Why humans are sometimes sexually attracted to foreigners or others from outside their community

In England there is a traditional song, All the Nice Girls Love a Sailor, here a lady sings All the Nice Girls Love a Sailor. We all know what sailors are but what is that indefinable something about a sailor that women can recognise? Sometimes girls and women form casual relationships with sailors but relationships with outsiders can be long term. A nice girl sometimes marries a sailor or other outsider. Men can be attracted to outsiders as well, an example is when a sailor falls in love with a girl at every port he visits.

Favourable mutations, ie mutations that help humans to survive and reproduce happen throughout the world, in all ethnic groups and in all communities. Favourable mutations take time to spread throughout humanity. When humans form sexual partnerships with others from a different community there is a chance that the outsider will give their child favourable genes that have not reached their community yet. An outsider with favourable genes that have not reached a girl or woman’s community may be from another racial group or from another country, he may alternatively be from another part of her country or from a different village on the far side of a hill.

Genetics cuts both ways. The sailor may have favourable genes that are not in the girl’s community. It’s just as likely that he has unfavourable genes that never were in her community or have been eliminated in her community. To explain why forming relationships with outsiders can improve reproductive fitness we need to take Natural selection into account as well.
 * Some children from mixed partnerships will have unfavourable genes from one or both parents and such children will tend to die. When they die the problem is eliminated.
 * Children from mixed partnerships can just as easily have favourable genes from either or both parents. In that case the fortunate children will tend to survive as will their children, the grandchildren of the original couple, the great-grandchildren will also tend to survive and indeed the descendants of the original mixed couple will tend to survive till all favourable genes that have been introduced have reached equilibrium in the community.

Evolution and Racism
Evolutionary theory does not lead to racism when correctly studied. As shown above the theory of natural selection provides a strong case for encouraging racial and other mixing. For more about evolution, creationism and racism see :- Evolution and racism