Arjuna returns and Yudhisthira answers a few questions. Mahabharata 78

While Bheema goes looking for the flowers Draupadi had desired,  a rakshasa named Jatasura manages to abduct the Pandavas. As Sahadeva gets free from him and begins to fight, Bheema appears at the nick of time and kills him.
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Arjuna appears one day in Indra's chariot to the great delight and relief of his brothers and Draupadi. Arjuna tells them about his penance and the astras he has acquired and about Uravashi. Also speaks about killing more rakshsas, Kalakeyas and Nivatakavachas, who were invincible to the devas, at the behest of Indra.
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They continue to stay at this Gandhamadhana mountains, enjoying its beauty and later move back to Dvaitavana. A few days before their move Bheema goes hunting and a python swiftly coils around him and Bheema with all his super human powers is unable to get free. Yudhisthira goes looking for Bheema and discovers him in the death grip of  a python. The python then addresses Yudhisthira and tells him that he is actually king Nahusha. He was born as a python as he was cursed by sage Agasthya for his arrogant behaviour and would release Bheema if Yudhisthira answers his questions correctly!
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The questions and the answers:
N: Who is a brahmin and what should he know?
Y: Whoever has these qualities; truth, patience,charity,character,non-violence,kindness and self-restraint is a brahmin. He should be aware of  the supreme state which is neither joy nor sadness.
N: Even a shudra has these qualities and I have not seen anything which is bereft of either joy or sadness.
Y: If a shudra has these qualities and brahmin does not have it, then shudra is not a shudra and brahmin is not a brahmin. As there surely is a condition between the hot and the cold, there should be a state between joy and sadness!
N: If a brahmin is defined only by his actions what is the point of being born as a brahmin?
Y: As anyone can have children from anybody, it is not possible to examine and establish caste only on the basis of birth! Hence moral conduct, integrity are very important. A brahmin who does not learn vedas is equal to a shudra.

They continue with their conversation and Nahusha also answers some questions Yudhisthiras has on dharma. Nahusha is then released from the curse of Agasthya and goes back to heaven. And Bheema gets free from the python's grip helped by Yudhisthira's superior knowledge about dharma and its nuances.

Interesting conversation to say the least! We are constantly reminded that varna was occupation-based initially. It changed later and society was  classified on the basis of caste by birth. My guess is that it did not take long for us to adopt to this basis of caste by birth. While upward mobility of a human because of his intellect and greater skills and knowledge did happen, probably more often in the begining of a civilised society, our innate nature would surely not permit a downward movement. Which parent would accept that his offspring did not deserve to be in the starta of society he was born into?  I cannot imagine, for instance, a brahmin declaring to the world that his son had failed to memorise the vedas and hence should  become a shudra or lower?

While it was a big deal about being a brahmin during the vedic times. Today, we are more familiar with the stories of a 'poor brahmin' than otherwise! I am not aware of any rishi being worshipped on a large scale! There are shrines dedicated to them in one corner of a temple  dedicated to either Vishnu or Shiva or their avatars. The most worshipped of the gods today, Rama and Krishna, were both born as khsatriyas.

 Brahmins had their good times, most recently with the brits, but in the present day dynamics, it is certain that many poor brahmins would not mind being called a backward class and get some benefits for themselves. How many non-brahmins, intelligent and skilled in debate would be thrilled to be called a brahmin?

 However, I am with Yudhisthira and his argument that a person's status should not be based on birth alone. It is even more relevant in today's context. But our style of democracy and the vote bank politics will not let caste die! It will flourish with all its ramifications.