EVOLUTIONARY EXPLANATIONS OF ANOREXIA NERVOSA

Evolutionary explanations relate to the adaptive nature of Anorexia Nervosa – (how they’ve helped the species survive)

There are 2 Evolutionary theories:

Reproductive Suppression Hypothesis

‘Adapted to Flee’ Hypothesis

REPRODUCTIVE SUPPRESSION HYPOTHESIS

(SURBEY, 1987)

Evolution delays the onset of sexual maturation in response to cues in the

environment about the probability of poor reproductive success.

It enables the female to avoid giving birth at a time when conditions are not conducive to

the survival of her offspring.

Anorexia Nervosa is a ‘disordered variant’ of the adaptive ability – when may feel unable to cope with biological, emotional and social

responsibility of womanhood.

REPRODUCTIVE SUPPRESSION HYPOTHESIS

weight loss was a strategy for suppressing reproductive capability

when food was in limited supply, pregnancy would have been risky for the mother and survival chances for the infant would have been reduced in the absence of contraceptives,

weight loss would prevent pregnancy at times when it would

be too risky

basic assumptions

REPRODUCTIVE SUPPRESSION HYPOTHESIS

the reproduction suppression model : because reproduction is costly to females, a

female facing conditions temporarily unfavourable to reproduction can increase

her lifetime reproductive success by delaying reproduction until conditions

improve the critical fat hypothesis : because a minimum amount of body fat (17%) is needed before menstruation begins and additional fat

accumulation (22%) is needed to maintain regular ovulation (Frisch, 1985; Frisch and Barbieri, 2002) altering the trajectory of

adolescent weight gain, or the loss of five pounds or so, could have been an effective

mechanism for controlling sexual maturation and fertility in ancestral females

based on 2 ‘models’

REPRODUCTIVE SUPPRESSION HYPOTHESIS

1. more females than males

2. attention from ‘undesirable’ males

selective pressures favouring reproductive suppression?

REPRODUCTIVE SUPPRESSION HYPOTHESIS

1.more females than males

- more competition from other females = not all females can mate… so those that don’t need to

‘save’ up for lost time

2. attention from ‘undesirable’ males

- the youngest females are the most vulnerable because they lack emotional maturity/confidence to rebuff unwanted attention = makes sense to delay reproductive ability until older (when more likely to

make the ‘right’ choice of a mate)

selective pressures favouring reproductive suppression?

IS THERE EVIDENCE TO SUPPORT THIS THEORY?

Amenorrhea & the onset of puberty is delayed

Based upon observations of species

― How are the symptoms passed on because this behaviour (AN) will decrease fertility & can kill?

― General problems with the Evolutionary theory

‘ADAPTED TO FLEE’ HYPOTHESIS (AFH –

GUISINGER, 2003)Symptoms reflect adaptive mechanisms that

caused migration when local famine conditions occurred.

Food restriction is a common feature when competition for food, and migration behaviour.

Therefore for modern-day individuals, those with a genetic pre-disposition to Anorexia, losing too

much weight may trigger ancestral mechanisms.

e.g. ‘Holy Anorexia’ in Middle Ages

(saints recognised for miraculous ability to live without food)

IS THERE EVIDENCE TO SUPPORT THIS THEORY?

Treatment Implications – Guisinger claims AFH ‘relieves therapists of the need to search for familial reasons for Anorexia’.

Awareness of this causal influence can help treatment and encourage parents to be more compassionate towards their child.

― This treatment implication is Reductionist as it is ignoring other possible and more complex explanations.

― How have the symptoms been passed on? Anorexia would function effectively in ancestral conditions but can be deadly outside the ecological setting.

GENERAL CRITICISMS OF EVOLUTIONARY APPROACH Reductionist – not search for more complex

explanation, such as the emotional relationships within families as a cause

Deterministic – view that an individual’s behaviour is shaped/controlled by internal forces rather than an individual’s will to do something

Cultural Influence – doesn’t acknowledge the

importance of cultural influences, e.g. if it is adaptive & innate then why doesn’t it happen in all cultures?