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Let's say that around 4-5 million years ago, members of the earliest proto-humans, maybe Australopithecus, get whisked away to another habitable planet/parallel dimension - doesn't matter how at this point but let's say they got there.

I want these Australo-dudes to take a divergent evolutionary path than the one that led to the Homo species (as far as I understand). Furthermore, I want them to develop the following characteristics/physiology:

  • I'd prefer that they keep their humanoid shape, but they don't have to - I'm leaning towards an almost squid-like body type but with some form of quadraped locomotion maybe 12-15 feet long
  • They lose their fur and develop a smooth exoskeleton and a kind of crest on the head - think kind of like the xenomorph from Alien
  • They develop four tentacles that they can use as additional limbs and as weapons
  • They are mostly blind but have some sort of extrasensory perception - perhaps echolocation or the ability to detect vibration from moving bodies
  • They are sensitive to sunlight and prefer the dark
  • They can move fast, reaching top speeds of 40-50 km/h

What kind of environment/atmosphere/catalyst would lead a primitive humanoid to evolve into the creature I'm proposing?

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    $\begingroup$ they keep their humanoid shape, but have tentacle and exoskeleton? $\endgroup$ – L.Dutch - Reinstate Monica Oct 19 '19 at 4:53
  • $\begingroup$ @L.Dutch edited for preference $\endgroup$ – Faz Oct 19 '19 at 4:59
  • $\begingroup$ I don't think it’s possible naturally. You need too great a degree of change in too short a period. The time period you mention is similar to the time it took for chimpanzees and humans to diverge from their common ancestor. $\endgroup$ – Slarty Oct 19 '19 at 7:58
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Certain aspects of an organism evolve very quickly, others very slowly. 4-5 million years is not enough time for all of these changes.

Things that can happen in that time frame would include:

Developing quadrupedal locomotion: Environmental factors that favor speed over manual dexterity could easily make this happen. A human will probably not get to feline like speeds in such a short amount of time, but perhaps something more akin to bear or elephant locomotion is doable. Since both can top out at ~40km/h, this is plausible.

Growing to a large size: 12-15 feet is about the maximum size for a mammal, but it might be doable with strong enough of environmental factors, that said, animals that big tend to struggle with top speeds.

Lose their fur: No mammal has ever truly lost all of its fur/hair, but it could become mostly hairless like a whale or a homosapien.

Develop a crest on the head: This could be the result of a single mutation, but for it to spread through the population, it will need to serve some aspect of survival such as acting as a form of natural armor to help protect the brain, or to increase surface area for stronger jaw muscles.

Mostly blind but have some sort of extrasensory perception This is a common evolutionary feature of creatures that live in caves or at ocean depths greater than 150m. Animals that evolve in these circumstances often become albino which would make them sun sensitive.

It is very unlikely that you would see this feature evolve alongside many of the other features:

  • If your proto-human is cave dwelling, then it will benefit more from bipedal locomotion and smaller size so it can continue to use its hands for climbing and be able to fit through narrow spaces.
  • If it became aquatic, it would still need to spend enough time near the surface to get air; so, it probably would not lose its eyesight. It would also begin to look like a sea lion or dolphin meaning it would not become quadrupedal, and certanly could not do 40kph on land.

That said, many mammals already have the potential for echolocation, but only a few species do it instinctively.

Things that can not likely happen in that time frame would include:

Squid-like body type/tentacles/smooth exoskeleton: This would take more like 500 million years. Primates are vertebrates, and you are asking about invertebrate features. Endoskeletons and Exoskeletons are two completely different solutions that nature found to the same no-skeleton problem. Once an evolutionary chain has solved that problem, it's not going to go back on 500 million years of success to start experimenting with a completely new solution when it has one that already works. It would simply take too many generations of being disadvantaged by intermediate features for evolution to cross that gap.

Best Case Solution: Convergent Evolution

In nature, there is a thing called convergent evolution which is where two unrelated creatures evolve to have similar features. One solution to this problem is to have an Octopus evolve to have human like features. It's genome already has many of these adaptations. An amphibious octopus may have evolved a sturdy exoskeleton to help it stand outside of water. Over time, its need to outrun terrestrial predators cause some of its tentacles to fuse into fewer and stronger appendages so it can run faster. Still being slower than most predators, it turns to the trees to live like a monkey. Here they develop whatever monkey/human like features you want them to have from evolving under the same niche. It can begin forming language, tool using, whatever. It may retain under developed eyesight from its ancestry of being a deep sea creature, it just never got better because it's always solved that problem with echolocation. Over time, it's natural forest environment begins to disappear and it needs to adapt to life on the ground. From here evolution pushes for a bigger and bigger body to make sure that it is too big for predators (much like an elephant.) In the end, you get the creature you are looking for, but it just didn't evolve from proto-humans at all.

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  • $\begingroup$ The function of the crest on the head can also be to attach powerful jaw muscles to. Some early hominids did really have such a crest on the head. $\endgroup$ – Yellow Sky Oct 19 '19 at 15:14
  • $\begingroup$ If I increased the time frame, would it be possible? Let's say I go back even further, 20+ million years to some of the earlier primitive primates like Victoriapithecus/Kamoyapithecus etc.? $\endgroup$ – Faz Oct 19 '19 at 18:21
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    $\begingroup$ More like 500 million years... primates are vertebrates, and you are asking about invertebrate features. Endoskeletons and Exoskeletons are two completely different solutions that nature found to the same no-skeleton problem. Once an evolutionary chain has solved that problem, it's not going to go back on 500 million years of success to start experimenting with a completely new solution when it has one that already works. $\endgroup$ – Nosajimiki Oct 21 '19 at 14:47
  • $\begingroup$ If the ‘crest’ exists to anchor muscles, it'll look like a bird's breastbone: hidden. $\endgroup$ – Anton Sherwood Nov 22 '19 at 18:09
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I wouldnt say impossible, but to achieve such drastic changes in the physiology you would need environmental conditions that change rapidly and very deliberately, and therefore less convincing that it was natural. You'll need several periods of rapid expansion in population and diversity of phenotypic qualities, followed by periods of highly selective stressors that weed off competing genes from expressing themselves. This cycle would need to happen often which again would suggest its deliberate and not natural. In the end the genetic makeup of this species would be so different there would be no way to connect their ancestry without physical evidence of these changes such as through fossils. The only evidence in their genes would be its base pairs, and it would only strongly suggest that they may have originated from the same world, but never without a doubt.

To increase height, warmer conditions could act as a selective pressure, and lighter gravity would permit them to grow without hindering their health.

Heat could also pressure loss of hair, or combined with sexual preference you could also explain the crest on the head.

The exoskeleton could be a gradual process where periods of high radiation kills off the individuals with lesser protection, followed by periods allowing the population to grow and mutate genes with higher radiation protection. However, if these populations have adequate housing, this really wouldn't be an effective way to enforce the genes we want.

The tentacles are an extreme change since they also have to be functional. This would probably require a stressor as soon as these people were transferred over, and it would probably be closer to extra pairs of arms rather than tentacles.
Any form of mutation that occurs should not hinder the reproductive success of the individuals, so if these individuals get shunned for these extra limbs they will not survive to pass on their genes. A lot of things need to happen physically and culturally for this change to pass on, and even more for it to become the only expressed form of the population's genes.

Bottom line is, whatever conditions you come up with for explaining your evolutionary path they will still seem farfetched or deliberate, especially after the fact that they have been transported to a new planet.

If that is not a problem, then you could introduce the tentacles as a genetic edit, and their survival through an exalted status within surviving cultures.

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