Although little is known of the prehistory of the peoples currently inhabiting Kenya, it is believed that the land has been more or less continuously inhabited since the birth of mankind - about 4.5 million years ago, as the numerous fossil finds around the edges of Lake Turkana, up in the far north of the country, elegantly testify. These discoveries of early hominids have earned Lake Turkana the title, 'The Cradle of Mankind', although still older finds were subsequently made in Ethiopia, to the north.

Within a multiplicity of tribes constituting around 42, the main distinctions that have been made by anthropologists, and to a lesser extent by Kenyans themselves, are based on broad ethno-linguistic classifications, which use the existence of common root languages as a basis of defining cultural (and racial) differences and similarities between peoples.

The cattle-herding Nilotes occupy the plains of the Rift Valley in the west of the country, which cuts across the whole of Kenya from north to south; the camel-rearing Cushites live in the desertic northeast; and the agricultural Bantu are in the more fertile highlands of central and southern Kenya, as well as in a few highland areas near Lake Victoria.

The Swahili, who are sometimes also classed as a distinct ethno-linguistic group, occupy the coast. The arrival of each of these groups can be sequentially dated, although ascribing precise dates to particular migrations and tribes is difficult if not impossible. It should be borne in mind that these classifications, and the names that are used, are almost entirely academic, and moreover were coined by European scholars rather than by Kenyans themselves. Periodic disputes arise among researchers as to the precise meaning of the classifications, and many alternative labels crop up.

The Cushites
Of the major ethno-linguistic groups, the first to arrive in Kenya were the Cushites, the first of whom (ancestors of the present-day Somali, Rendille and Wa-Boni) are believed to have entered north and northeastern Kenya around 2000-1000BC from Ethiopia. Some sources quote a figure of 9000BC for this, although it appears to confuse them with the hunter-gatherers. Needless to say, there's little evidence linking any particular ethno-linguistic group to any archaeological finds dating from that time.

Many subsequent migrations have since occurred, the latest in the mid-1900s, so that tracing the ancestry of any of these peoples is a confusing and probably pointless exercise. Cushitic-speaking peoples in Kenya broadly included the Eastern Cushites who are older hunter gatherer communities and later pastoralists. These are the Borana. The Southern Cushites such as the Iraqw (or Mbulu) who were displaced southwards to present day Tanzania or absorbed by incoming Nilotic and Bantu groups are no longer in Kenya.

The Nilotes
The next major linguistic group to arrive were the Nilotes who, as their name suggests, originally came from the Nile Valley, probably in Southern Sudan. The first of these peoples are believed to have arrived around 500BC, although Nilotic migrations only became substantial some five hundred years ago, with the arrival of the Luo and Maasai.

Their main direction of movement was southwards along the plains of the Rift Valley, which favoured both their cattle-raising lifestyle, as well as their rapid, all-conquering advance into the country. By the seventeenth and eighteenth-centuries, they had reached Tanzania, where their advance was finally stopped. Nilotes who have kept to their nomadic way of life, namely the Maasai, Turkana, Rendille and some sections of the Pokot, nowadays consider themselves as oppressed, dominated and discriminated against by the state and by the more numerous agriculturalists.

In Kenya, the Nilotes are often categorised into three subgroups:

• The Plain Nilotes, who speak Maa languages: the Maasai, Samburu and Turkana.
• The River lake Nilotes: the Joluo (Kenyan Luo), who are part of the larger Luo group.
• The Highland Nilotes who include the Elgeyo, Keiyo, Kipsigis, Marakwet, Nandi, Pokot, Sabaot, Terik, and Tugen.

The Bantu
The last major group to arrive (excluding the numerically-small but all-powerful Europeans in the nineteenth-century), were the Bantu-speakers, the first of whom probably arrived some 2000 years ago. Bantu-speaking peoples in Kenya include 3 of Kenya's five largest tribes, namely the Kikuyu (largest, with 21% of the national population), the Luhya (third largest at 13%), and the Kamba (fourth or fifth largest, with around 11% of the population).

Other Kenyan Bantu include the Chuka, Embu and Mbeere, Gusii, Kuria, Makonde, Meru, Mijikenda and the Taita.