"I don't think one can say there is a unit of selection. Any selection process selects on units at various levels, starting with ultimate replicators such as the gene, the individual, the community in which the individual is. All these things could be considered units of selection that are being selected simultaneously, and all of them are changing the frequency of the ultimate atom of selection, which is the gene, but it is not possible to say that the gene is the soul unit of selection."

W.D. Hamilton