Prepared by:

Mark A. Stull

SETI Program Office

Ames Research Center

[48] blank page

[49] How likely is the evolution of intelligent life and technological civilization? Assuming that some self-replicating molecule that we can call "alive" evolves on some planet, will biological evolution act over the eons to produce a diversity of living forms similar to that we see on Earth? Might many of those forms develop intelligence and technology, or is man but a fluke that arose on Earth only as a result of a combination of highly improbable circumstances? What factors determine whether or not biological evolution will lead to intelligent and technological species?

These questions have been asked many times, but satisfactory answers have not been forthcoming. Perhaps this is because we have lacked the data to enable us to understand evolution to the necessary degree. The past two decades have seen a revolution in our understanding of animal behavior and a deluge of paleontological discoveries, especially of fossil hominids. As a result, we are, perhaps for the first time, able to make a rough assessment of the probability that evolution will produce an intelligent, technological species, and have some degree of confidence that the assessment is correct. Our new knowledge has changed the attitude of many specialists about the generality of cultural evolution from one of skepticism to a belief that it is a natural consequence of evolution under many environmental circumstances, given enough time.

On November 24 and 25, 1975, NASA sponsored a Workshop¹ on the evolution of intelligent life and technological civilizations which brought together prominent physical, biological, and social scientists (see Section III-15). That workshop endorsed the estimate that the combined probability that both intelligent life and technological civilization would evolve, assuming the origin of life on an arbitrary planet, is at least 10^-2 The workshop considered the opinion of George Gaylord Simpson, who was not present, that the evolution of intelligence was so improbable that perhaps it did not even happen on Earth. Albert Ammerman, geneticist from Stanford, pointed out that when Simpson formed his opinion, in the early 1950s, much less was known about such things as the evolution of the hominids, the social structure and communicative abilities of the chimpanzees, and the social behavior of other animals. At that time man appeared terribly unique; today this is no longer true. It is easy to imagine how other lines could have led or might yet lead to intelligence and civilization here on Earth. Intelligence, complex social organizations, and even the manipulative ability which makes possible the use of tools, have been demonstrated to have positive survival value; hence evolutionary pressures will tend to produce them.

A recurrent theme of the workshop was that it is wrong to focus on particular "crucial" events in the long evolutionary chain that has led to our modern technology. That these events appear by themselves to be improbable is misleading, since a low probability for a particular event does not imply a low combined probability for all possible events similar to it. Furthermore, that there can be a high probability of certain results, however improbable each of the innumerable ways they may come about, has been demonstrated many times by biological evolution itself.

[50] Hans Lukas Teuber, neurophysiologist from MIT, pointed out that many organs have polyphyletic origins. The eye has been invented at least three times. The cephalopod eye, the insect eye, and the vertebrate eye all have totally different, independent evolutionary histories, but these histories have converged to essentially the same result. The neural networks in each of these eyes are shockingly similar. Indeed, any life-form evolving in an environment where the optical spectral band is important might well develop a light sensing organ with similar nerve structure. NevertheIess, octopi and vertebrates cannot see the same things. Octopi cannot distinguish mirror images. Therefore different evolutionary pathways cannot be expected to produce identical results. It is not unlikely that technological species are abundant in our galaxy, but it is very unlikely that elsewhere we will find men.

There was a wide range of opinions on what evolutionary factors were responsible specifically for hominid intelligence; probably many were important. Joshua Lederberg, geneticist from Stanford, thought that intraspecific warfare played a significant role. War seems to require rapid invention. Strategy discussions that are connected with the planning of warfare tend to involve a kind of verbal competition that is highly inventive. Furthermore, intraspecific conflict makes special demands on organisms that their battle with the environment does not: the difference is between intelligence against intelligence on the one hand, and intelligence against mere non intelligence on the other. Finally, warfare seems to involve the young; organisms not suited to it suffer the consequence that their genes are eliminated from the breeding population. However, the necessity of the evolution of such an institution as warfare cannot be said to be established. Territoriality is a common trait among Terran animals, and some of the social mammals, such as man and the hyena, exhibit, as one form of territorial behavior, organized violent conflict between social groups. But territoriality is not a basic biological trait; many species do not exhibit it. Bernard Campbell, anthropologist from UCLA, thought it was but a result of the primary need to compete for resources, and that other means of allocating resources might be possible.

Probably the most important stimuli to the development of intelligence in early hominids was the demands of communication and language. J. Desmond Clark, paleoarcheologist from the University of California at Berkeley, pointed out that an increased rate of evolution of the brain set in about 3 million years ago, and this was correlated with increased use of stone tools. Manufacture of artifacts is evidence of complex social structure which in turn implies need for improved communication; at the very least the techniques of manufacture must be taught to the young. But John Eisenberg, ethologist from the Smithsonian Institute, thought that some of the hominids' increased cranial capacity was related to a general increase in motor coordination. The "text book idea" that man is a puny beast is simply not true. He is a fantastically powerful and coordinated organism, especially in the hands and limbs. He has subtle and accurate motor control which gives him great physical ability. He has independent control of his fingers and motor control of vocalization. And he has a very complex feedback system which enables him accurately to determine the course of thrown projectiles, with a little practice.

There was general agreement that the need to adapt to a predatory way of life on the savannah stimulated at least the early development of manipulative ability, motor coordination, and complex social organization in the hominids. The arboreal environment of the hominids' ancestors cannot have produced these traits. No monkey or ape can control a thrown projectile the [51] way a man can; independent finger control is a uniquely hominid characteristic. Moreover, chimpanzees and other apes, though they use natural objects such as sticks for tools, have never developed a systematic tool-making ability. In captivity they can be taught to chip flakes from stone, but that they do not do this in the wild means nothing less than that their arboreal environment makes no demand on them to do it. Correspondingly, they have never evolved the motor control of the throat that is seen in the hominids, though chimpanzees have great natural ability to communicate by gestures. They cannot develop spoken language because they are physically incapable of pronouncing words.

Thus the demands of the savannah environment were probably responsible for the development of intelligence and technological society in man. But it does not follow that this type of environment is a necessary prerequisite to the development of these characteristics. Bernard Campbell thought it was crucial that an animal well adapted to life in the complex forest environment proved to be pre-adapted to an ecological niche on the savannah and was successfully able to invade it. This opened many new possibilities. Moreover, any animal is likely to expand its range into new environments given the necessary amount of preadaptation. Thus what appears most important in stimulating evolution is the presence on a planet of a large diversity of environments readily accessible to the inhabitants of each. The larger number of possibilities inherent in this situation will result in the greatest diversity of species, and will speed the development of traits having survival value, such as intelligence.

This requirement allows us to characterize planets likely to produce intelligent, technological civilizations. In the first place they must have heterogenous and time-variable environments. Bernard Campbell pointed out that in a very stable, homogenous environment no evolution at all occurs, even over indefinitely long time scales. On Earth the deep-sea echinoderms are evidence of this. John Eisenberg pointed out that on isolated land masses intelligence appears to have developed very slowly. For example, in Australia, Madagascar, and pre-Pliocene South America, there was development of many mammalian species, independent of that which took place on the contiguous land masses. On none of the isolated land masses did there develop mammals with large cranial capacity. We see this today in the mammals of Australia and Madagascar. This was also true in South America, although the development of these species was interrupted in the Pliocene, when the northern and southern continents were joined. Only mammals on large contiguous land masses developed both large bodies and large cranial capacities. It is unlikely that planets with limited contiguous land area will evolve intelligent terrestrial life very rapidly, while an aqueous environment is not conducive to the evolution of manipulative ability and hence technology. However intelligent dolphins may ultimately prove to be, they will never build radio telescopes or spacecraft.

Almost certainly once a species with the requisite intelligence, manipulative ability, and complex social organization has evolved, technological civilization will develop. Modern man is little different biologically from Cro-Magnon man. To go from a stone age culture to our present level of technological development required no biological evolution. All that was needed was the development of ideas, and their testing by trial and error. Philip Morrison pointed out that Turing had shown that once yes-no choices can be recognized in large numbers, one can program any mathematical computation, given enough time. Thus, once a system capable of conceptualizing [52] sophisticated internal models of external phenomena has evolved, it is only a matter of time before all possible ideas inherent in the available sensory perceptions are conceived. It is incorrect to focus on "critical" historical events in cultural evolution, just as it is incorrect to focus on single steps in biological evolution. For example, the importance of what might have happened had the Greeks lost at Marathon has probably been greatly overemphasized. Some developments that subsequently occurred might, to be sure, have been prevented, but others of similar type that did not happen could also have been stimulated.

The next stage in the evolution of hominids could be stimulated by our entry into space, including a search for extraterrestrial intelligence. Our past success has been due to our breaking of new ground -- to our acceptance of the challenge inherent in exploring new ways of life. This was true even for our distant ancestors who abandoned the relative security of the trees to compete with other carnivores for fleet-footed prey on the open savannah. Hans Lukas Teuber thought the urge to explore and seek new understandings is among our most powerful innate drives. This can only be true because exploration has had high survival value to us.

Thus it might be a mistake if, in our present time of environmental, political, and social crises, we turned our back on that great arena we have not explored the stars. Daniel Kevles, historian from the California Institute of Technology, said he viewed the matter as a religious man. He noted that everybody's assumption seemed to be that a search was worth conducting if it appeared that life were common. However, he thought it would be worthwhile should we not be convinced of this. A null result would be important. The justification of the experiment is that it is a very special test of whether we are alone; this goes beyond the benefits we may gain or the knowledge we could acquire. Only if we can demonstrate that the probability of intelligent life elsewhere is zero, should we not go ahead with the search; this, of course, is impossible, because we are here. Jack Harlan, historian of agriculture from the University of Illinois, thought we must learn what we can about the Universe; it is our destiny.

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