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Age-specific mortality rates in the influenza epidemics of 1911-1917 and the ‘Spanish’ influenza epidemic of 1918

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Defence

  • Humans have evolved numerous mechanisms to respond to physical, biotic and social threats.
  • The major causes of extrinsic mortality are biotic, and include competition for nutrient supplies with other organisms of the same or different species; predation; and infection by micro-organisms.
  • Detection of a stressor elicits physical, endocrine and behavioural responses that evolved to cope with the threat or perceived threat. There may be pathological consequences of inappropriate stress responses.
  • Pathogens and parasites have co-evolved with their hosts.
  • The adaptive immune system is a key component of protection against microbial infection in vertebrates. Its specificity is a consequence of variation and selection.
  • Variations in drug-metabolising ability may be an echo of past adaptive responses to new food sources encountered by migrating humans.


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