I believe the point about Southern dialects retaining more archaic words and features is largely accurate. It’s not simply that the Northern dialects have more borrowings or foreign influence distinguishing them from the Southern dialects; rather, they have undergone more internal innovation and linguistic change.
Southern dialects, in fact, share about 80%+ of their lexicon and vocabulary with the Northern Somali dialects.
To make this clearer, let me show a few examples of these innovations.
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As you can see, Northerners say weji for “face” instead of fool, which is the form used in the southern dialects. However, the original word still exists in Northern dialects in expressions like fool xuume (“ugly face”), showing that it has not disappeared entirely.
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Another example is how Northerners once pronounced gaal instead of geel (“camel”), a pronunciation preserved in certain clan and place names. Interestingly, this older form is still maintained in southern dialects. You can also see such variations reflected in old Somali poetry, where certain words or expressions, though less common in daily northern speech, appear frequently and align more closely with southern usage.
This doesn’t mean that Southern Somali dialects are inherently older than Northern ones; rather, it indicates that the Northern dialects have undergone more change over time. These differences are the result of processes of convergence and differentiation, which are closely tied to ecology and patterns of social interaction.
The final point you mentioned is similar to how we say that reer miyi (rural people) tend to preserve more traditional Somali expressions than reer magaal (urban people). In this context, it’s not a matter of a herding-versus-farming distinction, when they talk about Arabic dialects, but rather a rural-versus-urban one. In fact, much of the urban South historically spoke varieties closer to the Northern dialects.
Even the Tunni dialect of Barawa, for example, clustered more closely with Northern dialects, setting it apart from the Tunni dialect spoken in the countryside: