periods of evolutionary stasis which are interrupted by much shorter periods of evolutionary change." Evolutionary biologist Robert Trivers accused Gould of being "something of an intellectual fraud" for using claims that were "well known from the time of Darwin" (that evolution displayed "periods of long stasis interspersed with periods of rapid change") to support distinct but more "grandiose" claims regarding species selection, despite the "rate of species turnover [having] nothing to do with the traits within species—only with the relative frequency of species showing these traits". Some critics jokingly referred to the theory of punctuated equilibrium as "evolution by jerks", which reportedly prompted punctuationists to describe phyletic gradualism as "evolution by creeps." Darwin's theory The sudden appearance of most species in the geologic record and the lack of evidence of substantial gradual change in most species—from their initial appearance until their extinction—has long been noted, including by Charles Darwin, who appealed to the imperfection of the record as the favored explanation. When presenting his ideas against the prevailing influences of catastrophism and progressive creationism, which envisaged species being supernaturally created at intervals, Darwin needed to forcefully stress the gradual nature of evolution in accordance with the gradualism promoted by his friend Charles Lyell. He privately expressed concern, noting in the margin of his 1844 Essay, "Better begin with this: If species really, after catastrophes, created in showers world over, my theory false." It is often incorrectly assumed that he insisted that the rate of change must be constant, or nearly so, but even the first edition of On the Origin of Species states that "Species of different genera and classes have not changed at the same rate, or in the same degree. In the oldest tertiary beds a few living shells may still be found in the midst of a multitude of extinct forms... The Silurian Lingula differs but little from the living species of this genus". Lingula is among the few brachiopods surviving today but also known from fossils over 500 million years old. In the fourth edition (1866) of On the Origin of Species Darwin wrote that "the periods during which species have undergone modification, though long as measured in years, have probably been short in comparison with the periods during which they retain the same form." Thus punctuationism in general is consistent with Darwin's conception of evolution. According to early versions of punctuated equilibrium, "peripheral isolates" are