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I'm working with this alien race that looks and functions essentially like a mammal - skin, muscles, hair, internal bones, large size, etc. - but evolved from an insect or other bug. They're a large, about human sized, very territorial ambush predator species, and their planet is about Earth sized, filled with many unpredictable dangers such as predators and even carnivorous plants.

So far my only ideas as to how they'd acquire skin and an internal bone structure would be for their chitin to fuse together so they can become more flexible and chase faster, more agile prey, while their exoskeleton retreated to become an endoskeleton while still being made out of thick chitin, of course.

Mammalian traits that are not required: Live birth, warm bloodedness, and milk producing abilities.

Is this possible? And if it is, why would my creature evolve like this?

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    $\begingroup$ Mammalians are called like that because they have "mammae", which in Latin are breasts which, guess what, are used from the females to produce milk to feed their progeny. $\endgroup$ – L.Dutch - Reinstate Monica Dec 8 '19 at 19:58
  • $\begingroup$ I guess you have a point, but I didn't really have anything else to compare what I'm going for to. $\endgroup$ – FelisMiscellaneous Dec 8 '19 at 20:13
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    $\begingroup$ Insects are a terrestrial life form. Absolutely certainly an extraterrestrial species did not evolve from insects. (And anyway, insects are a very highly specialized class. You probably want your aliens to evolve from something more basal in whatever is the homologous alien phylum to our arthropods.) $\endgroup$ – AlexP Dec 8 '19 at 21:19
  • $\begingroup$ Oooh, arthropods. I like that idea. $\endgroup$ – FelisMiscellaneous Dec 8 '19 at 21:23
  • $\begingroup$ @FelisMiscellaneous : Although your idea does not work in hard SF, it does work for stories if you have some handwaving and don't focus on it too much. I suggest that you read the Prince Roger series. It is semi-hard, uses your general idea, and is a very interesting series if you can get over the cussing. $\endgroup$ – Marvin the Paranoid Android Dec 8 '19 at 23:19
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Yes, the scientific term for this is convergent evolution.

To be clear, we need a lot of different things in order to make this happen. We are talking about an extreme case of convergent evolution that probably takes hundreds of millions of years to happen.

In fact, a much shorter round-trip would be from mammal to ferocious insect-like mammal instead. Even just evolving into this insect/mammal monster directly from the dawn of time would be a shorter evolutionary trip, than the one we are talking about.

However according to the concepts of evolution, and as a thought experiment, moving from an insect to a mammal-like creature is possible.


Proof of concept: We need lots of different evolutionary pressures over a very long time

Evolution gives us the steps to change an organism's phenotype/morphology into something else; we just need to manipulate what traits give a species evolutionary fitness. In layman's terms, we need to influence what features are being passed down, so that we can control how the species changes over time.

We can do this by altering the organism's environment. This is very easy to do with artificial techniques like selective breeding. However on an alien planet we either need a lot of luck to make everything line up the way we want, or play god and do it manually:

If done manually, a super advanced civilization could theoretically make this happen in a lab. Or also planetwide with precision terraforming. However a lab would likely be hundreds of times faster, because we have more control. For example in a lab we could simply sterilize all the organisms that don't have the adaptations we want; thereby speeding things up.

In our case we have an uphill battle to first remove certain traits, before adding new ones. We need to lose useful traits like exoskeletons, and gain seemingly useless traits like looking like a mammal. The only way that this can happen is through shaping. Shaping is the incremental change of a thing, and after enough time and enough incremental changes we finally arrive at our destination (looking like a mammal).

In our case we would first need to gradually create an internal skeleton for our insects, and then gradually soften their exoskeletons into skin. After that we need to (again) gradually change their physiology into the shape of mammals.

This process could very well take a billion years, even in an environment that we have explicitly crafted for this purpose. It would be faster in a lab, but this still going to take a very long time.


Other considerations:

There is also one more very important thing to consider that I am sure you have not. Which is that after going through all these processes, will the insect even be an insect anymore? If it looks like a cow, moos like a cow, and acts like a cow. Well...it might not genetically be a cow... but it certainly isn't an insect anymore. Insects would just be a distant ancestor of your new species.


Conclusion:

Yes it is possible, but it is not straightforward and the outcome might not be what you actually want.

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  • $\begingroup$ Why the downvote? This is factually possible. $\endgroup$ – Tyler S. Loeper Dec 10 '19 at 15:31
  • $\begingroup$ convergent evolution is not going to change basic developmental aspects of an organism, like having exoskeletons. $\endgroup$ – John Dec 10 '19 at 15:31
  • $\begingroup$ Convergent evolution can change anything. Including removing an exoskeleton. There is no such thing is a limitation on evolution, except for some limitations on what biology itself can accommodate (for all species. For example the maximum size of the nervous system because of limitations on impulse speed). $\endgroup$ – Tyler S. Loeper Dec 10 '19 at 15:32
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    $\begingroup$ But it can go back to the drawing board. You can read about it right here (en.wikipedia.org/wiki/Evolution_of_biological_complexity). I can even tell you right now in general terms how it can happen; (1) new environmental pressures favors having a more robust internal structure (skeleton). Then (2) environmental pressures favors a softening of the exoskeleton because something is causing it to no longer be advantageous. And done. Now you have skin and a skeleton. $\endgroup$ – Tyler S. Loeper Dec 10 '19 at 15:40
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    $\begingroup$ evolving an internal skeleton is no the problem, reworking every muscle, their entire breathing system, chitin growth mechanism (chitin can't be reabsorbed like bone) , and most of their sensory organs all at the same time is the problem. once you have an exoskeleton that supports your musculature and sensory you can't loose it without loosing them as well. you are talking about a frame shift of unimaginable scale. the only way for this to occur is for insects to essentially de-evolve for hundreds of millions of years until they are basically worms again. $\endgroup$ – John Dec 10 '19 at 15:51
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Extremely unlikely.

Let's take a step back and analyze your question.

Can an insect evolve to look and function like a mammal?

What does it really mean? If an insect evolves into functioning like a mammal, that means it's filling a niche that was occupied by mammal-like creatures. So the real question is, what happened to those mammal-like creatures in your world? There are two possible scenarios:

1. All large land dwelling mammal-like creatures died out due to some catastrophe.

We know that this is entirely possible, from our own history. But, it's highly unlikely that there was an event that wiped out all land-dwelling creatures, unless it was a selective event by an intelligent race of aliens (or even a god-like power if you're in Fantasy territory). Assuming it's not, then it's highly unlikely that any single event can wipe out all such animals. And we know that what can happen if all of them are not wiped out; take a look around.

There's nothing really preventing you from going from an insect to developing internal bones and such, but it's such a drastic change that it will take much longer for it to happen than the time it will take for smaller species to fill that niche. Once they evolve to fill it (like on Earth where small ancestors of mammals took over from Dinosaurs), that nice is gone, and so is the evolutionary pressure (or incentive) for insects to turn into mammal-like creatures.

2. There never were land dwelling mammal-like creatures

Sure, insects were there long before the first fish jumped out of the water. But that's kind of the point too; it was easier for fish to walk on land and evolve into all the land animals we have today before insects actually filling that niche. Again, the point is time. It is such a fundamentally big change that for all practical purposes it's impossible, because well before that can happen other things can come in the way.

So, I'm afraid that your scenario isn't really possible.

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So if I'm understanding your question correctly, you are asking whether or not a creature that originally had an exoskeleton can evolve to have an endoskeleton and other such features.

Short answer, possibly.

The reason such an evolutionary event did not take place on our world is that before such highly improbable evolutionary changes occurred, our amphibian ancestors started to walk on land and munch on the ancestors of insects. This caused a great deal of competition which relegated exoskeleton users to having no probability of evolving 'mammal' like traits.

In short, the insect like creatures of your world would need no competition to evolve in the first place. How this comes about can be for you to decide.

As for how they would function...well, I posted a similar question to yours here:Can insects evolve their basic anatomy to grow in size? hope it helps. And Welcome to Worldbuilding!

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  • $\begingroup$ Oh man, thanks. This is probably the most useful answer I've gotten, so uh, thanks a lot. Again. $\endgroup$ – FelisMiscellaneous Dec 9 '19 at 0:55
  • $\begingroup$ Well, I try my best. $\endgroup$ – Seraphim Dec 9 '19 at 1:12
  • $\begingroup$ But there is at least one example of convergent evolution between insect and bird: the hummingbird and the hummingbird moth: fs.fed.us/wildflowers/pollinators/pollinator-of-the-month/… Of course the insect size limits still apply, but you could probably evolve an insect to resemble a mouse. $\endgroup$ – jamesqf Dec 9 '19 at 4:21
  • $\begingroup$ @jamesqf, While your example on convergent evolution id true, it not the subject that being discussed. I was talking about the physiological differences like respiratory and skeletal systems and how they could change to increase in size. $\endgroup$ – Seraphim Dec 9 '19 at 4:31
  • $\begingroup$ @Seraphim You might consider adding an important quote or two from your linked post, if there's something of particular relevance. $\endgroup$ – thanby - reinstate Monica Dec 9 '19 at 15:28
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It doesn't matter, you can have what you want anyway becasue you are talking about ALIENS they are not insects they are not mammals.

You just need to layout what characteristics you want them to have and ask if THAT can evolve.

You don't need to turn earth life in another form of earth life. It adds nothing unless you really want them to evolve from earth life that somehow got transported to that other planet. Alien life is not going to have the same evolutionary baggage earth life has, It is not going ot find the same solutions to anatomical issues. Alien life will have a unique combination of characteristics. asking it this way shoehorns earth evolutionary baggage into it making it a much more difficult question for no benefit.

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  • $\begingroup$ No its not, evolutionary baggage is a thing, it is the reason giraffe have a nerve 14ft long to travel a distance of 2 inches. features get locked in developmentally as new features evolve "on top" of them. Drastically reworking those features requires the loss of all the features they support, in the case of insects that would be things like limbs and eyes. $\endgroup$ – John Dec 10 '19 at 15:35
  • $\begingroup$ @TylerS.Loeper I'm just removing any mention of whether it is possible since it is not relevant to answering the question. $\endgroup$ – John Dec 10 '19 at 16:00
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    $\begingroup$ @Muuski, it's called the laryngeal nerve. You can Google the term, or this is really cool if you wanna watch: youtube.com/watch?v=cO1a1Ek-HD0 $\endgroup$ – Sach Dec 10 '19 at 17:54
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    $\begingroup$ Be advised it's a scene inside of an operating room. $\endgroup$ – Sach Dec 10 '19 at 17:54
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    $\begingroup$ yeah the history of the laryngeal nerve is weird, basically in fish (which have no neck) the heart is in front of hte nerve and as the heart descended into the torso the nerve is forced to take a longer and longer route to go around it, at each step making it longer is more advantageous, this adds more and more baggage to its developmental pathways until at this point the only way back would be too large a step, involving the right random change so many developmental pathways at once that it is more likely they would loose the nerve entirely which would be a big disadvantage. $\endgroup$ – John Dec 10 '19 at 18:47
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One drawback with exoskeleton is molting each time a stage in growth is completed. One thing for sure, the new exoskeleton must harden after the old one sloughs-off. In the mean time, the exoskeleton is too soft to carry the weight and is vulnerable to attack. For small insects, it is not such a big deal. For larger creatures, getting into the water is one way.

If you want a way to work around the problem, your bug's exoskeleton can be made-out of "plates" much like those of a tortoise shell: the plates can grow at their peripheries without the drawbacks of molting.

The second issue is lungs: Earth's bugs have tracheas, which are "air conduits" running from the "skin" all the way towards the center. Important junctions may increase in size into "sacks" which will serve as lungs. Inner tissues may become rougher to increase surface area and then become like gills or lungs. The imcreased surface area allows better gas exchange and allow the creature to grow larger and stronger.

Now, it is not easy to think how an exoskeleton may turn into an endoskeleton. I can imagine that a mutation may alter growth pattern to make the plates grow inward as well. If the part that grows inward connects a muscle, it may act as an endoskeleton. On the other hand, the exposed parts of the plates holn no role in skeletal support. They become incomplete and remain as cartillage. The cartillage is soft and flexible and acts as skin instead.

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GMO SF Magic!

Have your creatures be the descendants of bioengineered insects. Space travelers visited Earth in the distant past, admired the insect life, and collected specimens which they bred / engineered into servants or food animals or warriors, or all of that.

You could have an endoskeleton in the same way cephalopods have modified the molluscan shell into an internal pen.https://en.wikipedia.org/wiki/Gladius_(cephalopod) Like the squids your creatures could have a soft body like a maggot around a firm internal structure derived from the exoskeleton.

If something seems unlikely to evolve that can be the engineered piece. If you want something to have evolved you can make that happen over the several million years since specimens of this species escaped their creators. Or overthrew their creators: the heartwarming story of the shoggoths!

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  • $\begingroup$ 'the heart warming story of the shoggoths'...yea, sure, I can...kinda see that...yea? $\endgroup$ – Seraphim Dec 9 '19 at 19:05
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I'm sure arthropods could theoretically evolve to be mammalian via convergent evolution.

There are already some instances of that in our world! -Tarantualas do look somewhat mammalian due to their fur. -Bees make honey and wax from their bodies which is somewhat like milk. -Crocodiles have a kind of semi-exoskeleton, so an endoskeleton could evolve in an invertebrate. (Yes, crocodiles aren't insects, but you get the point)

Perhaps via: -an ice age to trigger more fur and warm-bloodedness -larger size to encourage the growth of an endoskeleton -colonial/child-bearing behavior

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