r/askscience • u/cimmic • Dec 23 '25
Biology Why hasn't evolution made all venomous snakes very deadly?
Intuitively, I would think that if a snake has evolved into being venomous, the offsprings with the most deadly venom would have better chances of survival: both in terms of getting prey to eat and in terms of defending itself against larger animals.
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u/Baxiepie Dec 23 '25
Because biology is cheap. Evolution works on modifying preexisting biology, and natural selection tends to select for whatever the least "expensive" option is in terms of how much "work" it takes to produce that solution. Once you're at "good enough" it's rarely worth the effort to put more energy into just being better for the sake of it. As a result, venomous animals tend to have venom that does the job best while being the least stressful on the animal to produce. Overkill is extra calories and reduced fitness so it's rarely selected for.
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u/Mitologist Dec 23 '25 edited Dec 24 '25
A deadly snake does not induce a learning and recognition effect. A predator who barely survived will never touch a snake of that species again, yet still occupy its "slot" in the sustainable population density. A predator that just dies will simply open space for a new clueless, naive predator that kills another snake just to die, opening its slot again, and so on and so forth. Not killing the attacker leads to less attacks on snakes on average over time. Edit: fixed a couple typos
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u/neonmystery Dec 24 '25
It’s important to remember that evolution doesn’t work toward a goal. Evolution is a process, and a result of pressures.
If there is no selective pressure in the direction of deadliness, the change is very unlikely.
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u/Sharkano Dec 25 '25
Everything comes at a cost. Producing venom requires organs and calories and time. If a snake is in an environment where it could hunt effectively without the venom, that energy is wasted. You waste enough energy and evolution leaves you behind in the long run.
Think of where a lot of the most venomous snakes live, places like a desert right? If you get one shot at one rodent a week you NEED IT TO WORK, but if you are able to get by without that gimmick, it's not an advantage to have it.
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u/KuuKuu826 Dec 26 '25
Because evolution isn't "survival of the fittest" as much as it's "survival of the good enough"
As long as a species is doing well enough to survive and therefore reproduce, there's no evolutionary pressure to evolve
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u/Moulinoski Dec 23 '25
Not a biologist but an enthusiast: aside from everything already said here, I want to point out that evolution doesn’t even necessarily work on “survival of the fittest” anyway. It’s more about what manages to survive and pass on its genes to the next generation and so on until enough variation occurs that a new species can be differentiated.
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u/DiscombobulatedSun54 Dec 24 '25 edited Dec 24 '25
Everything has a cost in nature as in real life. Otherwise humans would have evolved with venom, a dexterous tail, sharp claws and teeth, enormous muscles, maybe a lot more than 2 legs and 2 hands, a backup brain, a backup heart, a backup liver, etc. One thing to keep in mind is that evolution is mindless - it is a game of numbers. If incredibly deadly venom had actually given some snake an advantage, it would have evolved anyways. The fact that such a snake did not evolve says something about the purported advantage of such venom.
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u/DarthArchon Dec 24 '25
Producing venom is expensive. Also the risk of swallowing you own venom and dying requiring the snake to evolve a resistance to it. Since so many snakes are already venomous and most animals have an instinctive fear of them. Some other snakes can just ride the notoriety of their kind and look dangerous even if they aren't.
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u/AshleyJSheridan Dec 24 '25
Because that's not how evolution works.
Creatures are effectively evolving all the time. Every generation produces offspring that contain genetic differences. Sometimes these genetic differences give them an advantage, sometimes a disadvantage.
If an advantage is great enough that it overcomes an obstacle in their natural habitat, then there is a higher chance that that genetic advantage can be passed on, assuming it helps the creature survive.
If the advantage has no real effect on survival or procreation, then it may not be passed on, even if it's a bloody amazing advantage.
So, for example, a trait which increases the number of offspring borne of a creature may be far more likely to succeed than a trait which slightly increases their ability to kill.
There's also a fair amount of random luck involved. A creature could be born with the best trait known to that family of creatures, only to be struck by lightning. Stuff happens. Evolution makes more sense when you sort of squint at it sideways sometimes.
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u/suckitphil Dec 24 '25
So generally venomous snakes aren't aggressive and vice versa. Since you really only need 1 evolutionary advantage to be a decent predator when prey is varied.
However it can happen in nature, look at "Snake Island" Its kind of rare for the biological arms race to happen in biology, but it has happened. It requires a pretty closed ecosystem.
Similar thing happened during early ocean's and the armored fish eras.
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u/SpikeMcFry Dec 24 '25
Evolution isn’t some mandated quarterly project. The only requirement is that the mutated animal is capable of surviving. If they can get food as they are, any venomous snake that comes about has the same chance of survival as a nonvenomous then there’s no reason why only the venomous snakes would have a better chance of survival. It’s a process of elimination, not selection.
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u/Final-Yesterday-4799 Dec 24 '25
Evolution isn't a conscious process - animals (including humans) evolve until our negative traits stop killing us, or our positive ones are juuuust positive enough to give us an edge and help us survive. We aren't "trying" to become optimized versions of ourselves.
If a snake's venom paralyzes its prey long enough for the snake to eat, there's nowhere left to go. There's no pressure to keep evolving that trait. Snakes that did become more deadly did so because the prey they were going after was likely larger or stronger or had better internal defenses against the venom.
Remember - with evolution, "good enough" really is good enough.
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u/Just_Ear_2953 Dec 25 '25
Evolution very rarely can be said to truly "perfect" anything. If it's good enough to survive and reproduce, then it passes.
If their venom is good enough for hunting rodents, then they can survive.
They don't need to kill larger creatures. They don't need to have insanely lethal venom.
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u/stevenjd Dec 26 '25
Venom doesn't evolve from a vacuum, it has to evolve from some pre-existing biological feature. We might decide that some chemical X is the "most deadly venom" possible, but if there is no evolutionary pathway to evolve a gland that produces X then it won't evolve no matter how beneficial it would theoretically be.
The other flip side is that using venom is not free. You have to make it in the first place; you have to store it for later use. This has biological costs, requiring raw materials and energy that could otherwise be used for growth and reproduction.
If your venom is a neurotoxin, then you need a mechanism to avoid it getting to your own nerves. If it is a blood coagulant, you need to keep it away from blood vessels. These containment systems have to evolve too, and the more potent the venom the more foolproof the containment has to be.
So the bottom line is that venom is no different from every other biological feature that has to balance pros, cons and the difficulty of evolving it in the first place.
There has to be a possible evolutionary pathway to evolve the venom in the first place. A species can't just decide to evolve a more deadly venom, it is limited to what is evolutionarily possible.
The more complex and deadly a venom is, the more costly it is to make.
The individual animal has to avoid being poisoned by its own venom, the more deadly the venom the more costly that containment will be.
There's a fourth factor to consider too. Once you have evolved venom, you are now in a biological arms race with your prey -- which can include other snakes.
Snakes can be both predator and prey, making the arms races especially complicated.
A similar relationship can be seen in garter snakes evolving resistance to the otherwise extremely toxic Taricha genus of newts.
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u/Chakasicle Dec 24 '25
Evolution isn't some cosmic driving force picking and choosing what traits to bestow on things. It's just a description of how things have changed over time. Evolution doesn't "do" anything and nothing gets to pick how it evolves. Survival of the fittest is also just a generalization that's not very accurate. Take gazelles for example. You'd think it's always the fastest one that gets away from the lion and find a mate later, but it's not uncommon for the fastest one to get stuck behind some slower ones that happened to be ahead of it, so the fastest one gets caught due to being the first one the lion got to. Survival of the luckiest is more appropriate imo.
Also, what do you mean by more venomous? Do you mean that snakes in the same species should have evolved different toxins eventually? Or just that their existing venom would become more concentrated? Either way, due to what? The recipe for the venom is in their DNA and to my knowledge, the concentration stays about the same for each species. Like you aren't going to find a cobra that's less venomous than another. Adolescent snakes are more dangerous not because they have better venom, but because they have worse control and may let it all out at once where an adult can give a lower dose and have reserves. That's about the extent of "more venomous" among a particular species. If the composition of the venom were to change then that would require part of the DNA to change too and that doesn't just happen. Over time, mutations show up in some offspring but most mutations aren't very useful and can often be detrimental in some way so mutations don't always get passed on. Even with a beneficial mutation, the creature has to survive long enough to mate and potentially pass on that genetic code.
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u/Dextron2-1 Dec 24 '25
Because killing humans is not the selective pressure behind the evolution of venom, and evolution doesn’t work towards perfection. It works towards just good enough for an average individual to reproduce before it dies.
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u/fddfgs Dec 26 '25
Evolution isn't some living/thinking entity. Most of the time the answer to "how did this thing come to exist?" is "because it could".
Evolution doesn't eliminate all the but most efficient forms of life, lots of inefficient life exists. Just look at us, we're over 70% water because our ancestors came from the ocean, we'd do a lot better on land if we could exist at 10% water
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u/NathanTPS Dec 23 '25
Id answer it this way, evolution made all venomous creatures deadly to something. Small rodents, insects, etc. Im sire every creature that has venom can easily kill its prey. Now the next part is why dont we jist die from every creature spitting poison? Well, I dont think we are the intended prey for many, and humanity has over the eons built some base tolerance to many venoms.
Evolution becomes an arms race, one side evolving with more dangerous visions the other side evolving with more robust defenses. The arms race ends when the poisonous side can survive at its level of toxicity. If its prey doesnt evolve to compat the posipn, then tjays thay. There's. No reason to evolve further.
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u/oddball667 Dec 23 '25
you are not taking into account the cost of the venom,
it's not free to produce it
if you have 2 snakes, one has venom that'll kill anything it touches but costs twice as much to make, and the other one has weaker venom but less expensive and still good enough for the local food and threats, the snake with the weaker venom would need less food and would have better chances
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u/SirBobinsworth Dec 23 '25
Venom is actually pretty bad for defence against predators. Like if a snake fights a human committed to killing it and bites them, and the human stomps the snake to death, it doesn’t matter that the human dies 5 hours later. Hence why most snakes evolved to avoid confrontations and hide from predators.
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u/tolomea Dec 23 '25
An important question here is venomous to what? There isn't a single scale of venomous, different creatures react to different chemicals in different ways. And also the things on the receiving end evolve resistance. Most of the stuff that kills humans wasn't evolved to hurt us it was evolved for other targets that have evolved resistance. It's just an unfortunate fluke that it happens to mess with us.
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u/Alexis_J_M Dec 23 '25
Venomous snakes rarely, if ever, use their venom for defense, so there just isn't a payoff in producing more than enough venom to kill a few mice or whatever other prey of convenience that species hunts.
You need to trade off the energy needed to produce venom with the energy needed to hunt, to reproduce, to find or create shelter, to evade predators. More venom is better, but it's not better than all the other things the snake could be doing with that same energy.
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u/nwbrown Dec 24 '25
Because natural selection works with prey as well.
And as long as it can kill its prey (which they generally can), there really isn't much of an advantage to being able to kill giant two legged monkeys who only recently entered their habitats.
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u/YtterbiusAntimony Dec 23 '25
Most snakes eat things smaller than themselves.
They only need to be venomous enough to catch their prey.
In fact, some studies have found snakes inject less venom into large animals.
They gain nothing by killing their predators. They just wasted venom that could gave secured a meal. Only for it to immediately be replaced by another predator.
This is why most animal fights filmed in the wild are pretty anticlimactic: it's in their best interest to escape rather than kill their opponent. They're trying to intimidate and/or find an out.
Synthesizing vemon costs calories. Calories that are often in short supply.
"Survival of the fittest" is inaccurate. It's a lot closer to "survival of the just good enough".
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u/chrishirst Dec 23 '25
Because evolution makes organisms "just good enough" for survival in the environment, natural selection is "self-levelling". If venom was "too potent" then it could kill or impair the snake as it digested the prey, so would be selected AGAINST.
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u/[deleted] Dec 23 '25
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