People immersed in the life of a small town see a much smaller amount of environmental variation than those accustomed to cosmopolitan living - relatively more observed phenotypic variation should be a result of genetic variation. So cet par cosmopolitans are biased in an environmentalist direction relative to provincials, or to say the same thing, provincials are biased in an innatist direction relative to cosmopolitans (who are biased in an innatist direction relative to interdimensional travellers who've seen all sorts of logically possible human societies that haven't occurred in our timeline.)

It's not clear at all from this where the "unbiased" point would be (without a Bayesian incorporation of all other relevant information etc) or what that would even mean.