Dr. Salk has stretched an interesting essay into a rather long-winded book. His contention is that man is at a dividing point in terms of his cultural and biological evolution, the alternatives being ""maximizing self-expression and self-restraint. . . or limitless license which would unleash destructive and pathological greed at the expense of constructive and creative individuals."" On the whole he is optimistic about man's future, noting that ""the 'catastrophists' and harbingers of doom are in themselves evidence that Man possesses a signaling mechanism for sounding warnings of danger"" -- say overpopulation. While not being specific about the means, Dr. Salk assumes that somehow human population will stabilize at an ""optimal level."" He feels that because man is ""able to exercise learned behavior"" he might act ""wisely"" in shaping his future: ""by wisest we mean those who comprehend the survival-evolutionary process, as well as the being-becoming process, and who make choices such as enhance the possibility of existence rather than nonexistence, recognizing evolution as an essential and inexorable continuum of growth and development."" He makes virtually no mention of the many other authors who have addressed themselves to these same issues, either on a philosophical or experimental level. Unfortunately, too, his use of vague concepts like ""being,"" ""ego"" and ""becoming"" diffuse the discussion at the expense of clarity.