Religion and Politics Drives Spouse Selection

It may not be polite to discuss religion and politics with mere acquaintances, but these matters go to the core of our revealed preferences in our choice of a spouse.

On a scale of 0 to 1, where 1 means perfectly matched, physical traits (body shape, weight and height) only score between 0.1 and 0.2 among spouse pairs. Personality traits, such as extroversion or impulsivity, are also weak and fall within the 0 to 0.2 range. By comparison, the score for political ideology is more than 0.6, higher than any of the other measured traits except frequency of church attendance, which was just over 0.7. . . .
An important point of the paper apparently is that this correlation does not emerge through convergence over the term of a relationship. Rather, partners are strongly similar at the beginning of relationships.  

From here, via Gene Expression, both relying on Alford, Hibbing and Peter K. Hatemi, "The Politics of Mate Choice," Journal of Politics, April 2011. The sample size was 5000 married couples.