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 

Tod

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)