Velocci's central claim is that biological sex is not an objective feature of bodies but a historically invented, incoherent classification system. Scientists across zoology, eugenics, gynecology, sexology and early transsexual medicine continually redefined the criteria for "male" and "female" to preserve a binary while absorbing anomalies. The binary therefore persists because of its flexibility rather than in spite of it. "Cisness" is presented as the result of ongoing social and scientific labour that forces bodies into categories; the categories themselves are said to flex to fit most people rather than the reverse. The book frames this history as relevant to contemporary efforts that invoke "biological sex" against transgender existence.
The self-referential problem arises immediately once the claim is taken at face value.
If sex is not a real, objective distinction between two (or more) kinds of organism, then the language and practices that depend on that distinction lose their referents. "Transition" presupposes a starting sexed state and a target sexed state. Hormonal and surgical interventions are justified precisely as modifications that move the body toward the morphology, secondary characteristics or reproductive role of the other sex. If there is no underlying sexed reality to depart from or arrive at, the interventions become unintelligible as sex transitions; they are simply alterations of tissue without a coherent destination category. The same difficulty attaches to the term "trans" itself: the prefix implies movement across or beyond a boundary. Remove the boundary and the movement has nothing to cross.
Velocci's own historical material does not escape this loop. The book documents scientists who treated certain bodies as anomalous relative to male/female norms, then adjusted the norms or reclassified the bodies. That process only makes sense if the scientists were operating with some operative distinction they regarded as real enough to require management. Declaring the entire enterprise "incoherent" and therefore unreal does not dissolve the practical reliance on the categories; it simply relocates the incoherence into the critical stance itself. One cannot simultaneously assert that the categories are empty constructions and that medical and social practices organised around those categories are meaningful acts of affirmation or resistance.
A further tension appears in the book's political framing. Velocci links the historical construction of binary sex to power projects (racial hierarchy, exclusion of women from politics, later anti-trans measures). Yet the contemporary demand for recognition of transgender identity, access to sex-segregated spaces, or medical pathways still requires the categories to do real classificatory work. If sex is purely an instrument of domination with no independent biological content, then the demand that institutions recognise a change of sex category becomes a demand that the same power apparatus reassign the individual within an empty system. The critique of the system and the appeal to the system cannot both be sustained without residual reference to something outside pure construction.
Biologically, the claim also collides with the well-established anisogamy framework: the existence of two distinct gamete types (sperm and ova) that define the sexes across sexually reproducing species, including humans. Developmental pathways, chromosomal mechanisms and secondary sex characteristics are organised around the production of one or the other gamete type. Exceptions and disorders of sexual development exist and are medically important, but they are understood as variations or disruptions within a binary reproductive system, not as evidence that the system itself is unreal. Historical contingency in how scientists have named or policed the boundary does not erase the underlying reproductive dimorphism.
In short, the strongest version of Velocci's thesis, that sex is nothing more than a shifting, power-laden classification with no stable biological referent, renders the very practices and identities the book seeks to defend conceptually unstable. The weaker, more historically modest reading (that scientific definitions have been inconsistent and politically motivated) is compatible with ordinary biological realism and does not require the further step of declaring sex unreal. The self-refutation appears when the stronger claim is insisted upon. This sociology of knowledge book, therefore fails dramatically.
https://www.amazon.com.au/Sex-Isnt-Real-Invention-Incoherent/dp/1478033029
https://www.thecollegefix.com/penn-professor-claims-cisness-is-unnatural-sex-isnt-real-in-new-book/