‘It takes all the running you can do, to keep in the same place.’ In a coevolutionary arms race — predator and prey, parasite and host, attacker and defender — both sides improve constantly, yet the RELATIVE gap between them never closes. Stop improving and you fall behind. The effort isn’t wasted; holding the gap costs everything. Slide time and watch both climb while the gap holds.
The Red Queen hypothesis (Van Valen 1973): in antagonistic coevolution, each side’s adaptation degrades the other’s environment, so both must keep evolving just to maintain relative fitness. Absolute fitness rises without bound while the RELATIVE advantage stays roughly constant — a moving equilibrium with no fixed point in absolute terms. It explains the persistence of sex, of arms races, and why ‘progress’ can leave the balance untouched. A fail-loud self-check throws unless both sides rise while the gap stays constant. ◆ real evolutionary dynamics, node-verified.
The symmetric constant-improvement model is the idealisation; real coevolution fluctuates around the balance. The load-bearing point — effort maintains a gap it cannot close — is the exact content.