[coldcode]

Birds did not evolve from dinosaurs, they are dinosaurs.

Just read "Some Assembly Required: Decoding Four Billion Years of Life, from Ancient Fossils to DNA" by Neil Shubin. The pathway how a current species became what it is is quite surprising. Most features you see today came about as copies of other features that were repurposed over time, like feathers did not evolve to support flight, but for other reasons, and then lead to flight later. This idea of repurposing started with a Darwin comment in his last update to The Origin Of Species.

[throwaway894345]

I hear this a lot, but I don't understand in what capacity it is true. Why can we say "Birds did not evolve from dinosaurs they are dinosaurs" but not "Humans did not evolve from fish they are fish"?

[crazydoggers]

Birds are part of what’s called the Dinosauria clade. Clades are monophyletic meaning they encompass all the descendants of a common ancestor and all share common traits.

Humans and fish on the other hand can’t be grouped into a clade. That’s because it you trace back the common ancestor you’ll find other monophyletic groups descending from those ancestors.

Think of a clade as the end of a branch and all its leaves... whereas if you go far enough down you’ll find other branches that shoot off in other directions far off, even though they’re in the same main trunk.

https://en.m.wikipedia.org/wiki/Clade

[throwaway894345]

This seems like a rephrasing of the claim "birds are dinosaurs". "Birds are dinosaurs because birds are dinosaurs". Maybe the answer is "it's arbitrary; scientists decided that birds belong in the group 'dinosaurs' even though 'dinosaurs' and 'birds' are clearly distinct groups to everyone else"?

[phonypc]

Well, they're distinct groups to scientists too. Nobody is saying dinosaur and bird are interchangeable terms. All birds are dinosaurs, not all dinosaurs were birds.

[throwaway894345]

No one is saying that someone is saying that the terms are interchangeable :). The issue is that it’s not clear why “birds are dinosaurs” is correct but “birds evolved from dinosaurs” is not.

[phonypc]

I don't think "birds evolved from dinosaurs" is incorrect per se, but it evokes a common misconception of what dinosaurs are, so you get people responding "birds are dinosaurs."

Consider by analogy "humans evolved from primates." Well ya, but humans also are primates.

[phonypc]

I think the bird -> dinosaur relationship is more like human -> primate.

IIRC "fish" is kind of a fuzzy term. Like we would colloquially describe our common ancestor with frogs as a fish, but phylogenetically they would be closer to us than to some other "fish." Or something.

[jonchang]

Humans can be classified as lobe-finned fish, so it wouldn't be wrong to say that humans are fish.

[throwaway894345]

My question was more along the lines of "is it wrong to say 'Humans didn't evolve from fish because humans are fish'"? This is by all appearances the same argument the GP and others make when they say "Birds didn't evolve from dinosaurs; they are dinosaurs".