Attempts have been made to scientifically articulate sexual preference and physical sexual traits (Masters and Johnson). It is clear that there are degrees of sexual preference and physical traits. The only remaining scientific debate is measuring the subdivisions of the scale in between.
All the symbols, language and rituals involved in marriage are purely subjective exercises. Meaning is in people, not in things. Religion is nothing but a tool that dictates and reinforces subjective useless meanings on people. Marriage is a meaning with no independent physical attributes.