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Many of the intelligent species on Earth, including us humans, are predatory. One of the reasons for this is the nutrient content of meat; a pound of meat is very calorie and nutrient rich especially compared to a pound of plant material.

One of the reasons humans have been able to be so crafty is from these predatory features:

  • Flexibility to run, climb, and swim (and endurance)
  • Omnivorous
  • Eyes facing forward
  • Opposable thumbs
  • etc

My question is: How can a species evolve to levels of intelligence where they become capable of space travel while not being a natural predator? Such a species would have characteristics of prey, such as (but not limited to) outward pointing eyes, being herbivores, and with natural predators.

NOTE: I'm curious about how the species could evolve into human-like intelligence, but since classifying intelligence is tricky, I've used space-travel technology instead.

EDIT: Posthumously, I think my question might be too vague; so I'll specifically ask about food supply (since I mentioned it before): What could such a species eat to allow them the necessary nutrients while still being able to invent technologies and use tools?

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  • $\begingroup$ Early humans had natural predators. $\endgroup$ – Frostfyre Jul 22 '15 at 20:52
  • $\begingroup$ @Frostfyre I was not aware of this. Thanks! I have updated the question to omit that point. $\endgroup$ – Leon Jul 22 '15 at 21:10
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    $\begingroup$ Pierson's Puppeteers are a good fictional example. $\endgroup$ – Samuel Jul 22 '15 at 21:44
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    $\begingroup$ The Kzin disagree. How smart do you have to be to sneak up on a plant? $\endgroup$ – Thucydides Jul 23 '15 at 0:40
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    $\begingroup$ Elephants are considered fairly intelligent, similar to whales and dolphins in many respects including communication, social grouping and ability to comprehend complex signals from other animals (including humans). However, they're a bit big for many theories of how human sentience may have developed to apply; early proto-human species weren't much of a match for predators physically, so they adapted the intelligence to out-think them. Modern elephants and their predecessors like mastodons and mammoths are too large and well-armed to need much more intelligence than they have. $\endgroup$ – KeithS Dec 3 '15 at 16:43
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First note that we are omnivorous and almost all animals are herbivores will eat meat if they need the protein and it is readily available. The issue is that carbohydrates and cellulose are primarily built out of a carbon backbone. Muscles are protein which are largely made of amino acids (nitrogen basically). The fats in meat are also much more similar to human requirements compared to the comparatively few lipids in plants. It is only recently humans have been able to adopt a vegan lifestyle as suitable plant based alternatives have been developed. Herbivores succeed by synthesizing these products themselves but this is expensive.

An easy way to rectify this is to have a readily available high protein and high energy plant material which removes the need for omnivorous behavior from ever developing. This is kind of the role fruits play in the evolution of monkeys and bird (both of whom also obviously eat bugs and sometimes meat). If eating animals is dangerous but plants are easy, eat plants. If they are alien, make blood fruits or something which where amino acids absorbed by the roots deposit or large nodes on nitrogen fixing plants. You could also make carnivores or scavengers that you can argue aren't really animals so don't count (kind of like sponges, jellyfish, or plankton).

A hole in this is that a large amount of readily available food will result in overpopulation until the food is now scarce. Meat then becomes an attractive option again. There must, therefore, be other factors discouraging meat consumption (lack of available prey or poisonous flesh) or other factors keeping population small. The latter could (for a writer) be a way to promote intelligence as a useful trait. Farming and selective breeding of the food will also promote this.

Factor to keep population small include: predators, malnutrition due to a needed nutrient that isn't in animals, frequent devastating natural disaster which cover large areas, etc.

My personal favorite at the moment is a limited amount of livable habitat. If there is little atmosphere protecting against solar radiation but the plants can survive this, the population will need natural caves to hid in during the day but will need access outside at night to feed. The few large predators (who eat meat as they never evolved a way to digest irradiated fruit without getting cancer) will likely attack entire dens at a time. The driving force for intelligent evolution and teamwork would be many fold. Farming, mining, defense, and den maintenance promote group survival and so they get smart enough to do that. Games during the long days promote education, communication, and cooperation so become encourages during the days. Those who are most intelligent win games, learn to dig instead of just harvest, and teach all keeping them inside away from cancer (or however the damage manifests) increasing lifespan and reproductive life.

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    $\begingroup$ Not really a hole in your idea, as the amino-acid-plants are coevolving with the soon-to-become-sentient species, the plants can protect themselves with a hard casing that requires use of tools/fire to crack open. Thus the soon-to-become-sentient species will have an advantage in developing the intelligence required to use tools and/or fire. $\endgroup$ – Samuel Jul 22 '15 at 22:00
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    $\begingroup$ @Samuel that will be true for a while... until they learn that planting the easily opened (but still protected from radiation) ones eventually result in ones specifically bred to be opened. $\endgroup$ – kaine Jul 22 '15 at 22:06
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I don't think a species must necessarily be hunters in order to evolve intelligence; that's just the way it happened on Earth, by chance. Hands didn't really evolve to throw spears--they evolved to swing through branches.

All that is really required for intelligence to evolve is some way for a slightly more intelligent individual to survive slightly longer or breed slightly more prolifically than a less intelligent individual. In other words, intelligence will arise only in an environment where intelligence makes a difference.

This usually takes the form of a competition, to be sure, but not necessarily a predator-prey type of competition. A smarter individual might find it easier to hide from predators, or to gather up more food, or to build a better shelter, or to remember and avoid hazards, or to learn from their own mistakes and the mistakes of others.

There may be many paths to wisdom, and maybe not all of them are paved with blood.

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You don't need to look far to find intelligent herbivores here on Earth. All of the great apes, humans closest relatives, are quite smart, and all of them mostly eat plants. Gorillas are entirely herbivorous. Orangutans eat mostly fruit, but will scavenge things like bird eggs if given the chance. Chimps and bonobos are known to hunt a little bit, but most of their diet is made up of plants.

While predators do tend to be more intelligent then their prey that doesn't mean that all intelligent animals must be predators. A large brain doesn't impose a higher caloric or nutrient demand than a herbivorous diet can provide, just look at vegans. If you are interested in current theories as to how and why intelligence developed in humans you could start here: https://en.wikipedia.org/wiki/Evolution_of_human_intelligence

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    $\begingroup$ I see where you are going with this, but one of the issues with herbivore diets is time; many of those animals need to spend a large portion of their day eating in order to maintain muscle mass. And none of our evolutionary cousins are as tool-savvy as we are, especially not to the point of space travel. $\endgroup$ – Leon Jul 22 '15 at 21:16
  • $\begingroup$ @Leon Every animal is going to spend a large amount of its time feeding itself. Sure the great apes aren't as tool savvy, but is that because their ancestors didn't hunt as much as our ancestors? I'm not an anthropologist (it'd be cool if someone reading this was and wanted to chime in though), but I don't see predation as being all that important to the development of tools. Gorillas have high intelligence, forward facing eyes, opposable thumbs, and social groups, all while being entirely herbivorous. A few genetic nudges in the right direction and I see no reason why they couldn't use tools. $\endgroup$ – Mike Nichols Jul 22 '15 at 21:39
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    $\begingroup$ A larger brain doesn't impose a higher caloric or nutrient demand..just look at vegans.... no. Until very recently you could not possibly raise a child as a vegan and have them develop a fully functional brain. Vegans as whole are very recent. Note: I'm not critizing vegans but saying that it is possible because we have foods now we didn't have as homo erectus. $\endgroup$ – kaine Jul 22 '15 at 21:45
  • $\begingroup$ Kaine, documentation? While I agree that veganism would not likely have occurred to homo erectus, I am not certain that foods containing the necessary nutrients would not have been available to them. The biggest obstacle I can see is cobalamin. However, the presence of biologically active B12 in certain algae seems probable. This study suggests that a certain seaweed might contain active B12 (mdpi.com/2072-6643/6/5/1861/htm). The same group has also researched cobalamin in a certain fermented tea (pubs.acs.org/doi/abs/10.1021/jf030585r). $\endgroup$ – Obie 2.0 Jul 22 '15 at 23:59
  • $\begingroup$ None of this is to say that plant sources of B12 are either plentiful or easily available, but that there is currently decent evidence of their existence. I find it difficult to say with any certainty that homo erectus did not have access to them, depending on area. Recall that all sources of B12 are, in the end, derived from bacteria, so the existence of many types of fermented B12 foods would not be too unbelievable (not that homo erectus likely had fermentation). $\endgroup$ – Obie 2.0 Jul 23 '15 at 0:02
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On Earth, intelligence correlates strongly with a couple of factors:

  1. Meat eating (both carnivore and omnivore) >> herbivore & insectivore
  2. Social living >> solitary living

Of similar animals living in similar environments which display these traits, the ones with the above traits score higher in intelligence (EQ) ratings.

  • Domestic Dogs > Domestic Cats
  • Lions > Tigers
  • etc.

If you take predation "off the menu" for your planet's ecosystem, then you may need to rely upon social factors determining an animal's ability to mate. This could drive the population to higher intelligence, it might just take longer than it did on Earth.

Alternatively, if you wished to drive many animal species to higher intelligence, make a planet with lots of sophisticated dangers. Only the animals with high intelligence or high birth rates create children able to survive the environment.

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  • $\begingroup$ As a comment to this answer, the social living aspect in humanity came about because our estrus period isn't observable to us. Other animals go into estrus and emit pheromones that the males can pick up from miles away. The great ape branch of the animal tree lost both of those traits, making the males have to stick closer and mate more regularly with their females to insure the next generation. $\endgroup$ – Draco18s Dec 2 '15 at 15:47
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An animal that must "hunt" the plants that it eats would experience greater pressures towards developing greater intelligence than a grass eater.

Remembering where and when to find the ripe fruit, or how to avoid the poisonous leaves to access the succulent berries, or how to subtly direct the herd of dumb (and much tastier appearing) grazers along the paths you wish to take to avoid the direct attentions of predators would all be of benefit.

A low reproducing prey species would benefit from "out-smarting" the predators where a high reproducing species simply accepts the losses to predation.

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