Why aren't all snakes venomous?

[CaptHaddock]

Each life form on earth has evolved and adapted to its own needs and environment.

Why not ask why Polar Bears are big, fierce and have white fur whilst the Hippopotamus, who is also big and fierce has no fur ?

Why do humans have differing racial characteristics ?

Why do big fish eat little fish ?

I think you're missing the point. There's a genus - snakes. Some have characteristic "x" and some don't. Basic evolutionary theory tells you that if something's a straightforward win it should spread. If it doesn't spread that's because i) it can't, or ii) there's a countervailing pressure in the opposite direction. So given that - you'd think - there isn't much of a price in being venomous, and there are obviously multiple routes to becoming venomous, and given that it seems to be useful, they should all pretty much be venomous. That tells you that in fact there has to be - despite appearances to the contrary - a pressure in the opposite direction. Being venomous has to have a cost attached to it. Someone suggested that it's a straightforward biological/calorific cost, but I find it hard to believe that that's true. My suggestion is that maybe being a threat to humans gets you killed, which is why "stand up and be seen, rattle and hiss" spread. It might also be why biologists are mistaken when they say "Non-venomous evolved to look like the venomous to avoid being messed with". Maybe, in fact, the venomous evolved to look like the non-venomous to avoid being killed.

If your assumption that the capacity to produce venom comes with little or no biological cost were true, then it would indeed follow that we would expect venomous species to dominate, perhaps overwhelmingly. Since the observed data is that most species of snake are non-venomous, then it follows logically that you should question your assumption, to wit, venom production probably has significant biological costs associated with it, even if it is difficult to observe the actual biological costs directly.

Snakes are of the order, squamata, suborder serpentes, that includes many families, each of which includes numerous genuses.

Most venomous species of snake use venom for predation, not defense. Their basic reptile strategy of ambush hunting would require camoflage coloring for most species.

[Craig krup]

If your assumption that the capacity to produce venom comes with little or no biological cost were true, then it would indeed follow that we would expect venomous species to dominate, perhaps overwhelmingly. Since the observed data is that most species of snake are non-venomous, then it follows logically that you should question your assumption, to wit, venom production probably has significant biological costs associated with it, even if it is difficult to observe the actual biological costs directly.

Okay, but the trouble is that we know that some snakes are producing bucketloads of venom - the various shows in Bangkok and in other places see them milked constantly. I know they'll (probably) find it a lot easier to get plenty to eat, so it might be true that there's a big biological cost, but given the volume of cells involved I find it hard to believe that it's more of a cost than normal cell turnover in the rest of the body.

We're also left with the interesting fact that quite a lot of venomous and non-venomous seem uncannily alike. You can argue that there are only so many ways of being, or they had a common ancestor (maybe even one that was venomous) and losing venom was an evolutionary strategy, maybe because of the biological cost.

But you could question your assumption and contemplate my solution to the conundrum. Maybe there isn't a particularly large biological cost - making 4 grams of venom is no more difficult than replacing 4 grams of liver tissue - but being venomous increases your chances of getting your head smashed in.

It's a bit like being a wolf. Wolves are aggressive and chocolate labradors are cuddly. Ever looked at the relative numbers? Cuddles is the dominant strategy

[Thongkorn]

Does anyone know if a cobra has ever died becasue he bit his own lip by accident,

[stoneyboy]

Does anyone know if a cobra has ever died becasue he bit his own lip by accident,

No but there were reports of a Python crushing itself to death.

[ableguy]

Why don't all Issan girls marry farangs and become super rich, because there are ugly ones ( farangs of course ).

[luk AJ]

My question is why some snakes have enough venom to kill a human while their normal prey is no bigger than a mouse...how this works with the biological cost?

[bbbbooboo]

Question: what's got 4 legs and flies?

Answer: a dead sheep

[richard_smith237]

The question enters the 'evolution by intelligent design' thought rather than 'evolution by natural selection'...

The advantages and disadvantages vary with the climate and geography... the evolution over Epoch's perhaps allows for times when prey were different.

Reptiles have evolved over millions of years, venom has evolved over approximately 170 million years.... thats enough time for many many changes to the world as we see it.

Some species have lost venom... some species haven't... for some species the venom has become stronger..

When considering evolution by natural selection - a snake with more venom than another snake of the same species is at no advantage. However, at a period of time when the snake of the same species with less venom has not killed its natural predator its genes have not passes on.

This 'natural predator' may have come and gone in a time scale almost incomprehensible to us, however, the evolutionary fingerprint remains.

[richard_smith237]

If your assumption that the capacity to produce venom comes with little or no biological cost were true, then it would indeed follow that we would expect venomous species to dominate, perhaps overwhelmingly. Since the observed data is that most species of snake are non-venomous, then it follows logically that you should question your assumption, to wit, venom production probably has significant biological costs associated with it, even if it is difficult to observe the actual biological costs directly.

Okay, but the trouble is that we know that some snakes are producing bucketloads of venom - the various shows in Bangkok and in other places see them milked constantly. I know they'll (probably) find it a lot easier to get plenty to eat, so it might be true that there's a big biological cost, but given the volume of cells involved I find it hard to believe that it's more of a cost than normal cell turnover in the rest of the body.

We're also left with the interesting fact that quite a lot of venomous and non-venomous seem uncannily alike. You can argue that there are only so many ways of being, or they had a common ancestor (maybe even one that was venomous) and losing venom was an evolutionary strategy, maybe because of the biological cost.

But you could question your assumption and contemplate my solution to the conundrum. Maybe there isn't a particularly large biological cost - making 4 grams of venom is no more difficult than replacing 4 grams of liver tissue - but being venomous increases your chances of getting your head smashed in.

It's a bit like being a wolf. Wolves are aggressive and chocolate labradors are cuddly. Ever looked at the relative numbers? Cuddles is the dominant strategy

Only in recently evolutionary history manipulated by humans... ... since 'breeding'....

[Craig krup]

It's a bit like being a wolf. Wolves are aggressive and chocolate labradors are cuddly. Ever looked at the relative numbers? Cuddles is the dominant strategy

Only in recently evolutionary history manipulated by humans... ... since 'breeding'....

Yes, but cuddlers - and breeders - are every bit as much a part of the environment as rabbits and lions.

Besides, I don't think that's actually true. Dogs that were pro-social and able to imprint on the humans that rescued them as puppies survived. Most of the time they barked at snakes and brigands and ate the bits that humans wouldn't, the humans building the traps that the thumbless dogs found tricky. Now and again the dogs nipped off for a quick shag - the one thing they really needed other dogs for - and apart from that it's been one long fireside and cuddle-hound odyssey.

[slipperylobster]

Maybe the non-venomous snakes want to be venomous, but cannot afford it. Elsewise, it could be that they misused their venom (in a previous life), and are now suffering the consequences.

Edited November 25, 2015 by slipperylobster

[slipperylobster]

It's a bit like being a wolf. Wolves are aggressive and chocolate labradors are cuddly. Ever looked at the relative numbers? Cuddles is the dominant strategy

Only in recently evolutionary history manipulated by humans... ... since 'breeding'....

Yes, but cuddlers - and breeders - are every bit as much a part of the environment as rabbits and lions.

Besides, I don't think that's actually true. Dogs that were pro-social and able to imprint on the humans that rescued them as puppies survived. Most of the time they barked at snakes and brigands and ate the bits that humans wouldn't, the humans building the traps that the thumbless dogs found tricky. Now and again the dogs nipped off for a quick shag - the one thing they really needed other dogs for - and apart from that it's been one long fireside and cuddle-hound odyssey.

Thumbs are overated. I know several people who are "all thumbs"...and could not build a trap either.

There are other people that just play guitar/or paint a picture...with their feet. Lets toss the thumb theory out.

As for the snakes.....well, I suppose some have developed "people skills" and have no use for venom.

Edited November 25, 2015 by slipperylobster

[lvr181]

Ummm................why not engage the snake population in conversation to ascertain their point of view?

Why are not all humans female? Why is the Pope catholic? Do steam rollers roll steam? And so on and so on. A slow day at your residence perhaps, leading to some deep seated thinking?

Have a nice day my friend.

[CaptHaddock]

If your assumption that the capacity to produce venom comes with little or no biological cost were true, then it would indeed follow that we would expect venomous species to dominate, perhaps overwhelmingly. Since the observed data is that most species of snake are non-venomous, then it follows logically that you should question your assumption, to wit, venom production probably has significant biological costs associated with it, even if it is difficult to observe the actual biological costs directly.

Okay, but the trouble is that we know that some snakes are producing bucketloads of venom - the various shows in Bangkok and in other places see them milked constantly. I know they'll (probably) find it a lot easier to get plenty to eat, so it might be true that there's a big biological cost, but given the volume of cells involved I find it hard to believe that it's more of a cost than normal cell turnover in the rest of the body.

We're also left with the interesting fact that quite a lot of venomous and non-venomous seem uncannily alike. You can argue that there are only so many ways of being, or they had a common ancestor (maybe even one that was venomous) and losing venom was an evolutionary strategy, maybe because of the biological cost.

But you could question your assumption and contemplate my solution to the conundrum. Maybe there isn't a particularly large biological cost - making 4 grams of venom is no more difficult than replacing 4 grams of liver tissue - but being venomous increases your chances of getting your head smashed in.

It's a bit like being a wolf. Wolves are aggressive and chocolate labradors are cuddly. Ever looked at the relative numbers? Cuddles is the dominant strategy

Well, my intuition is that venom is costly to produce, not cheap. I can't find any research estimating the biological cost of venom production in snakes, but I did find a quote from a study on the metabolic cost of sperm production in Japanese macaques. I think it is reasonable to expect that venom and sperm might have similar costs, say, within an order of magnitude. The important point here, and one that I think you missed, is that you have to scale the product by the size of the animal producing it. Four grams is not much for a 180 lb. human. The highly venomous coral snake in the US weighs about 10 lbs. I don't find the weight of a venom injection, but of other species the range looks like from 10 mg to 90 mg per bite. Since biological cost is relative to the biomass, it is going to be more costly for a small animal like a snake than for larger mammals like humans. Also, reptile have lower metabolic rates than mammals so the cost for them of producing anything is higher.

But back to the Japanese macaques. The cost estimate for sperm production for Japanese macaques is from 0.8% of the basal metabolic rate to 6.0% So, let's say 1%. Now one percent is a lot in the competition for survival. All species are at all times engaged in the tradeoff of costs for benefits. 99% or more of all species are extinct, from which we can conclude that small differentials in either costs or benefits add up over time. As Branch Rickey once said, "Baseball is a game of inches."

As to the likelihood of human extermination as an element of selection pressure, it is possible, but I would not expect it to be large compared to habitat loss, for example. Dogs, horses, and other domesticated species have been selectively bred by humans for thousands or tens of thousands of years, which is to say that their reproduction has been completely controlled for that time. But not snakes.

Here is the abstract from:

http://www.ncbi.nlm.nih.gov/pubmed/16467956?dopt=AbstractPlus

How costly are ejaculates for Japanese macaques?

Thomsen R¹, Soltis J, Matsubara M, Matsubayashi K, Onuma M, Takenaka O.

Author information

Abstract

Much sexual selection theory is based on the idea that ejaculate is cheap. Since further details are unknown our aim was to determine the energy that primate males require for ejaculate production. We addressed this problem by measuring the energy content (in kJ) of ejaculates from Japanese macaques (Macaca fuscata) using standard bomb calorimetry. Then, we estimated the relative amount of energy that individuals require for ejaculate production by relating the net energy content of ejaculates to males' daily basal metabolic rate (BMR). Fresh macaque ejaculate contains 3.0 kJ ml(-1). Assuming a mean volume of 2.7 ml an average macaque ejaculate contains 8.1 kJ. Depending on the individuals' body mass (6-13 kg) and the number and volume of the ejaculates, macaque males are assumed to use between at least 0.8% and at most 6.0% of their BMR for ejaculate production per day during the breeding season. Even when regarding only the minimal energy investment of 0.8% of daily BMR for ejaculate production, clearly ejaculates come with some cost for primate males.

[Craig krup]

If your assumption that the capacity to produce venom comes with little or no biological cost were true, then it would indeed follow that we would expect venomous species to dominate, perhaps overwhelmingly. Since the observed data is that most species of snake are non-venomous, then it follows logically that you should question your assumption, to wit, venom production probably has significant biological costs associated with it, even if it is difficult to observe the actual biological costs directly.

Okay, but the trouble is that we know that some snakes are producing bucketloads of venom - the various shows in Bangkok and in other places see them milked constantly. I know they'll (probably) find it a lot easier to get plenty to eat, so it might be true that there's a big biological cost, but given the volume of cells involved I find it hard to believe that it's more of a cost than normal cell turnover in the rest of the body.

We're also left with the interesting fact that quite a lot of venomous and non-venomous seem uncannily alike. You can argue that there are only so many ways of being, or they had a common ancestor (maybe even one that was venomous) and losing venom was an evolutionary strategy, maybe because of the biological cost.

But you could question your assumption and contemplate my solution to the conundrum. Maybe there isn't a particularly large biological cost - making 4 grams of venom is no more difficult than replacing 4 grams of liver tissue - but being venomous increases your chances of getting your head smashed in.

It's a bit like being a wolf. Wolves are aggressive and chocolate labradors are cuddly. Ever looked at the relative numbers? Cuddles is the dominant strategy

Well, my intuition is that venom is costly to produce, not cheap. I can't find any research estimating the biological cost of venom production in snakes, but I did find a quote from a study on the metabolic cost of sperm production in Japanese macaques. I think it is reasonable to expect that venom and sperm might have similar costs, say, within an order of magnitude. The important point here, and one that I think you missed, is that you have to scale the product by the size of the animal producing it. Four grams is not much for a 180 lb. human. The highly venomous coral snake in the US weighs about 10 lbs. I don't find the weight of a venom injection, but of other species the range looks like from 10 mg to 90 mg per bite. Since biological cost is relative to the biomass, it is going to be more costly for a small animal like a snake than for larger mammals like humans. Also, reptile have lower metabolic rates than mammals so the cost for them of producing anything is higher.

But back to the Japanese macaques. The cost estimate for sperm production for Japanese macaques is from 0.8% of the basal metabolic rate to 6.0% So, let's say 1%. Now one percent is a lot in the competition for survival. All species are at all times engaged in the tradeoff of costs for benefits. 99% or more of all species are extinct, from which we can conclude that small differentials in either costs or benefits add up over time. As Branch Rickey once said, "Baseball is a game of inches."

As to the likelihood of human extermination as an element of selection pressure, it is possible, but I would not expect it to be large compared to habitat loss, for example. Dogs, horses, and other domesticated species have been selectively bred by humans for thousands or tens of thousands of years, which is to say that their reproduction has been completely controlled for that time. But not snakes.

Here is the abstract from:

http://www.ncbi.nlm.nih.gov/pubmed/16467956?dopt=AbstractPlus

How costly are ejaculates for Japanese macaques?

Thomsen R¹, Soltis J, Matsubara M, Matsubayashi K, Onuma M, Takenaka O.

Author information

Abstract

Much sexual selection theory is based on the idea that ejaculate is cheap. Since further details are unknown our aim was to determine the energy that primate males require for ejaculate production. We addressed this problem by measuring the energy content (in kJ) of ejaculates from Japanese macaques (Macaca fuscata) using standard bomb calorimetry. Then, we estimated the relative amount of energy that individuals require for ejaculate production by relating the net energy content of ejaculates to males' daily basal metabolic rate (BMR). Fresh macaque ejaculate contains 3.0 kJ ml(-1). Assuming a mean volume of 2.7 ml an average macaque ejaculate contains 8.1 kJ. Depending on the individuals' body mass (6-13 kg) and the number and volume of the ejaculates, macaque males are assumed to use between at least 0.8% and at most 6.0% of their BMR for ejaculate production per day during the breeding season. Even when regarding only the minimal energy investment of 0.8% of daily BMR for ejaculate production, clearly ejaculates come with some cost for primate males.

Jesus, and I thought I had Jack Russell tendencies

I was thinking about it last night. Apparently the venom also makes it easier to digest the rat, but that's something a non-venomous snake would also have to do, so you'd have to net the cost of digestive enzymes and (say) hydrochloric gut acid against the cost of venom, so I'm still inclined to think there's something to explain.

[Gonsalviz]

Why do not all people have the same facial features, skin color, etc, etc.

[luk AJ]

Why do not all people have the same facial features, skin color, etc, etc.

Or same IQ..

[thailanddogerator]

Sorry to ask here also but do you know where to buy antivenin for Africa and South america snakes online ?

thanks.

[lvr181]

Pointing up to the sky, I said, "look at the dead bird" and all those round me looked up. Why?

This has to be an easier subject than "why aren't all snakes venomous"?