Evolutionary Exps for AN- BIO EXP

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  • Created by: imanilara
  • Created on: 06-06-16 16:08

Surbey 1987- delaying onset of sexual maturity AO1

  • Adolescent girls desire to control weight- adaptive mechanism for ancestral girls to delay the onset of sexual maturity in response to cues about the probability of poor reproductive success.
  • Would have been adaptive- allowed an indivdual to avoid pregnancy +birth at times that were not conducive to the survival of offspring.
  • A 'disordered variant' of the adaptive ability to alter timing of reproduction to fit more positive bio, emotional and social factors that enhance survival 
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Survey's theory AO2

  • Strength= based on observation that in a number of species, puberty is delayed/reproduction inhibited in times of stress or when female is in poor physical condition. Makes sense in promoting the survival of the offspring. 
  • Also supported- observation-menarche delayed in pre-pubertal girls w AN and amnorrhoea typical characteristic of AN= AN causes infertility in the short term- could be a technique used by ancestors
  • Weakness- defo gender biased- rests on the physiological effects of AN on female puberty and sexual maturity- clearly does not explain why men get it! 25% of AN ppl are men! we need this research to enrich understanding. 
  • Also effect of AN on male fertility much less pronounced- and so holds no adaptive significance in the EEA
  • Also it is presumptive- we cannot actually test what beh was like back then bc we weren't there- lacks historical validity. 
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Adapt to flee famine hypothesis - Guisinger 2003

  • Typical symptoms of AN eg hyperactivity, food restriction and denial of hunger may have been adaptive mechs by ancestors in times of localised famine.
  • The normal response to weight loss would be a desire for food, but for the ancestral nomadic foragers, wouldve been helpful to switch this response off to allow migration to more favourable environment.
  • Hyperactivity= migratory restlessness-seen in many species in times of food shortage prior to migration - in EEA starving foragers who deceived themselves about physical condition would have been more confi about moving to other area = more likely to survive
  • In modern day AN sufferers, too much weight loss may = these ancestral mechs 
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STRENGTH-Supported by evidence from twin studies - indicate genetic component of the disorder. 

  • Holland et al 1988- looked at 45 pairs of female twins where at least one twin had disorder. 
  • Found sig higher concordance w mz twins compared to dz twins- 56% compared to 5%
  • shows genetic influence of AN and that it may have genetic basis- a factor needed for the evol explanation to make sense - STRENGTH
  • However never 100% concordance, and so there must be other factors interacting other than biological - which is an issue for the evol approach. 
  • Also massive increase in prevalence of AN in the last 30 yrs which coincides w female models being thinner, greater social media influence and more muscly, toned men in magazines.
  • These messages intrusive and crucial factor in why young women develop AN- and increase in men being diagnosed w AN is +vely correlated w these images- we need more research!
  • PSYCHO-SOCIAL EXPLANATIONS- involving psych processes eg SLT provide alternative to biological approach to AN other than evol
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Last note...

Biggest issue w evol exps- how can AN be passed down by natural selection when it is undoubtedly and majorly detrimental to the human body.
Given the fact that evol exp's suggest natural selection favours behaviours that promote survival and reproductive success- using this approach to explain a disorder that induces death and infertility is a stretch. 

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