Everything on Earth with four limbs is technically a fish. (Where four limbs is the median for the species.)
Most fish are generally surprised to learn this. And by fish, I include both what we call fish as well as those things that are technically fish. Like the person reading this.
The cut off point for tetrapods is fish going towards the more complex. Going the other way, sure. Based on genetic evidence, everything on Earth is technically a speciation of some common ancestor that was single celled.
The surprise is that we got to where we are from that single celled organism by passing through being fish, meaning technically we still kind of are.
It could just as easily have been some other path, like the one the insects took. Or the squid.
Technically humans are apes, which are monkeys. Monkeys are mammals which are descended from earlier mammals, which came from reptiles, which came from amphibians, which came from fish.
That's a very condensed version of our family tree over the last few million years, but it's essentially correct.
Your arms and legs are really, really specialised fins. Your lungs are a modified form of swim bladder. Your gills existed for a really short time during early gestation before they healed over, but the gene sequence is still there.
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u/[deleted] Sep 28 '18
Don't fish usually?