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Evolving Snake Venom

Author(s): Tod Schimelpfenig
Posted: April 18, 2010

Have you heard the story of evolving snake
venom?  Apparently snake venom in
general is becoming more potent and, gasp, snakes have been interbreeding and
sharing potent neurotoxins.  Alas,
while this is good stuff for horror movies, it’s not yet been scientifically
demonstrated and probably isn’t true.

There were several media articles in 2009
describing the increasingly potent snake venom.  Since then I’ve been asked a number of times about this
concept, and have listened to people state this as a fact.   There is an
article in the most recent Wilderness and Environmental Medicine  (WEM)
Journal that discusses this question in depth.

According to the authors, both very reputable
snakebite researchers, it’s only speculation that snake venoms are quickly
evolving, or becoming more toxic.

The concept that snakebites are becoming worse has
not been demonstrated in the medical literature.  The perception that they
are worse can be influenced by media drama,  especially ‘real-life’
television drama or the dramatic images of a few isolated bites that circulate
on the internet.   The WEM paper describes how an isolated case report
became media drama when opinions of experts who questioned the hypothesis
of rapidly evolving venom were not included in the lay press articles.

Venom composition and toxicity varies within
populations of the same species of snake, which may account for the different
s/s and an illusion of evolution.   If the average envenomation is indeed becoming more severe, the paper
offers several other possible explanations including larger snakes, more
provoked bites, and the difficulty of comparing severity in the face of
changing snakebite treatment protocols over the years.

I’ve heard that the Mojave rattlesnake is
interbreeding with other populations and spreading it’s neurotoxin around.  This has not been demonstrated.
 The  “Mojave neurotoxin” has been identified in some
isolated Southern Pacific rattlesnake populations, but these are not near
populations of Mojave rattlesnakes.  It may well be that we are simply
getting better at identifying the many toxins in snake venom.

The article also discussed the pace of evolution,
which doesn’t match the rapid changes supposedly happening.

So, we don’t know if venom is rapidly evolving or
becoming more potent.  We do know
we are always vulnerable to the dramatic story, especially if in involves
snakes, spiders or other creepy crawlers.

Take care 


Hayes W and Mackessy S.  Sensationalistic Journalism and Tales of
Snakebite: Are Rattlesnakes Rapidly Evolving More Toxic Venom?  Wilderness
and Environmental Medicine, 21, 35-45 (2010)

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