among the stars and nebulas, one may never discover the existence of life on other worlds in this universe (even if it does exist). Life-forms may have emerged and vanished before the existence of this solar system, or organisms will appear on other planets in the remote future. Another possibility is that superior beings elsewhere may not be interested in the human species; if they are intelligent enough to discover humankind, then they are wise enough to stay away. The human animal has nothing to offer such superior visitors from deep space.
Furthermore, it is possible that other universes with life-forms have existed before this one, are coexisting with this world, or will exist after this particular cosmic epoch has ended. Consequently, the questions raised by exobiologists may never be answered in the affirmative, even if life does exist elsewhere. The same is true for questions concerning exoevolution.
Perhaps numerous inhabited planets do orbit stars in this galaxy and in others. Concerning the organic evolution of life-forms on other worlds, what is possible? If planetary systems are common, then do Earthlike worlds elsewhere harbor biological activity needing carbon and liquid water (or is life elsewhere based on another element, for example, silicon or boron)? The human quest for cosmic life and intelligence may even find fossils and artifacts on other worlds.
Four billion years of biological evolution on this planet have produced a staggering spectra of organisms, ranging from bacteria and plants to invertebrates and vertebrates. This creative unity of global life includes such diverse life-forms as worms, sponges, sharks, turtles, snakes, and elephants. Among the very social creatures are species of insects, birds, and primates (especially the pongids and hominids). Yet, most of the species that have inhabited this world are now extinct, for example, all the trilobites, ammonites, and dinosaurs have vanished from the biosphere.
As if organic evolution on Earth is not difficult enough for many to accept, especially biblical fundamentalists, then the discovery of exoevolution will challenge all thinkers to seriously reassess the place that humankind occupies in dynamic reality.
The only process of organic evolution that is now known to science is the one taking place on Earth. However, exobiology infers exoevolution. Environments are never fixed anywhere in nature. No doubt, the struggle for existence pervades this universe. As on this planet, life-forms elsewhere would have evolved to meet the challenges of their changing habitats. One can only speculate on what directions organic evolution and adaptive radiation have taken on other worlds. Perhaps human explorers will find species similar to ants, whales, and the apes; and maybe even the technological remains of past civilizations, or the existence of cognitive biorobots of superior intelligence, will be discovered in this cosmos.
If life-forms are found elsewhere, then future scientists and philosophers would participate in the critical study of comparative exoevolution. Or if human beings send themselves and other life-forms into outer space, then these plants and animals will evolve in strange new habitats (thereby making the study of exoevolution a certainty). In fact, the human species itself may evolve into a new form of life as it adapts to living among the distant stars.
Are we completely alone in this material universe? If not, then contact with extraterrestrials will be the most momentous event in human history. In fact, the Nietzschean Overman may have already emerged somewhere in this universe. Cosmic aliens with superior intelligence could be wise, benign, creative, and compassionate, or they could be indifferent and evil. Certainly, their achievements in science and technology will be far beyond our comprehension.
Moreover, cosmic microbes may cause diseases that could bring the human species (if not all terrestrial life-forms) to extinction. The cosmic quest for life elsewhere is not to be taken lightly.
Exobiology and exoevolution directly challenge geocentrism, zoocentrism, and anthropocentrism. The discovery of organic evolution beyond the Earth will make this planet and the human species even less significant than they now are. If intelligent beings are discovered elsewhere, then the human animal will no longer be something special in this universe. Such an incredible event would have an awesome and lasting impact on humankind’s science, philosophy, and theology (not to mention the inevitable psychological and sociocultural changes to the self-centered human species). Giving priority to science and reason, and with courage and humility, future naturalists will need to accept the true place of our human species in material reality from a cosmic perspective and within the evolutionary framework.
For most scientists, the origin of life on Earth was a strictly materialistic event. The subsequent history of living forms on this planet has been a long, complex, contingent, unpredictable, opportunistic, and inefficient process of biological evolution. Organic evolution is also nonrepeatable, irreversible, and subject to material constraints.
Homo sapiens sapiens is a product of, dependent upon, and totally within evolving nature. Because of the staggering necessary sequence of improbable events that had to occur in order to bring human beings into existence, it is unlikely that the human species will meet its exact duplicate on a remote world. Nevertheless, at least once, with the recent emergence of the human being, this dynamic universe became aware of itself.
Rational speculations are very important, but there is no substitute for evidence, observation, and communication. It is conceivable that processes of evolution elsewhere in this universe have produced forms of life similar to, or remarkably different from, those species that have emerged on the Earth over billions of years. In fact, the possibilities for life-forms inherent in exoevolutions on other planets seem endless.
Of course, extinction and evolution are two sides of the coin of life. A comet strike or global plague or nuclear war could wipe out the human animal and most, if not all, of the other species on Earth. In fact, this vulnerable planet has already experienced at least five mass extinctions. Similar horrific events may have already eliminated all life-forms on some other worlds.
There is no evidence of a preestablished direction or preconceived purpose or preordained goal for this cosmos that gives the human species a central position in material nature. This universe is clearly independent of and utterly indifferent to humankind; until now, the human species has played no special role in the existence of reality. There was cosmic time before the appearance of the human animal, and material nature will endure after the extinction of life and consciousness on this planet.
At some time in this millennium, reminiscent of the young Charles Darwin in a Brazilian rain forest, a naturalist may stand on another world and marvel at forms of life beyond humankind’s present imagination. Another intriguing possibility remains: the survival and fulfillment of the human species may depend on its working in consort with sentient life-forms still to be encountered elsewhere in this universe.
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