Nepal consists of two primary ethnic elements: Mongoloids, who migrated to Nepal by way of Tibet, Sikkim, Assam, and northern Bengal; and Indo-Aryans, who came from the Indian plains and from the sub-Himalayan hill areas to the west of Nepal. There are also small remnants of Dravidian tribes. Bhotes, of Tibetan origin, are the principal occupants of northern Nepal. In the central valley, Newars and Murmis predominate, the former being responsible for most of the agriculture and trade. Less numerous groups include Gurungs and Magars in west-central Nepal and Kirantis and Rai in the east. Sherpas, a Himalayan people, have become well known as guides for mountain-climbing expeditions.