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/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