Monday, July 4, 2011

Fainting and Evolution

A dear friend of mine from middle school's mother prompted this post.  She woke her husband up at 3am and said that she felt like if she didn't go to the hospital right then that she might not make it to the morning.  Due to unknown causes, she had developed a bacterial infection throughout her body.  At its worst the doctors gave her 5% chance of surviving.  Her body fought back by pulling blood from her extremities and pooling it around her intestines and stomach.  The lack of blood flow to her hands and feet caused them to turn black, go necrotic and they're now battling to save as much of her hands and feet as possible.  So far she's lost half of her right foot and the fingers of her left hand.  As someone who cares about her well being and someone who's interested in evolution I'm left wondering why the hell this's happened.  Why would the body react that way?

Turns out sever bacterial infections aren't the only time the body pools blood around the intestines and stomach.  It's actually the reason you faint.  It happens during hypothermia.  It's a shock response.  It happens during extreme blood loss.  There's a number of situations where evolution tells your body to pool large amounts of blood around your intestines and stomach.  Let's consider some reasons why.

  • Hypothermia
    • Extremities are the greatest source of heat loss--pool it in the core to reduce heat loss
      • Downside is you're more likely to get frost bite

  • Blood Loss
    • If the blood loss is from your core near your vital organs then you're screwed.  If it's from one of your extremities and you can reduce the blood flow enough for it to clot then you just might save yourself.

  • Fainting
    • Psychosomatic Causes
      • Fear
      • Pain
      • Shock
      • The sight of blood and guts (fear?)

    • Methodology
      • The vagas nerve increases blood flow to the intestines and stomach
      • Blood flow to the extremities (including the head and brain) is reduced
      • Most common in teens and elderly--elderly because of poor blood flow, teens because of a mismatch of size and physiological capabilities
      • Brief in duration--heart rate and vasoconstriction return to normal momentarily
      • Very different from the famous fainting goats that have full body simultaneous muscle contractions
      • Also very different from opossums who are quite alert and don't just pretend to be dead, but also rotten, by secreting a foul smelling substance from their anus and frothing at the mouth

    • Possible Evolutionary Causes
      • To Play Dead
        • Limit Damage
          • If on your own you can't win maybe going limp will...
            • Buy time for the group to respond
            • Make your group feel bad that you're helpless and rally their help
        • Cause Predator to Lose Interest
          • Fight versus meal
            • Because of our size maybe a lot of predators don't think of us as a meal so much as they think of us as a threat.  Playing dead might eliminate that fear and cause them to move on.
          • Maybe many predators don't hunt out of hunger (since so many hunts are unsuccessful and they can go long, long stretches without eating [polar bears can go 8 months while hibernating with pups]), but instead hunt out of the thrill of the hunt, the chase, the excitement, a desire for power, to conquer.  Maybe by playing dead the predator might temporarily be disappointed and lose interest.
        • Not expect you to flee or fight
          • They think they can take their time eating you and then--surprise you're gone!!
      • Defecation/Excrement
        • Maybe the flood of blood once served as an aid to evacuate the bowels and cause potential predators/assaulters to be grossed out.

1 comment:

  1. Could the syncope response provide an evolutionary benefit to the species as a whole by increasing the probability of death of the individual? If the individual doesn’t recognize any benefit to the species the brain invokes syncope so that the individual does compete with its other members for resources.


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