Cichlid fish as a model for understanding social dysfunction.

The use of Child Sexual Abuse Material (CSAM) has increased substantially over the past decade. The urgency of this issue is highlighted by the record-high number of suspected CSAM URLs reported in 2024 by , reflecting a 202% increase in illegal content compared to the previous year. Potential explanations for this exponential growth include evolving supply-side dynamics such as the financial incentives derived from sexual extortion, the use of realistic, AI-generated content (; ), as well as self-generated material shared on messaging platforms (). Importantly, this increase does not necessarily indicate a corresponding rise in underlying sexual deviance. Rather, it appears to be driven by situational factors linked to the increasing accessibility and normalisation of online pornography, which may inadvertently facilitate exposure to extreme, and in some cases illegal, material. Understanding if and how non-illegal pornography use can escalate towards the consumption of extreme or illicit content is therefore essential. The motivations driving the consumption of CSAM are complex and varied, challenging the prevailing assumption that all CSAM consumers have a pre-existing sexual preference for child material. Alternative explanations emphasise a distinct pathway: the escalation of mainstream pornography consumption (; ). This pathway is driven by a progressive need for increasingly extreme pornographic content to achieve the same level of arousal. The underlying mechanism is desensitisation: prolonged exposure to mainstream pornography reduces arousal responsiveness, prompting individuals to seek greater novelty and intensity of content to reach the same level of arousal (; ; ). Consequently, diminished arousal to readily available, non-illegal pornography can lead to extended search behaviour and exposure to progressively more extreme content, in some cases resulting in the consumption of CSAM. In such instances, the primary motivation may shift from a specific sexual interest towards thrill-seeking behaviour and the pursuit of content extremity; individuals may initially be drawn by the shock value and novelty, rather than the depiction of children per se. This hypothesised escalation pathway represents a critical yet understudied mechanism that may explain how some individuals progress towards illegal content. Despite recognition of this risk, substantial uncertainty remains regarding how this process manifests in non-clinical populations, particularly how engagement with various non-CSAM genres and themes relate to patterns of content escalation. To address this gap, this study examines individuals’ pornography consumption through the clustering of different content types. Pornography research has long struggled to establish a consistent taxonomy capable of classifying the vast heterogeneity of available material (; ). Classification approaches vary considerably, from broad distinctions between normophilic (e.g. vaginal or oral sex) and paraphilic content (e.g. violent, coercive sex, fetishistic; ) to groupings based on user demographics (). Although some favour granular operational classifications focusing on content complexity (e.g. performer characteristics, sexual vs. non-sexual behaviours and setting; ), a thematic framework based on explicit content categories consumed is often more practical for studying escalation. Focusing on themes prevalent across major content platforms provides a direct means of understanding how users navigate and progress through readily available, non-illegal material towards illegal CSAM. Therefore, a clearer empirical framework for categorising and analysing how content types co-occur in user consumption patterns is essential.