Island gigantism | Hacker News Reader

Island gigantism

en.wikipedia.org

90 pointselsewhen29 comments

Mentioned in the infinite monkey cage, big things also get smaller when on islands, as though there is an ideal size.

https://www.bbc.co.uk/programmes/p0gr7m49

I think the rule of thumb is that small animals tend to get larger when isolated, and larger animals tend to get smaller.

Yes. Island gigantism and insular dwarfism (https://en.wikipedia.org/wiki/Insular_dwarfism).

It's a shame that these aren't parallel. Why couldn't it be "insular gigantism" or "island dwarfism"? (But not both!)

What’s even worse is that Island Gigantism is a Germanic derived word followed by a Latin derived word, while Insular Dwarfism has the etymologies the other way around.

… that’s literally written in the first paragraph of the original linked article.

Something something reversion to the mean...

Reversion to the mean is a phenomenon resulting from random sampling. In island gigantism/dwarfism, the distribution of the population changes due to various causes. So not really the same at all, as far as I can see.

There is an ideal size and it’s determined by the size of the island. For a given size of island there’s a maximum size of predators that it can support. You want to be big enough that these predators aren’t much of a threat, but small enough that you can keep your own population size viable.

There's also the consideration that animals just don't grow as large if they don't get the necessary food.

Like how humans used to be so much shorter in the Middle Ages.

I wonder why humans don’t exhibit this. Is it because we can come up with ingenious ways to feed ourselves and aren’t completely dependent on the environment? Or maybe we do, south East Asians are really small compared to say a Polynesian.

There was Homo floresiensis, a relatively close relative of ours, also called the "Hobbit". For modern humans, there simply are no known populations that have been isolated for long enough on a small enough island to exhibit dwarfism. We're pretty good with boats and we supposedly have been very mobile for most of our history, and even if stuck we're capable of controlling our numbers and exploit our environments very well. I believe there are adaptations among Pacific Islander communities that increase metabolism efficiency and similar traits so we're not immune to this kind of pressure.

I wonder if it is just a matter of timescales? Behaviorally modern human showed up, banged some rocks together, and then launched satellites into space ensuring that we’d never truly be isolated in an evolutionary blink of the eye.

Perhaps the tardigrades spilled on the moon by the lander crash will become giants

Related but small:

Island gigantism and dwarfism the result of evolutionary island rule - https://news.ycombinator.com/item?id=26826178 - April 2021 (2 comments)

Interesting. I always thought it was cool that Hawaii is basically free of land-predators with the exception of the massive centipedes. Maybe this explains how they got so large.

https://en.wikipedia.org/wiki/Scolopendra_subspinipes

Tangent, but I just finished a wiki rabbit hole from this link you provided, very interesting read, but also found out that there is one species of millipede that actually has 1000+ legs.

https://en.wikipedia.org/wiki/Eumillipes

I wonder whether early accounts of this phenomenon by 18th C. explorers may have inspired Swift in creating Lilliput and Brobdingnag.

https://en.m.wikipedia.org/wiki/Moa

New Zealand seems to be a good example of this.

Also, fascinating how there were no humans at all there before the 13th century.

I wonder how long it takes to lead to this effect, and if humains have been isolated long enough at one point in history to have had a local effect.

Well, humans are pretty big already, and big animals on islands tend to get smaller [0], so the opposite may have happened. One theory of the origin of homo floresiensis [1] is that they were the result of insular dwarfism on homo erectus.

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

[1] https://en.wikipedia.org/wiki/Homo_floresiensis

Rodents of Unusual Size? I don't think they exist...

Feels like they're desperate for a pattern but focusing on size (which can either increase or decrease) is oddly specific. The headline of the article should probably be "insular animals tend to differ from continental counterparts" which is really all you can extrapolate from this "rule"

Is this what inspired the idea of "Monster Isle", where giant monsters dwell?

I don’t think people necessarily follow this rule.

People have gotten a lot taller in the last several millennia. Perhaps our island just earth itself?

People have gotten taller in the last few centuries, but pre-agriculture humans were pretty tall. Early agricultural societies could feed more people, but often with worse nutrition.

Also smaller weaker humans survive better in an agrarian society than in a hunter gatherer society.

Hominids have shown insular dwarfism: https://en.m.wikipedia.org/wiki/Homo_floresiensis

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