Let’s evolve a poison container:
Fine. However, let us recall that evolution tends not to build stuff from scratch if it does not have to - it usually takes something that already exists and modifies it to suit the new purpose. In the case of poison containers it often starts with a salivary gland and modifies that.
The substance must not be harmful to the carrier.
Saliva is not harmful, even though it does help in digesting food - the lining of the mouth and the teeth are already resistant to saliva. As the saliva moves towards poison the mouth can also move in parallel to resist. Failures die from their own poison and do not reproduce. It is also worth noting that most snake venoms are not technically poisons. If you drink some it will be broken down by your digestive system and rendered harmless. It is only dangerous if it is injected directly into your bloodstream, thus bypassing your digestive system.
The container is built but is empty. It is required that the container hold at least one effective dose of poison. Refill must be automatic, so a sensor is required.
Salivary glands are already leakproof and are already built. They already have a sensor and an automatic refill system.
A filling system is built.
Salivary glands already have a filling system. All that is needed is a change in the ingredients.
The substance contained now needs a feed line to the point of exit, i.e. fangs.
There is already an existing feed line to the mouth. The exit point of the feed line needs to move and teeth need to change their shape.
The fangs, which were solid, must now be hollowed. The feed line must connect to each.
The probable intermediate was a U-shaped cross-section fang with an open channel. Some existing snakes use this system. Extending the sides of the U will close over the channel and give a hollow, O-shaped, fang. There is often more than one way for evolution to get to a destination.
A muscle must be added to the container to apply pressure to release poison.
Already present in a salivary gland.
Modification to autonomic system in brain to contract muscle to force sufficient poison into feed line to be injected.
Already present for salivary glands - saliva is released when there is food in the jaws.
Modification to “instinct” that converts bite/crush and kill to inject poison and kill.
Not by much - bite + saliva is very similar to bite + venom. If you have ever observed reptiles eating then you will notice that they are not strong on crushing/chewing as they do not have cheeks - stuff falls out of the sides of their mouths. Swallowing large chunks is much more their style. Many non-poisonous snakes swallow their prey whole.
It would be useful to have the sensor in the container alert the carrier when it is empty for purely survival purposes, i.e. no more ammo in the poison container.
Such a sensor is already present in salivary glands, which are kept replenished automatically.
It is my view that the law of probability precludes all of this from happening, even if millions of years are supposedly involved. I find all dating methods (yes, I’ve read up) entirely questionable.
Your personal views are not relevant to science. Particularly so if you do not realise that poison glands are mostly modified salivary glands; starting from a salivary gland changes the odds considerably as many of the required subsystems you have described are already in place. Have a look at
Properties of a Toxin from the Salivary Gland of the Shrew, Blarina Brevicauda for an example of exactly the sort of evolution I am talking about.
By modifying a pre-existing component, such as a salivary gland, evolution can develop a new component without having to start from a blank sheet of paper. Salivary glands are already present in the mouths of tetrapods and they are an obvious candidate for evolution into poison glands.
rossum