Step 1: Look at the contrast in the text.
The author sets two ideas side by side, not erotic, but economic. One is rejected and the other is accepted by the writer.
Step 2: Pick the accepted idea.
The accepted word is economic. The rejected word is erotic.
Step 3: Match to the options.
Option 4 uses the accepted word. Options 1 and 3 are the rejected idea or close to it, and option 2 appears nowhere in the passage.
Step 4: Support from the example.
The hungry bachelor shows that a wife brings food, which is an economic gain. This agrees with the choice.
Final Answer:
Marriage in primitive societies is economic, not erotic.
\[\boxed{\text{Option 4}}\]