Transcription
Let's imagine it's the dead of night and you're on some remote island just minding your own business when suddenly you hear something rustling through your camp and you grab your flashlight expecting maybe a rat or a lost seabird. But what you find defies your expectations as instead you see a crab the size of a garbage can lid with claws that could snap your hand like a pretzel stick just casually attempting to steal your cooking pot. And the worst part, this isn't even unusual here. Welcome to the absolutely unhinged world of island gigantism.
Now, you might think being stuck in an island would make things smaller, considering how there's less food, less space, and fewer resources. And that makes sense and all, but that's not how it really works, at least not all the time. As sometimes evolution does the exact opposite, making small things giant or big things even bigger. And so give an animal a few thousand years of isolation on some random island, and suddenly you've got rats the size of house cats, insects that could probably arm wrestle you, and giant crabs that have literally evolved to climb trees and smash open coconuts. And scientists call this phenomena the island rule, or if you're feeling fancy, Foster's rule, after the biologist J. Bristol Foster, who first described this madness in 1964. And what Foster basically discovered was that islands are where nature gives the beta test its weirdest ideas. And like every beta test, these ideas don't always work out.
And one test that obviously failed is an animal so famous that we often think of it as the poster child for extinction, the dodo bird. But what most people don't know is that the dodo, i.e. Raphis kakalatis, is actually a poster child of island gigantism as well. You see, this wasn't some weird unique bird lineage. This was a pigeon. A giant overgrown one, but a pigeon nonetheless. Now, you might not be able to guess that just by looking at it, but the dodo does in fact belong to the pigeon and dove family. But while your average pigeon weighs maybe 300g and spends his time defecating on statues, the dodo was 17.5kg or 39lb of pure flightless pigeon. And in other words, 58 times heavier. It stood a little less than a meter or 3ft tall, had wings that were basically decorative at that point, and a beak that had evolved from pecking seeds to "mess around and find out." With one account saying word for word, "their war weapon was the mouth, with which they could bite fiercely."
So, you might be thinking, why would a pigeon, a bird so impressive in flying and geavigation that they've been used as a communication method for over a thousand years, would just lose their ability to fly? And the answer is actually fairly simple. Mauritius, the island where they're from, has no native predators to worry about. And so the dodo simply had no reason to maintain the ability to fly, seeing that flying is metabolically expensive, requiring highly specialized structures and massive chest muscles. So the dodo just stopped. It got fat, likely happy, and waddled around eating fruits and fallen seeds like it owned the place, which to be fair, it kind of did. And so the dodo's entire evolutionary strategy was pretty much "be big and be fearless," which worked great for millions of years until it didn't. You see, they were so unafraid that when Dutch sailors arrived in 1598, the dodos would literally just walk up to them to say hi, being their fat, happy self. But then, uh, this proximity would also allow the sailors to club them to death if they so chose to, which, uh, they unfortunately did a lot. And the last confirmed sighting was in 1662, less than a century after humans discovered the island, with the dodos going from ruling an island paradise to being extinct so fast that for years afterwards, some even thought the stories were false and that they were instead mythical animals, which we now of course know they're not and are one of the best known extinct animals worldwide.
But while everyone knows about the dodo, almost no one seems to know about its neighbor, the Rodriguez solitaire, scientifically known as Pezops solitarius. And guess what? This wasn't just another giant bird. It was also another giant flightless pigeon that lived in Africa. Specifically on the Rodriguez Island just 560km east of Mauritius, which also made it a relatively close cousin to the dodo. But here's the real kicker. It was even larger than the dodo. While the dodo was more round and chunky, the solitaire was tall and lean with males standing up to 90cm or 35in tall and weighing up to 28kg or 62lb, making them over 50% bigger than even dodos. And on top of that, the sexual dimorphism was insane with males being up to 66% heavier than the females with them topping out at 17kg. Which to put that into perspective would be like the average American man now weighing 227lb or 103kg and making it the most extreme size difference between sexes in any neo-tropical bird ever.
But here's where things get properly weird, or well, violent. While their wings, just like the dodo, had become useless for flight, they had evolved to become useful for another purpose entirely, chiefly as weapons. You see, both sexes had bony knobs in their wings that were the size of musket balls, being able to grow 3.3cm or 1.3in across, which in case you're not a war historian, would be around the size of a ping-pong ball. And as alluded to, these were not just for show, as the solitaire would use these weaponized wings to beat the absolute h double hockey stick out of their rivals, swinging them so fast and hard that contemporary accounts claimed it made a sound like thunder. And fossil record certainly backs this up with many solitaire wing bones showing signs of healed fractures, evidence of just how brutal these battles were. And while some have suggested that these fractures may be the result of hereditary bone disease rather than battle wounds, all extant birds where carpal spurs and knobs are present have used them as weapons literally without exception. And this would also make sense considering unlike their peace-loving cousins, the Rodriguez solitaire evolved on an island that received significantly less rainfall than Mauritius, meaning resources were scarcer, which likely put evolutionary pressure of becoming extremely aggressive. Oh, and, uh, they also had a wicked bite. But unfortunately, similar to the dodo, they laid just one egg at a time, which isn't exactly great when it comes to species survivability. However, unlike the dodo's extinction, the solitaire lasted longer, but not by much, as by the mid-700s, they were gone. So, another giant pigeon deleted from existence. Except this one went down swinging its ping-pong ball fists, or rather wings.
Now, at this point, you're probably thinking that everything that becomes giant on an island is a bird. And you wouldn't exactly be wrong there, as there are plenty more examples of birds getting huge, even bigger than those I mentioned, which we'll get to later. But mammals also got their fair share of gigantification as well. And nowhere is this more obvious than with rodents, as islands seemed to have a particular talent for turning cute little mice and rats into absolute units that would make Tom and Garfield think twice. Take the Canary Islands for example. These volcanic islands off the coast of Africa were once home to Canariomys bravoi, the Tenebrif giant rat. And these things weren't just big, they were huge, being about the size of Yorkshire terriers. In fact, when we compare them to their closest mainland relatives, the African grass rat, we find that these guys got over five times bigger despite only diverging 650,000 years ago, which just to put that into perspective is about the same amount of time of divergence as Neanderthals and modern humans. And while Neanderthals are certainly absolute units, imagine if there were the 900lb or 400kg type of absolute units, as that's basically what the Tenebrif giant rat is to the grass rat.
And then there's the Saint Kilda field mouse, Apodemus sylvaticus hirtensis, which is basically evolution's attempt at speedrunning "insert gigantism." As what's interesting about these guys is that this isn't some ancient species that's had millions of years to get weird. In fact, it hasn't even had hundreds of thousands. This is a regular mouse that was brought to a windswept Scottish island maybe a thousand years ago tops, and possibly by Vikings because of course Vikings are involved somehow. And in just a millennium, which in evolutionary terms is basically yesterday, these mice have grown significantly larger than their mainland relatives, all the while being on an island, which is basically Scotland's attempt at remaking Ireland. Just kidding. Being cold, wet, windy, and mostly grass. But for these mice, paradise. No cats, no rats, no competition, just them, the green outdoors, and a thousand years to get progressively more chunky. However, with all this said, I will note that most cases of island gigantism do seem to happen in warmer environments.
And if you were to for some reason become ruined on the island of Flores in Indonesia, let's just say good luck, as this island seems to exist solely to make biologists question their sanity. And getting ruined here would suck for multiple reasons. You see, this is the exact same place where they found extinct humans. Humans known as Homo floresiensis, an extinct cousin of ours who actually coexisted with humans for a hot sec. But these were no giants. Instead, being essentially dwarves who barely stood over a meter tall or 3'7" experiencing something called island dwarfism, the second half of the island rule. And so, if given a long enough time, perhaps your descendants would join them in short kingy, which didn't seem to farewell for our cousins. But even if you're only marooned for one generation, you're not out of the woods yet. As don't be mistaken in thinking this dwarfism applies to the rest of the animals as well, as while humans went small, others went big. Including, of course, in typical fashion, the rats. Meet Papagomys armandii, also known as the Flores giant rat, which might sound like something out of a low-budget film, but is absolutely real and absolutely massive. As while your average rat weighs maybe 300g, unless it's of the New York City variety, in which case all bets are off, the Flores giant rat weighs up to 2.5kg or 5.5lb. So massive, like I said. And why? Well, because why not? The largest carnivore on Flores is a monitor lizard too busy eating carrion to hunt a roided-up Master Splinter. But that's not to say they couldn't take them, as these monitor lizards are really Varanus komodoensis, i.e. the Komodo dragon, the largest lizard on Earth.
Now for a long time these guys have been considered a textbook example of island gigantism seeing that they live on islands and are well, giant, weighing up to 150kg or 330lb and measuring up to 3m or 10 feet long. However, recent research has shown that these guys likely descended from an already giant monitor lizard that evolved in Australia, which in turn means their size is through something called phyletic gigantism, which is basically when a whole lineage just trends toward becoming absolute units as opposed to purely the island making it big. But, and this is the important part, island life let it stay big. Everywhere else, giant monitor lizards went extinct. Be it competition from other predators, climate change, or just humans with pointy sticks. But on Flores and a handful of other Indonesian islands, there are no big cats, no bears, no wolves, etc. So being a 3m long lizard with toxic drool and a monopoly on being terrifying is just perfect. And considering their origins in Australia, it might not surprise you to hear that there are islands here which have also been inflicted with the insanity that is island gigantism. And when I say islands, I'm talking about New Zealand, which technically is an island part of the Australian continent.
Now, New Zealand is basically what happens when you take an island, remove all mammals except bats, and then let evolution go off its medication, and the results are exactly as insane as you'd expect. No pun intended. Let's start with the living nightmare that is the giant weta, which are specifically species in the genus Deinacrida. These things are basically what happens when my childhood nightmares meets reality, i.e. giant crickets. And giant they are, with specimens being recorded to weigh up to 70g. In other words, heavier than your average sparrow by twice that is. Now, thankfully, they can't fly and can barely jump, which is again because of how massive they are. So, in other words, they're basically just large, scary potatoes with legs. But despite their terrifying appearance, they're actually vegetarian. So, the only thing you really have to worry about from them is the heart attack.
Now, with this said, the weta is a small fry compared to what used to roam New Zealand, the moas, especially the giant moas, who evolved to fill the same niche as herbivorous mammals, except of course they were birds that stood up to 3.6m tall or 12ft and weighed up to 278kg or 613lb. And in a very unusual case, not only were these guys just flightless and giant, but they actually had no wings, not even vestigial ones. There was no humerus, no radius, no ulna, and no carpals with basically the entire upper limb being absent from skeletons. The only thing there was was a tiny finger-sized scapulocoracoid, a fused remnant of the forelimb's girdle's coracoid and scapula. And I can't emphasize enough how unusual this is. Because out of literally every other flightless bird, dead or alive, the moas are the only ones completely lacking wings. So, in other words, they were basically feathered giraffes that forgot they were supposed to be birds.
But despite their sizes, they were not the kings. As hunting these walking skyscrapers was Hieraaetus moorei, better known as the Haast's eagle. And let's just say if you're hunting Big Bird's cousin, you better be big yourself. And, uh, they were. Not only were they giant for an eagle, they are in fact the largest eagle that ever lived, period. And could weigh up to 40lb or 18kg while having a wingspan reaching 10ft or 3m. And while that might not sound huge, you have to keep in mind the fact that of the largest extant eagles, none have been verified to exceed 9kg or 20 pounds in the wild. Meaning even the largest are about twice as small as Haast's eagles. And yet wild eagles of that much smaller size can still kill deer, antelope, and sometimes even wolves with their prey often weighing many times their size. And so unsurprisingly, these absolute units of an eagle were giant killers having talons that were literally the size of tiger claws. And they put those to good use, hunting prey the size of cows, likely diving at speeds that would let it strike with enough force to break bones. And based off of the Māori stories of the Pouakai, a monstrous bird from their legends and stories, these eagles likely turned these weapons against the human invaders, too, which entered New Zealand about 700 years ago. But unfortunately, these humans proved too much in the end, leading to the extinction of the moas, which in turn led to the gradual extinction of the biggest eagle this planet has ever seen.
But while the moas and Haast's eagles are gone, New Zealand still has one absolutely ridiculous yet adorable bird bumbling around. The kakapo, scientifically known as Strigops habroptilus. And this guy isn't just ridiculous looking. It's like in typical island gigantism fashion, they are big with them actually being the world's largest parrot with males weighing up to 3kg or 6.6lb and measuring up to 64cm or 25in long, meaning about twice the size of the next largest parrot, the Hyacinth Macaw. And beyond its size, it's basically everything a parrot shouldn't be. It can't fly. It's nocturnal and is the only parrot in the world that uses a lek breeding system, which in case you don't know what that is, is basically equivalent to guys at a frat party, being a mating system where males gather in a specific region to quote unquote display for females who then choose a mate based on the best of these displays. And just like a frat party again, these guys smell, but perhaps a bit better. Being described as a combination of honey, papaya, which in case you didn't know, both tastes and smells like vomit, and I quote, "musty, violent cases." So certainly a unique scent in any case. And the smell is actually so strong that predators can easily track them by scent alone from far distances, which is a terrible evolutionary strategy when you can't fly.
But perhaps the only thing worse than that is what they do when they decide to breed. As you see, those displays I was talking about earlier basically consist of the kakapo singing the song of its people to as many things as it can, or at least as long as it can distance-wise. What happens is that males create these elaborate B-shaped depressions in the ground, which basically act as acoustic amplifiers, and they then proceed to sit in these bowls and produce a deep booming sound that's so low frequency that it can travel 5km or 3.1mi through dense forest. And just as a cherry on top, they do this for 6-8 hours every single night for up to four months. Meaning 960 hours of booming per mating season. So they better hope it turns to banging with all that effort they're putting in. Pun intended. But the ingenuity of the low frequency is also a problem, kind of. As while the low frequency itself means it carries for longer, it also makes it so that females cannot always accurately tell which direction it's coming from. So, in other words, you basically have males crying their hearts out for their Juliet while the females are just wandering around the forest like, "Where the heck is that coming from?" And probably also, "How do I shut him the h double hockey stick up?" And it gets worse, as at least some of the males are desperate enough during mating season to try mating with pretty much anything, including people's heads, whether being famous or perhaps infamous footage of a kakapo named Sirocco attempting to mate with zoologist Mark Harwood's head. Yeah. And since then, scientists have even built a special ejaculation helmet to help collect sperm from overly excited males, which can then be used in artificial insemination programs. And no, I'm not kidding.
And ultimately, the kakapo is so evolutionarily weird that it almost went extinct just from being bad at existing and of course from humans showing up with their pesky pointy sticks. And by 1995, there were only 51 left, even though they can live up to 80 years, possibly more. But thankfully, a conservation program was then set up which had the first success in years when it came to saving them. However, while it did keep them from going extinct, it wasn't as successful as one might hope. And as of 2024, there are only 244 kakapo left, with every single one of them being closely monitored and restricted to certain areas. Oh, and, uh, they also all have names.
But anyways, considering the density of animals made giant around Australia and New Zealand, maybe there's just something in the waters of the Pacific that makes things grow huge. Because it's not just here. Take New Caledonia for example, a French territory east of Australia. This place is home to Rhacodactylus leachianus, also known as the New Caledonian giant gecko, the largest gecko in the world. And this thing certainly lives up to its title, being able to grow to 43cm or 17in long and weigh up to 500g. Meaning, it's a gecko about the size of a squirrel. And to really put that into perspective, your average house gecko weighs maybe 2g. So this guy is 250 times heavier. In fact, not only is it the current largest gecko in the world, it is also the second largest of all time, only being surpassed by the Gigantophis, a species which funnily enough used to live in New Zealand, but actually does come from New Caledonia as well, with it having been possibly 50% longer and several times the weight. And the New Caledonian giant gecko is so big that it routinely eats other lizards, birds, and even small mammals, having a strong enough bite and pointy enough teeth that it can absolutely hurt you if you piss it off. And, uh, that's kind of easy considering they're known for being absolutely psychotic in the temperament department, with even their breeding behavior basically consisting of a first date where they bite each other and thrash violently, often accompanied with locking jaws. How cute. But hey, if they survive that, I guess that means they're fated. So, unsurprisingly, these guys are highly territorial, and they communicate this through a series of growls, chirps, whimpers, and whistles. They sound more like they're coming from a, well, honestly, I have no idea, but certainly not a reptile. And when threatened, they often won't run. They will instead stand their ground, make funny noises, and probably fight you. And in fact, they're so aggressive that many cases of cannibalism have been noted. And they're generally chalked up to territorial defense. And like some of the other island giants we've talked about, these guys are also long-lived, being able to live for decades, with some individuals in captivity having reached 50 years old. Which on the flip side, a house gecko would be lucky to make it to seven. And on their native islands, indigenous Kanak people actually fear them because of an old superstition, which is that the geckos can cling to your body and pull out your soul. And given their size, attitude, and, uh, those sounds, I'm not entirely convinced that's just superstition.
But like I said, there must be something in the water of the Pacific, as it seems like the entire region is cursed with gigantism as no matter where you go, you'll find islands scattered around with animals that have no business being that big. Take the Lord Howe Island stick insect for example, also called the tree lobster, which probably tells you everything you need to know. This thing is as thick as your thumb and longer than your hand, being up to 20cm or 8in long and weighing 25g or 1oz. So, likely hundreds of times heavier than your run-of-the-mill stick insect. And what's crazy is that these things were actually thought extinct after rats were introduced in 1918 with them being declared so just 2 years after. But then decades later, scientists found a dead one on a sea stack known as Ball's Pyramid, which is basically a 500m tall rock just jutting out of the ocean. And lo and behold, following a new expedition to look for them, a population of fewer than 30 individuals were found, having survived in this vertical, basically barren rock face for 80 years, presumably out of pure spite. But as of 2012, the Melbourne Zoo has successfully bred over 9,000 of them and thus taking them out at the brink of extinction. And yes, obligatory, it's over 9,000. Now, I will mention we're not exactly sure if this size is a result of insert gigantism, considering it has no closer related mainland relatives that we know of. So, it's hard to say for sure, but let's just assume it is.
And speaking of big animals without a spine, we can't forget about the king of island invertebrates himself. And really, the king of land invertebrates in general, Birgus latro, i.e. the coconut crab. Now, this thing is what I'd imagine what happens when evolution asks, "What if we made a crab, but like a horror movie version?" and then doesn't wait for any input because first off, these things are huge. And I mean huge. We're talking over a meter or 3ft across and weighing over 4kg or 9lb. In other words, more like a small dog with an exoskeleton rather than any normal kind of crab. Well, technically a hermit crab, but still. And get this, nowhere is safe from these creatures. As despite being ground dwellers, these crabs made nightmare fuel can climb trees. Yes, trees. And up to 10 meters or 33ft high at that. But that is not all. Because of course it isn't. Despite only weighing a fraction of the heaviest animals on land, they have the strongest recorded grip strength of any terrestrial animal, period, with a crushing force up to 3,300 Newtons, which for reference is about as strong as a lion's bite. And just a reminder, this is again coming from a crab. Well, hermit crab. And they use this power for exactly what you'd expect, or at least what I'd expect. Taking names and kicking butt. And by that, I mean cracking open coconuts, which really shouldn't be that surprising given their name, and being a general menace to society, as coconut crabs are notorious thieves, with their nickname even being the robber crab or palm thief. And they'll steal pretty much anything. But they especially like shiny objects. And there are even reports of them stealing knives from camps. And apparently this applies to birds too, as coconut crabs have been photographed dragging away full-grown seabirds, which were dead because they killed them. Yeah, vicious.
So, with all of this said, and having toured a fraction of the world's weirdest islands and meeting their oversized inhabitants, you're probably wondering, why does this keep happening? What is it about islands that make evolution turn Davids into Goliaths? And as it turns out, there are actually several mechanisms at play here, and they all pretty much work together to synergistically create these island monstrosities. First, there's the predator problem, or rather the lack of a predator problem. You see, on the mainland, being small usually means you can hide better and need less food. But remove those predators, and suddenly being small is less useful. As without anything trying to murder you every 5 seconds, you can afford to get bigger. And being bigger offers a bunch of benefits, including better thermoregulation, meaning you won't freeze to death as easily. And then there's the fact that you can eat food that smaller animals generally can't get or can't process. It also means you can store more tissue for when times get tough. But of course, a lot of it is also driven by internal competition as being bigger means you can fight off competitors for the best territories and mates, which thus snowballs into bigger and bigger offspring. And sometimes the change starts before natural selection even gets involved with something called the founder effect, which in this case is when a few individuals are able to better colonize an island in the first place and thus their genetic quirks become the default setting. The island itself also matters with smaller islands generally pushing species to more extreme changes quicker as fewer species, limited resources, and isolated gene pools crank up the evolutionary pressure into overdrive. But perhaps the most important factor of them all is the ecological release. You see, when you're on an island, entire ecological niches might be completely empty, which results in the arrivals picking up niches they're already occupied on the mainland. For example, if there are no large herbivores, birds might become moas. No mammalian predators. Eagles become Haast's eagles. No one competing for coconuts. Crabs become nightmare fuel.
Now, overall, it would seem that island gigantism is pretty much a uniformly good thing considering the advantages it gives. But that's not exactly the case. And here's where things get a bit depressing. You see, being a giant on an island is great until it suddenly and catastrophically isn't. Island giants have one fatal flaw. Well, one big fatal flaw. They evolved in a bubble. No predators means less fear. Less competition means no competitive arms race and no serious threat means less defense mechanisms beyond being big. So when humans show up and, uh, we always do, these giants basically become walking buffets with each messian strapped to their backs. I mean, take a look at the moas, gone within 100 years. Haast's eagle starved shortly after. The dodo and solitaire deleted. The Tenebrif giant rat gone. In fact, an overwhelming number of animals with insular gigantism are either extinct or near extinct. And this is likely a trend which will continue to happen for these island giants.
But I will mention something I alluded to, which is that the island rule doesn't have to make things big. It can also make big things smaller. And that is why the island of Flores had both giant rats and tiny humans. But that is a topic for another video. But regardless, the main takeaway is perhaps that islands make evolution act, well, weird. Give it isolation, remove some pressure, add some weird constraints, and suddenly you've got crabs that can climb trees and crack coconuts, insects the size of mice, and pigeons that forgot how to fly, and probably how to poop on statues as well. Thanks for watching and until next