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So there’s a small animal species that live pretty simple lifestyles of eat, don’t be eaten, reproduce, and that’s it. They live in forest/jungle or swampy environments, eat a wide diet of insects or occasional plants, and are hunted by larger, faster predators (fish-like creatures and bird/mammal-like creatures) on both ground and in water. They’re relatively social, with part of “don’t be eaten” including “hang out with many others of your species” (strength in numbers!).

This species evolves an ability to give off exosomes that basically contain information and memories of a sort, which—if inhaled and successfully “integrated” by another organism’s brain—are then transferred to the other organism too. These aren’t individual or conscious memories, though, but rather deep genetic “stimulus and response” instinct-like memories. The key is that the information in the exosomes is not usually unique to an individual, since it’s on an instinctive/genetic level and normally would be inherited through the species. I always assumed this ability would have evolved for some sort of increased social awareness and communication, but I’m open to any ideas to get it evolutionarily established.

What advantage could an ability like this offer to this species, to share a genetic-level instinct with others (either others of its kind, who presumably would be lacking it—perhaps accounting for genetic and instinctive variation among different groups of the species, if some know something that others don’t—or even with other species for some reason?)

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    $\begingroup$ (a) You are allowed to ask one and only one question. You are distinctly asking two (your title question and your body question). Please pick just one (I'd advise the post body question, the title question violates the help center's "Book Rule," meaning it's too broad). (b) As asked, the question is pretty opinion-based (e.g., brainstorming, which is discouraged per the help center). Can you tell us more about the creature's environment? Predators? Prey? Those kinds of details narrow the focus and bring the question into scope. Thanks. $\endgroup$
    – JBH
    Jun 13, 2023 at 15:46
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    $\begingroup$ @MichaelK Asking how anything can evolve violates the help center book rule. Further, humanity barely understands how we evolved. Speculating about how a fantasy creature can evolve is VTC:opinion-based brainstorming. On the other hand, asking how a creature's physiology would be beneficial in the proverbial here and now, that can be within the scope of the site. They are not the same question. (If you want to debate this, be prepared to explain how my eyes are beneficial to me today, and how they evolved. Their usefulness today has nothing to do with what they originally were.) $\endgroup$
    – JBH
    Jun 13, 2023 at 16:18
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    $\begingroup$ How would this not be used and abused by viruses, bacteria, parasites. etc? That is, there is strong reason for this feature to not exist. $\endgroup$ Jun 13, 2023 at 18:51
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    $\begingroup$ @inkwell87 hand waving is one way to prevent abuse. One attack is the infection modifying the exsomes to cause behaviors useful for infection.Another attack is for the infection to mimic an exsome and be fast tracked into vulnerable locations. Yes this would require specialization, but that's what infections usually do. $\endgroup$ Jun 13, 2023 at 22:38
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    $\begingroup$ @JBH Would something along the lines of “What potential evolutionary benefit would the ability to “share instincts” have?” be better? $\endgroup$
    – inkwell87
    Jun 14, 2023 at 3:50

4 Answers 4

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Fast information dispersal in an ever-changing environment

One way this could be beneficial is in an environment that is ever-changing and unpredictable, with many (nearly) unique challenges that change too fast for biological evolution to keep up.

For example, there may be many different kinds of food, but a type of food that is edible today may become poisonous (or be replaced with a poisonous variant) within the next few days. If no general pattern or strategy can be found to distinguish between edible and poisonous food, creatures relying on adaptation via genetic evolution would soon die out from eating poisonous food (or starve because they do not trust even otherwise edible food sources).

However, these exosomes would provide them with a way of quickly communicating the necessary information among all individuals. Once "red berries" are determined to be currently edible via trial-and-error, the rest of the pack is quickly updated and free to enjoy this safe food. And once the information is no longer valid and some individuals are poisoned, either the affected creatures themselves or witnesses to their death again update the instinctive responses of the rest of the pack via transfer of new exosomes.

Another example would be the presence or identity/shape of predators and other dangers. Once a new type of predator appears in the environment, they will initially be successful at hunting these creatures, but quickly find that individuals have learnt to avoid them instinctively even without personal experience.

A necessary requirement would be that "instincts" relayed via exosomes are temporary and can either be easily overwritten by more recent exosomes or decay naturally unless continuously refreshed.

This mechanism is similar to the pheromone markers of real-world animals like ants or bees already mentioned in other answers, but it has some differences:

  • Pheromone markers are typically applied to the environment (e.g. marking a path to follow towards the food), while exosomes can be shared at one's leisure when the conditions are right. This way they are more like bees' dances in that information is transmitted only within the safety of the hive, without relying on random passerbys to discover it or risking spreading information to unwanted recipients like predators.
  • Exosomes can be transmitted recursively even by individuals that did not make the original experience. This helps spreading the information in situations where not all members of the pack regularly come in contact with each other.
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Frame challenge - This is anti-evolutionary

Let's ignore the "how" and look at the "what" of this ability. Species X gives off tiny particles that, if inhaled by other members of species X, will reprogram their brains with one or more instinctive behaviour.

Evolution relies on promoting favourable incremental mutations, so that if a member of species X develops a better ability to survive - whether by being more efficient at finding food or more successful at attracting mates or better at avoiding predators - then it has a greater chance of its offspring surviving and eventually dominating the gene pool.

The problem with the inhalable instincts is that they will tend to re-normalise instinctive behaviour that counters the favourable mutation. Let's say that the latest mutation is a better digestive tract that lets species X digest (previously inedible) berry Y. This should be a beneficial, inheritable mutation, except that the newly mutated creature and its offspring will be overwhelmed by inhaled, programmed instincts from the vast majority of existing individuals saying "avoid berry Y, it's not good for you". The mutation is likely to be lost because the programming will prevent the physical benefit being realised.

Similarly, a mutated individual who has developed a skin or behaviour to allow it to camouflage itself is probably best served with a "freeze if you spot predators" instinct, but is overwhelmed by the "run for shelter if you spot predators" instincts it inhales and so on. Not to mention what happens when the environment changes and the old instincts become a suicide pact - "never leave the vicinity of the creek" is a bad idea when it dries up for good.

Evolution relies on a survivor bias. The "programmed instincts" do not. So, being overly influenced by programmed instincts will result in the affected subspecies dying out when competing with the subspecies that keep evolving and not relying on inhaling "yesterday's wisdom".

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    $\begingroup$ Yes can't emphasis how bad an adaptation this is, it basically prevents behavioral evolution, which is normally one of the fastest thing to evolve. $\endgroup$
    – John
    Jun 13, 2023 at 23:31
  • $\begingroup$ That makes sense, though I should note that not every single instinct of these creatures would be “contained” in the material put out (in fact all the information in the exosomes could be within a specific field such as social or navigation-related behaviors, which may require some very specific circumstances and mutations to pose an issue) so only a beneficial mutation specifically in contrast with one of the instincts provided would be a danger. With that said, the problem may be uncommon enough that the adaptation could still arise and, although potentially would pose an issue (continued) $\endgroup$
    – inkwell87
    Jun 14, 2023 at 1:46
  • $\begingroup$ later on, may either 1. have the problem be countered in some way sooner or later if possible (that’s almost a whole other topic/question though), 2. if the problems are small enough, and few and far between enough, maybe just be an evolutionary flaw that is simply lived with? or 3. species X may perhaps even be domesticated in that time (actually a concept I originally had for what this species may be used for in a setting) since that ability may be useful to an advanced species, giving species X protection from survival dangers and possibly altering the nature of that ability itself $\endgroup$
    – inkwell87
    Jun 14, 2023 at 1:52
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    $\begingroup$ Small gripe: evolution is not survivor bias, it is procreator bias. Whatever that makes the genetic traits thrive and keep reproducing. $\endgroup$
    – MichaelK
    Jun 14, 2023 at 8:17
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    $\begingroup$ I note that what the OP suggests is not all that different from pheromones and language, which suggests it can be viable, as long as they're not overwhelming. $\endgroup$ Jun 14, 2023 at 15:05
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Olfactory communications is very common in the animal world (even humans engage in it... albeit it, not as strongly as our sense of smell is one of our least developed senses... we still use it for a lot of important instinctual reactions). In fact, it's one of the primary communication methods used by many social insects. Ants, for example, use scent markers to follow trails to sources of food. As they return, the markers become stonger, attracting more ants to the food. Flowering plants use scents to attract pollinators to their pretty flowers... lean in for a sniff or a drink of that sweet, sweet nector, come away with a body covered in pollen... go to another flower and do the same... and pollen touches the stamen and boom... that's how fruit is made (it's the birds and the bees!).

Other animals use scent markers, often as a form of messaging systems. Canines (especially males) often encode scent markers into their urine, leaving a message for other dogs to find later that and pick up and recieve the message. This becomes more frequent of the dog is in a new area and male dogs will often mark areas even if they have empty bladders.

Even among humans, we have some strong involuntary reactions to certain scents... but it's often used to enhance taste... and since we evolved from foraging omnivores, developing a refined sense of taste helps us to understand what's good to eat and what needs to be avoided... That thing that smells sweet? That's good you can eat that (it has sugar, which tastes sweet and has ALOT of energy to make a body go). Bitter? Leave it behind... it's icky (Because most alkaline metals taste bitter and all alkaline metals are poisonous to humans... and among the worst poisons too, as hard metals can't be processed by the body meaning they stay in you for life and the build up will kill.). Spicy? Also poisonous... but you can eat small amounts (Most sources of spicy food are biochemicals used by plants as poisons to fend off animals from eating them. Unfortunately, being evolved from foraging omnivores means humans have some pretty tough digestive systems that can break down poisons... not only does spicy biochemicals don't work on us, we've actually forced some plants to get even spicier... so we can eat them. Spicy foods also will cause us to activate our sweat glands in response... which cools us off.).

One of the most consistent ways we communicate using smells... is one of the most disgusting things we do... and there's a good reason for why it's so disgusting... and why the smell is so potent. The smell of vomit is one of the most potent smells to a human being and is so terrible, it will cause those who smell it to almost vomit themselves... but this is actually a good evolutionary reason for this. As a social animal that lived in large groups of omnivores, sometimes the hunters/gathers brought back something that they shouldn't have... and they eat it... and their body tells them that was a bad idea and get it out the fastest way possible. The poor fella "tosses his lunch" but he brought that rancided ick home for everyone to eat... and now the whole tribe is about to eat it... best signal them to not do it by sharing in the pain... some might have... others might not... but let's make sure we don't kill the whole tribe... hence "vomit" is one of the worst smells for a human to experience... better to starve and eat something good for you later, than to foodie around and find out.

That all said, most instinctive behavior is learned by species with high intelligence (especially mammals... babies needing milk means at least one parent is there to teach her kid how to be... whatever they are.). Mom teaches the kid how to find food without her around... kid gets the training they need to survive and by the time mom kicks them out, mom has hopefully trained them enough to fend for themselves (sometimes dad helps too. We may joke about Tiger Mom sterotypes, but real Tiger fathers are known to be so protective of their kids, they will kill cubs that don't belong to them to give their kids an edge... then kick them out of the house when they start getting old enough to have their own babies.).

Scent plays an important role because finding food is usually done by tracking a scent (Humans actually didn't evolve this... but we were so good at finding food through other means, we didn't need it and ended up in a sybiotic relationship with the one animal that could hope to keep up with us... the dog is man's best friend because we use similar hunting tactics to them and they have skills we lack and vice versa. Dogs have better sniffers, we have better eyesight, communication skills, and endurance.).

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    $\begingroup$ So how exactly would you say these examples can match or parallel a benefit/function offered by the exosome memory-sharing trait? It’s worth noting that despite being inhaled, I’m not sure if I’d call the exosome thing olfactory communication—the inhalation is just a delivery system into the bloodstream (through lungs) and brain, and I don’t know if scent receptors would necessarily pick up on microscopic vesicles. The stuff you get from the exosomes is less like the smell that makes you lose your appetite and more like the instinct that tells you “if you smell that, know it’s not safe to eat” $\endgroup$
    – inkwell87
    Jun 13, 2023 at 20:53
  • $\begingroup$ "The human nose is particularly sensitive to these sulfur-containing compounds, which is no surprise given that they are often associated with things to avoid." scientificamerican.com/article/… - forget about exosmes and put pheromones back and you have ants and termites being evolutionarily extant and unchanged for the last 300M years. Humans, "able to sense small volatile thiols down to 0.3 ppb" (1ppb = 0.001 μm/m) ... the size of micro vesicle = 0.1–1.0 μm. $\endgroup$
    – Mazura
    Jun 14, 2023 at 16:45
  • $\begingroup$ SO2 molecules are 0.054μm and you can smell that '[crap]' pretty well. If you're asking what why or how, it's copper. "The hypersensitivity comes down to the metal copper, according to a team of chemists from the U.S. and China." - "just a delivery system into the bloodstream" - that's drugs. Olfactory communication uses the nervous system not the cardiovascular. $\endgroup$
    – Mazura
    Jun 14, 2023 at 16:48
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    $\begingroup$ @inkwell87 " I’m not sure if I’d call the exosome thing olfactory communication" By it's simplest definition, communication is the transmission of information. So it's definitely communication. The blood heading to the brain carries oxygen, not information, which transfers through the stimulation of nervous system. The brain it's self is not capable of receiving nervous stimuli (if you poke someone's brain, they won't feel it like they would if you poked other organs). So in order to get information to the brain, you need to stimulate nerves capable of receiving information. + $\endgroup$
    – hszmv
    Jun 14, 2023 at 17:38
  • $\begingroup$ @inkwell87 + And things that do not stimulate nervous senses will not be perceived as information the brain can receive. What's more, the blood entering the brain is screened by the "Blood-Brain Barrier" (BBB) which is a semi-permeable membrane that allows things the brain needs from the blood to enter the cerebral fluid while keeping out foreign agents and blood soluble that could cause damage to the brain, so this would mean that unless a species is specifically evolved to allow this substance to enter the brain, it won't be allowed to leave the bloodstream. $\endgroup$
    – hszmv
    Jun 14, 2023 at 17:46
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Bacteria do this all the time (It's called "horizontal gene transfer"), except they don't just blast out the exosomes willy-nilly for random passers-by - which would include predators, which might evolve to "follow the scent" as it were - to happen across. Instead, they employ a primitive version of sexual intercourse to share genes in this manner, only doing it up close and personal and within the safety of their cell walls.

Now, your small, generalist, social critters with "strength in numbers" instincts are already going to breed like rabbits. It would just be a quick hop, skip and jump to hijack their "breed as often as possible" instincts to allow horizontal gene transfer, and even allow the sex organs (which are immuno-isolated) to decide whether a particular adaptation or instinct is a good choice, with the brain (also immuno-isolated) getting a say itself later on.

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