Starting with Encounter at Farpoint, at the very start of the series, when Riker first meets Data in the holodeck, Data, when asked if he considers himself superior to humans, says, "I am superior, Sir, in many ways, but I would give it all up to be human."
He has a desire, a want, and a longing to be human. Isn't this an emotion in itself? There's no reason or need for him to have such a desire. If it's programmed into him, he would be able to find it somewhere in his memory and perhaps (if it's not read-only) re-write it.
Where could this desire come from if it's not from envy or longing or some other type of emotion? Is it possible he had this and some other simple emotions all along?