 When modeling how these interactions generate macroevolutionary patterns, PE presents the dominant (i.e., equilibrium) state as one of population-level morphological stasis—a state in which speciation attempts often occur but generally fail to take. These periods of stasis are occasionally interrupted (i.e., punctuated) by periods of population-level morphological change—periods of successful speciation. This bifurcated model (depicting states of both stasis and change) is one in which species behave a little bit like organisms: speciation begins to look like reproduction, and extinction begins to look like death. Crucial to this picture is the claim that once a new species comes into existence, it mostly exhibits stasis. The analogy is by no means perfect (Havstad 2016 in Other Internet Resources), but it did open up a new field of theoretical exploration. What if the differential speciation and extinction of whole lineages is a lot like the differential survival and reproduction of individuals in a population? PE may not logically imply species selection, but it does point in that direction by suggesting that species resemble organisms in relevant ways—for instance, by having comparable integration and cohesion, enough for populations to block directional change in favor of stasis.