Futures

We perceive the past as fixed and the future as open. Every being that is conscious at any moment perceives earlier and later times in that way. Every moment is the present to any being that is conscious within it. There is no unique present unless we say that the eternal present intersects time at every moment - or at every conscious moment? Maybe less complex conscious organisms experience only immediate sensations with minimal memory and anticipation? However, zero memory and anticipation would entail an experience beginning and ending simultaneously, the temporal equivalent of a mathematically flat plane.

Abstractions become concrete when sf writers speculate:

mankind has devolved into Morlocks and Eloi by 802,701 AD;

mankind has evolved into Danellians a million years hence;

in 25,000 AD, birds, now called "Birds," have become intelligent and threaten to exterminate mankind.

Sources:

Wells, The Time Machine;

Anderson, Time Patrol and The Shield Of Time;

Blish, The Quincunx Of Time and Midsummer Century.

Alternative futures that might be compatible in some vaster framework. All three authors have allowed enough time for not only historical but also Darwinian processes to occur.