Evolution acts on populations, not individuals. You will never ever get an individual ape that gives birth to an individual human, or even an ape that gives birth to an individual semi-human. You would see an individual ape give birth to an ape that was virtually identical to its mother but with a teeny tiny genetic difference from her. They're both still the same species and will always be the same species.
Think about a rainbow. We can all say that the colours in a rainbow are Red, Orange, Green, Blue, Indigo, Violet. Everyone knows that, right? We could clearly point to a picture of a rainbow and point out where each colour was on the rainbow.
However, at what point does the Red become Orange..? Sure, you can point at Red and you can point at Orange, but at what point is the rainbow Red and then the next point Orange?
That's impossible to answer except by making an arbitrary declaration; "*There* on the rainbow is Red, but a micrometer further down the bow, it's Orange." Yet, you probably couldn't put those two colours next to each other and tell them apart, could you? You would require a pretty sophisticated and sensitive chromoscope to tell the difference.
That�s *exactly* how it is with the mother and daughter, and in the same way you can start with one species and with lots of tiny changes over a long period of time you can get the equivalent of easily identifiably different species, much like the Red and Orange in our rainbow.
At some point in the past, there was a species of ape-like creatures. They were most likely geographically dispersed, possibly through the fact that the amount of food the environment could provide only supported a certain number of individuals, or because they had become separated by a river or a mountain or something. For the ease of illustration, we�ll say that the two groups were separated by a river.
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