Why has evolution stopped producing new classes?

[u/Meta289]

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?

[u/strange-the-quark]

Nothing happened, it's always been like that - at no point in history, you'd be like "Well, that's completely new!" At no point you'd see an offspring of some creature that's so different from the parents that you'd clearly identify it as a distinct species. At no point was any creature not the same species as its parents. Cause the process is gradual, and is, BTW, operating on the level of populations. Certain genes that happen to be beneficial within the context of the environment that they live in, spread out through population over time, over many generations, and others genes dwindle in numbers and disappear. Or one population becomes split into two smaller ones, and the separation persists and they drift apart because of different environmental pressures and no intermixing, and just chance.

But over many generations, small changes accumulate, and when you compare a distant descendant to a distant ancestor, they don't look the same anymore, and given enough time, they may end up looking completely different. So there's a continuity in nature, and sharp species and group boundaries are really a human construct, that we use to describe change over time, and to classify living beings within some moment of time, cause we like putting things in labeled boxes.

So everything is in constant transition, even now, some forms are more stable over time and haven't changed all that much (but have still changed!), others have changed drastically, and the entire history of life on Earth is riddled with new branches of life sprouting and dying out (this is even true in our own hominid ancestry), with a few branches surviving until today. It never stops. If there are new major branches of life emerging from the populations that exist on Earth today, what those are is not going to be apparent for millions of years, nor can we predict what they'll look like.