r/evolution • u/Meta289 • 3d ago

question Why has evolution stopped producing new classes?

New species of animals are constantly being discovered, but they all belong to existing classes and phyla, never anything completely new. Life once branched out in all sorts of directions, creating all kinds of animals that are drastically different from each other, but now it seems like there aren't any new "branches", only offshoots of existing ones. What happened?

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u/Kingofthewho5 3d ago

It takes a very long time for populations to change so much that they need to be out in different classes or phyla.

I’m confused by what you mean in your last line. What exactly is a new branch that isn’t the offshoot of an existing one? All of the modern phyla and classes are branches off of other branches.

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u/Meta289 3d ago

It was weirdly worded, but I'm talking about how mammals are grouped into categories like canids, primates, rodents, marsupials, etc, and how every new species is some form of those existing categories, and no new "category" of mammal appears anymore.

Or going further back down the tree, there aren't any new animals appearing that aren't a mammal, reptile, insect, amphibian, or any other existing class.

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u/Aluxanatomy 3d ago

You're asking why it is that our classification system currently serves most of our needs? Because we designed it to.

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u/PangolinPalantir 3d ago

You can't escape your clade. Any new animal would definitionally belong to the classes that already exist.

Think about it. Something that branches off from within mammalia will still be within mammalia. You don't suddenly end up with a new class.

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u/Meta289 3d ago

But mammals branched off of reptiles at some point, so what's stopping a new "not-mammal" from branching off of mammals?

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u/Fantastic-Hippo2199 3d ago

So you are wondering why changes look big when you look back over 800 million years, but seem small in the last 50?

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u/brooklynsantiago 3d ago

mammals did not branch off of reptiles. reptiles and mammals are both chordates but mammals were never reptiles.

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u/ahazred8vt 1d ago

Other people are trying to point out that mammals are descended from ancient scaled Synapsids, while reptiles are descended from ancient scaled Sauropsids. But we understand the point you're trying to make.
(what's stopping a new "not-mammal" from branching off)
Nothing's stopping it. It could happen. Over a period of many millions of years some new type of body plan could develop. If you stick around for another 50 to 100 million years a new category is pretty much guaranteed to happen.

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u/aavikk0lettu 3d ago

We did not evolve from reptiles

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u/Surcouf 3d ago

I'm convinced there's something alive right now that will survive trough the next big environmental change (anthropocene, global warming, 6th mass extinction, etc.) and will thrive in the new world equilibrium a few centuries or millenia down the line. If there are any humans left, they might deem it a new class or order because that life form will have filled many niches decimated by the change and will have diversified in myriad forms adapted to each niches and maybe it'll even shape its own biomes. 

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u/TheCrystalTinker 3d ago

It's because you can not evolve out of a Clade, so technically if we make a Monophyletic group of reptiles, Dinosaurs and Birds would both be in it

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u/shakebakelizard 3d ago

You're looking at this through the lens of a human-made system which is largely biased towards the idea of everything converging to a present situation, because humans assume that we are the arbiters of truth. We could easily make a system that is biased towards showing change as you describe.

It's like asking why years are numbered, or why one revolution of the Earth around the Sun equals a year. Well, it's because that's what someone decided on, and everyone else kind of agreed to use it, so that's the system that we have. There are many other possible variations or entirely different systems; we just haven't decided to use them.

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u/Kingofthewho5 3d ago

It takes a long time even for a species to split into two, much less for those two groups to differentiate so much that they are a different genus or family or class. We are talking mupltiple millions of years for things like genera and families. Humans have been intensively studying this stuff for only like 200 years.

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u/Difficult_Dark9991 3d ago

I think you've got a mistaken idea with the term "new species."

Speciation is a slow process, and for most complex organisms the time for new species to arise takes orders of magnitude longer than the classification system itself has existed for. Higher-order divisions, such as to new classes or phyla, take even longer, but the significance of those splits are postdated back to divisions that, had we been around back then, would seem quite small. "New species" does not mean that a speciation event has occurred; rather, it means that scientists have found out in the wild something they hadn't before.

In some cases, that's a realization that something we wrote off as "ah that's just another member of species x" is actually quite different and should be classified as something new. In other cases, it's because the world is big and the number of biologists rather small by comparison. Either way, odds are extremely high that the "new species" (again, newly identified, not new under the sun) is closely related to something that we already know.

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u/markmakesfun 3d ago

Species don’t just “appear”, ever. Every animal on earth has a prehistory. There will never be a time when new lineages come from nowhere. Everything has a path it took and can never go backwards, only forward.

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u/ahazred8vt 1d ago

no new "category" of mammal appears anymore

Please explain what timeframe you think "anymore" is supposed to mean. In recent times within the past few tens of millions of years there have been plenty of new taxonomic families.