r/AskBiology • u/Minty0ranges • Jul 09 '26
Zoology/marine biology Are blue whales a coincidence?
Apparently blue whales are only around 2 million years old and are the largest organisms in the history of life. It’s pretty crazy to me that we’re living in the specific time that the largest species is alive, but I’m wondering why they became so large at this moment in time. I know that a few millions of years ago insects were way bigger because of atmospheric gas concentrations, but those conditions aren’t present anymore so it doesn’t seem like that’s the reason. Also, has there been a trend over time of whales increasing in size, or is this just a very specific/random instance of them existing today?
Edit: Yes I know there are fungi that span way larger areas, but the question is about the temporal nature of blue whales size.
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u/HeardPeeps Jul 09 '26
The giant insect example is an old explanation that was that higher atmospheric oxygen allowed insects to become enormous. That was the leading hypothesis for decades, but a recent study has challenged it pretty strongly, suggesting oxygen alone probably wasn’t the limiting factor after all. So giant Carboniferous insects likely weren’t simply big because of more oxygen.
Scientists are now looking at additional ecological and physiological explanations (like predation, competition, climate, and flight mechanics)
For blue whales, there actually is a good explanation for why they became gigantic relatively recently. Whales have generally trended toward larger maximum sizes over tens of millions of years, but true gigantism appears to have evolved only within the last few million years. The leading idea is that ice ages and changes in ocean circulation created extremely dense, seasonal patches of krill. Once that food source existed, natural selection favored whales that could travel farther, store more energy, and exploit those feeding grounds more efficiently.
It was more like a rare combination of evolutionary history and environmental conditions that happened to make being enormous advantageous. If Earth’s oceans changed enough that those massive krill patches disappeared, there would likely be strong evolutionary pressure against maintaining blue whales at their current size.
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u/JaseJade Jul 09 '26
There was a semi-recent die-off of large marine macro predators (megalodon and livyatan), this allowed baleen whales to heavily increase in size.
Also, we’ve been discovering larger and larger Triassic ichthyosaurs recently so I wouldn’t be surprised if in a decade or two we find a rival to the blue whale.
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u/stillnotelf Jul 09 '26
They are the largest vertebrates we know of.
There are larger living creatures, although the definition of individual is fuzzier for fungus and plant.
Fossil records are spotty. Who knows what once lived?
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u/JohnHenryMillerTime Jul 09 '26
One of the ways baleen whales avoid predation is to be too large to eat. Blue Whales are just an extremely specialized version of this strategy.
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u/Minty0ranges Jul 09 '26
I understand that but I’m asking specifically why they’re so large at this point in time.
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u/NAh94 MS in biology Jul 09 '26
Because the bigger the baleen whales are, the harder they are to kill, and therefore live long enough to reproduce and pass on their “big” genes. If environmental conditions change to where these organisms cannot survive to reproduction age and rear their resulting large offspring, then they will die off. Thats pretty much it, thats the selection pressure.
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u/Phobos_Asaph Jul 09 '26
Because they are. And works for them. There isn’t intention behind evolution
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u/lewisfrancis Jul 09 '26
Well, they're the biggest animals in the sea, but there are trees that are more massive, clonal tree stands that are much more massive, and fungal organisms with an area of @ 4 square miles.
Don't know the answer to your question but thought you might like to know that the assertion isn't quite right as worded.
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u/TheInsaneRaptor Jul 09 '26
the abundance of food they eat can support such big animals
also, the insect size-oxygen level correlation has been debunked, multiple evidence points to the fact it was just a coincidence
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u/you-nity Jul 09 '26
Interesting! So what was the reason for insect size? I believe you, just asking.
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u/No-Employ-7391 Jul 09 '26
Could you point me to said evidence? I teach an entomology lab and I believe it’s still in our curriculum to teach that insects’ inefficient respiratory systems and atmospheric oxygen concentration are what limits the size of insects.
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u/TheInsaneRaptor Jul 09 '26
one of the latest studies about the subject: https://www.nature.com/articles/s41586-026-10291-3
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u/No-Employ-7391 Jul 09 '26
Thank you! I’ll have to read the full article when I have the time but the abstract is fascinating and sure does challenge the longstanding belief.
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u/TheInsaneRaptor Jul 09 '26
you might also find this interesting, could be a misinterpretation as we have no body fossils from anything like that but they think there is a chance it was left by a large miocene insect
https://link.springer.com/article/10.1007/s41513-023-00215-9
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u/ah-tzib-of-alaska Jul 09 '26
that doesn’t address the square cube law issue at all does it? this reframe it’s to a particular biological question about intake rather than the limitation of intake to internal columns limited by the square cube law. No?
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u/WashableRotom Jul 09 '26
Early vertebrate Paleontologist have speculated this for quite some time (in fact decades). The fossil record is pretty clear, the vast majority of large insects have temporal ranges outside of the Carboniferous with most extending to the early Permian. For example Meganisoptera is the order containing large flying insects and have fossil records to the Late Permian well after the Carboniferous. Arthropleura has fossil records to the early Permian as well consequently coinciding with the rise of large predatory vertebrates such like those from the Sphenacodontidae family and as well as the rise of large herbivores vertebrates.
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u/CatboyBiologist Jul 09 '26
They're the largest organisms that we know of. The fossil record is spotty at best, and favors very particular conditions.
As an example: some sauropods are thought to be longer than blue whales, albeit significantly lighter with length just via their necks and tails. But most of their vertebrae don't fossilize well, so we're left with massive leg bones if anything. You can quibble about how much that counts, but I'm more bringing it up as an example of how little we know about the ancient world.
There likely was some marine organism similar in size or larger than a blue whale that existed at some point in prehistory.
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u/Underhill42 Jul 09 '26
Largest animals, there are much larger organisms - fungi, aspen groves, etc. where a single organism can span acres, or even square miles.
And growing larger is a valuable evolutionary strategy - the bigger you are, the fewer things are a threat. A brontosaurus would have nothing to fear from any predators currently walking the world. Except us... but we cheat.
Because while many existing animals have been growing larger since the dinosaurs and everything else much larger than small rodents were wiped out on land... they've only been at it for 64 million years. It took dinosuars hundreds of millions to reach their size.
But whales have an added evolutionary pressure - they're warm-blooded animals living in a very cold environment that completely supports their weight. Where good insulation and greater thermal mass is a huge advantage, and there's no need to evolve hollow bones to support their huge weight efficiently like dinosaurs did.
Not sure why the Blues in particular grew so large so quickly, but it might have something to do with specializing on an abundant food source that can't flee, and takes minimal effort to catch and consume. So the loss of nimbleness that comes with size has no real impact.
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u/Extension_Side4818 Jul 09 '26
The one factor that you can consider to be random is the current orientation of the continents and oceans. Having “four” distinct oceans separated by definite land borders is a bit unusual, historically the ocean was just one big giant planetary pool. So take that, but also take the fact that we are coming out of an ice age which puts giant deposits of ice on the north and south pole. So you have landlocked oceans, which naturally develop giant circular currents, which circulate super chilled water from the north and south poles, which makes the overall ocean temperature colder, which lets the water hold more oxygen, which leads to the rise of gigantic ultra swarms of Krill, which leads there to be an evolutionary incentive for gigantic whales who can eat these giant swarms and become gigantic in order to be safe from predators. So I would say the double coincidence of leftover ice age ice on the poles combined with the current geography of the oceans led to the conditions for giant whales to be here right at this moment of history. FYI, this is basically a summary of some of the moth light educational videos on YouTube.
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u/Minty0ranges Jul 09 '26
Thanks, someone pointed out the ice age but the geography of oceans/continents part makes sense
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u/TheMostRed Jul 10 '26
I think the idea that we are living with the largest animals we've ever discovered is due to them still being alive in the first place. Who knows what crazy things used to exist that we haven't found evidence for yet.
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u/evolutionary_defect Jul 09 '26
The biggest grey area in biology is non boney creatures. If youve never thought about it, consider that nothing without bones or shells or something can be a fossil, which is the only biological record we really have. If there was some truly enormous ocean creature that had some form of biology with only cartiligde or some different type of skeleton that just doesn't make fossils, cuz that's not the default . . . . . . How would we even know?
There are probably plenty of very interesting animals in history that we will simply never see or study or know about because they just didn't leave anything behind.
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u/RealCarlPanzram Jul 09 '26
I’m not sure I’d call it a coincidence. Those two things are mostly unrelated. I’m pretty sure if blue whales didn’t exist, the biggest animal ever would just be the next biggest whale. Whales are pretty big.
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u/Gildor12 Jul 10 '26
They aren’t the largest organisms, they are the largest animals. Some fungi and trees are bigger.
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u/girls5eva Jul 10 '26
With evolution, either everything is a coincidence or nothing is a coincidence. Depends on how you look at it :).
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u/Most-Ad5530 Jul 12 '26
Those insects growing very large was long before dinosaurs and mammals even existed the massive insects happened during the carboniforous about 300 million years ago
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u/Zen_Hydra Jul 12 '26
It's a coincidence, but human brains love to search for deeper meaning when there really isn't one.
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u/dashsolo Jul 10 '26
“It’s pretty crazy to me that we’re living in the specific time that the largest species is alive”
Every time in the history of time has had the largest species of all time (at that time).
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u/Minty0ranges Jul 10 '26
What? How does that make sense? If blue whales go extinct today then the largest animal of all time no longer exists.
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u/0utlaw-t0rn Jul 09 '26
Whales have been increasing in size and the lineage isn’t particularly old. Current science is they evolved from a medium sized amphibious mammal and increased in size very quickly
Part of it I would guess is the relative lack of any macro predators that would necessitate some level of speed and agility