Evolutionary theories in disordered eating psychopathology

It was disappointing to find that the editorial by Murray et al ¹ ‘Evolving eating disorder psychopathology: conceptualising muscularity-oriented disordered eating’ made no mention of evolutionary formulations of eating disorders despite the somewhat suggestive title. This is a significant omission, as evolutionary theories provide a cogent explanatory framework not only for the newly described male variant of eating disorder referred to in the article but also for eating disorders as a whole. Also, the editorial's title promised to deliver a new conceptual framework for eating disorders in the light of this new variant, but all it did was produce the familiar tautology regarding cultural body ideals that has had such poor explanatory value in the case of female eating disorders. The formulation's lack of predictive power has meant that little, if any, progress has been made in the past few decades in researching the aetiology of these conditions despite the huge quantities of data collected. The weakness of the cultural norm (of desirable shape, beauty etc.) formulation is evident from the fact that it attempts to explain the phenomena of eating disorder by assigning causation to the very thing it is meant to explain (e.g. the drive for thinness in women or muscularity in men).

Hence, if these societal ideals are arbitrary and not related to any underlying biologically based motives, we should observe the reverse pattern in some societies (e.g. more men than women wishing to be thinner and more women than men wishing to be more muscular), but there is no evidence of such a scenario.

The sexual competition hypothesis (SCH) for eating disorders ² is an evolutionary formulation that can help answer the ‘why’ question that has so far defeated mainstream, non-evolutionary theories. It proposes that all eating disorders stem from the phenomenon of intrasexual competition taken to pathological extremes. In the case of females, competition is primarily through the display of signs of youth (where thinness is a marker for youth). Youth is a major determinant of reproductive potential in females, whereas men compete among themselves through the display of physical dominance and prowess, which is enhanced through the size and muscularity of the upper body. The increase in the rates of eating disorders in the past several decades in Western and Westernised countries is explained by the ‘mismatch’ between the human psychological systems for mate attraction and retention and for competition with same-sex rivals that evolved in small-scale societies on the one hand, and the novel realities of the modern urban Western environment on the other.

The SCH has been supported by findings of studies of disordered eating in non-clinical populations (female undergraduates) both in the USA ³ and the UK. ⁴ Further support for predictions made by the SCH came from another US study of disordered eating in a non-clinical population of male and female homosexual and heterosexual participants. ⁵

The consistency of the clinical features of eating disorders across different high-income countries, as well as their persistence (or even rising levels), argues strongly against the arbitrary cultural standard view dominant in eating disorder circles and in favour of a model in which these disorders are the outcome of a gene–environment interaction.