@tokyo_0
Apologists cherrypick Gita verses like (4:13, 18:41) but those refer to varnas being established at the moment of creation (RV 10.90.12) and not how they'll be passed on.
There's a clear reference in 9:32 of 'pāpa-yonayaḥ' (sinful birth) while 17:23 claims Brahmins came from 'Supreme Absolute Truth' itself.
Karma earned in past life decides next birth or caste. IF it was decided by occupation not birth, whole doctrine of karmic cycle and rebirth falls apart.