With only four Relatively Adequate Hypotheses detailed in World Hypotheses: A Study in Evidence (1942), Stephen C. Pepper himself left the door open for additional root metaphors and world hypotheses that might be adequate.
At 75 years of age, Pepper published Concept and Quality (1966) where Selectivism was presented as either a refinement of Contextualism, or a new world hypothesis.
In 1972, following the publishing of [Introduction to Systems Philosophy](https://thelaszloinstitute.com/about/ervin-laszlo/) by [Ervin Laszlo](https://thelaszloinstitute.com/about/ervin-laszlo/), Pepper suggested in a book review of the possibility of Systems Philosophy as a World Hypothesis.
In a doctoral dissertation on A Critical Appraisal of Root Metaphor Theory (1987), a modified version of Selectivism called Neoselectivism was proposed by [Ronald K. Hoeflin](https://www.usiassociation.org/post/usia-vice-president-dr-ronald-hoeflin).