How The Snake Got Its Venom

Question from Robert:
What would be your reasoning as to how the evolution of venomous snakes could have happened? Obviously, the first snakes did not start off with venom glands in their heads. That means that they were getting along just fine without any venom to kill their prey for hundreds of thousands or millions of years. So why in the world would venom glands evolve inside their heads? That is not ‘natural selection’. Indeed, that is completely unnatural. A creature wants to keep poison out of its body! So why would any creature start to make poison inside its body? That makes no sense at all. And it would potentially be extremely dangerous to that creature.

But just for the sake of argument, let’s say that such a totally bizarre thing occurred. So now what? You have snakes with venom glands in their heads. How in the heck are the snakes supposed to get the venom into their prey? That would be 100% impossible for snakes to do that without hollowed out, syringe-like, very sharp fangs.

That’s a HUGE problem. That means that snakes which somehow evolved venom glands, would then have to evolve syringe like teeth. And there is absolutely no way that could happen because that would require forethought and planning. And it would totally go against the theory of natural selection. Also, by the time that snakes could have strangely evolved syringe like teeth, their venom glands would have already been naturally phased out because those glands would have been totally useless for an extremely long time. But again, just for the sake of argument, let’s say that this second totally bizarre thing occurred. Now snakes would have had to evolve a structure that would connect the venom gland to the syringe like teeth. How could all of these bizarre things happen accidentally? …. or naturally?

Answer by SmartLX:
We don’t have to rely on my reasoning, not when Scientific American has a full article on this exact subject and Wikipedia has a good summary sitting right there. What the heck, here’s the National Geographic article too. These are literally the first three results when you Google “evolution of snake venom” so I guess you didn’t start there.

The first snakes actually did start off with venom glands because the glands first evolved in the ancestors of snakes, four-legged burrowing lizards more similar to the Komodo dragon. The proteins in venom share DNA with compounds that do other jobs. One is saliva, which breaks down organic material for digestion. Immune system proteins, which attack foreign elements in the body, are another. One compound that isn’t mentioned is stomach acid, but this is another dangerous substance that is essential to normal bodily function. We need poisons in our bodies to survive, only they’re poisons we’re able to tolerate because of how they’re produced and contained. Venom evolved many times over throughout the animal and plant kingdoms, because it has lots to build off.

As for delivery systems, of which there are many, you don’t need much of a starting point. Toads secrete poison on their skin and let it sit there, because the only animals they want to poison are those who try to eat them, so any number of bodily glands could have switched their purpose. Spitting cobras squirt venom forward, so what if they started by just plain spitting, or to be more specific, gleeking? With this technique, even humans can shoot liquid a long way from the body straight from a gland. A gland with a naturally effective nozzle like this can slowly evolve into either a weapon that can be aimed or a hard retractable tube that can inject, because every little bit closer it mutates to either one of these makes for more effective hunting and defense, and ultimately a better chance of survival.

With the specifics covered, let’s look at the overall nature of your challenge because it is VERY similar to those that have come before. You point to something remarkable and ask how it could have happened, and implicitly assert your own explanation by elimination after assuming no good answer is forthcoming. A textbook argument from ignorance (a harsh name, sorry, but the official one) and thus an informal fallacy, which is a failure of the premise of an argument to support its conclusion. It fails for several reasons: obviously it’s rebutted if an alternative answer is presented, but even if not it relies on the assumption that if you and I can’t think of a way then it’s impossible. We’d have to be gods ourselves for this to be true. I point out this fallacy whenever it comes in because it is the basis of many of the arguments for God, and every creationist argument. As a result, these arguments are only good for reassuring yourself and those who agree with you, because by themselves they have little power to persuade.