Most uses of projected venom or other unpleasant substance seem to be defensive rather than offensive. One reason for this is that it’s expensive to make the dangerous substance, and throwing it away wastes it. This cost is affordable if it is used to save your own life, but not easily affordable to acquire a single meal. This life vs meal distinction plays into a lot of offense/defense strategy expenses.
For the hunting options, usually they are also useful for defense. The hunting options all seem cheaper to deploy: punching mantis shrimp, electric eel, fish spitting water...
My guess it that it’s mostly a question of whether the intermediate steps to the evolved behavior are themselves advantageous. Having a path of consistently advantageous steps makes it much easier for something to evolve. Having to go through a trough of worse-in-the-short-term makes things much less likely to evolve. A projectile fired weakly is a cost (energy to fire, energy to producing firing mechanism, energy to produce the projectile, energy to maintain the complexity of the whole system despite it not being useful yet). Where’s the payoff of a weakly fired projectile? Humans can jump that gap by intuiting that a faster projectile would be more effective. Evolution doesn’t get to extrapolate and plan like that.
Jellyfish have nematocysts, which is a spear on a rope, with poison on the tip. The spear has barbs, so when it goes in, it sticks. Then the jellyfish pulls in its prey. The spears are microscopic, but very abundant.
Yes, but I think snake fangs and jellyfish nematocysts are a slightly different type of weapon. Much more targeted application of venom. If the jellyfish squirted their venom as a cloud into the water around them when a fish came near, I expect it would not be nearly as effective per unit of venom.
As a case where both are present, the spitting cobra uses its fangs to inject venom into its prey. However, when threatened, it can instead (wastefully) spray out its venom towards the eyes of an attacker. (the venom has little effect on unbroken mammal skin, but can easily blind if it gets into their eyes).
Fair argument
I guess where I’m lost is that I feel I can make the same ‘no competitive intermediate forms’ for all kinds of wondrous biological forms and functions that have evolved, e.g. the nervous system.
Indeed, this kind of argument used to be a favorite for ID advocates.
There are lots of excellent applications for even very simple nervous systems. The simplest surviving nervous systems are those of jellyfish. They form a ring of coupled oscillators around the periphery of the organism. Their goal is to synchronize muscular contraction so the bell of the jellyfish contracts as one, to propel the jellyfish efficiently. If the muscles contracted independently, it wouldn’t be nearly as good.
Any organism with eyes will profit from having a nervous system to connect the eyes to the muscles. There’s a fungus with eyes and no nervous system, but as far as I know, every animal with eyes also has a nervous system. (The fungus in question is Pilobolus, which uses its eye to aim a gun. No kidding!)
Most uses of projected venom or other unpleasant substance seem to be defensive rather than offensive. One reason for this is that it’s expensive to make the dangerous substance, and throwing it away wastes it. This cost is affordable if it is used to save your own life, but not easily affordable to acquire a single meal. This life vs meal distinction plays into a lot of offense/defense strategy expenses.
For the hunting options, usually they are also useful for defense. The hunting options all seem cheaper to deploy: punching mantis shrimp, electric eel, fish spitting water...
My guess it that it’s mostly a question of whether the intermediate steps to the evolved behavior are themselves advantageous. Having a path of consistently advantageous steps makes it much easier for something to evolve. Having to go through a trough of worse-in-the-short-term makes things much less likely to evolve. A projectile fired weakly is a cost (energy to fire, energy to producing firing mechanism, energy to produce the projectile, energy to maintain the complexity of the whole system despite it not being useful yet). Where’s the payoff of a weakly fired projectile? Humans can jump that gap by intuiting that a faster projectile would be more effective. Evolution doesn’t get to extrapolate and plan like that.
Jellyfish have nematocysts, which is a spear on a rope, with poison on the tip. The spear has barbs, so when it goes in, it sticks. Then the jellyfish pulls in its prey. The spears are microscopic, but very abundant.
Yes, but I think snake fangs and jellyfish nematocysts are a slightly different type of weapon. Much more targeted application of venom. If the jellyfish squirted their venom as a cloud into the water around them when a fish came near, I expect it would not be nearly as effective per unit of venom. As a case where both are present, the spitting cobra uses its fangs to inject venom into its prey. However, when threatened, it can instead (wastefully) spray out its venom towards the eyes of an attacker. (the venom has little effect on unbroken mammal skin, but can easily blind if it gets into their eyes).
Fair argument I guess where I’m lost is that I feel I can make the same ‘no competitive intermediate forms’ for all kinds of wondrous biological forms and functions that have evolved, e.g. the nervous system. Indeed, this kind of argument used to be a favorite for ID advocates.
There are lots of excellent applications for even very simple nervous systems. The simplest surviving nervous systems are those of jellyfish. They form a ring of coupled oscillators around the periphery of the organism. Their goal is to synchronize muscular contraction so the bell of the jellyfish contracts as one, to propel the jellyfish efficiently. If the muscles contracted independently, it wouldn’t be nearly as good.
Any organism with eyes will profit from having a nervous system to connect the eyes to the muscles. There’s a fungus with eyes and no nervous system, but as far as I know, every animal with eyes also has a nervous system. (The fungus in question is Pilobolus, which uses its eye to aim a gun. No kidding!)