Did humans evolve as a mating pair? If not how did humans reproduce and if they did evolve as a male and female why are we to assume that the occurance took place in the same geographical area?
Yes. They must have come from Hetero Erectus.
Your question assumes something that is not a part of the theory of evolution, so let me take a moment to try to clear this up.
The theory of evolution does not postulate a lizard giving birth to a bird, or any other change of such magnitude. If this were the case, your question, where would an individual with such an extreme adaptation find a mate, would be a good one.
Rather, the theory of evolution suggests small changes, where one generation is almost the same as the previous, and there is no trouble interbreeding for any of the individuals in a population.
When two groups become separated those changes can move in different directions, and if the two populations are under pressure from environmental changes, they may drift apart rather quickly. In time, the two populations may no longer be inter-fertile, which is the definition of a species.
But, at no time would the theory of evolution suggest that changes from one generation to the next would be so extreme that an individual could not mate with other members of the population. Should such an extreme mutation occur, the theory of evolution would suggest that that individual would not survive to reproduce.