Anorexia and Bulimia

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Human Uniqueness Compared to "Great Apes": 
Absolute Difference
MOCA Domain: 
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Anorexia nervosa and bulimia are primary disorders of eating that commonly develop in middle to late adolescence and follow a chronic course. Anorexia is described in most developed nations, is much commoner in females and includes a disordered concept of the individual's body image, the individual believing themselves to be overweight. Bulimia - episodes of bingeing - sometimes followed by attempts at regurgitation, is less common, but overlaps with anorexia nervosa.


Timing of appearance of the difference in the Hominin Lineage as a defined date or a lineage separation event. The point in time associated with lineage separation events may change in the future as the scientific community agrees upon better time estimates. Lineage separation events are defined in 2017 as:

  • the Last Common Ancestor (LCA) of humans and old world monkeys was 25,000 - 30,000 thousand (25 - 30 million) years ago
  • the Last Common Ancestor (LCA) of humans and chimpanzees was 6,000 - 8,000 thousand (6 - 8 million) years ago
  • the emergence of the genus Homo was 2,000 thousand (2 million) years ago
  • the Last Common Ancestor (LCA) of humans and neanderthals was 500 thousand years ago
  • the common ancestor of modern humans was 100 - 300 thousand years ago

Possible Appearance: 
100 thousand years ago
Background Information: 

Anorexia is estimated to have an incidence of between 8 and 13 cases per 100,000 persons per year and an average prevalence of 0.3% using strict criteria for diagnosis. The condition largely affects young adolescent women, with between 15 and 19 years old making up 40% of all cases. Approximately 90% of people with anorexia are female.
There is a characteristic psychological picture. The individual is pre-occupied with her (less commonly his) body image, believing herself to be overweight and/or mis-shapen. There is a desire to be thin, accompanied by an aversion but also a pre-occupation with food. The individual may sometimes be particularly concerned with the preparation of food for others, but avoids it herself. There is generally weight loss (<85% predicted body mass is specified for DSMIV diagnosis), and amenorrhoea. The condition is often episodic, with perods of exacerbation, but chronic. There is a significant mortality.
The affected individual under pressure to increase her food intake commonly resists these, and may take steps to avoid such pressure and conceal the food she has not consumed.
There is an association with obsessional and ritualistic behaviours and traits, and possibly with the autistic spectrum.
Bulimia is more recently recognised and less common. It is related to anorexia in that individuals with anorexia nervosa may sometimes engage in episoodes of "gorging" food. This usually occurs in solitude, maybe at night, and may be followed by attempts to regurgitate.

The Human Difference: 

No clear descriptions of anorxia nervosa occuring in natural primate populatons have been identified.

Universality in Human Populations: 

It appears that anorexia nervosa occurs in all "developed" human societies, although whether at the same rates is unclear.

Mechanisms Responsible for the Difference: 

The well-defined psychological correlates of anorexia nervosa indicate that this is something more than a disturbance of the metabolic control of food intake. It is the "idea" of food, and its relationship to body image that is disturbed. And this occurs in a social and family context. One must also take note of the psychiatric concomitants, particularly the obsessional phenomena. It is therefore conceivable that the disturbance of these mechanisms is human-specific, and depends upon precisely those mechanisms that distinguish humans from the great apes.

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  1. Epidemiology and course of anorexia nervosa in the community., Keski-Rahkonen, Anna, Hoek Hans W., Susser Ezra S., Linna Milla S., Sihvola Elina, Raevuori Anu, Bulik Cynthia M., Kaprio Jaakko, and Rissanen Aila , Am J Psychiatry, 2007 Aug, Volume 164, Issue 8, p.1259-65, (2007)
  2. Features associated with excessive exercise in women with eating disorders., Shroff, Hemal, Reba Lauren, Thornton Laura M., Tozzi Federica, Klump Kelly L., Berrettini Wade H., Brandt Harry, Crawford Steven, Crow Scott, Fichter Manfred M., et al. , Int J Eat Disord, 2006 Sep, Volume 39, Issue 6, p.454-61, (2006)