Snake Venom: Snake venom kills tens of thousands of people every year, but new research is turning it into cures that may save the lives of many more Photo by Joe McDonald/Corbis/Scanpix pix

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As predators, snakes are missing a few key attributes. They have no legs to chase down their prey, no paws to knock down quarry, and no claws to hold their victims. But none of these deficiencies matters much, because evolution has handed snakes the ultimate weapon: venom. With it, the several hundred types of venomous snakes can kill or debilitate before their victims escape.

Their venom has given snakes the ability to be small yet effective hunters, and they have spread to fill every ecological niche—as long as the environment is warm enough for them to stay in motion. Snakes live everywhere from treetops to the forest floor, in deserts and in the oceans.

In general, scientists agree on how snakes’ venom glands evolved, but that’s not the case for the poisons themselves. Some scientists think that venom is composed of modified proteins from the snakes’ spit that already functioned to break down and digest the prey. Some also believe that the ability to produce poison has evolved independently among the different species of snakes.

But Australian researcher Bryan Fry, one of the world’s leading experts on venomous snakes, has another theory. He has discovered, with the help of DNA analysis, that the vast majority of the proteins and enzymes found in venoms closely resemble substances found in other parts of the snakes’ bodies—substances, for example, that have a function in the liver, or in the digestive organs or some other system. The genes that control the production of these substances in other organs somehow became activated in the salivary glands, where they produce substances that, once modified and refined, are able to help kill the snakes’ prey in an increasingly effective manner.

Fry also believes that this ability arose a single time, well over 100 million years ago, in one of the earliest ancestors of modern snakes. It then spread to all snakes, but it was only highly developed and refined among the three taxonomic families that we now consider poisonous.
Venom, in other words, is older than snakes themselves.