'I AM, YOU ARE, HE IS, I LIKE, SHE LIKES' are all examples of subject verb agreement (also called 'concord'). If there was no agreement you would say: I AM, YOU AM, HE AM, I LIKE, SHE LIKE.
When the English language evolved from its European roots, it still needed to change the shape of a verb in relation to its subject (as Italian does today).
With input from Norwegian invaders/occupiers/settlers over a couple of hundred of years the language eventually settled on current use: Some more examples are I GO, HE GOES; I PLAY, SHE PLAYS, etc.
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