The problem of 'other minds'--how can I know that other people have minds like mine, that they're not zombies or robots or Republicans?--is one of those things that gives philosophy a very bad name (synonymous with intellectual wankery) and makes philosophers easy to ignore.
Reasoning along the evolutionary lines of the previous post, we can easily argue that it's not really a problem at all. Our assumption that all human beings have similar minds is licensed by the fact that we are a single species and thus we are all products of the same evolutionary processes. We are all descended from those African creatures who eons ago evolved brains capable of self-consciousness and the imaginative constructions that we lump under the category of 'mind.' That solves the problem to my satisfaction, but if your mind (which I conclude you possess) still insists that we can't tell whether that man walking down the street is a Blade Runner robot or a Max Brooks zombie or a lizard creature from V or one of the wanking dead, I suggest you put down Chief Broom's namesake, take a close shave with Occam's Razor, and stop insisting upon absolute certainty. With apologies to Ockham, certainty is for theologians, not thinkers.