Making a Tree from Designed Objects?

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basically because human has mammary glands (and some other traits). so i think that its logical to call them mammals. but human as a fish?

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I canā€™t prove anything to you. I canā€™t even offer you evidence because youā€™re unwilling to receive it. But I direct your attention to the vast phylogenetics literature, in all of which humans are mammals, which are amniotes, which are tetrapods, which are sarcopterygians, which are fish.

Of course. Do you find that surprising?

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So a human is a mammal because of their shared characteristics, good.

Now, could there be a definition of fish based on shared characteristics?

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sure. but there is a big difference between human as a fish and human as a mammal.

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Yeah theyā€™re two different things. But you got the point, thereā€™s a definition of fish based on shared characteristics that includes humans, just as thereā€™s a definition of mammal based on shared characteristics that includes humans.

Humans are also vertebrates. This group is defined basically as all animals with a spine.
Humans are also tetrapods. Thatā€™s a group defined by all members having four limbs.

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I will add that this is not the modern definition of either group, nor, really, was it ever. Some vertebrates, i.e. hagfish and lampreys, donā€™t exactly have spines. Some tetrapods, such as snakes and whales, donā€™t have four limbs. These days, groups are defined phylogenetically, and even Linnaeus relied not entirely on essential characters but on nested hierarchy. Whales were mammals, and mammals were tetrapods, therefore whales were tetrapods.

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