The evolution of snakes has been amazing, as they have made so many huge changes in a relatively short time (100 million years or so).
- Digestion. The main challenge faced by snakes is digestion – they mostly can’t bite off bits of their prey, or chew, so they have to swallow them whole. Since some snakes can dislocate their jaw and have folds of skin around their jaw, they can swallow very large animals, even equal to their own weight. Obviously, when they have just eaten, this is going to hinder their mobility, so they all try to find a safe place to wait, and then digest the meal as quickly as possible. In addition, they want to digest the food before it goes bad, so they can switch their digestion ON, and turn the rest of their metabolism OFF, and digest very large meals very quickly. They are also most vulnerable when they are hunting, and this also favours their method of having infrequent but very large meals.
- Length and legs. Snakes have lost their legs – it is thought that they were originally small lizards that preyed on insects, which then went underground into small tunnels in search of ants and termites - the legs got in the way and eventually shrank away (they are still there in snake embryos, but don’t develop). However, in all embryos there is a switch that “buds” new vertebra on the spine. For snakes, this switch has been “re-programmed” to give a lot of vertebrae – the most found so far is over 500 ! Their skeletons are relatively delicate, so the fossils are rare.
- Single organs. Another remarkable feature of snakes is that with all the dual organs – lung, kidneys, heart – half of them have become vestigial and withered away, so that snakes only have one of each, or two ventricles in the case of the heart
- Venom. Some snakes have developed highly poisonous venom, and this varies greatly between species, and even between different individuals of the same species. The compounds in the venom are produced by slight variations from “normal” metabolic pathways, and this is one of several examples where snakes have adapted their genetic makeup and cellular functions in very unusual ways that the scientists are still researching, including by doing full genetic mapping.
- Senses. When the snakes went underground, they lost the sense of sight. But when they re-emerged, they mostly re-evolved it, but in different ways. This includes some species with infra-red vision, which gives them sensitivity to heat
This is such a number of remarkable coincidences, that it is almost as if they are evolving TOWARDS a pre-existing archetype, rather than by random mutations