From Jungle To Stars

"Hunters of the Sky Cave," VI.

"...would the whole long climb of man, from jungle to stars, fall back in destruction...?" (p. 193)

That is a grandiose phrase for a work of space opera. But then that is what all space opera implies, that all past history, even if not explicitly referred to, has been a long climb to Out ride the sons of Terra, and Up leaps the race of Earthmen. (see here) 

Anderson did write historical and even prehistorical fiction so his works reflect this "long climb" better than those of many other sf writers.

At the space opera stage, "man" has enemies like the Merseians who try to reverse his "long climb." Then it is that the course of future history is decided by the exploits of heroes like Dominic Flandry.

I think that mankind potentially has a great future but not that it necessarily involves physically traversing interstellar spaces, especially not if FTL remains impossible. Wherever we are, we are in the midst of the cosmos and can look out into it.