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In the land of Dracoriri, there are dragons. There weren't always dragons, once humans were the dominant species, but then magic-an unexplained phenomenon-invaded earth alongside creatures from another world, the foremost being dragons exist and now humans have fallen into a new niche. But, as dragons emerged, a strange phenomenon was observed by humans among the new species: variable intelligence.

Some dragons acted with an animal cunning, clearly intelligent but not quite sapient, incapable of speech and driven by instinct. Their eyes were dark, and as a general rule, these "darkeyes" or drakes resembled animals, like how Crashdrake resemble cassowary or how Stealthdrakes resemble Velociraptors.

However, other dragons had intelligence rivaling that of humans, being clearly sapient and capable of both (human) speech and higher thought patterns, with brightly colored eyes and glowing pupils. These dragons tended to look more like how 'traditional' dragons; Silverns are sheathed in silver scales, clearly reptilian, and have a wyvern body plan, with two batlike wings and two legs, while Goldrakes are big, covered in golden scales, with two batlike wings and four legs.

Got it? Good, because this is where it gets tricky. Brighteyed dragons never have darkeye offspring, they're never born darkeyed. However, darkeyed species can be born brighteyed, or can have brighteyed children, and its rumored they can even become brighteyed somehow, though no one has confirmed this or how it could happen. Furthermore, if a darkeyed dragon has a brighteyed child, it means nothing-such dragons are not in fact more likely to have brighteyed children, and neither are their offspring.

I have no idea how this could work, so here I'm asking: how could this work? How could dragon intelligence be so consistent and yet so inconsistent at the same time?

Thank you for your feedback, I appreciate it!

Note:

Thanks to Palarran for bringing the need for clarification to my attention. Many of the "darkeyes" or drakes I've envisioned so far have indeed been wingless, but drakes can and do have wings depending on species.

Furthermore, brighteyes are not limited to the same body plan as Silverns and Goldrakes. As examples, two species of brighteye, Chimerake and Swordrake, are wingless, and the two are quadrupedal and bipedal respectively. Furthermore, Mesmerake, another species of brighteye, are serpentine and possess only two arms, maybe a pair of wings, and of course fins (they're based on Sirens, the fishy not the birdy kind specifically).

As for interbreeding, no brighteyes and darkeyes do not interbreed. Why would they? Brighteyes have intelligence and sophistication far beyond that of darkeyes, and darkeye species are seen as inferior (for reasons that should be obvious). It's pretty much unthinkable.

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    $\begingroup$ Q: there must be competition for food, amongst these dragons.. only their brain differs.. do these bright eyes dragons have significant higher chance to survive ("evolutionary advantage") thanks to their better brains, in your world ? If that is so, the dark eyed dragons would become extinct. $\endgroup$
    – Goodies
    Feb 8 at 23:53
  • $\begingroup$ I suspect that the OP intends the phrase "how this could genetically work" to mean they want answers with minimum reliance on the supernatural (magic/gods/etc.), not specifically that they need it to be genetics (although genetics might be a good reason). Is that correct? $\endgroup$ Feb 8 at 23:56
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    $\begingroup$ Can these dragons ever cross-breed with each other? I see "dark-eyed" animalistic dragons (the description isn't clear, but apparently these have no wings) and two distinct varieties of "bright-eyed" intelligent dragons (two-legged Silverns and four-legged Goldrakes). Having different numbers of limbs in the same species like this is immediately a problem: how do the wingless dark-eyes have any way of giving birth to (or laying eggs, etc.) bright-eyed dragons with two legs, or even the four-legged ones? There's bigger problems for realism than the variable intelligence at this point. $\endgroup$
    – Palarran
    Feb 9 at 1:02
  • $\begingroup$ @JoinJBHonCodidact: I edited, please let me know if it improves the OP. The idea is that I want an explanation, preferably a logical one based in science, for why intelligence among dragons is consistent in some ways and inconsistent in others. $\endgroup$
    – Alendyias
    Feb 9 at 2:17
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    $\begingroup$ As for brighteyes not being interested in darkeyes of the same phenotype, imagine a human woman as beautiful and sexy as a supermodel, but unable to talk or think much. Many intelligent men would still be interested... brains aren't everything. Of course, neither is beauty, but it isn't insignificant either. Marriages between dark and light skinned humans was once unthinkable... but some people thought the unthinkable, and here we are today. $\endgroup$
    – Monty Wild
    Feb 9 at 12:43

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This question has a simple answer, but the answer has little to do with genetics.

If brighteyed dragons can only have brighteyed children, but darkeyed dragons usually have darkeyed children but occasionally have brighteyed children, and on rare occasions become brighteyed themselves, then to say that there is a genetic component may be incorrect.

If we consider brighteyed (d) to be a recessive trait and darkeyed to be dominant (D), then perform the following brighteyed/darkeyed Mendelian crosses:

dd × DD = 100% Dd darkeyed.

dd × Dd = 50% Dd darkeyed, 50% dd brighteyed.

We would also get:

Dd × Dd = 25% DD darkeyed, 50% Dd darkeyed, 25% dd brighteyed.

However, the OP has said that darkeyed dragons are not more likely to have brighteyed offspring (more likely than what?), and that brighteyed dragons always have brighteyed offspring. So... this can't be genetic, as even if brighteyed is dominant, two heterozygous brighteyed dragons would have 25% darkeyed offspring.

Now, we don't know if the OP is considering only the mother or both parents in the statement that brighteyed dragons always have brighteyed offspring. Either way, it doesn't matter.

What is something that will always be transmitted to offspring? Not a gene-mediated trait, that's for certain. How about a pathogen/symbiote? That's more likely.

If we say that being brighteyed is caused by the presence of a symbiote, then the symbiote can be transmitted from mother to her children quite easily... even in a potentially egg-laying species. If the OP desires, it may also be transmitted from father to offspring if the dragons are internally fertilised.

While the darkeyed parent would usually be immune to the brighteyed symbiote as if it was a pathogen, having it present since conception would make it an accepted part of an individual's body. However, a darkeyed adult may come into contact with the symbiote and may on rare occasions prove to not be immune, and may become a host, in which case a rare spontaneous adult darkeyed to brighteyed transition would be seen to have occurred.

Now, if this symbiote causes dragons to have bright eyes and to be more intelligent, by whatever mechanism, that's the answer.

Additionally, if this symbiote has a different set of metabolic proteins to the host dragons, there may exist a substance that is a symbioticide... that kills only symbiotes, leaving the host unaffected. In the case of being exposed to such a substance, a brighteyed dragon could thus become a darkeyed dragon. It might lose its bright eyes and/or its intelligence, depending on whether the symbiote becomes the observable trait(s) or stimulates the dragon to produce the observable trait(s). In the latter case, the trait would persist even after the symbiote was lost, but would no longer be heritable.

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    $\begingroup$ Can't be Mendelian. You can get arbitrarily small percentages if it's a polygenic trait. If the percentage is small enough and dragons aren't having too many children then it's not going to be obvious if some have a higher likelyhood of having smart offspring. If I flip a coin a dozen times and it never comes up heads, I can probably guess that my coin didn't have the same odds as someone else's fair coin. If I play the lottery a dozen times and never win, I can't really say that my odds were worse than those of the person who did win once. (Of course that doesn't address adults changing.) $\endgroup$ Feb 9 at 16:46
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    $\begingroup$ +1 You could also reverse things, i.e. bright eyes is the natural state, and the pathogen/parasite causes dark eyes; bright-eyed parents have bright-eyed children via heritable immunity $\endgroup$ Feb 9 at 18:38
  • $\begingroup$ Thanks so much! It took awhile, but after much deliberation, I have figured out a good way to explain the brighteyes, based mostly off of this answer, but I did find the others interesting and useful. Good work everyone! $\endgroup$
    – Alendyias
    Feb 12 at 21:49
  • $\begingroup$ @thegreatemu a parasite causing dark eyes doesn't work. You could get a failure of immunity causing the offspring of darkeyes and brighteyes to be darkeyed against the OP's statement to the contrary. You could also get spontaneous brighteyed to darkeyed transitions, again contrary to the OP's statement. $\endgroup$
    – Monty Wild
    Feb 15 at 13:34
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Epigenetics and development:

For dragons, magic is like a nutrient. They need it to survive. But how much magic an individual gets is based on the mental ability to tap into magic. A cunning but unintelligent dragon lives off the background magical radiation in the environment, but they suffer serious developmental deficiencies, lacking enough of this magical nutrient. Eye color is just a handy marker that is also affected by this same lack of magic. Those dragons without only develop into a few stunted body plans. This does not mean those dragons aren't fierce or potentially large - only that they are stunted in normal development.

But since magic is altered and controlled by brain functions (like "spells," which are really simple mind tricks to harness magic), intelligent dragons subconsciously gather and manipulate sufficient levels of magic to allow normal development of their offspring. There MAY be transfer of magic male-to-female, but most likely the magic is simply supplied to offspring prior to (egg laying? Birth?). Or it could even be a transfer from adjacent intelligent adults to any nearby gestating egg.

If an egg from a less intelligent dragon is exposed to a sufficient magic by whatever incidental means, then the offspring will be intelligent.

So let's assume dragons have an instinctive desire for fully functional offspring. You could even have some fun with this. Perhaps dragons subconsciously kidnap well educated and intelligent humans (princesses?) to keep around their eggs on the instinctive knowledge such people tend to uncontrollably harness and shed extra magic. They might be willing to let smarter dragons gestate their eggs to increase the odds of normal development. They may even be genetically primed to leave their nests unguarded in the presence of those with magic (wizards/witches) because those potential egg-snatchers are more likely to lead to fully developed (intelligent) offspring.

  • In a separate answer I addressed one possible way in which a single genetic line could give rise to a wide variety of body forms, including winged, un-winged, un=limbed (wyrm) and multilimbed body types, which may be relevant to your question and the varied body forms of your dragons.
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  • $\begingroup$ Since you're using magic, you could do magical glowing eyes if you want. $\endgroup$
    – Malady
    Feb 9 at 17:07
  • $\begingroup$ @Malady You certainly can, and I'll admit that would look cool, but since the question is about both magic AND genetics, I'll leave that to the OP. I tend to want as little magic in a magic answer as possible. $\endgroup$
    – DWKraus
    Feb 9 at 18:18
  • $\begingroup$ This is basically the answer I wanted to write when I read the question, but you did a better job than I was going to. My answer basically: epigenetic trigger and exposure to a stimuli, and intelligent species of dragons maintain a child rearing/prenatal care habit of whatever results in brighteyes. $\endgroup$ Feb 9 at 18:50
  • $\begingroup$ This answer would be better if it addressed why darkeyed dragons wouldn't go extinct through being out-competed by their fully functional counterparts. As is, it sounds like a birth defect and/or mental disability that would be heavily selected against. $\endgroup$
    – Drake P
    Feb 9 at 23:24
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    $\begingroup$ @DrakeP I agree. But remember, in this world, magic didn't exist, then it did. So dragons couldn't exist before then. After, the only dragons to exist initially would be unintelligent dragons. Besides, evolution doesn't always benefit the "superior" individual. Dire wolves are extinct, but not regular ones. The grizzly was smaller than the short-faced bear, but took over similar niches because the short-faced bear died. The dumb dragons could be less of a threat, or smaller and needing fewer resources, willing to survive at all costs. $\endgroup$
    – DWKraus
    Feb 10 at 3:51
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Diet

A dragon is bright-eyed if the parents ate certain foods before conceiving the egg, or fed those foods to the child. (Or both.) Vital nutrients are involved. These foods can be preserved safely.

Bright-eyed dragons ensure they have a supply of the food beforehand, or they do not have a child. The thought of their child reverting to animalhood is too horrible to be considered.

Or perhaps it's actually essential to a bright-eyed dragon's life, so they will die and so not reproduce without it.

Dark-eyed dragons sometimes accidentally blunder into this food. Bright-eyed dragons don't care.

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  • $\begingroup$ That would happen only if the brighteyed dragon A: knows about the food, B: can get the food and C: is able to resist reproducing in the absence of B. $\endgroup$
    – Monty Wild
    Feb 9 at 1:24
  • $\begingroup$ True. But it could happen. $\endgroup$
    – Mary
    Feb 9 at 1:28
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    $\begingroup$ For a carnivore, assume a common herb or plant is the trigger. An intelligent dragon seeks out seasoning to add variety to their diet. An unintelligent dragon doesn't. A human, given a supply of salt, MIGHT never eat food with salt, but it's incredibly unlikely. $\endgroup$
    – DWKraus
    Feb 9 at 1:44
  • $\begingroup$ @Mary, it could also happen that the brighteyed dragon doesn't know or can't get the food, and can't resist reproducing, in which case it invalidates the 'Always has brighteyed offspring' part of the question. $\endgroup$
    – Monty Wild
    Feb 9 at 2:05
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How about education?

Dragons wouldn't necessarily be social by nature, so cooperative learning opportunities are more limited than in human society. They're also very long-lived, and don't learn as quickly as humans. So, born ignorant and at the whim of their instincts, they seem like animals.

However, centuries of experience and observation may provide intellectual (magical?) development. Those that survive that long can attain sapience (power?) and communicate with humans on a level of reason.

Those that had attained this threshold would likely not let their offspring roam free until they had conveyed the wisdom and power of their own learning, fearful that they're not safe enough without that knowledge/power. (Or they have some form of hereditary memory, if you prefer.)

So light-eyed parents have dark-eyed children, but keep them under wraps until they become light-eyed. (Or go for hereditary memory and simplify this explanation.) But any dark-eyed individual can attain the threshold through their own efforts, or with the help of a light-eye.

Why the eyes change color could be a hand-wave, or you could invent an in-universe explanation.

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  • $\begingroup$ Interesting, thank you for your perspective, I appreciate the new idea and the simple logic behind your answer! Genius! $\endgroup$
    – Alendyias
    Feb 9 at 17:14
  • $\begingroup$ Here's an idea...maybe the eye coloring is done intentionally by dragons who have achieved sentience (and their children), as a recognition sign, or it might be a symptom of a disorder that all dragons are born with, but intelligent dragons know how to treat. $\endgroup$ Feb 9 at 20:40
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I'm not sure this can be achieved purely by genetics, so let's use a mixture of magic + genetics.

At first all dragons where drakes; then suddenly and seemingly out of nowhere an intelligent dragon (simply "dragon" from now on) hatched from an egg*. It grew up realizing it was different, and thought to be unique until suddenly another dragon hatched from a drakes' egg... and then another... and then another...

These dragons, being so different, began to separate themselves from the rest and form their own "society". Being intelligent, they soon started their research to find out why and how they where born different, and realized that, at some point of the year/season/month, a wave of magical energy crossed some areas of the world and, if a drake's egg was exposed to this magic wave, the unborn offspring would eventually hatch as a dragon and not a drake.

*assuming your dragons are oviparous; this is not mentioned in your question but it's the way its usually represented

For the point that all dragons' offsprings are dragons too, I think of two possibilities

  1. The traits that this magic energy give to drakes to make them dragons are indeed imbued into their DNA, so it is inherited from the parents.
  2. Having found out how this magic wave works, they started to control their mating seasons so every time an egg was laid, it could be exposed to this magic to ensure a dragon would hatch from it. It is not allowed (and frowned upon) to lay an egg outside the "magic wave season", and no dragon wants to have a drake so everyone complies to this rule without hesitation.
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in Beowulf's Children , the sequel to the legacy of Heorot this was done by one of the creatures visiting a pool by accident as a youngling and picking up a parasite there. A parasite gives them a brain inflammation that changes their pathways as they grow, causing their brain to grow differently than the rest of their species. Like encephalitis or similar. Though I may be misrepresenting the story.

There the creature becomes aware of this and decides to force it's children through the same process to allow them to be more than just an animal. (Since it can reflect and plan while the rest of it's species mostly just reacts. and the fact that they can plan means they have a huge advantage over the other.

I'm not sure if this is exactly how it went it's been a few years but that's the gist of it. A parasite / illness could cover your scenario, especially if you don't want the children of such a creature to automatically be intelligent. It also opens up the option that with effort you could reproduce it. (possibly at some risk to the subject)

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    $\begingroup$ Interesting, this gives me an essential idea that could tie in how the world fell to the dragons....thank you very much! $\endgroup$
    – Alendyias
    Feb 12 at 21:47
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This basic idea was already used as part of the plot in Marie Brenna's series of "Dragon naturalist" novels.

In those books, one thing that strongly affected the size, color, and intelligence of some dragon species was the incubation environment of their eggs. This has real-world precedent among some reptiles and amphibians.

You could easily use the same thing ... which would also provide a mechanism for the humans to either exploit or supress dragon brighteyed traits.

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  • $\begingroup$ How would incubation temperature differ if an egg has a non-caregiver brighteyed parent/father and a darkeyed caregiver/mother? $\endgroup$
    – Monty Wild
    Feb 9 at 12:29
  • $\begingroup$ First, why assume that the female is inevitably the caregiver? Second, the incubation difference can be within the range of random possibility; it's just that brighteyed parents know how to ensure it. $\endgroup$
    – FuzzyChef
    Feb 9 at 17:18
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It is just a hitchhiker

Eye color has nothing to do with intelligence, it's just a hitchhiker mutation, meaning that it doesn't effect fitness or reproduction rate, it's jut randomly associated to another gene which causes a huge fitness boost (let's say that this gene is responsible for intelligence). The darkeyes and lighteyes don't mingle with each other, so it could be possible that the small population of dragons which were the ancestors of all the smart ones were by chance all homozygotes to the lighteye gene (Founder effect) and the phenotype remained because of interbreeding. Even some sexual selection could've helped for the phenotype to subsist, nobody wants to mate with that guy who has the dark eyes of our dumb cousins, am I right? If we assume that the lighteye allele is recessive to the dominant darkeye allele, that would explain the random lighteye offsprings of the darkeye dragons especially if the gene's mutation rate and the number of lighteye alleles in the gene pool are both low. So there's a low chance for the formation of a new lighteye allele and it's unlikely that the homozygote lighteye will meet another homozygote (or even a heterozygote).

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Diet
Just being big is expensive in terms of energy. Flying is much, much worse. Breathing fire doesn't help. Being intelligent, on top of that, is ridiculously expensive. A huge percentage of our calories and inhaled oxygen goes directly to our brains.

For a dragon to end up intelligent, the parents (intelligent or not) must have access to huge amounts of energy in their diet. If they don't the genetic switches that control things like big brains, fire-breathing and flying get shut off in succession. Once the egg develops, you're set for life with what you have.

This is the overall genetic plan for survival. It's the only way to survive the lean times while conferring advantage when reasonable.

Once you gain intelligence, you have the ability to figure that out and to plan ahead for your kids. Assuming you want the competitors ...

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Borrowing from the Schlock Mercenary Kreely species, sentience is the result of an infection at an early age, stage of gestation, or exposure of the egg. All dragons can be carriers of it, but within the Darkeyes, it doesn't survive as long after exposure. Thus, for a given Darkeye, they may be exposed to the infection and pass it along to their offspring, but generally they develop "normally", but for the Brighteyes, their system incubates the infection and thus their children are always exposed to it at that early stage. Eventually, this may lead to the Brighteyes realizing that interaction with the Darkeyes (possibly during battle) is what results in Brighteyes being born into Darkeye broods, and either intentionally suppress that infection during interaction to prevent Brighteyes from forming, or engage in something closer to genetic warfare by influencing more Darkeyes to brood Brighteye young.

Eventually, as with the Kreelies, it may lead to them intentionally maintaining two lines of the species, one intelligent and one not, especially if the Darkeyes are useful as pack animals, meat sources, etc, not to mention the possibilities of Brighteyes trying to ensure that the "right sort of dragons" are the ones given the chance at intelligence and they can maintain their unintelligent slave labor force.

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