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Many mythological humans vary in depictions. Let's use Trolls from Scandinavia as an example. Some are said to be giants compared to humans (I'd imagine twice the height), and some, like Danish Trolls, are said to be the same height or smaller than humans.

enter image description here

Same for other big species such as Ogres, Cyclops, and Orcs. They can either be twice the height as humans, or the height of a child. Considering the necessities of animals being huge (bigger heart, higher blood pressure,thicker limbs,etc.) How could a species biologically evolve and exist with such varying heights without Darwinism being in the way?

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    $\begingroup$ Galileo proved that giants could not exist, by using the square-cube law. What is that you don't find satisfying in his reasoning? $\endgroup$ – L.Dutch May 8 '18 at 13:22
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    $\begingroup$ @L.Dutch: T. rex apparently stood 12 feet tall at the hips, which is well within the range suggested by the OP of twice human height. $\endgroup$ – nzaman May 8 '18 at 13:34
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    $\begingroup$ @nzaman, because it evolved to reach that size. But there was no T.Rex twice that size, because it would have weighted 8 times its original weight with bones just 4 times more resistant (Galileo's proof) $\endgroup$ – L.Dutch May 8 '18 at 13:37
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    $\begingroup$ @L.Dutch: But that does not prevent another species in the same genus evolving to be a mere 3 feet tall, with proportionately lighter bones $\endgroup$ – nzaman May 8 '18 at 14:02
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    $\begingroup$ Yes, we call then humans. $\endgroup$ – Vincent May 8 '18 at 15:46
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If we look at the range of human sizes recorded today: We have Robert Wadlow ad 2.72 meters and Chandra Bahadur Dangi with 0.55 meters, So Humans are already appearing with a variation of 1:5

If we look a a species apparently more prone to genetic variations: Smallest dog I could find is the chihuahua starting at 0.15 m shoulder height to the Irish wolfhound of 0.9 m we get to a high variation of 1:6

So you´d really need to invent anything, just make the variation genes a little bit more unstable to get a more common spread of the extreme small and big specimens.

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    $\begingroup$ even human populations have a wide range, male Efé average 142cm while the average male in the Tutsi average 182cm. keep in mind diet and quality of life can have a big impact on this as well. your average netherland male is 184cm. $\endgroup$ – John May 8 '18 at 14:43
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    $\begingroup$ Also consider the Pygmy Mammoth: en.wikipedia.org/wiki/Pygmy_mammoth $\endgroup$ – superluminary May 9 '18 at 15:04
  • $\begingroup$ However, dogs are maintained (by us) in a state of differentiation which is arguably unlikely to persist over millions of years. To be crude, dogs have never invented ladders, so a male chihuahua and a female wolfhound are going to have...problems. In consumation. If you know what I mean. And the other way around is almost certainly going to produce an intermediate pup too big for the mother to bring to term. Of course, a size spectrum which is the equivalent of ring species is possible. $\endgroup$ – WhatRoughBeast Feb 12 at 17:36
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No need to go purely mythical for your reseach. Have you looked at any real hominid species for inspiration?

Homo florensis is a, now extinct, hominid species. It is theorised that they had an average height of 1.1 m. It has a nickname of "the hobbit" and was actually almost named Homo Hobbitus.

It is not in our direct ancestry but is rather a cousin, existing at the same time as some of our own taller ancestors. It was even initially thought to have existed at the same time as modern humans, but further date-testing pushed the date back.

Some of our older ancestral cousins, Homo australopithicus were only around 1.4 m, but still occassionally used both hands and feet for walking. But that was quite awhile ago.

Homo neanderthal was about the same height as modern humans, if not slightly shorter. Cro-magnan was also about the same height as humans. Both existed at similar times to our older Homo sapien ancestors. If you had provided the same healthy diet that we have now, it can be argued that they could be taller than modern humans. (I think it more logical to have them as the basis for your giants rather than tall and slender elves. I think I'm being a bit speciest).

I found this helpful, not entirely accurate image, on quora of Hominid height development. The second image from the Natural History Museum gives a better sense of when the different species overlapped. You can see immediately that several "species" (see main edit) of hominid existed around and at the same time.

Hominid heights enter image description here

MAIN EDIT: Our research into our hominid past is still incomplete. As such we often are basing entire new species on incomplete skeletons. We could quite possibly be measuring intra-species variation as entirely different species by accident/incomplete data. We can successfully interbreed with several of the other hominid branches, eg cro-magnum and Neanderthal etc. (many Homo sapiens have H.neaderthal DNA in them).

Darwin did not know about genes and genetics.

Non-Darwinism does not deny or dispute common descent or the fact of evolution. It is only concerned with denying or downplaying the "Darwinian" mechanisms of evolution, such as natural selection or sexual selection.

Because of this, you can still use theories of genetic drift and isolation to explain your geographically distinct Giant and Troll characteristics. So tall Giants in one area and short Giants elsewhere. These different Giant tribes could still interbreed and could technically be considered the same species.

If you happen to provide a hearty mead and protein sources for some of your Giants and not for others, get some of your dwarves to live somewhere else besides those dank caves, and give some of your orcs some medical care, this could also explain some of the smaller height discrepancies.

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  • $\begingroup$ I think those heights come from darwinistic evolution. The OP is asking for nom-darwinistic approaches. $\endgroup$ – Renan May 8 '18 at 16:02
  • $\begingroup$ @Renan I had a quick peek at the definition of non-darwinism. From rationalwiki.org. From what I can gather, because darwin didn't know about genetics it can be argued that all genetic mechanisms could be considered non-darwinism. Even though, neo-darwinist synthesis has reconciled genetic mechanisms with Darwin's natural selection. Therefore, genetic drift and isolation, which is the primary theory on H.florensis height and dwarf characteristics could still hold true for the OPs wide ranging giants and trolls etc. $\endgroup$ – EveryBitHelps May 8 '18 at 16:14
  • $\begingroup$ @Renan it's all abit confusing. Especially when we have several hominid species that did successfully interbreed repeatedly with each other. Modern homo sapiens have a fair bit of neanderthal in them. So for this question I think it's still fair to discuss interspecies height differences as it could provide inspiration. It's not like tigers and lions creating ligers and tigons who have difficulty interbreeding. It could be that we have defined various hominid species based off eg a single jawbone, when it is in fact just natural variation within the species. $\endgroup$ – EveryBitHelps May 8 '18 at 16:18
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    $\begingroup$ @EveryBitHelps Being from the field, I can assure you that there’s iron-clad consensus, and there’s no confusion about it whatsoever. The page you’re quoting is describing pseudoscience (that’s the whole point of RationalWiki), and it’s doing so in a somewhat confusing way. $\endgroup$ – Konrad Rudolph May 9 '18 at 10:31
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    $\begingroup$ @EveryBitHelps Well the idea of the that wiki is to explain pseudoscience, and why it is bad (hence the “rational” in the name). They are firmly on the science (rather than the “pseudo”) side. That said, RationalWiki does have a reputation for bad editorialising and making confusing statements. Wikipedia is generally a better resource. $\endgroup$ – Konrad Rudolph May 9 '18 at 10:35
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You specifically asked,

How could a species biologically evolve and exist with such varying heights without Darwinism being in the way?

From this, I am assuming you mean a single species having variations in size, versus a range of related species being different sizes (but the similar sizes within each species).

First, we can answer a broader question: Is it possible for a single species to produce individuals of varying size (on the order of 2x difference in size)?

The answer to that is definitely yes. There are lots of examples: for instance, Canis familiaris domestic dogs. A single species with at least the same variation in size as the trolls you're asking about. In this case, the variation was basically due to human meddling by selecting genetic patterns to emphasize a specific desired trait.

Of course, as you pointed out, the species needs to be able to support the size range (ie heart size, bone strength, etc). It's hard to answer this for a mythical species since we don't have an actual physiology to study. Further, it's hard to address the reasons why a mythical species would develop such different size ranges in sub-populations, but the good news is, you have a template to go on (the trolls you mentioned) and enough leeway to develop your own answers as part of your storyline.

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If we do not hold tightly to genetics, (or simply have several gene combinations result in a wide variety of sizes), it is simple to have a species with that trait.

The primary problems with such a variance come from the difficulty of interbreeding between the different sizes.

For example, a Chihuahua and a Great Dane can interbreed, but the mechanics of the act itself may be difficult and awkward, and a female Chihuahua likely couldn't bring a Great Dane mix to term.

Here are 3 ways to address the 2nd point (carrying to term).

  1. The smaller female's system (hormones, etc) naturally prevents a fetus from growing too large during pregnancy.
  2. Your trolls are, or are similar to, marsupials. The children are born very small, and continue to grow and develop externally.
  3. Your trolls lay eggs. The size of the eggs is fairly uniform across the species, so may appear quite small when compared to the larger trolls.

Here are 2 ways to address the 1st point (the act).

  1. Your trolls make use of external fertilization, such as fish might use. They may build dams to create beaver-style ponds for this.
  2. Your trolls make use of entirely non-biotic means of reproduction. Perhaps two trolls must gather and consume a large amount of clay that they regurgitate (or otherwise excrete). Then together they sculpt this into their child, adding stones, seeds, gems, etc, as well as a portion of life energy, as they craft it. The size, shape, and appearance of their child is entirely based on how much clay they gathered and what form they give it.
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  • $\begingroup$ Marsupials are real? $\endgroup$ – SK19 May 8 '18 at 21:59
  • $\begingroup$ @SK19 I hate to break to you, but marsupials are a myth perpetuated by us Australians. I mean, seriously, giving birth to an undeveloped foetus, which then crawls into a specially evolved pouch? Come on! The most famous is the Drop Bear which kills hundreds of unsuspecting American tourists every year by dropping on the tourists' heads as they walk under trees. $\endgroup$ – CJ Dennis May 9 '18 at 1:33
  • $\begingroup$ @CJDennis Ah, alright, I just confused them with Marsupilamis en.wikipedia.org/wiki/Marsupilami $\endgroup$ – SK19 May 9 '18 at 1:42
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    $\begingroup$ @SK19 Ooh! Next time I go to France I'll have to see if I can pick some up! $\endgroup$ – CJ Dennis May 9 '18 at 1:51
  • $\begingroup$ @CJDennis You can't fool us. We all know that Australia itself is the myth. Even if there was something on the bottom of the world, anything on it would just fall off. $\endgroup$ – Michael Richardson May 12 '18 at 13:36
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Sure.

elephant family comparisons https://homero13.deviantart.com/art/All-species-of-Mammuthus-446196499

bears smallest to largest https://serchio25.deviantart.com/art/bear-species-73640712

sauropod size comparisons

There are plenty of examples of animal lineages in which species show the size range you want and greater. Bears are the closest to actually exhibiting the size range of the trolls you ask about. Elephants show an even wider range and sauropods an immense range.

As regards Galileo and square-cube law (and I could not find Galileo's exact words on the subject) - it is true. But just as one can demonstrate the possibility of a human lifting 600 pounds by locating a human and having him lift 600 pounds, so one can demonstrate the possibility of giant animals by locating giant animals.

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  • $\begingroup$ The question pertains to a single species – i.e. all members are able to interbreed, from the tallest to the shortest – rather than a lineage or genus. $\endgroup$ – rek May 8 '18 at 14:11
  • $\begingroup$ @rek I didn't know giants could interbreed with trolls or ogres? :) I do get your point... $\endgroup$ – EveryBitHelps May 8 '18 at 14:23
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    $\begingroup$ @rek Technically a Chihuahua and a Great Dane can interbreed. The mechanics of the act itself may be awkward, and a female Chihuahua likely couldn't bring a Great Dane mix to term. $\endgroup$ – Michael Richardson May 8 '18 at 16:25
  • $\begingroup$ @MichaelRichardson The examples in the answer above are not comparable to breeds of dog, they are distinct species. $\endgroup$ – rek May 9 '18 at 22:10
  • $\begingroup$ @rek Generally, yes, though there are reports of mixed Polar/Brown bear animals. My comment was more a counter example, showing that a single species can have a wide range of sizes without needing to resort to animals that simply look similar. $\endgroup$ – Michael Richardson May 12 '18 at 13:42
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Possibly the different types of trolls could be members of the same species at different stages of life. Trolls could change their appearance radically between each life stage, the way caterpillars turn into butterflies, as well as suddenly growing much larger each time.

Note that a typical human will grow about four to six times taller during their lifetimes, and some have grown much more than that.

A newly hatched crocodile might be only one foot long and grow to be 15 times as long and about 3,375 times as massive.

Newly hatched sauropod dinosaurs would be curled up in their eggs before hatching, and still could not be more than a few feet long when hatching, judging from the largest known dinosaur eggs. But depending on their species, they might grow to be more than 15 times, longer. A four foot long baby that grew to be 80 feet long would grow 20 times longer and 8,000 times as massive.

And some Sauropods grew much bigger than that.

If the legendary and controversial Amphicoelias fragilimus and bruhathkayosaurus were as big as the largest estimates, adults could possibly have been forty or fifty times as long as newly hatched juveniles.

So it is easy to believe that the different stages of the troll life cycle could be less different than tadpoles and frogs, and range in height by a factor of only four or five.

Note that many human children can walk and run well by the time they are two feet tall, and the tallest human was almost 9 feet, or 4.5 times that tall. And there was allegedly a prehistoric man over 11 feet tall judging from his leg bone.

The tallest living and prehistoric bears could rear up and walk on their hind legs for a time, at heights of 10 to 15 feet.

The extinct ape Gigantopithecus blacki is sometimes believed to have been bipedal and 10 or 12 feet tall.

A large elephant can rear up on their hind legs and tower about 20 feet tall. And a large circus elephant was taught to walk on his hind legs for hundreds of feet.

Prehistoric giant ground sloths could stand up to a height of about 20 feet, partially supported by their powerful tails.

Thus if the trolls change their shape a bit every time they morph into a larger stage of life, they can have a size range much larger than you probably need.

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Isolate the populations, add in different cultural preferences for mate selection, wait a bunch of generations, vastly different sizes.

Expanded; in group A women only allow the tallest men in their generation as mates. In group B the women only allow the shortest to mate. (Or the men selecting, there are cultures that do each, doesn't mater). Much time passes. The populations start adjusting to this preference and over time the heights change.The reasoning for the preferences are up to the author and can be either part of the plot or just along the lines of 'eh, they like 'em short in group B's culture.

Sexual selection is a very strong component of Darwin's theory of evolution and it is completely realistic to have this be the engine by which your species evolved these differences.

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