I dont think this is true. Caste system came into existence mainly due to Aryans, fair skinned people and todays majority of brahmins are fair than the rest of the indians who are either black or brown skinned. Having said this, it is these very same brahmins who have now become muslims or in some cases christians in kashmir, Goa and kerala. May be nature just wanted to convert these brahmins into these “religions” as they were not magnanimous enough to help people outside of their community. In kashmir, they are suffering even now, which on the surface looks like a religious issue.
In many cases, perhaps for their livelihood, brahmins also started the practice of Idol Worship. No wonder, nature again reacted by destroying many such idols in the guise of “invaders” like Ghazni or Ghouri.
Having said this, i would also like to add that i dont abhor brahmins, i have many friends who are brahmins. and neither do i believe in Islam or christianity, and nor do i have plans coverting to these religions.