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102 After Biology The missing link in all past SETI arguments, argued Steven Dick, has been a failure to account fully for the effects of cultural evolution—in particular, the future evolution of biological intelligent beings to a post- biological state. Cultural evolution, which is proceeding much faster than biological evolution, has been a huge force in human adaptation, enabling us to do what none of our primate relatives can do. Only humans can accumulate knowledge over long periods of time and trans- fer it so that the next generation can improve on it. The possibility that many extraterrestrial beings will be postbiologi- cal becomes an increasingly important factor as the lifetime of techno- logical civilizations is extended. That lifetime need be only thousands of years for cultural evolution to have drastic effects on societies. If technological civilizations typically last more than a few hundred years, the result will be a postbiological universe (there may be a transition period populated by human/machine cyborgs). Assuming a linear development of extraterrestrial civilizations over time leads to a conclusion that more than 99% of intelligent life will be postbiological. Such creatures, who may be essentially immortal, might have characteristics that we ascribe to God: omniscience and omnipotence. Long-lived artificial intelligences could improve the prospect of contact. Short-lived biologicals like us might find themselves intercept- ing communications of postbiological beings. Dick hinted at the ambiguous implications. Postbiologicals would have a great capacity to do good—or evil. Statistics The phenomena that the Drake equation assumes to take place are only those we are sure have taken place at least once, except for the last factor: the longevity of civilizations. This is the one area in which we are totally ignorant; we do not know if there is a limitation. Because introducing a limit minimizes our estimates of the numbers of civilizations that we might detect, the equation may be too conservative.** One approach to this question is to look at the longevity of our ancestral species. The 10 or so hominid species that preceded modern humans came and went at a rate of about 200,000 years each. As ours began at least 130,000 years ago, we soon may be due for a change. This has less optimis- tic implications than Philip Morrison’s estimate that the lifetime of an average species on Earth is close to 5 million years, or evolutionary biolo- Probabilities: Longevity