The lethal scorpion venom originated from a common protein used as part of the creature's immune system, scientists have found.
Researchers led by Shunyi Zhu at the Chinese Academy of Sciences found that that a similar process may have involved in the evolution of most of the venom in the animal world.
While most scorpions, which have a tail that delivers venom, only give a human victim a few bad days, 25 of the 1,700 known species can kill a person.
Researchers looked at proteins in the scorpions called defensins, compounds found in many plants and animals that fight bacteria, 'Inside Science News Service' reported.
They sequenced the genetics of the amino acids in defensin and found that all it took was a change in a single gene to turn the defensin into a poison.
Scientists believe scorpions originated on land and were eventually swept into the ocean, evolved during the time they spent there and then reemerged, perhaps 400 million years ago.
"I guess the emergence of toxins from defensins is a consequence of adaptation of scorpions to their decreased size that increases difficulty in capturing prey when they emerged from the seas," Zhu said.
Scorpions were larger in the water but had to shrink physically over the course of their evolution on dry land, and it became harder to kill and catch some prey. So they developed venom, the report said.
The study was published in the journal Molecular Biology and Evolution.
