"Yudhishthira in the Mahabharata says the following: The marks of the shudra are found in a brahmin; but a shudra is not necessarily a shudra nor a brahmin a brahmin. in whomever a brahmin's marks are found, he is known as a brahmin and in whomever they are not found, him we designate as a shudra."
January 1, 1970
https://en.wikiquote.org/wiki/Caste_system_in_India