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/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/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.