that was your characterization of the process of evolution. Not mine.
Chihuahuas have been bred out of wolves in a few thousand years. Some species are more plastic than others. Without DNA from the various intermediates, you cannot make assumptions about how long it takes to breed significant changes in form, or how many mutations it might take.
At any rate, many of the characteristics of humans are probably the result of female choice, a very rapid method of selection.
Essentially, they are the same animal (just one is smaller in size). There is not one animal created through thousands of years selective breeding in which we increased their intelligence by several factors.
I suspect that if you were to find a living female Homo Ergaster and tried to breed her with a modern day Homo Sapien they would not be able to produce childern. Just like you couldn't breed your wolf with shelton pony.