Consider the following statements about the socio-cultural evolution of Punjab:

1. The geographical position of Punjab has historically made it a center of invasions, leading to the assimilation of multiple cultures and communities.
2. Despite multiple foreign influences, Punjab has remained culturally isolated from external traditions.
3. The region has played a key role in the evolution of major Indian religious and philosophical traditions, including Sikhism and aspects of Sufism.
4. The rigid caste system was never present in Punjab due to the Sikh principles of equality.

Which of the above statements are correct?