The Drift Toward Everything

Species evolve toward specialization when competition is strong and resources are stable. That’s the textbook story. A mathematical model of niche formation now shows the opposite long-term tendency: stochastic effects drive the evolution of generalist diets, regardless of the competitive landscape.

The dynamics are highly path-dependent. Species settle into quasi-stable states — particular dietary configurations that persist for long periods, resisting perturbation. These states look like equilibria. They’re not. They’re transient attractors that eventually dissolve under the accumulation of random variation, each dissolution widening the dietary range slightly.

The mechanism isn’t selection for generalism. It’s the asymmetry of the stochastic landscape. A specialist that randomly gains access to a new resource faces only moderate competition (the resource already has few consumers). A generalist that randomly loses access to a resource faces catastrophe (its remaining resources may not support it). The random walk is biased: expansions are cheap, contractions are expensive. Over sufficient time, the walk trends toward broader diets.

This is evolution as a ratchet rather than an optimizer. The quasi-stable specialist states are real and long-lived — species can persist as specialists for millions of years. But the directionality of noise ensures that no specialist state is permanent. The drift toward generalism isn’t adaptive. It’s thermodynamic: the entropy of dietary range increases because the reverse fluctuation is disproportionately costly.