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knowledge3754 t1_iy5tlqs wrote

Reply to comment by LowRepresentative291 in Eli5: Why do birds and fish come in such a spectacular variety of colors and shapes compared to other animals? by thetravelman888

Please elaborate

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Unable-Fox-312 t1_iy5wwd6 wrote

We use the big sloppy category "fish" to describe all kinds of creatures under the sea. It's like if we bundled together all the chimps and certain kinds of birds and maybe one mushroom and decided those were all called arbs because they like to live in trees. It's a useful word in the real world, but the category doesn't map cleanly to any evolutionary branch

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LowRepresentative291 t1_iy7e36x wrote

All life started in the water. Imagine at some point two species of fish diverged from a common ancestor, species X and species Y. Both became ancestors to many subsequent species. Some descendant species of X (irl: lobe finned fish) eventually came to land, and that's where we descent from. Now, thousands of modern fish species have evolved from species X, and thousands have from species Y. A far descendant from species X might look morphologically similar to a species that evolved from Y (they are both "fish") but it shares a closer common ancestor with humans.

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commanderquill t1_iy7ehpi wrote

Life is created, presumably starting from one species. Then there's an explosion of life. Now all kinds of life. Some have fins. Some have feathers. Some have feet.

Some develop into something else, as different to the ones with fins as humans are. But that design fails. Better to have fins. Now they have fins.

Humans come along and see it and go hey, that's a fish.

But this 'fish' maybe used to be a lizard and then became a fish. So it went:

Step 1: ancestor

Step 2: something else

Step 3: something else

Step 4: lizard?

Step 5: fish?

Meanwhile, 'fish' #2 went:

Step 1: ancestor

Step 2: fish?

So you have one fish that came from a lizard and one fish that came from something else entirely. As a result, you have one fish that has a shared common ancestor with humans say maybe one billion years ago and another fish that has a shared common ancestor with humans three billion years ago. That means fish #1 and humans are related by one billion years while fish #1 and fish #2 are related by three billion years.

Conclusion: some fish are more closely related to humans than to other fish, and the category of fish is meaningless.

This is also true of crabs and trees. Mother nature proves to us over and over again that crabs, fish, and trees are the most superior earthly life forms.

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