First And Last

We can think of perhaps eight sf authors who have each written one or at most two future histories and we can then compare their works with no less than eight future histories written by one author, Poul Anderson. Further, Anderson's first future history, the Psychotechnic History, and his eighth, Genesis, are so dissimilar as to seem to belong to different fictional categories.

In the Psychotechnic series, many planets bear life and many intelligent species cross space faster than light whereas, in the single text of Genesis, life is rare and post-organic intelligences emanating only from Earth cross space slower than light. Interstellar travel is the only common idea and these two conceptions of it are diametrically opposed.

Also, the fictional history of the Psychotechnic series has been superseded by the ongoing course of events whereas Genesis looks like standing indefinitely - except that so many exoplanets have now been detected that maybe unicellular life at least is quite common? But how much of it has made the difficult transition to multicellular life? Hopefully, much more will be learned in our lifetimes. New future histories begun now might be superseded quickly.