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Why Do Islands Induce Dwarfism? (sapiens.org)
98 points by mhb on June 21, 2016 | hide | past | web | favorite | 50 comments



Islands can also induce gigantism [0]. My understanding is that is the microcosm allows certain species to thrive or perish and we see a more dramatic change in size as a result.

[0] https://en.wikipedia.org/wiki/Island_gigantism



What's funny is that, for us humans, the whole planet is kind of a big island today isn't it? (Edit: not everywhere ofc) I wonder how large humans will get in a number of generations from now.

Found an interesting article about that topic: http://www.bbc.com/future/story/20150513-will-humans-keep-ge...

Looks like we are record holders in height already, let's see how far we can get!


I think regular human size can vary a lot by level of resource consumption - the principle being the larger the mother, the larger fetus and so the larger the resulting adult.

Obviously, if a height increase/decrease trend continued for a while, one assumes genetic variations which aided this would be selected for but it seems that the change itself doesn't necessarily need genetic as such.

See height increases in Japan: http://www.nytimes.com/2001/02/01/world/tokyo-journal-the-ja...


From my observation, I notice that a lot of younger generation Chinese adults are likely to be taller than their older fellow country people as well. I have many Chinese coworkers and even the female coworkers are at least 5 feet 5 inches or taller (for young male coworkers, they are usually at least 5 feet 8-10 inches). Nutrition certainly plays a big role in determining one's height.


I believe the N vs S Korea example supports this theory as well.


Wouldn't the biggest factor simply be limited resources? The same reason why the average man was 5 inches shorter in 1750 than he is today.


Actually, Foster's rule indicates that predation being the main threat leads to smaller animals, while the restriction of resources being the main threat leads to larger animals.

> The same reason why the average man was 5 inches shorter in 1750 than he is today.

This is more likely dietary changes than resource restriction—we may not have had industrial farming, but the average person wasn't starving either. But you need access to plentiful, high levels of protein to maximize your height advantage.


Foster's rule is actually the reverse of that.

Which can be seen intuitively because non-human predators pick off the weakest and smallest of the pack.


This depends on the size of the animals in question compared with the largest practical size for an animal in that environment. Large animals will get larger, because this improves their chance of fighting back against similar-sized predators (think lion vs. antelope). Small animals will get smaller, because this allows them to evade much-larger predators (think cat vs. mouse).


> But you need access to plentiful, high levels of protein to maximize your height advantage.

Hence a resource restriction?


Probably the same reason storms on Jupiter are larger than storms on earth.

You can't be bigger than your container.


Yes. That's what I'm getting at. In fact animal size and storm size are probably predicted by a power law curve to the surface area of the environment


I don't know, Polynesians and Samoans seem plenty large to me.


Yes, but they've been living there for only a few hundred years, or a couple thousand at most. The article was referring to populations living in island environments for much longer durations.


They also have a very different food, cultural, and military environment than the isolated hobbits would.


Polynesians and Samoans traveled between islands, often by rowing.


Ideas: (1) Richest foraging environment may be out in the open on the shoreline. If any other predators are present, or even if there is simply harsh environmental exposure (sun/wind) then a smaller physical size to take advantage of shelter may be advantageous. (2) Mountainous interiors. I believe it is well documented that short people have better luck climbing and descending steep slopes due to a lower center of gravity. (3) Low dietary variation or reliance on foraged protein rather than large land mammals. (4) Safety from predators may lead to a younger age of reproduction, accelerating change.


Intriguing. I wonder then; does this mean our spacefaring descendants will be smaller for the very reasons outlined in the article?


Just finished binge watching The Expanse. There, the first generations of offworlders grow very tall, thin and weak. Clearly, there is a strong evolutionary pressure on them to grow much smaller, and fix their spongy bones. Imagine the difference between a small child and a 7 foot tall weakling with osteoporosis, accelerating at 12 Gs in an emergency situation.

Btw, the show was fairly good, imo. Deep, and nearly hard SF.


Many suspect spacefaring will require us to become quite small indeed. It will become ridiculously uncompetitive to drag around a meat body and pressurized environment.

Think of something like The Field Circus from Charles Stross's "Accelerando".


Seems like only a tiny crazy subset of humans will ever want to give up the freedoms of having a meat body and being able to move it in a pleasant atmosphere. After all, what's there to do in interstellar space? The idea of turning ourselves into space probes is a dystopian, inhuman proposition.


Doesn't low (or lack of) gravity decompress the spine or something, inducing a very slight increase in the height of current astronauts?


Its not that slight. 2-3 inches


I imagine the lack of gravity will probably be a bigger deal than the "island effect" of having an isolated population.


the foxes example is interesting as there are foxes everywhere, and the further into the CA or African desert or into Arctic - the smaller the foxes are. Pure thermodynamics - like surface/volume ratio - would suggest otherwise. It most probably has to deal with [lesser] reliability of food availability, similar like in islands case.


It's the bottleneck effect duh. https://en.wikipedia.org/wiki/Population_bottleneck As others have noted Polynesians are huge and didn't turn into dwarves.


Aspects of this island evolution were part of the plot in the marvelously detailed sci-fi book from Kim Stanley Robinson: Aurora.

TLDR: Interstellar multi-generation spaceships are essentially genetic islands.


Just finished this novel. Great hard sci-fi space opera.


Maybe the principle that height is also proportional to speed should be taken into account?


Imagine the Komodo Dragon on a continent. Yikes!


I live in England , this is true.


Although they are representational of all islands, Tonga and Samoa disagree.


Reading this I had a silly thought: "What if we are the 'giants' of old ?"


Biblical giants? They were half fallen angel, half human. Not many Christians (and maybe even Jews) believe this, but if you study the context of Genesis 6 and the rest of the Bible anytime it speaks of Noah's flood and judging of angels, they coincide (especially in the New Testament in the book of Jude) then there's the Book of Enoch, which isn't in protestant or Catholic Bibles, but the Ethiopians have it in theirs, and it speaks about how the angels took human wives to themselves. The Liger hybrid species explains scientifically the nephelim (or Giants) hybrid species to some degree, how it can be so massive is explained by the DNA. These are the views of some Christians, but again, assuming Biblical giants, there's a lot of different factors into play.


Man, it would be so amazing if we could somehow attribute ancient stories of dwarfs, trolls, giants, to humans meeting other hominid species that we coexisted with.


Or encountered the remains of, as seems to have been the case of dinosaurs becoming dragons.


From what I've heard, dinosaur bones tended to be taken for the bones of giants, at least in the Middle Ages. Dragons were much older than any awareness of dinosaurs; most medieval myths about dragons trace back to the draco standard carried by late-Roman cavalry. (See https://en.wikipedia.org/wiki/Draco_%28military_standard%29 .)

This, by the way, means that there really were dragons in sub-Roman parts of the Dark Ages world: Wales and Cornwall, for example, where draco-bearing cavalry (including King Arthur's, if there was a King Arthur) were fielded probably until the 600s or 700s.


Dragon mythology as an explanation for dinosaur bones seems pretty straight-forward. I'd even say that "dragon" was just the early word for "dinosaur", and the mythology is based on an earlier extrapolation of characteristics from fossil remains than what we use today. A somewhat less strict extrapolation, but even today a lot of what we 'know' about dinosaurs is pure guesswork.

But dinosaur bones driving myths of biblical humanoid giants? That's a much bigger stretch. Most dinosaur bones are pretty non-humanoid, and people who are generally a lot more familiar with human and animal skeletons than we are today wouldn't mistake one for the other. Also, while dragon mythology is mostly reasonable based on fossil evidence (except for the flying and fire-breathing... and gold hoarding) giant mythology is completely different. The biblical texts and non-biblical books like Enoch give them names and actions that are much more historical sounding than mythological. You don't get details like that from big leg bone fossils.

So, I don't buy dinosaur bones as the source of giant mythology.


I have no idea where dragon myths or giant myths originate; giants are easy to guess, but dragons are a strangely common belief for creatures with so little basis in reality. (Plasma cosmology has a very interesting explanation for dragons, and for a lot of other strange things in human history, but the physics of that theory are pretty bad.) I'm just mentioning what it is that dinosaur bones were identified with in the Middle Ages -- centuries before anyone knew that there had ever been such things as dinosaurs.

(To an extent, dragons fall into the same category as unicorns, griffins, and phoenixes: not mythology so much as really bad zoology. All four of these species were believed to exist in the real world as contemporaries of medieval humanity, sometimes surprisingly nearby -- like griffins in the Caucasus.)



Well height variation still occasionally occurs within all populaces everywhere. "Giants" and "dwarves" as a distinct race was probably a drunken glimpse of different looking people from other villages, in a dark wood or the like.

A related thought is that if there ever was any other intelligent species on Earth, noticeably different than humans, we wiped them out long ago.


But given that in fantasy, all the populations seem to be technically the same species (hence able to breed half-elves, half-dwarves, quarter-veelas, etc), the another likely outcome is that the variation would go away over time


Following this thought experiment, it could be that half-breeds are sterile hybrids and can't reproduce, kind of like mules (horse + donkey). Then you wouldn't get genetic normalization.

If they have a different number of chromosomes it's likely.


I thought that as well, but for instance in harry potter one of the characters is quarter-veela, implying that one of the character's parents is a half-breed, and was able to reproduce. I'm unsure if there are other quarter-breeds in other fantasy universes.


Hybrid speciation can happen, where the hybrids don't breed with the parent species but do with each other.


With mules?


No. Mostly plants. But, there are some interesting animal examples.

https://en.wikipedia.org/wiki/Hybrid_speciation#Known_cases_...


I guess not really, but a search for "fertile mule" shows lots of resources discussing female mules giving birth.

(which I think illustrates the complexity more than it does anything else)


For a second I read that as, "Quarter-Veals" and my confusion was total.




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