[Irish Wolf]

There was an Original Sin of sorts, but it wasn't a sin of Men, but rather of Morgoth, who'd been watching for the rise of the Second-Born in order to attempt to corrupt them at the source. (He succeeded in the case of most Easterlings and Southrons, but there were those who resisted his corruption and fled West seeking the Light.) Morgoth's surrounding darkness and evil was what led Men to begin fearing the dark. (In fact, in my current reread of The Silmarillion, I'm near the beginning of Akkalabeth, the tale of the downfall of Numenor to the whispers of Sauron.)

On the other hand, the Elves had their own Original Sin, in the foolish oath of Feanor that no one else should ever possess the Silmarils. That led to the Doom of Mandos, the Kinslaying, and a great many more evils descending therefrom.