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PERSPECTIVES IN BIOLOGY AND MEDICINE Volume 15 · Number 2 · Winter 1972 DARWINIAN EVOLUTION AND THE PROBLEM OF EXTRATERRESTRIAL LIFE THEODOSIUS DOBZHANSKY* The heretic Giordano Bruno was burned at the stake in Rome on February 19, 1600. Among his heresies was his belief in a plurality of worlds inhabited by rational beings. The inquisitors who condemned Bruno surely did not doubt that heavens are inhabited. They insisted, however, that God and saints and angels dwell not on another planet but somewhere above the clouds and the firmament. It was really Copernicus, and after him Galileo and Kepler, who showed that heavens are not a sphere enveloping a centrally located earth, and thus raised the question of the abode of extraterrestrial life. The idea that man is the sole rational life in the universe seems incredible and even distasteful to many people. Popular imagination always fancied material or incorporeal beings residing in extraterrestrial habitats and craved to communicate with them. From 1877 on, some serious astronomers claimed to have seen "canals" appear and disappear on the surface of Mars, and this was freely interpreted as evidence of a technologically advanced civilization using irrigation for its agriculture. Less serious observers reported seeing flying saucers and other unidentified flying objects and expected Martians or other visitors from outer space to disembark from them. Better observations, as well as space flights, brought disappointments to believers in extraterrestrial manlike beings. Neither the moon nor the planets (other than the earth) in our solar system can credibly be supposed to harbor manlike inhabitants. Some kind of primitive life is improbable but is not completely ruled out. Believers * Department of Generics, University of California, Davis, California 95616. Perspectives in Biology and Medicine · Winter 1972 I 157 now look beyond the confines of the solar system. The survey of biological science edited by Philip Handler [1] contains the following statements: "Given manifestations of intelligent activity no greater than we ourselves produce in the form of radio transmission, existing terrestrial technology is capable of detecting such activities over distances as enormous as 1000 light years, within which range there are 10 million stars," and "a serious, well-funded search for extraterrestrial signals should be organized on a worldwide basis."1 Stating the Problems The demonstration by Darwin in 1859 and 1871 that the living world, including man, is a product of evolutionary development placed the problem of extraterrestrial life in a new perspective [2, 3]. If such life exists at all, it must also have evolved from some simple beginnings. In our day, spectacular advances of molecular biology and biochemistry led to a revival of interest in the problem of the origin of life from nonliving matter. Plausible schemes of how life could have arisen on earth, and by extension on earthlike planets if such actually exist elsewhere in the universe, have been worked out. It must, however, be stressed that the problem of the origin of life is quite distinct from that of its subsequent evolution. Assuming that life has in fact arisen, what inferences or predictions can one draw concerning its evolutionary development? Cosmologists and exobiologists (specialists on life outside the earth) who speculate on this topic assume lightly that the development would be on the whole like that of life on Earth. The climax predicted with astonishing confidence is the emergence of humanoids, manlike rational beings, and the eventual appearance of extraterrestrial civilizations and technologies as advanced as ours or more advanced. Hence the proposals to organize "a serious, well-funded search for extraterrestrial signals." Evolutionary biologists have mostly steered clear of these issues, probably finding them too speculative. G. G. Simpson [4] is a conspicuous exception. His incisive analysis of "the nonprevalence of humanoids" led him to conclude: "The assumption, so freely made by astronomers, physicists, and some biochemists, that once life gets started anywhere, humanoids will eventually and inevitably appear is plainly false. The chance of duplicating man on any other planet is the same as the chance that the planet and its organisms have had 1 Although one of the 175 "contributors" to the survey, I have seen the whole of it only after its publication. 158 I Theodosius Dobzhansky · Extraterrestrial Life a history...


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