This question might – sadly – be more justified than it ever should. Such a topic might disappear in EOF quickly, but I wouldn't dismiss the question entirely.
The obvious, easy answer would be: To learn! (*)
Humans are very complex lifeforms not limited to some fixed set of innate skills. But rather than only learn from own experience, we are additionally able to imagine, to plan and learn on abstract level combining different pieces of knowledge… just by talking, reading and thinking about them.
The complexity and amount of our knowledge and skills leads to the need for efficient knowledge transfer (and specialization because nobody can learn everything).
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Now to the (*) marking above:
Why did I say the question is...