page_title: Evolution of snake venom
hierarchical_section_title: Evolution of snake venom
caption_attribution_description: English: A Pacific rattlesnake (Crotalus oreganus) eating a small mammal in Joshua Tree National Park. Photo by NPS/Kristen Lalumiere
context_page_description: Venom in snakes and some lizards is a form of saliva that has been modified into venom over its evolutionary history. In snakes, venom has evolved to kill or subdue prey, as well as to perform other diet-related functions. The evolution of venom is thought to be responsible for the enormous expansion of snakes across the globe.
  The evolutionary history of snake venom is a matter of debate. The common view of this history before 2014 was that venom originated just once among all Toxicofera approximately 170 million years ago, and then diversified into the wide range of venoms seen today. Under this hypothesis, the original toxicoferan venom was a very simple set of proteins that were assembled in a pair of glands. Subsequently, this set of proteins diversified in the various lineages of toxicoferans, including Serpentes, Anguimorpha, and Iguania. Several snake lineages subsequently lost the ability to produce venom, often due to a change in diet.
  The single-origin hypothesis suggests that the mechanism of evolution in most cases has been gene duplication followed by natural selection for adaptive traits.
context_section_description: Venom in snakes and some lizards is a form of saliva that has been modified into venom over its evolutionary history. In snakes, venom has evolved to kill or subdue prey, as well as to perform other diet-related functions. The evolution of venom is thought to be responsible for the enormous expansion of snakes across the globe.
  The evolutionary history of snake venom is a matter of debate. The common view of this history before 2014 was that venom originated just once among all Toxicofera approximately 170 million years ago, and then diversified into the wide range of venoms seen today. Under this hypothesis, the original toxicoferan venom was a very simple set of proteins that were assembled in a pair of glands. Subsequently, this set of proteins diversified in the various lineages of toxicoferans, including Serpentes, Anguimorpha, and Iguania. Several snake lineages subsequently lost the ability to produce venom, often due to a change in diet.
  The single-origin hypothesis suggests that the mechanism of evolution in most cases has been gene duplication followed by natural selection for adaptive traits. Some of the various adaptations produced by this process include venom more toxic to specific prey in several lineages, proteins that pre-digest prey, and a method to track down prey after a bite. These various adaptations of venom have also led to considerable debate about the definition of venom and venomous snakes.
  The idea that venom had a single evolutionary origin has been called into question by a 2015 study, which found that venom proteins had homologs in many other tissues in the Burmese python. The study therefore suggested that venom had evolved independently in a number of snake lineages.
caption: The venomous rattlesnake Crotalus oreganus eating its prey, which it uses its venom to subdue
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