Definitely not marriage unless you expand the definition to mean "any long-term romantic pairing of any configuration in numbers and gender." Not trade or war either as many economies / geographies can support neither. Xenophobia, maybe. I'd have to re-read the book.
Music, as mentioned below, is one. Also Humor. Sibling and parental incest avoidance is one as well. There are a lot more but they're not coming to the front of my head right now.
Go nuts. It's really a great book.
Definitely not marriage unless you expand the definition to mean "any long-term romantic pairing of any configuration in numbers and gender." Not trade or war either as many economies / geographies can support neither. Xenophobia, maybe. I'd have to re-read the book.
Music, as mentioned below, is one. Also Humor. Sibling and parental incest avoidance is one as well. There are a lot more but they're not coming to the front of my head right now.