he wrote : p = fpnhflfifc `` what it means , '' harry adams said , `` is that the probability , p , that intelligent life will evolve in any star system is a function of the probability that the star will have planets , the number of habitable planets , the probability that simple life will evolve on a habitable planet , the probability that intelligent life will evolve from simple life , and the probability that intelligent life will attempt interstellar communication within five billion years .