Dandavat pranamas,
When I was in India I saw the scriptural reference. I thought I had it with me, but when I looked through my papers today I couldn´t find it. But the original system was that the persons who had brahminical qualities received upanayana samskara. This is also in harmony with the teachings of the Gita:
samo damas tapah saucam, ksantir arjavam eva ca
jnanam vijnanam astikyam, brahma-karma svabhava-jam
"Internal and external sense control, austerity, purity, forbearance, straightfrowardness, knowledge, realization, and theism - certainly these are all the natural duties of the brahmana section."
Bhagavad-gita 18.42. Translated by Aksayananda Swami, published by Sri Chaitanya Saraswat Math.
Here it clearly says that the brahmanas are those who naturally have those mentioned qualities. If one becomes a brahmana in the hereditary way, why does not the Lord state so?
It is like the people who call themselves Goswamis even though they can´t _control their senses_, it is a type of deviation from the original system.
I will get back you later with above mentioned reference.
Humbly,
M R D