According to quality and according to work, the social order is divided into four. The most intelligent class of men are called the brahmanas, and the next intelligent class of men, namely the politicians, or one who wants to take part in administration, they are called ksatriyas. And the next intelligent class of men, those who are busy in production - because we want food - so the productive class of men is called vaisya, mercantile. And the laborer class of men, namely one who is neither intelligent nor administrator nor trader, but wants to live at the shelter of somebody, master, they are called sudras. The brahmanas, the ksatriyas, and the vaisya, they would never accept subordination, service, under anyone. But the sudras, as it is stated in the Bhagavad-gita: paricaryatmakam karyam sudra-karma svabhava-jam [Bg. 18.44]. By nature, a sudra wants to take shelter of somebody else and live. So at the present moment, the Kali-yuga, the sastra says, almost everyone is a sudras because nobody can live independently.
Lecture on Srimad-Bhagavatam 5.5.1, London, 30 August, 1971