Often these verses in Chandogya Upanishad are quoted to claim that chandogya upanishad says varNa is by birth. Let's see these slokas of Chapter 5.10, as I translate and interpret it. Executive Summary of Chandogya Upanishad Chapter 10 Due to Sun and Moon's effect on Earth, day, night, summer and winter solstices, years etc happen in cycles. Due to effect of moon, ancestral worlds of life is formed in Earth which also follow the cyclic pattern, releasing gases to sky, changing the atmospheric contents, forming clouds, bringing rain to distant lands and bringing out advanced life forms that devas eat (plants, trees, wood). Being that eat these plants and their products, evolve into 2 kinds, based on the work they do. Those species said to do attractive work (produce something) called brahmana, ksatriya, vaizyas and those species said to be stinking work of scavenging like dogs, pigs, candalas.But then there's a third kind who are just born and die without any evolution call...