The origination of the I

In my opinion, one of the most mind boggling questions to grapple with is: When did I arise?

When I say “I” I do not mean the physical body, I mean “I” as the subject of experience.

Assuming this subject was not present before the origination of my physical body, there must have been one moment in time, when it suddenly came online.

What was there before? What purpose does this “I” subjectivity serve? Is it optional?

Paul Gauguin’s “D’ou venons-nous” (1897)