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Emotion and cognition: Lecture 8 notes

Lecture 8: Psychopathology in humans and nonhuman primates – why do humans get depressed?

 

Depression in humans

  • Feelings of sadness / emptiness
  • No interest or pleasure in activities
  • Weight changes
  • Insomnia or hypersomnia
  • Agitation or retardation
  • Fatigue or loss of energy
  • Feelings of worthlessness
  • Poor concentration
  • Recurrent thoughts of death

Evolution an depression

  • Depression is common
  • High heritability
  • People with depression have less children
  • Paradox: Why did natural selection not eliminate depression from the population?

Prevalence and heritability

  • Lifetime prevalence (USA): 19.2%,  (NL): 17.9%
  • University students: 30.6%
  • Persistent depressive disorder (USA): 4.7%
  • Heritability = 37%

Why do humans get depressed?

  • Cry for help
  • Reaction to losses
  • Seasonal – no activity in winter
  • Energy conservation
  • Rumination – solving problems
  • Association with inflammation/infections
  • Mismatch

Mismatch hypothesis

  • We are not adapted to modern environments, but to ancestral environments. This results in a mismatch.

Testing mismatch hypothesis -test 1

Chimpanzees in the wild – less mismatch

Captive chimpanzees – more mismatch

Captive chimpanzees were more likely to show signs of depression:

  • Depressed hunched posture
  • Social withdrawal
  • Easily irritated or angered
  • Loss of interest in activities
  • Weight loss or gain
  • Awake or easily awakened
  • Difficulty falling asleep or excessive sleep
  • Poor concentration

Environment of Evolutionary Adaptedness

  • Savannah-like environment
  • Hunter-gatherer society
  • Nomadic lifestyle
  • Physical dangers
  • High infant mortality
  • Food scarcity

Mismatch hypothesis – test 2

Developing countries – less mismatch

Developed countries – more mismatch

  • It was found that the higher the GDP per capita is somewhere, the more people suffer from mood disorders

Key environmental changes

  • Obesity
  • Different diet
  • Less physical activity
  • Less sunlight
  • Less sleep
  • Less social interactions

Mismatch hypothesis – test 3

Rural areas – less mismatch

Urban areas – more mismatch

High prevalence of diagnoses in Stockholm, Sweden, compared to Swedish rural areas:

  • Depression
  • Anxiety
  • Diabetes
  • Hypertension
  • Asthma
  • COPD

Mismatch hypothesis – test 4

Hunter-gather societies – less mismatch

Modern societies – more mismatch

  • No signs of depression were found in Kaluli, a hunter-gather society in New Guinea

Mismatch hypothesis – test 5

Co-sleeping babies – less mismatch

Babies sleeping alone – more mismatch

When co-sleeping:

  • Less infant crying
  • Less sudden infant death syndrome
  • Higher self-esteem
  • Less anxiety
  • More satisfaction with life
  • More social competence

Mismatch hypothesis – test 6

More physical activity – less mismatch

Less physical activity – more mismatch

Prospective study in adolescents:

  • Each additional hour of physical activity per week - reduction in depressive symptoms of 8%

Mismatch hypothesis – test 7

More mismatches – more depression

Less mismatches – less depression

Mismatch questionnaire with scales:

  • Lack of sleep
  • Lack of exercise
  • Lack of natural daylight
  • Lack of time
  • Lack of green environment
  • Lack of social relations
  • Lack of contact with family members
  • Materialism

Mismatch correlation with depressive symptoms (BDI): 0.6

Conclusion

Modern humans behave like captive apes

Solution

Do we all need to become hunters and gatherers again...?

Mindfulness: Non-judgmental and accepting awareness of the present moment

  • Mindfulness improves mental health
  • It prevents depressive relapse

General conclusion

An evolutionary informed psychiatry and developmental psychology may improve mental health and children’s education

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