SB 12.2.35
ity esa manavo vamso
yatha sankhyayate bhuvi
tatha vit-sudra-vipranam
tas ta jñeya yuge yuge
Translation:
Thus I have described the royal dynasty of Manu, as it is known on this earth. One can similarly study the history of the vaisyas, sudras and brahmanas living in the various ages.
Purport:
Just as the dynasty of kings includes exalted and insignificant, virtuous and wicked monarchs, varieties of human character are found in the intellectual, commercial and laboring orders of society.