Future Historical Culminations And Human Changes

Given enough time, either natural or artificial selection will change humanity: one example from James Blish and four from Poul Anderson.

Blish

In The Seedling Stars, Book Four, "Watershed," Adapted Men have spread through the galaxy and now colonize a changed Earth.

Anderson

In "The Chapter Ends," humanity evacuates Earth and the Galactic periphery because the human way of mentally controlling cosmic energy interferes with the way used by inhabitants of gas giants. 

In "The Horn of Time the Hunter," colonists of an extrasolar planet have become aquatic.

In Twilight World, Epilogue, descendants of post-World War III mutants terraform outer satellites and reclaim Earth.

In "Starfog," a human planetary population has adapted to a much higher radiation level than their Terrestrial ancestors and has become a different species.

Larry Niven

In "Safe at Any Speed," if we can take this seriously, the whole population has inherited genes for good luck - so that interesting stories have become impossible to write: end of the Known Space future history series.

Olaf Stapledon

In Last And First Men, eighteen human species, some of them artificial, inhabit Earth, Venus and Neptune.