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On "Earth" species that are higher up the food chain tend to have more advanced brains. I won't tell everyone what they already know, but just for illustration: chimps are capable of making tools and sign language and more while horses can't. Yet clearly, Dressage is no small feat, and still reflects how they have the common mammalian trait of learning from experience.

What I want to do is decouple this relationship between food chain locus and "cleverness." I hesitate to define a yardstick because I think common sense is best here, but if we must, let's define "cleverness" as:

  • Problem solving ability
  • Pattern recognition
  • Plan development

We could argue some herbivores have this kind of intelligence, but it's not at the same degree as some predators. Also not really interested in cognitive/sensory intelligence, like superior depth perception. Purely for illustration: imagine a deer-like creature digging a pitfall around the area it wishes to graze in, so that when pursued it would know where to jump and leave the predator to fall into the trap.

Question

What kind of natural / evolutionary forces need to be in play in order for my world to obtain an equilibrium such that herbivores possess superior intelligence to carnivores?

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    $\begingroup$ Counterpoint: Many humans are vegetarians. Humans (whether vegetarian or not) are clearly smarter than most if not all non-humans, including carnivores. $\endgroup$
    – Darrel Hoffman
    Feb 17 at 14:21
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    $\begingroup$ @DarrelHoffman humans are already born with very capable brains, which are on itself the result of years of evolution over a CARNIVOROUS diet. $\endgroup$
    – Josh Part
    Feb 17 at 16:08
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    $\begingroup$ Maybe that's part of the answer then - maybe you've got voluntary herbivores. They evolved as meat eaters, decided it was unethical/distasteful or otherwise 'not allowed' and the stopped. $\endgroup$
    – Sobrique
    Feb 17 at 16:21
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    $\begingroup$ Gorillas are probably the third or fourth most "clever" species on Earth, and are basically herbivores. I don't think "cleverness" has so much to do with the diet; it probably has more to do with the opposable thumbs. You can't really evolve tool use, arts and technology if you can't hold tools. $\endgroup$
    – workerjoe
    Feb 17 at 17:14
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    $\begingroup$ @JoshPart I'd say more that humans are omnivores, rather than carnivores. That in itself may be a huge advantage. Carnivores die if there isn't an adequate supply of game in the area. Herbivores do the same if there aren't sufficient plants of a type they can eat. Being able to eat basically anything means you can survive temporary shortages of one or the other thing by switching to what you have when other foods are unavailable. So maybe omnivores have the most advantage and thus can become more intelligent. $\endgroup$
    – Darrel Hoffman
    Feb 17 at 18:13

6 Answers 6

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Intelligence requires energy

Can you believe this? Humans use their intelligence to conclude that vegetarianism is a better lifestyle! This despite the fact that the only reason intelligence evolved in the first place is because a carnivorous diet provided the energy necessary to power that evolution and higher brain functions. Though some (probably all) would argue with me, the reason vegetarianism works is because our protein-and-fat-derived intelligence allows us to (and this is important) craft the development, growth, harvest, and processing of plant matter to sustain our divine ascendancy to reason.

But that lovely fact exposes a perfectly reasonable answer to your question...

If plants evolved to provide the source energy needed to evolve intelligence, then the only reason herbivores wouldn't evolve human-like sapience (hah...) would be the unlucky chance encounter with a large enough group of carnivores that they got wiped out.

So, what does your evolution need?

  • A world filled with high-energy, high-fat, high-protein plants (or a combination of plants in a large enough area to provide the aggregate effect).

  • Time (in the form of safety).

And one other thing...

  • The need for problem solving.

Nature vs. Nurture

You've heard the old adage of nature vs. nurture? Am I really bad because I was born that way, or was I taught to be bad? In short, never underestimate the effect of your environment on the development of intelligence. Bring too much adversity and you wipe out your developing intelligentes herbivorus. Bring too little adversity and intelligence never develops. So, you also need...

  • Just the right amount of adversity over that long period of time.

Which is one of the many reasons why Darwin marketed the process as the survival of the fittest. Overcome enough obstacles while enjoying the right kind of diet and a plant will develop intelligence.

enter image description here
Image courtesy the Farscape Encyclopedia Project

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    $\begingroup$ There is no evidence of that the kind of plants really matter that much outside of conversations specific to human evolution. Yes, WE need to eat plants and animals rich in Omega-3 fatty acids for proper brain development because our bodies can not produce it themselves, but most other animals can produce their own Omega-3 from pretty much any food source... so the kind of foods you need to eat is not really relevant in a more general context. An intelligent species could just as easily rely on low quality vegetation and a higher quality metabolic system. $\endgroup$
    – Nosajimiki
    Feb 17 at 18:13
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    $\begingroup$ @Nosajimiki you seem to have missed an important point. It's not the specific nutrients that matter, but the calorie density. Think about cows - they spend a significant amount of time and energy just processing their food. That's what happens with low quality vegetation. I don't know how you'd get a "higher quality metabolic system" without abandoning the premise of being science-based. $\endgroup$
    – Rob Watts
    Feb 17 at 19:01
  • $\begingroup$ @RobWatts Sure, cows spend a lot of time chewing and eating grass, but there is another animal on this planet that mostly eats grass too: humans. Wheat, rice, oats, corn, rye, etc. are all grasses which make up most of a typical human's diet. Human intelligence made low quality food sources like this more viable thanks to the invention of milling and agriculture; so, instead of thinking a cow cant be smart because it spends too much time eating to make things, imagine how much it would benefit from being smart if it could make things to pre-process its food like we do. $\endgroup$
    – Nosajimiki
    Feb 17 at 19:37
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    $\begingroup$ @Nosajimiki ...that's kinda the point of this answer. Humans used their intelligence to turn low-quality food sources into high-quality food sources. The answer is saying that would need to somehow happen naturally. You seem to be putting the cart before the horse with cows - yes cows could pre-process their food to fuel intelligence, but they need intelligence first in order to figure out how to pre-process their food. $\endgroup$
    – Rob Watts
    Feb 17 at 19:47
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    $\begingroup$ @Nosajimiki No, humans don't eat grass. They eat grass seeds. That's a massive difference! Surely you wouldn't say a man eating an apple is eating a tree. Seeds in general are very energy and nutrient-dense repositories (it's what needs to support the seedling until it can produce its own). And even that took intelligence and tools to start with - not to mention loads of selective breeding. We're not yet at the point where we could actually process grass itself into a good food source - heck, we can't even make it into a good fuel source (yet), a much easier prospect. $\endgroup$
    – Luaan
    Feb 18 at 10:18
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I think you have oversimplified the picture, and lost a lot of important things in the process.

First of all, there is a fundamental difference between carnivore and herbivores when it comes to their feeding: one of the two doesn't have to worry about its candidate meal running away.

However it doesn't mean that all carnivores are always more intelligent than all the herbivores at any moment, nor that herbivores can be always and at any moment more intelligent than all carnivores.

A carnivore who cannot outsmart an herbivore in any situation will soon be a starved carnivore and its species will be extinct, and an herbivore which is constantly "dumber" than the carnivore trying to feed on it will also soon be dead and extinct.

Episodes play a big role in the daily struggle between carnivores and herbivores: a snapping twig can make the difference between a miss and a lunch when a carnivore is trying to ambush an herbivore, same as a dead end on an escape route.

If you really want to push the boundaries on the herbivore side, you can try with something that make also the plants react to being fed upon and enact some countermeasures. Like it happens with some acacia trees, which start producing tannin when giraffes eat their leaves: the giraffe have learned the mechanism and cope with it by feeding going toward the wind, so that they can find unalerted trees. This means that they can recognize a pattern (when I eat leaves, they become bitter. The trees upwind from my feeding place are not bitter, those downwind are), make a plan and solve a problem (when I feed I should move upwind to find non bitter leaves)

However, for what I have said above, herbivores will never be consistently smarter than carnivores.

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    $\begingroup$ Interesting final point, but maybe it's somewhat abstracted from the spirit of the question, as I read it. The point of the question is precisely how a world can side step these types of issues. I had also reached a similar conclusion initially but I couldn't convince myself of it in the end: primitive carnivores can kill smart(ish) herbivores consistently: crocodiles and the like. Curious thought experiment nonetheless. $\endgroup$
    – Arash Howaida
    Feb 17 at 6:13
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    $\begingroup$ One problem with the giraffe example is that there's no guarantee they recognize the pattern. Acacia trees evolved to do that over time, so giraffes easily could have evolved behavior to compensate. For the giraffe, it may be that feeling the wind on their face while eating feels pleasant, so they tend to walk that way while they eat. $\endgroup$
    – Rob Watts
    Feb 17 at 19:06
  • $\begingroup$ "an herbivore which is constantly "dumber" than the carnivore trying to feed on it will also soon be dead and extinct." Oh, if only it were so simple! In reality, prey animals can be extremely dumb, and extremely successful at the same time. The life on this planet evolved myriads of strategies to reproduce effectively, and "being smart" is just a tiny sliver of them. You don't need to be smart to form herds; indeed, preprogrammed behaviour can get pretty complex without ever touching on the rolling ball of intelligence explosion. $\endgroup$
    – Luaan
    Feb 18 at 10:23
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    $\begingroup$ @RobWatts Evolution is even simpler than that. Once upon a time, there were different giraffes. Some of them wandered to the nearest tree to continue feeding, some went against the wind, some followed the wind (and a hundred other behaviours). And much the same with the trees. The trees that communicated got an advantage, and eventually displaced the ones that didn't. And the same way, the giraffes that happened to have the behaviour that countered that adaptation got an advantage, and displaced the ones that didn't. Evolution isn't a directed process - it's just (complicated) statistics. $\endgroup$
    – Luaan
    Feb 18 at 10:26
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    $\begingroup$ @Luaan I was hypothesizing about why they behave the way they do. Your statement is about how the behavior came about. To combine my statement with what you said, the giraffes who genetically enjoyed feeling the wind on their face displaced the ones who genetically enjoyed feeling the wind on their back. A contrast to my statement would be the belief that the giraffes are actually smart enough to realize "if I go against the wind the leaves taste better". $\endgroup$
    – Rob Watts
    Feb 18 at 16:43
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Intelligence is (theoretically) a major survival advantage. That's the reason it is evolutionary selected for. For carnivores, this is easy to explain: being more intelligent makes you able to hunt better and defend yourself better. You can craft weapons, nets, traps, and dwellings. All of these things increase your chance to survive long enough to procreate.

For herbivores, the same story is true. Being intelligent gives you access to more food and better protection from predators. If you can use tools, you can access the insides of hard nuts or better dig up roots. If you can make traps, weapons, and dwellings, you can better defend yourself. We see aspects of this all throughout nature. Look at beaver lodges as a huge example. Also, while not technically an herbivore (aquatic life is it's own beast), sea otters use rocks to break open shellfish.

The big question here is not "how can herbivores develop intelligence?" but rather "how can dumb carnivores be viable?" There are a couple options here, and you can use any combination of them.

  1. There is only one very intelligent herbivore species. While the carnivores will eat those herbivores if they get the chance, they tend to go for easier game (i.e. the less smart herbivores) for their main sustenance. See, for example, crocodiles in Florida who occasionally eat humans but mostly eat other stuff.

  2. The carnivores have substantial physical advantages over the herbivores they hunt, making it a competition of brains vs brawn. See, for example, chimps and jungle cats (a natural predator of the very smart chimps).

  3. There are a lot of the herbivores relative to the carnivores. Thus, to the herbivores, the carnivores cause occasional population loss rather than an existential threat. This is generally true of herbivore to carnivore population ratios in general, but intelligence would probably skew it a bit heavier towards the herbivores because they can band together. See, for example, herd animals on a savanna and lions.

Other answers have some discussion of the nutritional requirements to support intelligence. While intelligence is nutritionally expensive (humans use about 20% to 25% of their calories on their brain), it also can solve for the problems it creates. Humans are able to sustain their massive brains on vegan diets. The key things here are heavy consumption of legumes and the use of cooking to improve the nutritional value of food. If you want to have an environment that emphasizes this, have lots of protein and fat rich plants that have a high intelligence requirement to access. Walnuts are a great example; lots of protein and fat, but you need to be able to use basic tools to get at the edible part.

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    $\begingroup$ Another scenario (or more specific scenario 1) that would allow for dumb carnivores would be a cold blooded ambush predictor. It just waits until prey is detected and in range before attacking. $\endgroup$
    – Gault Drakkor
    Feb 17 at 21:57
  • $\begingroup$ @GaultDrakkor And there's plenty of just such "trap-making" animal-eaters. Like spiders, or really even crocodiles. $\endgroup$
    – Luaan
    Feb 18 at 10:28
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    $\begingroup$ The problem is, you're looking at "intelligence is an advantage". But that's not the full picture. The real accounting is more like "intelligence has some advantages, and some disadvantages". There's many alternatives that evolved in life on Earth, and intelligent animals are extremely rare. Indeed, there's an argument to be made that human intelligence isn't really an adaptation to the "natural environment" around us, but to other humans. And even more fantastically, that our biological evolution has essentially been hijacked by a virus of memetic evolution. $\endgroup$
    – Luaan
    Feb 18 at 10:30
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Instead of trying to buff herbivores, nerf the carnivores

Imagine a world of trash. Maybe a precursor civilization has polluted the world, maybe it's an experiment, maybe it's just an accident that nobody bother to clean up, you tell me.

1. Nutritional energy for cognition

This world have a lot of fertilizer runoff or equivalent on the surface, allow the plants to grow strong and nutritious, allowing herbivores can have enough energy to sustain some form of intelligence. Since this is artificial fertilizer, it can even have some exotic mineral (Ca, Zn, etc.) that rarely exists in nature yet our brains need.

2. Preventing carnivores from developing intelligence first

Unfortunately, this world is also hit with a lot of heavy metal contamination, which means anything carnivorous will eventually accumulate too much toxin, and die off. The higher on the food chain we go, the quicker the accumulation.

Intelligence is not all that powerful on its own, without support from a longer lifespan to accumulate knowledge, an overlap in generations to facilitate education, social aptitude to share knowledge, etc. Throw a spanner into one, and the rate of developing cognition is slowed down, maybe enough for herbivores to catch up.

3. A need for problem solving ability that do not involve other living beings

Again, we do not want to involve any other species in this drive for cognition, seeing as this would require that animal to be equal to the herbivores in intelligence. So you could add that not only the planet is covered in pollution, its climate pattern is also damaged to the point that it has extremely volatile and unpredictable weather.

Emphasis on unpredictable, so your herbivores cannot just select for an instinctive behavior that will protect it once, and keep it to the end of time. Also emphasis on volatile, and maybe widespread as well, so no amount of toughness, or overwhelming number will save them on its own.

That way, the weather will select for animals that have:

  • Problem solving ability: Each type of natural disaster will require different countermeasures. For example, forest fire require you to get to ground, and run to water, while flood need you to get to high ground instead. Since the weather is extreme and unpredictable, animals that cannot solve problems quickly cannot thrive.
  • Pattern recognition: When long-term prediction of random disaster is not feasible, the ability to quickly notice and understand the beginning stages of a disaster is highly valued. Each second you realize the danger is a second you can prepare for it.
  • Plan development: While the long-term prediction of weather is not allowed here, long-term preparation for it is not. Building nests underground near water to avoid fire, have escape routes to avoid flood, food storage in case of flash freeze, etc., having the correct counter on hand allow this herbivore to thrive.

4. Remember to provide the little details

Make sure that the manipulators evolved on your herbivores are something that can continue evolving, like a limb, tentacle, or elephant trunks, have more than just one of them, give them social instinct to group together and exchange resources and ideas. So long as an herbivore gets to be a civilization first, it will both give drive for more intelligence, while out-competing any other sentient-wannabe. Which will end up with an herbivore become the dominant intelligent species of your world. (If you are asking for how herbivores on average get to be smarter than carnivores, I got nothing there)

... Until the herbivores meet up with whoever created such a world, and get a practical demonstration of the benefits of eating meat

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An arid planet could have this effect

A planet mostly covered in deserts means that herbivores are constricted to watering holes, river banks, and other really obvious places for predators to go to hunt for them. These fertile zones are so small and narrow that hiding from predators means going inland where there is no food or water, and only risking the journey back to these oasises when absolutely necessary.

This makes being a predator very easy. Hang out by the water, and eventually the food will have no choice but to come to you, so intelligence is not super important. Ambush predators are generally not as smart as predators that have to roam a larger territory looking for animals to eat.

However, intelligent herbivores don't need to get play this eternal game of "eat and run". Intelligence means you can learn to make in inhospitable landscapes more survivable. Your smartest herbivores will learn to dig wells and irrigation to create safe zones out side of the predator rich natural water zones... and if predators start to show up, they abandon these artificial oasises which soon fall into disrepair and become dead zones again. Other herbivores may learn to survive by being able to remember where dozens of individual shrubs are just barely hanging on over an area of several square miles; so they need exceptional memories, spatial awareness, and enough self awareness to take good care of these plants so that they don't eat themselves out of long term survival. Some herbivores will need live off of raiding the store houses of the really smart agricultural herbivores meaning they will need to be smart enough to avoid the traps and plans of the really smart herbivores who are trying to keep them out.

Lastly, intelligent creatures do not tolerate intelligent competition. If your herbivores win the smarts race to weapons and tool use, then they will kill off any predatorial creatures who begin to become intelligent enough to represent a real threat.

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Adversity drives the intelligence, and it needs to be changing adversity. If it's just a constant environmental adversity, the species evolves to the point of surviving the environment, and then stops. So with predators, both sides of the equation get more and more complex. Eventually, one side or the other evolves true intelligence and wins. They either control or wipe out the other at that point.

The herbivores will need to have a reason to evolve some way to manipulate their environment with fine control. Maybe some of your plants take a delicate touch to eat without getting poisoned by thorns or symbiotic protective species.

Most likely, it will be a herd species, since that seems to provide the optimal survival strategy for herbivores before intelligence. As they get closer to true intelligence, their communication becomes more complex, they start spending more time in abstract thinking to control the predators, etc. High calorie food helps with the larger brain as mentioned in several answers, but also with providing a surplus to allow leisure time to develop ideas. Now you have a species already evolved to work together cooperatively, that has the ability to use tools, communicates to exchange ideas, and have gained the problem solving intelligence to take the fight to the predators. They are well on the way to civilization.

Niven's Pierson's Puppeteers eventually wiped out all of the predators on their planet, but I don't think that would be the best way to go. Without predators, the idea of war and fighting could easily fall by the wayside, and then the species can be enslaved by the first carnivore species that comes along.

I would think that some of these herbivores, having learned to hunt predators, will have enjoyed it. Free time and bigger brains means more time to explore ideas they wouldn't have before, so hunting may become a sport that keeps predators around. Then your species never forgets that there could be OTHER carnivores out there.

You may even end up with herbivorous Klingons.

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