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ET and SETI
by Michael Shermer
FATE :: November 2007

Shortly after the SETI program was launched in the early 1960s, the evolutionary biologist George Gaylord Simpson outlined his skepticism in a 1964 Science essay with a title befitting his conclusion, “On the Non-Prevalence of Humanoids.” Evolutionary theorist Ernst Mayr concurred, presenting his skepticism in a debate on the likelihood of success of the SETI program with the astronomer Carl Sagan.

“Life originated on Earth about 3.8 billion years ago, but high intelligence did not develop until about half a million years ago.” That is, for the first 98.6 percent of life on earth there was no advanced intelligence. For the two billion years after life began there were only simple prokaryote cells.

Eukaryote cells with a nucleus and other modern characteristics evolved about 1.8 billion years ago, followed by three groups of multicellular organisms: fungi, plants and animals. Of the 60 to 80 phyla of animals, only one, the chordates, led to intelligence; and only one of these, the vertebrates, developed intelligence; and of all the vertebrates—including fishes, amphibians, reptiles, birds, and mammals—only mammals developed intelligence; and of the 24 orders of mammals only one—us—has intelligence. Mayr concluded definitively, “Nothing demonstrates the improbability of the origin of high intelligence better than the millions of phyletic lineages that failed to achieve it.”

Given these brute facts about evolution, why would anyone bother to listen for ET’s signal?

Carl Sagan provided an answer. First, we don’t need “humans” per se, just “creatures able to build and operate radio telescopes. They may live on the land or in the sea or air. They may have unimaginable chemistries, shapes, sizes, colors, appendages, and opinions. We are not requiring that they follow the particular route that led to the evolution of humans. There may be many different evolutionary pathways, each unlikely, but the sum of the number of pathways to intelligence may nevertheless be quite substantial.”

Sagan notes that there are trends in evolution that lead to SETI optimism: “other things being equal, it is better to be smart than to be stupid, and an overall trend toward intelligence can be perceived in the fossil record. On some worlds, the selection pressure for intelligence may be higher; on others, lower.”

Our sun is not a first-generation star in our galaxy; there are stars (and thus solar systems) 10 billion years old. Sagan asks us to imagine two curves: “The first is the probable timescale to the evolution of technical intelligence. It starts out very low; by a few billion years it may have a noticeable value; by 5 billion years, it’s something like 50 percent; by 10 billion years, maybe it’s approaching 100 percent. The second curve is the ages of Sun-like stars, some of which are very young—they’re being born right now—some of which are as old as the Sun, some of which are 10 billion years old. If we convolve these two curves, we find there’s a chance of technical civilizations on planets of stars of many different ages—not much in the very young ones, more and more for the older ones. The most likely case is that we will hear from a civilization considerably more advanced than ours.”

In 1982, Carl Sagan published a petition in Science urging the scientific respectability of SETI, for which he garnered many distinguished signatories, including such biologists as David Baltimore, Melvin Calvin, Francis Crick, Manfred Eigen, Thomas Eisner, Stephen Jay Gould, Matthew Meselson, Linus Pauling, David Raup, and E. O. Wilson. The petition proposed that in addition to debating the issue, the hypothesis should be tested by running the experiment: “We are unanimous in our conviction that the only significant test of the existence of extraterrestrial intelligence is an experimental one. No a priori arguments on this subject can be compelling or should be used as a substitute for an observational program.”

The SETI search continues and we all await its outcome....

Read the rest of this article in the November 2007 issue of FATE

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