Progress, man's distinctive mark alone.
Robert Browning, A Death in the Desert
Man is now the only hominid species on Earth, but until recently — until about 30,000 years ago — we shared the planet with at least one other human species. We certainly co-existed with Homo neanderthalensis, and we may have co-existed with Homo erectus. (30,000 years seems a long time, but it is a mere instant in the Universal Year; even in the history of our species it represents less than a third of the time we have been in existence.) This realization — that once we were not alone — is quite recent, as many anthropologists used to think only one species of hominid could have existed at any one time; in this view the Neanderthals must have been our ancestors. Recent evidence, however, seems to rule out this possibility. Studies of mitochondrial DNA from Homo sapiens and Homo neanderthalensis show that they were two genetically distinct species. The finding is backed up by recent computer reconstructions of the skulls of Neanderthals and early modern humans: skull development was quite different. So it seems certain that Homo sapiens and Homo neanderthalensis are separate species, sharing a common ancestor in the distant past — perhaps as long ago as 500,000 years — before evolving in separate ways. It seems equally clear that, although there may have been a small degree of interbreeding, the Neanderthals contributed nothing to the modern human gene pool.226
Earth may have been home to 20 or more hominid species at various times, and some of these species must have co-existed. The simple picture of hominid evolution — an ape-like creature gradually evolving into "more advanced" species and culminating finally with Man — is wrong. Rather, Homo sapiens is the last remaining twig on what was a convoluted branch of the evolutionary tree. The various hominid species each occupied a niche, and each possessed various skills and attributes.
our knowledge of earlier hominid species is sketchy, but we know much more about our closest relatives, the Neanderthals. (our closest relatives still in existence are the great apes, with whom we share a common ancestor that lived some 5 million years ago.) It is instructive to remember the abilities and achievements of our sister species. Individual Neanderthals must have lived short, hard lives, but as a species they survived for a long time — much longer than mankind has been around; they inhabited a large area of Earth; they coped with severe swings in climate; in short, they successfully filled a biological niche. There is some evidence that Neanderthals buried their dead (though whether this practice was associated with the ritual accompanying modern human burials is doubtful).
There is also some slight evidence, from analyses of Neanderthal skulls, that they may have had the physical capacity for speech (though it seems more probable that they lacked the capacity to communicate in the way that we do). It is particularly interesting that they had a form of tool technology, called Mousterian (after the French cave of Le Moustier where such tools were first discovered). Mousterian tools are made of stone and take a variety of basic forms. The Mousterian craftsmen, then, were presumably able to hold several patterns of tool design in their minds and, combined with their deep appreciation of the properties of stone, produce quite beautifully constructed implements. The Neanderthals may not have matched the achievements of humans, but they were no mugs.227
However, during their period on Earth, Neanderthals demonstrated little in the way of creativity or innovation. If they created art, it has not survived; if they made music, their instruments have not survived. And their technology, though reasonably effective, was not subject to the sort of progress we have come to believe is inevitable. The late Mousterian tools were not significantly better than those of the early Mousterian. Neanderthals soon learned how to work stone, but then learned little else — not how to work bone or antler for tools, for example. So if we accept that Neanderthals were intelligent, then we have an example of an intelligent toolmaking species surviving for more than 100,000 years without making significant technological advance. They edged into extinction — for reasons not entirely clear — without inventing the ratchet much less the radio telescope. Perhaps this situation is mirrored on other worlds. Perhaps for some reason (lack of language, lack of a "creative spark," lack of hand-eye coordination, lack of whatever) alien species reach the level of toolmaking and then remain at that level. Perhaps the Galaxy abounds with species that are experts at handling wood or stone or bone, but that never develop further. We do not hear from ETCs because none of them have the required technology: in other words, communicating ETCs do not exist.
One weakness of this suggestion is that it requires all toolmaking species to develop in the same way. It is unconvincing in the same way that some of the "sociological" explanations fail to convince when they require all ETCs to behave in the same way. After all, even if hominid species in general have been poor technological innovators, one member of the hominid family is exceptionally innovative. One hominid species out of about 20 discovered the benefits of continual innovation; if that ratio is found elsewhere, the odds of finding ETCs would not seem so bad.
Before rejecting the suggestion completely, however, it is worth remarking that for much of our history we were not much better than the Neanderthals when it came to technological innovation. Only 40,000 or so years ago did our technology and art began to dazzle.228 (The cave art of the
Cro-Magnons is truly dazzling. It is recognizably human and speaks to us across millennia. It is unlike anything appearing before that date.) Until this explosion of creativity, the two surviving hominid species appear to have been equally stagnant. Why the sudden change? There are several possible explanations. Perhaps the development of language triggered the creative explosion. Perhaps the explosion occurred much earlier, but artifacts prior to 40,000 years ago have not been preserved. Perhaps the humans of more than 40,000 years ago were anatomically modern, but did not possess modern brains. Or perhaps cultural knowledge accumulated slowly until, 40,000 years ago, it passed a critical threshold. We do not know. Perhaps whatever caused this explosion of creativity was a fluke, an accident. If it was, then we might expect the number of communicating ETCs to be small.
One last point. Inherent in the formulation of the Fermi paradox is the notion of an exponential growth in knowledge and technology. Perhaps most of us believe, consciously or otherwise, that early humans were in the "flat" part of the exponential curve: progress came slowly. Then, as time passed, progress fed upon itself and we end up today with computers obeying Moore's law. We extrapolate this exponential curve into the future and imagine our descendants having access to tremendously powerful technology; and, if ETCs are much in advance of us, we expect them to possess tremendously powerful technologies. But maybe this is wrong. In Nature, exponential curves never continue indefinitely. Perhaps the idea of technological progress continuing until a species can travel or at least communicate over interstellar distances is wrong.
This suggestion seems unduly pessimistic, at least to me. Even with our present technology, we can make a stab at communicating with the stars. Give humanity another 100 or 1000 years, and who knows what it will achieve.
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