[racer-v]

Each step along the way must produce a net benefit or it gets discarded.

Maybe so, but the benefit could have just been individual fitness signalling (like a peacock's tail) without providing any advantage to the species as a whole until the big "payday".

[dkural]

A peacock's tail can be seen; how do you propose the other sex fell in love with the brainier homo sapiens? It's a lot more likely that intelligence provided a net benefit.

[racer-v]

"That man that hath a tongue, I say is no man,

If with his tongue he cannot win a woman."