My father (who is a biologist) thinks that a sapient species must be a true omnivore because if it were an obligate herbivore (like a koala or a sloth), it would not have enough nutrients to develop a big brain and if it were an obligate carnivore (like an axolotl or a penguin), it would not have enough carbohydrates to turn into electricity.
Whales and Elephants and Orangutans
Whales are purely carnivorous and Elephants are purely herbivorous. Orangutans are almost exclusively herbivorous. They all have big brains and, along with the other great apes, are widely considered the most intelligent classes of animals.
Orangutans are usually claimed to eat mostly fruit. But it's hard to find a study that distinguishes between fruits and nuts/seeds which have significantly different properties. In particular coconut flesh has about the same energy density as meat.
Dolphins. They have brains as big and as active as humans, eating only fish and other sea creatures. They have tactics and strategy and possibly even limited tool use, and some scientists believe they are also sentient and sapient.
Sure, their sapience is not a scientific consensus (yet?), but at least it is discussed as something that can be true, and needs to be proven further, or disproved scientifically. The state of discussion on dolphins proves that it is at least possible for carnivores to attain sentient & sapient level.
It's not necessary, but it does help
Nutrient-wise, it isn't impossible to grow a big brain on a one-note diet (a high-fat diet does make brain development easier, but in an environment where nutrients are readily available the lack of meat isn't going to be a deal-breaker), but the main benefit of intelligence is the ability to adapt one's behavior - including feeding behavior - by learning.
The more foods you can eat, the more beneficial it is to be able to learn how to eat them, while a specialist that only eats one kind of food anyway doesn't need to learn, it can just be born with the instincts it needs to eat that one kind of food. Because of this, generalists like crows, raccoons, and badgers are often smarter than their specialist counterparts overall.
But this isn't always the case. Elephants are herbivores, but they are smart because they need to remember where the water is in an environment where water holes are a vital resource and appear and disappear periodically. Orcas are carnivores, but they are smart because they eat a wide variety of prey that are all vulnerable to different kinds of attacks. Monkeys are smart despite being predominantly herbivorous because they need to remember which fruits are nutritious and which are poisonous. And any social species will generally be smarter than their solitary counterparts because they need to keep track of relationships among the group, regardless of what they eat.
if it were an obligate carnivore (like an axolotl or a penguin), it would not have enough carbohydrates to turn into electricity.
This makes absolutely no sense whatsoever. Protein is actually very beneficial for brain growth, in particular neuron density. Big cats are obligate carnivores and highly intelligent.
Carnivores like canids and lions are also highly social and must regularly solve problems of life or death. This seems like a perfectly good basis for evolving sapience.
Maybe, but not directly because of nutrition. I think the other answers give good animal examples of very intelligent carnivores and herbivores. As for people, I have some coworkers who are strict vegans, others who have been on a strict keto diet for years. Both groups are healthy and very intelligent people. I think we all agree that omnivorous diets are not a requirement for intelligence.
But, that's not the point of being omnivorous. Being omnivorous means we can live anywhere. Humans live on every continent, in every climate, and at a huge range of altitudes. Very few other species can make that claim. I heard that the brown rat is the only other animal that lives in as many places as people do. There might be others, but the list is not long. It's not just our synthetic fibers and air conditioners that allow us to live everywhere. We spanned the globe as stone age civilizations. Mostly because wherever we went, we could eat things we found there. You have to be a flexible omnivore to cover a whole planet. Spreading out over a huge area is probably a prerequisite of forming societies.
The other side of the coin is that you kind of have to be intelligent to be an omnivore. Identifying food, finding and evaluating new sources of food. It's hard. Most omnivores in the animal kingdom are pretty intelligent. Apes, bears, rats, raccoons, ravens etc.
As pointed out in the comments: being an omnivore means being less efficient. It might be necessary to have higher intelligence to compete with specialized eaters in environments where food is plentiful.
There are exceptions, obviously. Catfish are omnivores, but rate low on animal intelligence measures. It seems most likely that there isn't much of a real link between omnivorousness and intelligence except they're both good things to be (in some circumstances).
As evidenced from the fact that a good number of humans are perfectly fine being vegetarian, it's entirely possible to get all the necessary nutrients from vegetation for intelligent thought. I've seen a few theories that toss around the idea that only an omnivorous species would be capable of advancing towards intelligent thought because of the flexibility in behavior. While it is true that omnivores can have a higher range of behavior patterns than pure herbivores, there's no theoretical reason why a vegetarian species couldn't follow the same path as homo sapiens, especially given that (as stated above), our ability for rational thought isn't meat-dependent.
That isn't to say that being a herbivore is preferable to an omnivore - it very much isn't. The ability to consume a larger range of food is a distinct advantage that omnivores possess.
EDIT: To address everything drawing a distinction between evolving intelligence and maintaining intelligence - I don't see any difference. Evolution isn't hurdle based, there's never a point where you have to surpass something achieved through evolution even if you aren't going to use it. To have two arms, you don't need to first have four. To breath oxygen, you don't need to first be able to breath carbon dioxide. To have a perfectly functional brain that can run on vegetables, you do not need to first have a brain which must run on meat. If a human brain can survive on only vegetables, there's no reason to assume that it must have undergone a stage where it survived on meat.
Furthermore, we aren't discussing humans. This is a question of 'sapient species', which mean we're discussing whether it is theoretically possible for a sapient species to be a herbivore rather than an omnivore. That means that even if, hypothetically, humans did at one point need meat for their brain to function and now they don't, the fact that we do not need meat now to maintain our intelligence is proof that a sapient species can theoretically be a herbivore. The question of whether or not humans could have survived as herbivores, given the Earth's food web, if a fascinating one, but it's not what's being addressed right now.
The question merely is 'Do sapient species need to be omnivores?', and the answer is 'no'. You might have to assume a perfect ecology with bountiful plants that provide the nutrition that humans usually obtain from meat, but it nonetheless is possible.
The distinction between carnivore, herbivore and omnivore is not that strict. It's more about "default" behavior, than about ability/inability to consume different kind of food.
For example a lot of dogs - obligate carnivores are being fed with pasta and/or porridge. It is not good for their health, for sure, but dogs are still able to live and breed on that diet. Or take wild horses: in winter, when there is low food they can start hunting for small rodents. Domestic horses can eat meat.
Evolution has a lot of examples of diet change. One of the most known - all dinosaurs are descended from carnivorous biped lizards. But still they evolved to all kind of diets. Even our "cousins" gorillas are herbivores, while we are omnivores.
So sapient species must not be a true omnivore, but it would still practice omnivore behavior in hard conditions.
Nope, many species show otherwise
There are a number of species out there which are probably sapient or close to it, and which exhibit a wide range of dietary habits.
Carnivorous - Odontocete cetaceans (particularly dolphins) are highly intelligent and exclusively carnivorous. Notable orcas (Orcinus orca) are Tyrannosaurus rex-sized apex carnivores and along with bottlenose dolphins are quite likely our closest rivals in intelligence, showing evidence of intellectually complex traits like language and non-biological culture. It is debatable how intelligent mysticetes are but if they are it would add filter feeders to this list. Many coleoid cephalopods show high degrees of intelligence and all of them are carnivores.
Herbivorous - Elephants are obligate herbivores (indeed, they eat a lot of vegetation every day) and are extremely intelligent. Parrots rarely if ever eat animal matter, feeding on fruits and nuts, and are intelligent enough to actually be taught the proper usage of grammar. Gorillas are highly intelligent and almost never eat meat, feeding on high-fiber vegetation. Orangutans specialize in rainforest fruits like durian, but will eat meat.
Omnivorous - Humans, obviously, though we are abnormally specialized for a carnivorous lifestyle compared to most of our relatives, but only relatively speaking (our diets are more like bears than the fruit-and-nut dominated diets of most other primates). Chimpanzees and bonobos are also omnivorous. Crows and jays are extremely intelligent and omnivorous. Pigs are often not considered sapient, but they are fairly intelligent and are often considered to be "runners-up" when talking about sapience.
What it seems like is the only thing "necessary" for high intelligence is a food supply that is calorie-rich enough to balance out the high energy demands of a large brain. Unpredictable food supplies with irregular abundance cycles (forest fruit, grass and water on the savannah, seasonal fish abundances) in particular select for complex problem solving and long memories. Protein-rich foods usually help, though I have no idea where gorillas and elephants get the necessary calories.
Several answers have pointed out purely carnivorous intelligent animals, but here's one that's on the other end. They live on a diet of mostly fruit and nuts and seeds. (Possibly the occasional insect, but not enough to be called an "omnivore".) And they are highly intelligent, capable not just of mimicking human speech but actually having a limited understanding of it. Watch some videos of African Greys identifying objects and in some cases even forming simple sentences. (Proof that they are not merely imitating.)
I will echo other answers; it's not required, but it helps.
What is required, generally, is an environment in which the development of intelligent problem-solving skills is viable as a survival strategy. There can't just be some basic trick to survival, like being able to tolerate temperature or pressure extremes or high acidity/alkaline environments, etc. If all you need to survive your environment is a good tolerance to cold temperatures, a means of locomotion through your environment and a big mouth to catch food, you'd look like a whale shark if not an even simpler form of life. Sharks in general found a relatively primitive but highly effective overall strategy for body arrangement and instinctive food gathering strategies, allowing many of those species to become the apex predators of their environments. Intelligent they are not, however.
Intelligence is theorized to develop as a survival strategy. The food source of the animal in question is less important than the simple fact that it faces some existential threat within its environment, which it cannot outrun, outfight, hide from, or otherwise adapt physically such that this threat is mitigated. The only remaining strategy is to outsmart the threat; to develop mentally, such that a variety of skills can be brought to bear in combination, depending on the exact situation. An animal that is constantly tested in these ways by its environment, constantly having to think of new ways to survive, is an animal that, given sufficient time to adapt as a species to new and different threats, will develop sapience.
Biologically, sapience is a quality of the brain as an organ, so evolution of sapience necessarily requires the development of the brain; more neurons, more organization, more complex neural pathways that can store more sense-data and more efficiently recall and process it in ways that less intelligent animals seem incapable of doing. Along the way, several key features of sapient thought develop, including sustained conscious thought, abstraction, generalization, classification, symbolization, and imagination.
We have observed many of these traits in a number of other Earth animal species, none nearly as advanced as our own level of sophistication in these areas of thought, but offering useful glimpses into how - and why - we as a species may have developed our own intelligence, and what species may be following behind us. The list of candidates is quite diverse, and spans a wide swath not only of diet, environment and relative status in the food web, but even animal classification as typically ranked hierarchically. Many mammals, including most primates but also elephants, pinnipeds (seals/sea lions/walruses), dolphins, whales, swine, and even many rodents like squirrels, have demonstrated various features of sapient thought to a notable degree over their brethren. However, members of the bird class, like ravens and parrots, are also considered far more intelligent than many mammals. Even the humble octopus, classified in one of the least-developed phyla of the animal kingdom (the mollusks, most of them only a small step above filter-feeders in the Porifera clade), displays an extreme level of animal intelligence both physiologically and behaviorally.
Just within this short and definitely non-exhaustive list, you have the entire range of "carnivoricity", from the obligate herbivores in grazing species like the elephant, through hypocarnivores like rodents, swine and parrots, through mesocarnivores like crows and ravens, to hypercarnivores and obligate carnivores like the pinnipeds, dolphins and the octopus.
If anything, being a "mesocarnivore" aka "true omnivore" is a disadvantage to the development of intelligence, because it's one fewer problem to have to solve; getting food of the proper type for your metabolism is no longer a requisite, you can eat anything around you that isn't toxic to you (and plant matter isn't "poisonous" to a cat or other obligate carnivore, per se, the animal just doesn't get as much if anything from it nutritionally as they do from proteins and fats). Many hypercarnivores rank among the more intelligent animals, because as predators of large animals, they have often had to think their way around their prey's natural defenses; those who couldn't, didn't eat. On the other end of the scale, smaller hypocarnivores commonly learned to outthink their predators, who may have been nearly as agile as them and considerably larger; the prey animal's only hope to survive beyond a few seconds of sprinting would be to think fast.
Without thousands of evolved examples of sentience we cant say for sure one way or another, but it is a reasonable position to take in speculative fiction.
Without meat as a high nutrition food source the species wont have the energy budget for high intelligence brains.
Without plants as a high efficiency food source the species wont be able to generate the food surplus required for a society.
Good question! I think your questions has actually two parts:
- Can a non-omnivorous sapient species exist? answer:
Maybe if one day all humans become vegans. So yes this might be possible.
- Can a non-omnivorous sapient species evolve (from a non-sapient species). answer:
It is unlikely that a sapient species evolves while being on a non-omnivorous diet. The omnivorous diet provides an animal with a variety of resources and opportunities that gives it a competitive advantage over animals that are strictly herbivorous or carnivorous. Without this advantage we would have been dominated by other animals and not able to occupy niches that prefer a bigger brain.
In this case your dad is totally right. It was because of our diet that we could develop a bigger brain and build up the civilization and infrastructure we have today. Vegetarians do not like this fact. Anyway, within nowadays civilization it is for many people totally possible to live on only plants, especially now plant technology is advancing. (Steak lovers do not like this fact) Disclaimer: Whether you personally can live on only plants depends on your body type.
Strict carnivore is very likely (and a working implementations exist in nature, e.g. dolphins), strict herbivore is rather unlikely but certainly possible nevertheless (and also has a working implementation, e.g. elephants).
In principle, it is even possible to be sapient strictly autonomous, only just that isn't what happens evolution-wise because it's too "expensive" insofar as other strategies will bring forth something that makes you un-competitive.
What happens and what doesn't happen in evolution (or rather, what persists) depends on
a) whether it's physically possible at all, and whether your special properties are an advantage in the environment where you live b) whether you have sheer luck and aren't dying to a volcano eruption or lightning despite being the perfect super-animal c) whether you're just aggressive/malicious enough
a) is what brought most species into existence, c) is what made homo sapiens the dominant hominid (and dominant species, in general). b) falls under "shit happens". You can die out even if you are perfectly adapted.
That being said, possible is nowhere near likely. Nor is appearance or ideology related to what really works in a sustainable way (in a sense of working for 8-9 decades).
I think your father has a great sense of humour in the way he expresses his ideas but if he was writing a doctorate to support his thesis, he'd have to check all the variables - and the research would take him on a much longer journey of exploration.
To start with, one has to define sapient. I would define it as a being who knows its own existence and has a conscious sense of selfhood, something akin to identity and ego, not just individuality and personality. I breed and work with horses who live at liberty as a herd in a single, large paddock of 64 acres. They clearly have a sense of identity in that each knows his or her place in the social hierarchy, and each has a personality and individual habits via which they get their needs met.
But by the term "homo sapiens," we refer to a species in which some individuals are capable of high levels of abstract thought, analysis, synthesis, problem-solving and invention.
This requires a means of creating symbols that stand for concepts, things that don't exist as the levels of the five senses. We need languages, mathematics, measurement, chemical coding, musical scores, and so on. We probably need larynx, mouth, tongue and some kind of bellows to evolve speech (unless we were as species that could communicate in complex pheromones) as well as a neo-cortex sufficiently evolved to symbolise, codify and represent in communications.
And we need the means to manipulate the physical world, to experiment in accord with our thinking. To manipulate, we need something like hands - though perhaps they could be octopus-like tentacles or some combination of highly adaptable levers and grippers.
To evolve all of this, being a social species must be crucial to our survival. It must involve life and death issues that affect whether we can thrive and multiply. In my view, a herbivore doesn't need to be enormously smart - all they need to be able to do is find food and shelter, attract or fight for mates, defend their young, and run or hide from predators. They don't need to do much in the way of out-witting others or inventing. But the carnivore needs an immense amount of strategy and experience to catch prey that doesn't want to be caught. The omnivore may have the advantage of being better able to adapt to feast or famine in many different environments, but would need the willingness to experiment and a prodigious memory. So yes, being an omnivore does advantage the evolution of intelligence.
I believe that an intelligent species, whether carnivorous or omnivorous, will always be social and (unfortunately) aggressive, and will tend to take many generations to evolve complex ethics, customs and laws.
There may also be another factor required for sapience - to be born relatively helpless, no fur for keeping warm or avoiding sunburn, no poison glands, long horns, sharp fangs or hard hooves. To be so vulnerable requires great intelligence to survive and thrive. Yet another factor might be being born too stupid and helpless to survive. The prolonged childhood provides the opportunity for learning and for programming and conditioning the brain for its environment, while still allowing for adaptability. I wish I could have these discussions with your Dad. He sounds like an interesting thinker. :)
The answer given by the OPs' dad seems to relate to published studies that have observed that human brain development is positively correlated with both meat eating, and the cooking of our food. However, a correlation never indicates whether one of the things caused the other. In fact, both factors might have been caused by a 3rd as yet unidentified factor. (As in women's hemlines and the stock market).
Did our brains grow because we ate meat or did eating meat (cooked) free our hands and our minds up to focus on something beyond mere survival?
What meat and cooking gave us was the ability to efficiently process more calories in less time. Thus freeing us up to do other things. However, it was agriculture and the storage of food that began civilization and moved us away from our hunter gatherer phase. Was there a need for a sophisticated arithmetic and method of communication before then?
We have cave paintings that indicate an awareness of self from the outside since before agriculture. Several other species have this also. As far as I know, none has shown interest nor ability to capture that awareness in a fixed medium. I think these paintings show curiosity about something not having to do with life sustaining endeavors. Most mammals have shown an interest in play. The paintings also show the presence of an imagination and an awareness of time.
Could we have developed the ability to more efficiently burn calories without meat and without cooking? Could our world have developed some super-fruit (super-vegetable?) that readily fulfilled all or most of our nutritional requirements? It's possible and if so, meat might not have been necessary for sapience.
[Although an easy life without the need to think about survival and evasion of danger would probably not push towards a more developed brain.]
The question also ignores the possibility that non-carbon based life forms could evolve to a stage of sapience. Additionally, we have bacteria that eat oil.Showing that there are food sources other than flora and fauna that are available even on our own world.
So, the answer is: From the knowledge we currently have, the possibility of a non-omnivore sapient species cannot be ruled out. However, creating such a species would require quite a bit of planning for how that being could have evolved.