Mean Field Approach

 Fitness landscapes in biology are often over a discrete (sequence, traint, or niche) space (not Euclidean)

 The mean-field limit is obtained by considering the complete graph

            

 While   are random variables (distributions), in the large N limit    is a number, leading to

[Van den Broeck+Parrondo+Amero+Hernandez-Machado (1994); ....]

[J.-P. Bouchaud &  M. Mezard, Physica A 282, 535 (2000)[Munoz, Colaiori, Castellano, PRE 72, 056102 (2005)]

The probability distribution functions for  evolve according to the Fokker-Planck equation

  

 The (unnormalized) steady-state solution has the form [PRE 102, 052106 (2020)]

A combination of power-laws with cutoffs at small and large values.