The concept of the evolutionary explanation for anorexia nervosa

The evolutionary explanation for anorexia nervosa (AN) suggests that this condition has persisted in the population due to its adaptive survival value, shaped by natural selection. It proposes that AN may have provided benefits in certain environmental conditions in human history, allowing individuals or groups to survive under specific pressures, even though it appears harmful in modern contexts.

The reproduction suppression hypothesis as an adaptive mechanism

The reproduction suppression hypothesis (RSH), proposed by Surbey in 1987, frames AN as an evolutionary adaptation in females to delay sexual maturity and pregnancy during periods of food scarcity. This mechanism would prevent reproduction when resources are insufficient to support offspring, increasing the likelihood of survival for both the mother and potential children once conditions improve.

Key aspects of the reproduction suppression hypothesis

• Response to stress - Young females under stress, such as from perceived or actual scarcity, may react as if food supplies are low, triggering behaviours like severe dieting.
• Biological impact - Dieting and weight loss suppress reproductive functions, such as menstruation, preventing pregnancy until environmental conditions are more favourable for raising children.
• Historical advantage - In ancestral times, this delay could have ensured that energy was conserved for survival rather than reproduction during harsh conditions.

The adaptive response to famine hypothesis

The adaptive response to famine (ARF) hypothesis, put forward by Guisinger in 2003, suggests that AN reflects an adaptive behaviour during times of food scarcity, where populations needed to migrate to find better resources. The hyperactivity often seen in individuals with AN is interpreted as a form of 'migratory restlessness', motivating movement to areas with more abundant food supplies through reduced body weight.

Supporting and contradicting research evidence

Research into the evolutionary explanations for AN provides mixed findings, with some studies supporting the adaptive theories while others challenge the notion of survival value.

Supporting evidence for evolutionary explanations

Frisch & Barbieri (2002) study:

• Method - Investigated the relationship between body fat and reproductive functions in women.
• Results - Found that women typically require 17-22% body fat to menstruate and ovulate, aligning with the RSH that weight loss in AN suppresses reproductive ability during scarcity.
• Conclusions - Supports the idea that AN could be an adaptive mechanism to delay reproduction in unfavourable conditions.

Rakison (2002) study:

• Method - Used a questionnaire to compare eating attitudes and views on sex and marriage between individuals with AN and those without.
• Results - Identified a negative correlation, where higher levels of disordered eating were linked to lower attraction to sexual attention.
• Conclusions - Reinforces the evolutionary perspective that AN may suppress reproductive behaviour as a survival strategy.

Contradicting evidence against evolutionary explanations

Arcelus et al. (2011) study:

• Method - Reviewed 32 studies to assess mortality rates associated with AN.
• Results - Discovered that AN has a mortality rate of around 4%, the highest among mental disorders, with a significant number of deaths due to suicide.
• Conclusions - Challenges the idea of adaptive survival value, as such high mortality suggests AN may not confer evolutionary benefits.
• Evaluation - Highlights a major limitation, indicating that if AN were truly adaptive, natural selection might not sustain such a lethal condition.

Strengths, limitations, and practical applications of evolutionary explanations

Evolutionary explanations for AN offer a unique perspective by linking modern behaviours to historical survival strategies, but they also face criticism for oversimplification and lack of empirical support in some areas.

Strengths of evolutionary explanations

• Biological consistency with RSH - The fact that AN often halts physical signs of puberty, such as menstruation, supports the RSH, as it aligns with the theory's prediction that reproduction is suppressed to avoid pregnancy during scarcity.
• Theoretical support for persistence - If AN were entirely maladaptive, natural selection would likely have eliminated it from the gene pool over time, suggesting there may be some historical adaptive value.

Limitations of evolutionary explanations

• Gender and orientation discrepancy in RSH - The RSH focuses on female reproductive suppression, yet AN affects males and individuals of diverse sexual orientations, undermining the hypothesis as a universal explanation.
• Weak support for ARF - The ARF lacks substantial research backing, with Guisinger providing no direct evidence, and alternative explanations for AN (such as psychological or cultural factors) often having stronger empirical support.
• Neglect of other influences - Evolutionary theories can be overly simplistic, ignoring significant modern factors like media influence or societal pressures. A more comprehensive approach might integrate evolutionary ideas into a diathesis-stress model, where genetic vulnerability (from evolution) interacts with environmental triggers to cause AN.

Practical applications of evolutionary explanations

• Tailored treatment plans - Understanding the potential biological and evolutionary roots of AN can help clinicians develop individualised treatment strategies that address both the physical and psychological symptoms of the disorder, focusing on restoring health while considering underlying adaptive mechanisms.