Class system (open door) and the closed door Caste system

DBAWS Vol. 1
Castes in India, 1916.
"This sub-division of a society is quite natural. But the unnatural thing about this sub-division is that they have lost the open door character of the class system and have become self-enclosed units called castes. The question is: were they compelled to close their doors and become endogamous, or did they close them on their own accord? I submit that there is a double line of answer: some closed the door : others found it closed against them. The one is a psychological interpretation and the other is mechanistic, but they are complementary and both are necessary to explain the phenomena of caste-formation in its entirety." ~Dr. Babasaheb Ambedkar, (lines from "Castes in India," 1916, The paper presented in Columbia University.)