r/evolution • u/Confident_Dig_1073 • 7d ago
question How do herbivores evolve into carnivores?
I have a basic understanding of evolution
Life creates imperfect copies of itself, most of those imperfections are a detriment, but occasionally those mutations give it a higher chance of survival. Its a very slow process but it works.
But i cant wrap my head around how an animal can go from herbivore to carnivore? It would require so many detrimental mutations and decrease survival odds by alot until all those mutations came together & it was not only able to hunt, but eat & digest meat.
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u/nyet-marionetka 7d ago
Probably a saunter through omnivory. Many herbivores readily eat meat when it's available.
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u/TranquilConfusion 7d ago
Yeah, probably most mammals and birds are partly omnivorous. Going back and forth on how much meat or plants they eat is no big deal.
The difference can start purely with behavior, as meat is easy to digest and some plant foods (fruit) are easy to digest.
Now evolving from mostly-meat-eating to consuming *grass* is much harder, see pandas as a case of some poor suckers trying to do that and having a bad time of it. I guess there is so darn much bamboo around that the abundance makes it worthwhile?
What's really rare is evolving from parasite back to free-living. Not many species manage that, because parasites tend to lose traits like crazy once they can rely on their hosts for a stable environment.
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u/PriorSolid 7d ago
I was reading about demodex which are a kind of parasitic mite that lives on our faces and they require humans to produce melatonin as their primary wake up hormone
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u/RollinThundaga 7d ago
Aren't those the ones you inherit from your mother?
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u/PriorSolid 7d ago
mostly yeah, any skin to skin contact so breastfeeding is an easy way but they are relatively rare until you hit puberty since they eat oil in your pores
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u/ElkeKerman 7d ago
Pandas feed on bamboo shoots specifically, which are actually nutritionally similar to meat iirc
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u/Kirk-Joestar 7d ago
Bamboo shoots are not nutritionally similar to meat.
The Giant Panda’s macronutrient intake might resemble a carnivore’s need and they may resolve some of this through bamboo, but the quantities, vitamins, and minerals are not similar.
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u/swervm 7d ago
Herbivore/Carnivore is not on off switch. As with most of nature it exists on a spectrum and most herbivores do eat some meat especially when other food sources are rare. If there is an ecosystem with an abundance of animals and / or a shortage of vegetation the members of a herbivore species that can do slightly better eating meat will do better and be more likely to breed passing on their genetics. Over generations, if the environmental pressure persists, their descendants will develop more and more specializations to improve their ability to catch and digest meat.
There is really nothing that isn't on some sort of scale in nature and provides some benefit each step along the way. This is an example of irreducible complexity that always when you examine the thing that supposedly doesn't have any value unless it emerges complete actually has multiple stages we can see in nature or the fossil record that show gradual development with a benefit to fitness every step of the way.
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u/Ex_Snagem_Wes 7d ago
The biggest struggle for swapping to Carnivory is probably dentition. Opportunity and availability will always take precedent, but the body changing (and especially teeth) takes time
Digesting meat evolves well before sharp teeth to help process it better evolves. Even most Entelodonts didn't actually have teeth very good at eating meat! Meat is simply easier to process, so while it's definitely not an instant transformation to carnivory, the digestion end is far easier. Adapting from being able to digest a little meat to a LOT of meat is, relatively speaking, a minor change
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u/cflime 6d ago
A lot is opportunity. SW United States (not yet called that) went into a several centuries drought and all the raptors died or moved away. The seed eating strike stepped in to the ecological niche of predator... but it didn't have the raptor beak or talons. Still doesn't. It picks up field mice and flies them to a thorn bush and impales the poor little rodents, then rips them apart into pieces it can comfortably eat. White settlers called them butcher birds.
Then white settlers strung up thousands of miles of barbed wire and the killer strike had a new tool for butchery and their population went up accordingly.
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u/DurianBig3503 7d ago
Why would herbivory be the default?
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u/Confident_Dig_1073 7d ago
Its not the default. Lineages have gone thru herbivore, to carnivore, back to herbivore etc I just wonder how this happens. Its easier to understand how a species becomes herbivorous thats why i didnt ask that
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u/Cheesy-Cloaca 7d ago
Why should one direction's change be any easier or harder than the other?
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u/Confident_Dig_1073 7d ago
Its easier to hunt plants
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u/haysoos2 7d ago
But it's easier to digest meat.
Most herbivores have all of the equipment to be able to survive on meat just fine. It takes a lot less processing and digestion than something like leaves or grass.
For most the only real problem is catching/killing prey, and effectively tearing up flesh to eat, which for mammals requires quite different types of teeth.
For a bird, all it really takes is a slight shift in bill shape, and a suitable food source.
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u/Cheesy-Cloaca 7d ago
Is it? There are many more poisonous plants than poisonous meats. Organisms have to come up with other defenses when they can't run away, they're not helpless
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u/Demonicknight84 7d ago
Plants can be a lot harder to digest and often have toxins and thorns as defenses
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u/Rhyshalcon 7d ago
But they're much harder to digest. Any digestive system can handle meat, and it's much more rewarding than almost any plant-based food source.
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u/ah-tzib-of-alaska 7d ago
name animal flesh that’s toxic to eat
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u/Kailynna 7d ago
The Golden Poison Frog (Phyllobates terribilis)
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u/Cheesy-Cloaca 7d ago
But that's only because they load their bodies with bugs that are poisonous to eat, it's not inherent to the organism
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u/KristiAsleepDreaming 7d ago
Have you read about the carnivorous squirrels? A behavioral adaptation can be easier than a digestive system one. https://www.smithsonianmag.com/smart-news/squirrels-are-displaying-widespread-carnivorous-behavior-for-the-first-time-in-a-california-park-new-study-finds-180985707/
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u/PaleoJoe86 7d ago
An animal is already made of animal cells. It logically is easier to eat other animals. Eating plants requires ways to break down the plant cells.
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u/Sonora_sunset 7d ago
There are a lot more plants around than other animals, which is why there are a lot more herbivores and omnivorous than carnivorous.
Also not sure why you got voted down for a legit question.
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u/Ok-Barracuda457 7d ago
Deer eat squirels sometimes, dogs munch on leaves too, nothing is forced to eat solely one thing and diet is not forced by ancestry
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u/ThalonGauss 7d ago
Dogs aren't carnivores, they need meat to be healthy, but are omnivorous, cats are however carnivores.
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u/sisconking132 7d ago
Cats are hyper carnivores (meat making up over 80% ish of their diet). Dogs are just regular carnivores.
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u/ah-tzib-of-alaska 7d ago
cats munch on grass all the time
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u/Batgirl_III 7d ago
Not for nutrients and calories; the fiber in grass acts as a laxative and aids in that department… and if they eat a lot of grass it can induce vomiting and helps clear out the other end.
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u/ah-tzib-of-alaska 7d ago
uh-huh
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u/ThalonGauss 6d ago
cats cannot extract much nutrition from plants, their gut is too short. They are not in anyway physiologically equipped to deal with plant based nutrition.
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u/ah-tzib-of-alaska 6d ago
Except they are finding a purpose to eat the material, or benefits them. Now you just need time, pressure and mutation for a little natural selection. z doesn’t mean it’s going to happen, but even the obligate carnivore demonstrates the answer to the question
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u/ThalonGauss 7d ago
They absolutely do.
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u/ThalonGauss 6d ago
why yall downvoting this, I specifically mentioned that cats are carnivores, I just agreed with the comment that they munch grass, not that it is nutrious. You can buy cat grass, which is basically just fun for the cat to eat.
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u/Electrical-Berry4916 7d ago
Loads of herbivores will eat meat when it is available. Even deer, one of THE classic prey species, will eat carrion. From opportunistic scavenger to active predator isn't even a big jump. Chimps, for example, or raccoons. So, apparently, digesting meat does not require any particularly rare digestive devices. From there, you just need a caloric advantage from meat that is better than from vegetation, or a disruption of the vegetative food source, and wah-lah. New carnivore.
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u/TimeStorm113 7d ago
How often did that happen tho?
Carnivores becoming herbivores are more common , as all tetrapods used to be carnivores before herbivory evolved
But it might happen in birds
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u/sisconking132 7d ago
Birds due to needing to be light to fly have strong selective pressure against becoming highly herbivorous in the first place. There are only a handful of birds that are actually herbivores, and almost all of them are flightless. Being a herbivores requires fermenting the pant matter which takes time and space (not to mention is heavy).
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u/TimeStorm113 7d ago
I mean, grain and fruit also count as herbivores
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u/sisconking132 7d ago
Frugivore for fruit. There are lots of specific terms
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u/TimeStorm113 7d ago
Aren’t they just sub categories? Otherwise herbivores in general dont exist, as most would just be considered graminivores
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u/sisconking132 7d ago
Yes, they are but some distinctions are more important than others. Like the digestive tracts of primates that eat mostly fruit and nectar are very different from primates that eat almost exclusively leaves.
Fruit evolved to be digestible for seed dispersal and so doesn’t need the same complex gut as leaves (including grass)1
u/sisconking132 7d ago
It’s not just the stomach adaptations either, different types of herbivores have very different jaw and tooth morphology.
Grass and leaves require a lot of mastication to be ground into a literal paste to maximize surface area for the bacteria to work with.
Grains and Nuts also require strong jaws, but the teeth are often different
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u/AllEndsAreAnds 7d ago
I’m not an expert, but as I understand it, most animals are not obligate anything. From what I understand, most herbivores are not obligate herbivores, though a few truly are that specialized.
Many herbivores are opportunistic, and will supplement their diets with insects, eggs, birds, or other small animals when nutrients are scarce or to fortify their diets.
It’s best to think of animal diets on a continuum, with a few obligate herbivores, a few obligate carnivores, and everything else lying somewhere between them.
And if most animals have a little flexibility in diet/gut bacteria/digestive system, then mutation can give rise to variations of that biology and behavior, and natural selection can select accordingly.
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u/TommieTheMadScienist 6d ago
Herbivores evolved after carnivores and scavengers, not the other way around.
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u/WirrkopfP 7d ago edited 7d ago
It would require so many detrimental mutations and decrease survival odds by alot until all those mutations came together & it was not only able to hunt, but eat & digest meat.
Meat is actually easier to digest than plant matter.
There are surprisingly few mammals that are pure herbivores or pure carnivores. The overwhelming majority sits somewhere on the omnivorous spectrum.
- Deer and moose will happily munch on carrion. They are especially fond of bone.
- Sheep, Goats, horses and even cows will actively search and eat small ground nesting birds.
- Rats go absolutely feral if you throw living Crickets or locusts in the cage.
- Hippos will even eat each other.
- Squirrels are truly disturbing. There have been several cases of corpses found in the woods where the forensics had identification impossible by any means other than DNA because squirrels ate them to the point of being unrecognizable.
The only mammal I can think of that's a pure herbivore is the koala
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u/XXLPenisOwner1443 7d ago
>Rats go absolutely feral if you throw living Crickets or locusts in the cage.
Are rats not generally considered true omnivores? I've never heard it implied that people consider them herbivores.
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u/Relevant-Bullfrog215 7d ago
By way of Omnivory, which is fairly easy to move into from either direction.
Bear in mind that many herbivores will eat flesh opportunistically. You can go on youtube and find videos of cows and horses eating things like live birds.
I don't think it's too difficult to see how a herbivore that can occasionally supplement its diet with meat in times of scarcity could out-compete a herbivore that cannot, and that given the right selection pressures, might eventually evolve to a wholly Carnivorous diet (or at least mostly Carnivorous, as carnivores will also sometimes supplement their diet with plant matter).
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u/TerrapinMagus 7d ago
Well for starters almost nothing is a true Herbivore in the strictest sense.
Protein and energy in meat is often highly prized and plenty of herbivores will take the opportunity when presented. They aren't well optimized for meat consumption, but survival favors the opportunistic.
So you need a situation where an herbivore can easily obtain meat in order for evolution to start favoring their lineage over those who aren't taking advantage of the meat. Scavenging is one option, or else they begin to hunt very small game that don't require many adaptations to catch. As they get better at catching prey or tearing flesh over the generations, they may move on to larger or more challenging prey.
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u/TuverMage 7d ago
there is a benefit to eating meat. meat is more calorie dense than grass. Thing to understand is most creatures are actually opportunist omnivorys. meaning just because they mainly eat grass they won't say no to meat, ever seen the pic of a deer eating a snake? creative that through mutations eat more meat have a higher chance of survival and reproduction, meaning evolution favors them. the mutations get passed along. over the generations the mutations stack up enough to make notable different creature that prefers meat to grass.
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u/Shazam1269 7d ago
The same way carnivores became herbivores. Consider the giant panda and modern bees. The giant panda belongs to the order Carnivora (the group containing cats, dogs, and bears), but they feed almost exclusively on bamboo.
Modern bees evolved from ancestral, solitary hunting wasps that caught other insects for protein. Over time, they shifted to collecting flower pollen and nectar instead of hunting.
Here a discussion post about this topic that may help you wrap your head around the concept.
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u/sisconking132 7d ago edited 7d ago
Fun fact. Herbivory is the more derived state.
Animal life were all filter feeders, carnivores, and insectivores before evolving to eat plants. Being able to eat and digest plants evolved later. This has happened many times in multiple different groups.
Ancestral dinosaurs were carnivores, herbivores evolved later. Ancestral mammals were all carnivores or omnivores.
It is actually much harder to evolve to digest plant matter than to evolve to become a carnivore. Depending on the type of herbivore (eating mostly fruit and nuts [which technically isn’t Herbivory since that term is exclusive to eating leaves and grasses] is very different from eating grass and leaves) it is very difficult to evolve the traits to get sufficient energy from plant matter. Herbivores require a way to process cellulose using gut bacteria.
Becoming a carnivore from a herbivore is actually really easy. Meat is far more digestible than plant matter. Most herbivores eat some amount of meat when given the chance (even cows will eat snakes and dead things if given a chance). From there it just requires a population to go scavenging carcasses more often and occasionally killing and eating a smaller animal. Eventually the species is an omnivore. It’s a gradual shift from scavenging to more active hunting. Also the same traits that are an advantage when fighting over a carcass are often useful for taking down prey.
But yes. You are right, herbivores evolving to be carnivores is rare, but it isn’t because becoming a carnivore is difficult, it’s more that becoming a herbivore in the first place is extremely becoming a specialist.
If you think about it from an earlier perspective this makes more sense, all animal life evolved in the ocean before coming onto land. The ocean does not really have plants. There is algae and photosynthetic plankton, but nothing like land plants. There are not really sea herbivores (apart from herbivores that returned to the sea from land) so everything started out eating other animals and then had to evolve to be able to survive exclusively on plants.
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u/Szymcionorski 7d ago
Probably via omnivory. Initially herbivorous animals can (and do) eat things like carrion or small animals. Diversifying the diet would allow for better adaptation to the consumption of meat.
Adaptations for hunting could evolve later specifically for active predation rather than scavenging. Evolution doesn't always have to operate via direct jumping into a specific niche. Early fish didn't have to directly evolve into modern sprinting predators (such as cheetahs) but instead went through many intermediate phases with initial adaptations for relatively slow movement and breathing on land.
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u/Forward_Tax7562 7d ago
I’d argue carnivory would be the “default” and that herbivory came from it
This, without counting omnivory
The way I think about it, territory was a strong drive for the passing from aquatic to terrestrial life forms
Insects were one of the first to achieve this terrestrial advantage, who best to follow them up than highly territorial creatures who would push each others to the edge, the same edge crossed by insects which are food sources
Algae, filter feeding, etc don’t really require you to fight for territory (of course, this is a simplistic generalization)
From this I’d assume carnivory is the default drive for these changes, followed by omnivores who would take advantage of the vegetation, followed by herbivores
With the fact that herbivores require some amount of meat, either by scavenging bones, hunting small animals or insects from vegetation, while we don’t see this need for herbs as hard in carnivores
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u/Sickborn 7d ago
to start, herbivores developed out of carnivores originally. also, there’s different ways an animal could slowly start eating more and more meat without having to suddenly become a full on predator. exemplary pipeline: occasional carcass > carcass scavenging > sometimes eating helpless pray > predatory lifestyle. besides, a lot of carnivores scavenge too / bully other animals off their prey and don’t really like the hassle of hunting.
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u/davesaunders 7d ago
Think of it in terms of selection pressures. You have available resources in your particular area. Perhaps you normally eat plants, but there's a lot of competition for plants, and that is affecting your population's ability to compete in that niche.
Through various mutations, some in your population find that they're able to tolerate other types of food. That could be insects; it could be tiny little animals. If you're hungry enough, you're probably going to try to eat whatever you can reach. If you can digest that and get energy from it, then there's a really darn good chance that you're going to survive long enough to outbreed the other members of your population who can't eat the same foods. Over time, the population that can now eat these other food sources is going to outnumber the other population that could only eat the narrower food sources.
Alternatively, those populations diverge completely, and you end up with one species that still eats nothing but plant material. They're still found in areas where the competition was low enough that they're able to fit into the niche and be happy. The other population moves to a different location because they find that they're able to move away from where those plant sources were, because now they can eat other things. Both of those populations derive from a common ancestor that originally may have only been able to eat that particular plant source.
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u/ah-tzib-of-alaska 7d ago
herbivores aren’t as perfect herbivores as you think, even ungulates (like deer) are known to grab a bone they find and chew on it.
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u/NelifeLerak 7d ago
Eating meat is much more efficient than eating grass.
I guess sone animals evolved to be able to digest meat instead of being sick when eating meat. They probably became omnivores and started by eating already dead animals. Then they developed other adaptations to be able to catch prey more easily, and to chew meat more easily, and stopped eating grass.
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u/Trainer149 7d ago
"It would require so many detrimental mutations and decrease survival odds by alot until all those mutations came together & it was not only able to hunt, but eat & digest meat."
Now that's a hefty claim. Let's say you have an animal in a very barren environment, like the arctic or the desert. What kind of mutilations would be detrimental while aiding in carnivory? Take penguins and polar bears. Both are considered hypercarnivores, yet their ancestors would be omnivores. What mutations from ancestral birds and bears to those current lineages would be considered detrimental within their environments?
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u/FlounderLast8610 7d ago
It's certainly much rarer than the other way. In particular, large herbivores have never evolved into large carnivores. Ever. But smaller and/or more omnivorous animals have more routes available, such as being marooned in strange locations where the plants are less edible or having to change their diets in response to some other selection pressure, e.g. a larger body size necessitating more carnivory in generalized open-ocean fish due to straining algae from the water becoming more and more of a pain. The marine roots of vertebrate life mean a predatory lifestyle is the ancestral condition in vertebrates, which accounts for most of the predatory lineages we see in familiar landscapes.
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u/Long-Opposite-5889 7d ago
You are missing a couple things here. First, herbivores/carnivores is more a spectrum than a definite separation. Most herbivores consume meat in one way or another. Second, you say that most mutatuons are "detrimental" and thats not precisely true, there are many types, a lot of times they produce neutral changes and many other make smaller changes that are useful but not immediately positive for a specific thing. Think for example on an individual that has a mutation that allows him to be resistant to a given bacteria. It sound like an obvious advantage, right? What if that specific individual never faces infection by that pathogen? The "advantage" now becomes irrelevant.
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u/KronoAsh 7d ago
Could be the species ends up in an area primarily populated with poisonous plants, making their herbivorous diet more difficult, resulting in them needing to adapt to eat meat to survive.
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u/XXLPenisOwner1443 7d ago
Generally, more specialized animals tend to evolve from less specialized animals. It is only under extremely rare circumstances that a specialist transitions back into a generalist.
That is to say, most herbivores are evolved from slightly less herbivorous animals, ad nauseum, until you get to an omnivore. So too with carnivores.
Also, the nature of this process means that most animals on either side of the fence never totally eschew all food from the other side. Even horses, which have been evolving into greater and greater specialists of grass eating for millions and millions of years, occasionally take meat.
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u/Tombobalomb 7d ago
You only have to see a cow eat a bunny once to realize herbivore/carnivore are not rigid categories
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u/Underhill42 7d ago
Most herbivores are already opportunistic carnivores - deer for example will intentionally eat incautious birds when they can. Meat is just too rich in nutrients and calories and calcium to pass up.
When plants get rare, either due to disaster or just because you can't compete, you may try to focus on the more calorie rich animals.
If you're able to survive that way, then you'll slowly adapt to survive better, and eventually thrive. You MAY develop mutations that would be disadvantageous in your previous herbivore life, possibly even enough to make you an obligate carnivore. But there's no guarantees of that. And they're no longer relevant, because you're currently living primarily as a carnivore anyway, since your old herbivorous niche disappeared.
It's going back the other way that's a challenge, because you would have to re-evolve any vitamin synthesis pathways, etc. that you may have lost, since you didn't need them when you could scavenge adequate vitamins from the flesh of your prey
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u/JayTheFordMan 7d ago
Firstly, you have to rid yourself of the idea that mutations are necessarily deleterious, this is just not correct. Utations can be positive, neutral, or deleterious, determined so by how disruptive to function or through selection.
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u/joedenowhere 7d ago
I don't know, but my guess is that carnivores were around before herbivores. Fish, for example, are mostly carnivores, and they were swimming in the oceans before any vertebrates were living on land.
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u/Training_Rent1093 7d ago
Most mutations are neutral, not detrimental. Herbivores becoming carnivores are rare, in most omnivorous animals become carnivore or herbivore. A exemple of your question would be whale evolution. Their ancestor was herbivore, but in a land with less resources than the sea, selection favours those who enter the sea. In the sea, most food is meat, not plant, so one more selection pressure. The fossil record shows the changes: Dentition change from chewing plants to cut meat and lock prey in place. The digestive tract is reduced, with the appendix becoming very small, but multi-chambered stomachs remain. Microbes once used to digest cellulose are now used for digesting chitin of Krill, both carbohydrates.
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u/Opening-Function8616 7d ago
Most herbivores will eat meat when given the chance. Just a few days ago there were a few videos of a deer eating a bird or a squirrel eating a lizard. Given there's enough of that kind of food source around, they'll start specializing in it and evolve into it in the long run
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u/Sufficient_Kale_8561 6d ago
I've recently realized that theorically, nothing prevents herbivores from digesting meat. For exemple this study with hares is interesting https://boonstraresearch.weebly.com/uploads/1/4/4/1/144120451/peers.2018.scavenging_by_snowshoe_hares_in_yukon.pdf?utm_source=chatgpt.com
There are many cases where herbivores occasionally eat meat.
What separates them from carnivores is mostly anatomical adaptations (dentition, eyesight, specialized organs and tissues etc), but there isn't any physiological obstacle that would make them unable to eat meat. I would say they already made the toughest part of the path. Being able to digest plants demands a way more specialized physiology than a meat only regime. Evolving towards a carnivore diet is "easier" than the opposite.
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u/BoneSpring 6d ago
Single-cell predatory protists existed in the Precambrian.
Here I describe 0.1-3.4 µm circular holes in seven species of organic-walled microfossils from the 780-740 million-year-old Chuar Group, Grand Canyon, Arizona, USA, that are similar to those formed today by predatory protists that perforate the walls of their prey to consume the contents inside.
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u/Jazzlike_Standard871 6d ago
Herbivore is not the ancestral condition for land vertebrates. Also most Herbivore are opportunistic omnivores so yeah.
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u/Poopy-Drew 6d ago edited 6d ago
They don’t. I’m sure it has happened a few times but mostly the lines stay separated if anything it has always moved the other direction (not many herbivores in the ocean) lack of food or easier food would be the only but even then it’s from Omni to herbi not carni to herbi
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u/Truffignol 6d ago
I believe there was warfare between bacteria and other germs, before plants even existed.
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u/Careful_Cranberry364 5d ago
The teeth usually adapt to work best with whatever food is available / works best for that body
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u/Nothing-to_see_hr 4d ago
Ever see a chicken Hunt down and eat a mouse? I imagine the herbivores come across small animals like worms and caterpillars now and then, some will start to specialise in that.
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u/Most-Ad5530 3d ago
Herbivore -> omnivore -> carnivore (btw every one of those -> exists of millions of animals
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