The Congo Pygmies (African Pygmies) are those "forest people" who have, or recently had, a hunter-gatherer economy and a simple, non-hierarchical societal structure based on bands, are of short stature, have a deep cultural and religious affinity with the Congo forest and live in a generally subservient relationship with agricultural "patrons", with which they trade forest products such as meat and honey for agricultural and iron products. Though lumped together as "Pygmies" by outsiders, including their patrons, these peoples are not related to each other either ethnically or linguistically. Different Pygmy peoples may have distinct genetic mechanisms for their short stature, demonstrating diverse origins. Original Pygmy language(s) An original Pygmy language has been postulated for at least some Pygmy groups. Merritt Ruhlen writes that "African Pygmies speak languages belonging to either to the Nilo-Saharan or Niger–Kordofanian families. It is assumed that Pygmies once spoke their own language(s), but that, through living in symbiosis with other Africans in prehistorical times, they adopted languages belonging to these two families." The linguistic evidence that such languages existed include Mbenga forest vocabulary which is shared by the neighbouring Ubangian-speaking Baka and Bantu-speaking Aka (though not by the Mbuti, and this connection is not ancient) and the Rimba dialect of Punu which may contain a core of non-Bantu vocabulary. It has been postulated that ancestral speakers may have been part of a complex of non-Pygmoid languages of hunter-gatherer populations in Africa whose only surviving descendants today mostly ring the rainforest. A common hypothesis is that African Pygmies are the direct descendants of the Late Stone Age hunter-gatherer peoples of the central African rainforest who were partially absorbed or displaced by later immigration of agricultural peoples and adopted their Central Sudanic, Ubangian and Bantu languages. While there is a scarcity of excavated archaeological sites in Central Africa that could support this hypothesis, genetic studies have shown that Pygmy populations possess ancient divergent Y-DNA lineages (especially haplogroups A and B) in high frequencies in contrast to their neighbours (who possess mostly haplogroup E). Some 30% of the Aka language is not Bantu, and a similar percentage of the Baka language is not Ubangian. Much of this vocabulary is botanical, and deals with honey-collecting or is otherwise specialized for the forest, and much of it is shared between the two western Pygmy groups. It has been proposed that this is the remnant of an independent western Pygmy (Mbenga