Well that's not entirely true because of the way genes mix up (the whole idea of dominance and inheritance). This is what might allow two brown haired brunettes to have a blue eyed blonde child: the brown eyes and brown hair is dominant, and when the bits of the couple is mixed, you get two recessive traits (blonde hair / blue eyes).
Of course it's not even so simple as dominant / recessive because genes mix about in all kinds of other ways. So getting a true breeding pair from just one generation of people is not possible.
However, it's highly likely if we had a eugenics program whereby over a long period (say several hundred generations) we attempted to identify, and breed a "smart" race of people, it would happen (in the same way we've bred dogs that are smarter than other dogs).