Exogamy

The opposite of endogamy:

1. Sexual reproduction between organisms which are completely unrelated to each other.
2. Marriage between members of different groups, classes, or communities.

From the BioTech Dictionary at http://biotech.icmb.utexas.edu/. For further information see the BioTech homenode.

Ex*og"a*my (?), n.

The custom, or tribal law, which prohibits marriage between members of the same tribe; marriage outside of the tribe; -- opposed to endogamy.

Lubbock.

© Webster 1913.