The Chain of Accidents and the Rule of Law: The Role of Contingency and Necessity in the Evolution of Higher Intelligence
Shermer, Michael, Skeptic (Altadena, CA)
HUMANS ARE PATTERN-SEEKING, STORY-telling animals. We look for and find patterns in our world and in our lives, then weave narratives around those patterns to bring them to life and give them meaning. Such is the stuff of which myth, religion, history, and science are made. Sometimes the patterns we find represent reality--DNA as the basis of heredity or the fossil record as the history of life. Sometimes the patterns are imposed by our minds--the face on Mars or the image of the Virgin Mary on a window. The difficulty lies in distinguishing which patterns are true and which are false, and the essential tension pits skepticism against credulity as we struggle to determine the nature of reality.
That tension is at the forefront of the debate over how likely or unlikely the evolution of intelligent life is, particularly a culture-generating, language-producing, technology-using form of intelligent life such as ours. Evolutionary theorists are interested in the question because it taps into the relative roles of chance and law in nature and natural history. Astronomers and astrobiologists are interested in the question because it cuts to the heart of how likely or unlikely it is that we will find life on other planets or make contact with an extra-terrestrial intelligence.
Does the pattern of life's history and nature's laws indicate that our existence was preordained from the beginning, or does the pattern indicate that we are the product of chance events and random occurrences? (1) That is, is our existence a necessity--it could not have been otherwise? Or is our existence a contingency--it need not have been? A coarse-grained look at the question finds scientists roughly divided between astrobiologists and SETI (Search for Extra-Terrestrial intelligence) astronomers who tend to be optimistic, estimating a relatively high probability of intelligent life evolving in the cosmos (or re-evolving in an earthbound thought experiment), and biologists and evolutionary theorists who tend to be pessimistic, estimating a relatively low probability of intelligent life evolving elsewhere (or re-evolving here). Since the question cannot be answered by a laboratory experiment, we must turn to sciences that attempt to answer it indirectly, such as those employed by SETI scientists and evolutionary theorists.
The SETI Optimists
Astrobiologists and SETI astronomers base their optimism on numbers that they plug into the well known Drake equation, proposed in 1961 by the radio astronomer Frank Drake for estimating the number of technological civilizations that reside in our galaxy:
N = R[f.sub.p][n.sub.e][f.sub.l][f.sub.i][f.sub.c]L
Where N = the number of communicative civilizations, R = the rate of star formation in the galley per year, [f.sub.p] = the fraction of those stars with planets, [n.sub.e] = the number of earthlike planets per solar system, [f.sub.l] = the fraction of planets with life, [f.sub.i] = the fraction of planets with intelligent life, [f.sub.c] = the fraction of planets with communicating technology, L = the lifetime of communicating civilizations. (2)
Although we have a fairly good idea of the rate of stellar formation, and we are confident that a significant number of these stars have planets, it is too soon to estimate the rate of formation of earth-like planets because the technology is not yet available to detect planets smaller than Jupiter-size behemoths. In the SETI literature, a figure of 10% is often used, that is, in a galaxy of 100 billion stars, there should be 10 billion sun-like stars, one billion earth-like planets, 100 million planets with life, 10 million planets with intelligent life, and one million planets with intelligent life capable of radio technology. (3)
Although most SETI astronomers are realistic about the accuracy of such estimates, I was puzzled to encounter numerous caveats about L, the lifetime of technological civilizations, such as this one from SETI Institute astronomer Seth Shostak: "The lack of precision in determining these parameters pales in comparison to our ignorance of L. …