(http://en.wikipedia.org/wiki/Major_hist ... _selection)
If you look at the studies closer, you will see one where they found women prefer sweat smell that is different than her father's BUT not too different.
This helps prevent inbreeding but also helps prevent outbreeding.
Inbreeding is a concern if you date within close family such as a small isolated village. Lets say you are from Germany, then a girl from the East of the Country dating a guy from the West would be more than enough genetic difference to avoid inbreeding. The german could travel to Itally and probably find a genetic match. India or the Near East have girls with relatively similar genetics to Europeans according to the chart.. They also give reasonably high probability for genetic match, though less than Europe.
On the other hand, avoiding outbreeding is an important consideration too. It is possible that a German that travels to Congo will have a hard time finding a girl who is similar enough to him to be a match. A
It is possible to find a girl of another race who will be attracted to your genes/MHC but there are fewer as you increase genetic difference.
Look at this helpful chart to find races you would be compatible with.
