This question is inspired by the last paragraph of my answer here: Negating the negative effects of childbearing

(A follow up question to this can be found here: Methods to ensure gene flow in species with seperate sapient and non-sapient lifecycle)

I mentioned a concept for a species which I think would be interesting to explore, but which would require some creativity to have evolve logically. The idea is that the species combines R and K reproduction strategies, having many (hundreds) of young originally, but only investing energy into raising a very small number of them to adulthood as sapient creatures. This is done by imagining that the species start out as non-sapient and only some will later metamorph into full sapience. I'm trying to figure out how such a creature would evolve, if it could happen, and perhaps some of the other biological requirements to make it realistic.

for this example imagine a creature that's mating starts out similar to frogs. When two sapient adults reproduce the produce hundreds, or thousands, of eggs which are left unprotected by the parents to develop into a sort of tadpole like creature on their one. These creature are not sapient. These non-sapient 'tadpoles' (they don't have to look like tadpoles, just an analogy) will try to survive on their own and many will die to predators or even competition with siblings quickly in the first few weeks. Eventually the parents will come back to the breeding spot where they left the tadpoles and will pick a small number of the strongest/fittest tadpoles that survived to raise as their children.

The few tadpoles that are chosen by the parents (probably only 2-5 in total) will undergo some sort of triggered metamorphosis to start developing more complex brains and begin the growth into true sapience, a growth that would require years of rearing and upbringing (you can't have true sapience without learning almost everything from scratch). Call those that go through the metamorphosis as being in their S phase, for sapient.

However, in addition to the few young the parents choose to raise there would be other tadpoles that survived and were not chosen by the parents. Those tadpoles not picked by their parents stay in their original phase without the metamorphosis into sapience, call this phase T for tadpole. Lets say that the unpicked T phase tadpoles will continue to grow and develop without parental support. Those T phase young that survive long enough (and very very few will) eventually develop into full T phase adults and be capable of reproducing on their own. These T phase adults can mate, with both T and S phase adults, to produce young of their own, all while still not being sapient.

The idea is to have both R and K reproductive strategies in one species, so I'm imagining the parents put extensive effort into raising the few sapient phase children they choose, and put little or no effort into the remaining T phase children, instead leaving them to strive to survive on their own. Thus the parents benefit from both lots of young with little effort on their part, some of whom may manage to beat the odds and survive to reproduce, and also have a few carefully groomed children they will raise and ensure reach adulthood. They get the benefits of both reproductive strategies.

For that matter S phase parents who are not ready to raise children would presumably still mate and simply leave all of their children as T phase without choosing any to raise any to S phase. They get the freedom of choosing rather to favor R or K reproductive strategies based off of their situation (though if not enough choose to raise young as sapient phase your eventually end up with only T phase young).

The question is how to make such a species work. My biggest question is how to justify their evolving (the sapient phase being the harder part to justify), and justifying their having an evolutionary niche which causes this to be a stable reproductive strategy (ie they don't split into separate populations or evolve to be entirely S or T phase individuals). Any other suggestions about the physical and evolutionary implications of such a species, or even their evolutionary psychology, is always welcome but isn't required.

For the sake of this question lets assume that the creatures are sapient but have not reached the level of culture where they would start to use technology to alter or modify their evolved breeding behavior. For instance they won't yet have excess resources which they could use to take care of T phase children or be domesticating/raising T phase individuals, just letting them run wild.

Some things I can already guess are likely for what I have already described, you can skip the below if you want, or argue with any of it...

  1. There would have to be a large 'feral' group of T phase creatures. They are capable of breeding and expanding on their own even if they didn't have an influx of young coming from the sapient adults breeding. Many of the current T phase adults are not children of sapient adults, but of mated T phase individuals.

  2. Sapient adults must have a significantly higher reproductive success rate then non-sapient adults, to justify the massive energy and expense parents put into them when the parents could be investing in simply having more T phase children.

  3. There must be a way for the genetics of the T phase creatures to reenter the gene-pool of the sapient phase adults, otherwise speciation would occur quickly. I'm open to any suggestions for this to happen. The most obvious one that comes to mind is that sapient males that are unable to find sapient females to mate may choose to mate with non-sapient females and raise one or two of those as sapient children as a single father. Likewise sapient females could mate with T phase males, but that seems less likely. Presumably it would be considered preferable to mate with sapient phase adult since they were the pick of the litter as T phase children, and a mate would be able to better judge their biological fitness for producing sapient children if they are also sapient. Any other way to increase the gene flow between the sapient and non-sapient phase would be interesting to know, as I see this being the biggest hurdle in justifying such a mating strategy.

  4. They would almost have to have an evolutionary ingrained method of identifying their offspring, by sent, sight, sound whatever, in order to ensure they only pick children that are genetically 'theirs' to raise into sapient.

  5. They almost certainly started as R strategy non-sapient creatures, with the sapient phase coming later. Though how you justify a metamorphosis into sapience evolving is the real question.

  6. The non-sapient creatures are likely not very intelligent, R strategy animals are usually mostly instinctual and not quick learners. Despite the potential for metamorphosis into more intelligent species this does not mean T phase are all that bright. There likely also smaller for much the same reason.


One other complication to this being a stable strategy comes up. How do we keep the sapient males from constantly mating with T phase females and out competing their t phase counterparts? Presumably their sapient is a sufficient advantage as to make it fairly easy to compete with non-sapient males for reproductive rights. Two approaches come to mind.

First, that T phase males grow to be physically stronger then their sapient counterparts (possible because they invest less nutrients on brain power). This means it is not as easy for a sapient male to out compete with T male for mating rights. I don't like this as much it seems that a R strategy creature doesn't have any right to grow larger then a K strategy one. More importantly this would make it harder for T and S phase to mate and mating between them have to be at least semi-common for gene-flow reasons.

A solution I like better is to imply that males actually have a heavy investment in reproduction, equal to that of females. Perhaps in addition to fertilizing eggs they secrete some sort of nutrient rich substance which provides nutrition for the young during their early development. Thus both males and females have a non-trivial caloric investment in reproducing. They can still reproduce semi-often, perhaps as often as every few months, but both males and females have reason to be selective about mates because both have equally high investments into child production and limited mating opportunities.

  • $\begingroup$ Answered, but I could blab on about this kind of thing for a long time. If you want to be subject to such a terrible fate, I'm all for doing it in a chat. $\endgroup$ Commented Feb 12, 2015 at 6:35
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    $\begingroup$ An easy and clean way might be to introduce a parasite-like organism that helps transform to the S phase. You could even make this natural evolution as the parasite might kill off weaker individuals making the fact that Ts grow up to adulthood a biproduct of 'modern society' (Parents will control which of their offspring will be given 'the gift of sapience') $\endgroup$
    – dot_Sp0T
    Commented Feb 12, 2015 at 9:23
  • $\begingroup$ @plaugeheart honesty I think the idea is interesting enough that I could talk for awhile on it. Sadly finding time I'm free to talk for an extended timeperiod is hard lol $\endgroup$
    – dsollen
    Commented Feb 12, 2015 at 15:05
  • $\begingroup$ I know exactly what you mean on that. Let me know though; the chat here at least is very convenient if you can only talk for a few minutes at a time in bursts. $\endgroup$ Commented Feb 12, 2015 at 17:36
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    $\begingroup$ Consider how bees produce queens using a slightly different feeding and larvae housing regimen that allows the queens to develop ovaries and eggs. There's no reason a similar process couldn't be used to develop additional brain matter - perhaps the whole frontal lobe would be dependent on this sort of specialist diet and environment. Hopefully someone will flesh this out into a real answer... $\endgroup$
    – Adam Davis
    Commented Jun 28, 2017 at 17:58

6 Answers 6


Oh boy, lots of question here! Let me see if I can keep from going on for three pages...

So you asked:

How could they evolve?

My first thought is that they started out in a temperate or tropical environment that heavily favors r-selected breeding. Lots of food, great weather, some major predators that like to eat them but the carrying capacity of the environment is never a real limitation on their ability to reproduce like bunnies. Then something Really Bad Happens that destroys some but not all of this environment and makes it inhospitable for everything but the best-adapted life. While it gets most of the proto-critters in that area, it also wipes out their major predators, and perhaps introduces some kind of novel resource (a high-energy food, perhaps) that lets any slightly smarter proto-critter that wanders into there occasionally score a huge jackpot in the survival lottery.

Now let's make the phase transition between the really nasty wasteland and tropical bunny-town abrupt, but not at all impassible for the proto-critters and their predators. Some of them are going to keep wandering into the wasteland, most of them will die, but the extremity of the environment begins working on them. Proto-critters that survive the wasteland start getting progressively smarter, but can still wander back to the more temperate zone to sow their wild oats and thus keep gene flow going between the populations.

I think you could potentially see your S phase crop up among the wasteland-dwellers, in this scenario. They'd still be living in the nastier, more dangerous area in the present day, but they'd go back to the temperate one to breed, since the wasteland will kill off something like 99% of the T phase, versus the more "moderate" 75% that get culled in the temperate zone. This separates the S phase and the T phase out into two separate niches that they can uniquely exploit (T phases reproduce faster, S phases benefit from being less predated upon and having [some resource] out in the wasteland in relative abundance).

The ability of S phases to induce T phase development might show up later.

This is, of course, a just-so story, but a lot of evolutionary origin stories are.

Some other stuff

In no particular order...

  1. You might want to introduce some substance that adult S phases produce that induces transformation in T phases. Think of royal jelly in bees--it's fed to all castes of bee initially, but it causes a transformation into a queen in larvae that are continuously fed it through the mechanism of the protein royalactin. Actually, now that I think about it, this gives another evolutionary option for your critters: They used to be eusocial, but the reproductive caste actually evolved sapience (rather than just getting bigger and progressively more useless and reproducing all the time), while the non-reproductive caste got their gonads back. In this situation, S phases may actually exploit their non-sapient T phases to forage and feed them. Everybody wins. This wouldn't be domestication per se as it would be the exploitation of the old eusocial patterns--even though T phases can now breed on their own, they still have psychology that makes them congregate around a related S phase and share food.

  2. Ability to recognize near-kin through scent and other markers (perhaps genetically transmissible behaviors like fixed action patterns) isn't a really crazy idea, and it's already especially pronounced in eusocial species (because it lets them avoid having other individuals cuckoo into their nests--though it's not infallible). So it's completely plausible that S phases are very good at smelling out their own children, and it's also plausible that there are some S phases "working on" (i.e., evolving) a reproductive strategy that lets them cheat and get another S phase pair to raise their T phases to sapience.

  3. I think your idea of S phases breeding to T phases is actually a pretty good one for continued gene flow. Another option might be that S phases see their T phase grandchildren (great-grandchildren, great-great-great grandchildren), rather than direct offspring, as valid targets to raise into sapience. This works especially well if each S phase has some T phase that naturally congregate around it; they might notice one of their nth-generation descendants is already naturally very clever and decide to uplift it.

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    $\begingroup$ I particularly like your idea of eusocial culture being the basis for this species to evolve. However, I still feel like there may not be enough gene flow for a stable evolutionary niche. Your option 3 is possible, but anything beyond grandchildren and it seems like there would be too little shared genetics to benefit from upraising them. they aren't lacking kids of their own so there is little need for adoption. Maybe a reason why occasionally S parents would benefit from mating with T even if an S mate were available? Would T bring in genes that would help? maybe to prevent inbreeding? $\endgroup$
    – dsollen
    Commented Feb 12, 2015 at 15:02
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    $\begingroup$ @dsollen Yeah, I'm still chewing over that one myself. Inbreeding avoidance would be a good reason for them to outcross like that--perhaps T phase who are different enough genetically are more attractive than an S phase who's closer genetically. (But an S phase with very different genetics would also be very attractive.) So if they've got no particular drive to pair-bond exclusively (which having a higher parental investment for males would unfortunately encourage), they may have an S phase primary mate and a harem of genetically diverse T phases on the side. $\endgroup$ Commented Feb 12, 2015 at 17:30
  • $\begingroup$ @plaugeheart I agree with what you said and inbreeding would justify everything in my original post. The only problem is I keep thinking I want a large enough society of S phase to have interesting culture/science, and it seems that large a breeding pool minimizes inbreeding. I'm nay-saying my own idea because it works but hurts story telling options! Unless there is a way to justify strong culture while still having outcross being needed. Could different evolutionary forces encourage evolution of other traits in T phase that S still benefit from occasionally breeding into their pool? $\endgroup$
    – dsollen
    Commented Feb 12, 2015 at 18:31
  • $\begingroup$ @plaugheart another idea, what if only one sex was ever raised to sapience? That would ensure the two phases interbreed always and gene flow is constant. If so which sex would be raised to sapience (I assume males, generally you want your strong offspring to be male so they can better compete for mates and your weak offspring to be female because their always get mates). If that happens would the T phase males ever stand a chance to compete with sapient males for mates? does it makes sense for a species to upraise 2/3 male 1/3 female or any uneven division? $\endgroup$
    – dsollen
    Commented Feb 12, 2015 at 18:37
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    $\begingroup$ An Idea on the sexual dimophism thing. whey not have your offspring being 'hermaphrodite'. when these T types are raised into S types they become 'male' due to the extra attention. The remaining T will then loose the 'male' part of thier hermaphoditeness and become female. Now you have the opportunity of inteligence in both sexes, and the possibility that adult T females could decide to take care of some younger undifferenciated T. So now we only need something from the male that pushes differentiation to male S types, without wich the surrogate T female parents do not give rise to S males. $\endgroup$
    – DaveM
    Commented May 7, 2015 at 10:49

You say they will benefit from both reproductive strategies, but they will also bear the cost of both strategies. What justifies the huge up-front investment in producing a horde of offspring, as well as the long-term investment in a few?

If sapient members are superior, those who waste less on laying masses of eggs will dominate, eventually reducing the number of offspring to those it could care for into sapience. If non-sapient are at all fit for survival, they will quickly out-breed the sapient since far more non-sapient are produced (and non-sapient cannot produce sapient while sapient still produce primarily non-sapient). You say they are not resource constrained, but why would a species which reproduces so prolifically not rapidly fill up its territory? Eventually they will start competing for the same resources (food, nesting sites, mates), and just the sheer weight of numbers will eventually push the sapient into extinction (even if the sapient are completely superior on an individual basis).

If I could offer an alternative - the non-sapient are juveniles who failed to develop fully. Sterile, consuming little (no expensive brains or reproductive organs to feed), but performing some necessary contribution. They could be more brightly colored or noisy to distract predators (leaving the sapient more likely to survive), instinctively perform some useful task (building termite mounds) leaving the breeders to concentrate on breeding or raising young (eusocial behavior), or perhaps a very high rate of mutation just results in a lot of malformed individuals. The sentient adults choose the best of a generation to nurse - the selected ones get fed from parental secretions (only so many nipples to latch on to while the rest go off and tadpole), getting the right hormones to develop what will become the adult organs, while the gonads and brain are effectively vestigial for the non-sapient.

This gives you the mixed population without the species divergence problem, or the out-competing problem.

  • $\begingroup$ This is why I suggested in my answer that the sentients live in an environment totally inhospitable to the non-sentients--otherwise it is pretty likely one would outcompete the other due to reproductive strategy. They'd need to have separate niches (the disaster->evolution idea), or the sentients would have to have another way to control reproduction in the non-sentients (the former eusocial idea). $\endgroup$ Commented Feb 12, 2015 at 20:16
  • $\begingroup$ Blurgh. Sapient, not sentient. I know the difference between the words and I keep exchanging them. $\endgroup$ Commented Feb 13, 2015 at 1:29

Here is a possible scenario.

  1. The sentience is the result of symbiote/parasite that a large percentage of the host species is genetically immune/resistant to.

  2. The host species is prey for a larger pack-hunting carnivore.

Point 1 gives the sentient forms a reason to pick their own offspring (or that of another sentient) for "uplift", as most of the general population is not compatible. Leaving a portion of their offspring in the wild will keep the vulnerable genes circulating in the wild, just-in-case.

Point 2 gives a reason for the sentient form to deliberately not out compete the non-sentient form, as they can intelligently find a way to avoid/defend against the carnivores, so the non-sentient form is more likely to be preyed upon. This gives a reason for a large non-sentient/sentient population ratio.


First problem I have with this is the relationship between sapience and parental choice. Explaining this part to me is that hardest part.

The reason is, if a parent has to choose which children are 'raised' then how did the first 'raised' parent come about? Chicken and the Egg. Sooo I think you'll need to modify how sapience comes about. Maybe the parents keep the ones who appear to have that certain something? There could be a high death toll (like most animals that reproduce this way, fish, frogs etc.).

Maybe for what ever reason the genes are not quite as rigid as ours and so has a much wider range of possible outcomes, lots of chaff with the wheat. The parents would try and shift through and look for the 'best' to save, but others might make it with differing levels of intelligence, some debatable as too their actual sapience. Some could be a Tarzan, missed but develop just fine etc.

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    $\begingroup$ I kinda like the thought that some rare T phases would be able to bootstrap themselves into sapience. It does neatly answer the chicken-and-egg problem of where the first S phases came from if sapience usually requires induction (like through something like royal jelly). Perhaps it takes either an S phase-specific chemical substance OR a very rare set of environmental cues, and when the second case happens, you get your Tarzan S Phase. This is also the gist of Monty Wild's suggestion. $\endgroup$ Commented Feb 13, 2015 at 1:32

My take on this is that there is an unusual environmental trigger for transformation from T-Phase to S-Phase. It may be so rare that only a few T-Phases encounter it naturally and are transformed, but S-Phases are smart enough to recognise this substance and deliberately administer it. Perhaps they can also cultivate or mine it, whatever it is.

Anyway, there would need to be a trade-off in fitness with the T to S transformation. Perhaps this would require the growth of a larger brain, requiring the transforming T to eat more of a particular type of food, and if enough of this food could not be obtained, the transformation might abort or go wrong. Perhaps having a larger brain and no training would lead to inadvisable curiosity that would be more likely to lead to deaths than had the transformation not taken place at all.

This would mean that you'd have your necessity for training new S-phase individuals, rather than just selecting them all for brain expansion, and only training those you could handle.

  • $\begingroup$ I do like the idea there being an environmental trigger that can induce the change. $\endgroup$ Commented Feb 13, 2015 at 1:33

Assuming T and S phases have similar biology, spawning huge numbers of T phase offspring is going to create pressure on food resources for the S phases and the chosen few who are going to be metamorphosed. Not a significant stumbling block, but something to think about which will effect the social relationship between S and T phase populations.

Edit: Oops this is really old, and someone said this already. I like the idea though. Any progress on it?

  • $\begingroup$ Welcome to world building. I appreciate your interest, your always welcome to answer on old questions. However, for the record, something like this should be done as a comment to the question, not an answer, since it only elaborates on the problem, without a solution. As to your question, no sadly not enough. I still like the idea and have every now and then jumped back to it, but as of now the big hurdle is lack of gene flow from T phase back to S phase to prevent specization. I have a question linked to this addresing that with some good ideas, but it's still not enough IMO $\endgroup$
    – dsollen
    Commented Jul 21, 2017 at 18:55

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