I must conclude that the first contact with extraterrestrial life will be determined by the known probabilities of speciation. It is an undeniable fact that complex organisms are rare on earth, while simple organisms flourish in abundance. There are millions of species of bacteria, and thousands of species of insects. There are only a few species of primates, and only four of great apes. There is but one species of man.

With this frequency of speciation goes a corresponding frequency in numbers. Simple creatures are much more common than complex organisms. There are three billion men on the earth, and that seems a great many until we consider that ten or even one hundred times that number of first contact would consist of a plague brought back from the bacteria can be contained within a large flask.

All available evidence on the origin of life points to an evolutionary progression from simple to complex life forms. This is true on earth. It is probably true throughout the universe. Shapley, Merrow, and others have calculated the number of viable planetary systems in the near universe. My own calculations, indicated earlier in the paper, consider the relative abundance of different organisms throughout the universe.

My aim has been to determine the probability of contact between man and another life form. That probability is as follows:

These considerations lead me to believe that the first human interaction with extraterrestrial life will consist of contact with organisms similar to, if not identical to, earth bacteria or viruses. The consequences of such contact are disturbing when one recalls that 3 per cent of all earth bacteria are capable of exerting some deleterious effect upon man.

Later, Merrick himself considered the possibility that the first contact would consist of a plague brought back from the moon by the first men to go there. This idea was received with amusement by the assembled scientists.

One of the few who took it seriously was Jeremy Stone. At the age of thirty-six, Stone was perhaps the most famous person attending the symposium that year. He was professor of bacteriology at Berkeley, a post he had held since he was thirty, and he had just won the Nobel Prize.

The list of Stone's achievements—disregarding the particular series of experiments that led to the Nobel Prize—is astonishing. In 1955, he was the first to use the technique of multiplicative counts for bacterial colonies. In 1957, he developed a method for liquid-pure suspension. In 1960, Stone presented a radical new theory of operon activity in E. coli and S. tabuli, and developed evidence for the physical nature of the inducer and repressor substances. His 1958 paper on linear viral transformations opened broad new lines of scientific inquiry, particularly among the Pasteur Institute group in Paris, which subsequently won the Nobel Prize in 1966.