That's not how evolution works (Score 1, Redundant)

There is no point where we stopped being something else and started being humans because evolution happens in small gradual steps. Over very long periods of times, the individuals of a population are so different from their ancestral population that if you could take a present individual, travel back through time, it couldn't reproduce with members of the ancestral species.

Think of it. If two animals had an offspring that had evolved into some new species, with whom would it reproduce? It would be the only one of its species. Two animals may have an offspring with a slight mutation which proves to be favorable. This offspring can still reproduce with other members of its species because that little mutation doesn't make it different enough to be genetically incompatible. Since this mutation is statistically favored, it will spread across the members of a specie as generations pass by. Many such mutation will accumulate over long periods of time leading some very different animals than what you started with. Never will you see any big difference between one generation and the next.

If a population is suddenly separated, each sub-population will accumulate different such mutations such that over a long period of time they members can no longer reproduce if they were to somehow meet again. Hence, they species has split into two species.

Incidentally, we do not descend from Monkey's nor Neanderthals. They are more of our cousins than our ancestors.