Biological essentialism is the claim that biological instincts cannot be overridden and therefore activism to change the way most people naturally behave, on a timescale shorter than thousands of years of human evolution, is a waste of time and potentially dangerous due to the increasingly draconian means that are expected to be used to enforce the change. A common counterargument to such fears is that a middle ground can more realistically be reached, since humans are malleable to some extent.
Biological essentialism has gained popularity in the incelosphere in the late 2010s. Some biological essentialists blackpillers promote fatalism, believing that it is impossible to change human female nature (gender essentialism), so we should just "give up". Other biological essentialist blackpillers like Jordan Peterson say one should embrace natural human behavior, and use the resulting hierarchies to enforce monogamy to solve or at least mitigate the incel problem.