We show that mutual benefit cooperation can favor the evolution of a preference to interact with individuals that are similar to themselves with respect to one or several arbitrary cultural tags. One necessary requisite to obtain this result is an asymmetry between partners in such a way that one of them (actor) proposes the cooperation and elects the partner, whereas the other (receiver) never rejects the offer because cooperation always reports benefits. The advantage of individuals possessing allele for preferential assortment is due to receiving more offers of mutually beneficial cooperation when there is linkage disequilibrium between the assortment locus and the cultural tags. An especially favorable scenario for the evolution of such preference is a subdivided metapopulation. In this case, the homogeneity within populations and the divergence between populations is favored, facilitating the existence of ethnic groups.