Despite speaking a Bantu language (Bantu came from central Africa), the agricultural Embu and Mbeere are one of the few Kenyan peoples whose oral traditions seem to locate their origins within Kenya, in fact very close to their present location to the southeast of Kirinyaga (Mount Kenya).
Tradition also speaks of a time when they were hunter-gatherers and used to live in "caves", meaning rock shelters or hollow trees in forests, much as the indigenous Kenyan groups of hunter-gathers such as the Okiek ("Ndorobo") did until the twentieth-century. Tradition further states that the Ndorobo visited the Embu a long time ago but did not stay, though it's more likely that the Ndorobo were there before the Embu arrived, and were either displaced or left when the forests began to be converted to farmland.
The numerically smaller Mbeere (around 100,000, as against an Embu population of around 450,000) live to the south of the Embu in the lower Kiangombe Hills. Despite their proximity to the British during the colonial period (Embu town was a major colonial centre), the Mbeere have always kept themselves apart (and have been kept apart) from the Kenyan mainstream.
The Kiangombe Hills are only barely fertile and poorly watered, dominated by thorn scrub and dust, which meant that the British had little interest in the area or the tribe, who were consequently left to themselves. As a result, some aspects of traditional culture lingered longer in Mbeere than they did in Embu, although nowadays they're both pretty much part of modern Kenya. The Mbeere are closely allied to the Embu, to whom they are related.
In times of famine - which strikes the Mbeere more frequently than the Embu - the Embu would supply staple food like maize and beans in return for goats, skins, sorghum and pigeon peas. Historically, the Embu also fought for the Mbeere, on a famous occasion in which the Kamba tried to oust the Mbeere from their land. The Embu and Mbeere jointly own sacred groves (matiiri) in Mwea, which is one of their traditional places of origin.
Medicine is the work of a specific clan called the Igamuturi, of which the hereditary family of the Mutia (the overall Embu chief) are part. Their origin is said to be a place called Gacavari, from where they also spread medicinal knowledge to the Mbeere and Kikuyu. It seems likely from this and other clues that the Igamuturi are descendants of a people indigenous to the Mount Kenya region who predated the arrival of the various groups that later became the Embu and Mbeere.
They may therefore be related to the various Kenyan hunter-gatherer groups still in existence, who traditionally lived in forests and were (and are still renowned as) experts in plant-derived medicines, as well as witchcraft.