 Memory consolidation is just one psychological phenomenon, and so its “ruthless” reduction to molecular events doesn’t establish a general claim about unitary mechanisms across widely divergent taxa for other shared cognitive kinds. For that argument, Bickle turns to principles of molecular evolution. The first principle holds that evolution at the molecular level—changes to the amino acid sequence of a given protein—is much slower in functionally important (“constrained”) domains than in functionally less important ones. The second principle is that molecular evolution is much slower in all domains of “housekeeping” proteins, especially in ones that participate in cell-metabolic processes in many tissue types. These two principles imply that these molecules, their domains, and the intracellular processes they participate in will remain constant across existing biological species that share the common ancestor that first possessed them. (This is what Dubnau and Tully refer to above as a “universally conserved” molecular switch.) In the end, any psychological kind that affects an organism’s behavior must engage the cell-metabolic machinery in individual neurons. In the brain, causally speaking, that’s where the rubber meets the road. But that’s the machinery conserved across existing biological species—changes to it, especially its functionally constrained domains, have (almost) inevitably been detrimental to an organism’s survival. So we should expect that the molecular mechanisms for any causally efficacious cognitive kind be “universally conserved”. The discovery of these shared mechanisms of memory consolidation is not some isolated case, but follows from the core principles of molecular evolution. As “molecular and cellular cognition” proceeds, we should expect more examples of unitary realizers—ruthless reductions—across species for shared psychological kinds