The theory of punctuated equilibrium or punctuated equilibria in evolution. This theory argues that once species appeared in the the fossil record they became stable, showing little net evolutionary change for most of their geological history. This state they called stasis. When significant evolutionary change occurred, the theory states that it is generally restricted to rare and geologically rapid events of branching speciation called cladogenesis. Cladogenesis is the process by which a species splits into two distinct species, rather than one species gradually transforming into another. Eldredge and Gould argued that the degree of gradualism in evolution commonly attributed to Darwin is virtually nonexistent in the fossil record, and that stasis dominates the history of most fossil species. In 2016 the paper and Eldredge and Gould was available from blackwellpublishing.com at this link.