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80 systems or the scale of cosmic time. NASA SETI program manager John Rummel declared that it is better to perform experiments than to be walled off from the real world by the opinions of experts. Sagan responded to Mayr by pointing out that as microorganisms are our ancestors, they did evolve “smartness.” Extrapolation from our example would suggest that there are enormous numbers of Earth-like planets stocked with many species, and that at least one of those species would develop high intelligence and technology in much less than the lifetime of its star. The selection pressure for intelligence may be lower on some worlds, but it may be higher on others. As this debate continued, Mayr conceded that life elsewhere in the universe is probable. He had acknowledged 10 years earlier that the probability of the repeated origin of macromolecular systems with an ability for information storage and replication can no longer be doubted. Yet, he still challenged the likelihood of intelligence and “electronic civilizations.” Although “physicalist” thinking may be appropriate for physical phenomena, he found it quite inappropriate for evolutionary events or social processes such as the origin of civilized societies." Skeptics have been particularly dubious about other evolutions to brains like ours, emphasizing that it was by no means a sure thing on Earth. They cite the specific sequence of events that produced human intelligence, arguing that this sequence is highly unlikely to be repeated anywhere else. Some find that encephalization (the ratio of brain to body size) has increased at a remarkably uniform rate for at least half a billion years. These studies, wrote Drake, “seem to shout loudly that we can expect to find intelligence wherever initial circumstances and time have been sufficient.”' Others argue that there have been considerable variations in the rate of encephalization among primates. Brain size in some hominid species remained static for a million years, anthropologist Richard Klein reported, as did their cultures. He saw human evolution as three or four sudden and profound events spaced between lengthy stretches of time when little hap- pened. According to one theory, hominid brains were allowed to expand by a genetic change 2.4 million years ago that reduced the powerful jaw muscles they had shared with their primate relatives; this removed a con- straint on encephalization.” Probabilities: Intelligence How Brains Evolve, or Don’t —Frank Drake, 1974"