Additionally, Lorenz addresses behavior in humans, including discussion of a "hydraulic" model of emotional or instinctive pressures and their release, shared by Freud's psychoanalytic theory, and the abnormality of intraspecies violence and killing.

"[6] Leach writes that where Ardrey focuses on territoriality, Lorenz aims to demonstrate that "animal aggression is only a 'so-called evil' and that its adaptive consequences are advantageous or at least neutral.

He commented that those against the book, especially S. A. Barnett, T. C. Schneirla, and Solly Zuckerman, were specialists in animal behaviour, while most of the favourable reviews came from "experts in other fields".

[7] The zoologists Richard D. Alexander and Donald W. Tinkle, comparing On Aggression with Ardrey's The Territorial Imperative in BioScience in 1968, noted that few books had been reviewed so often "or with as much vehemence in both defense and derogation" as these two.

Both, in their view, tend "to rekindle old, pointless arguments of the instinct vs. learning variety"[8] and both include "some peculiarly nonevolutionary or antievolutionary themes.

[9] However, Fromm noted that the ethologist Nico Tinbergen had rejected the hydraulic theory, and that Lorenz himself "modified it" in 1966, but without indicating that in the English translation of On Aggression.

[9] Fromm cites evidence from neuroscience that aggression is "essentially defensive", arising in "phylogenetically programed brain areas" for fight or flight when an animal or person feels threatened.

Wilson compares aggression to "a preexisting mix of chemicals ready to be transformed by specific catalysts that are added," rather than "a fluid that continuously builds pressure against the walls of its containers.

In Dawkins's view, the idea of group selection was "so deeply ingrained" in Lorenz's thinking that he "evidently did not realize that his statements contravened orthodox Darwinian theory.