JLA: Primeval #1 (1999)

The World's Greatest Heroes must save humanity from de-evolution -- but first face it themselves -- in this Prestige one-shot! When eons of evolution are erased in a heartbeat in Dallas, the JLA finds that the source is a grotesque, thoroughly mad disciple of long-vanished gods who plans to turn back the clock on the entire world! Striving to hold things together, the Leaguers slowly come to the realization that their powers are slipping away -- or going out of control -- with every second, as they themselves return to their ancestral roots. How will our champions save humanity from extinction if they can't save themselves?