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".
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.
