If you believe in evolution, you must also believe that significant genetic variety within the human species. (Evolution proceeds by individual mutation followed by breeding competition: every species subject to evolution is full of competing mutations).
And if you accept that changes in brain structure lead to changes in intellectual capacity (e.g. dogs and humans differ in intellectual capacity because their brains differ); and that the human brain has evolved and is subject to further evolution; then it follows that there must exist a plurality of different human brain mutations with different intellectual capacities: in short, different kinds of minds. (And since most of these mutations will have been around for a while and have had time to breed, we should expect that some individual mutations exist within very large numbers of brains; ergo, while the eye sees such doubtful categories as Poles and Portuguese, blacks and whites, men and women, we could perhaps with some justice speak of different brain populations; which probably do not overlap with any of the former categories).
This has two important and seemingly contradictory consequences regarding how we should treat the opinions of others.
In cases of objective knowledge – is buying GM stock a good move? -- we are well advised to consult the opinion of others because their brains may see something – some important clues or some subtle causal relations between clues and facts – which ours do not. In such cases, it is most useful to consult those with brains as different from ours as possible because we are hoping to look at a particular problem from a different vantage point in the hope of discovering something previously invisible. We are trying to borrow their cognitive system to look at the outside world.
In cases of subjective knowledge consulting with others is not entirely useless, because we do not have perfect introspective vision (i.e. we do not always know how we feel or why); in such instances learning about the feelings of others who find themselves in our circumstances can shed important light on our own problems. (This includes matters of taste: observing how others furnish their living rooms, for example, can be a rich source of good ideas).
But in such instances, we need to consult with those whose brains are as similar to ours as we can find because the question how a totally different brain might work in our particular circumstances, while amusing, is, practically speaking, useless.
So far, OK?