- Ethnocentrism: Ethnocentrism is the belief that one's own culture is superior to others, and it can limit cultural diversity by promoting the idea that other cultures are inferior.
- Inbreeding: Inbreeding involves the reproduction of individuals within a closed gene pool, which typically does not contribute to cultural diversity.
- Cultural Relativism: Cultural relativism is the understanding and acceptance of different cultures, but it does not directly increase diversity.
- Immigration: Immigration introduces individuals from diverse cultural backgrounds into a society, leading to an increase in cultural diversity.
Step 1: Understanding how cultural diversity increases.
Immigration directly contributes to cultural diversity by bringing in people with different cultural practices, beliefs, and traditions.
Final Answer:
\[
\boxed{\text{The correct answer is (4) Immigration.}}
\]