The big difference between Somali and other Eastern Cushitic (EC) languages in their cognation with Arabic and Egyptian may partly reflect knowledge bias, since the present author can more readily ascertain Somali than the other Cushitic languages. However, this ascertainment can still temporarily serve as an indication of what may be expected in the cognation between Cushitic and the two other branches.
It is true that pre-Islamic Arabic loanwords may sometimes disguise themselves as cognates. Yet this does not necessarily favor a southern origin, since the Northerners were not themselves from the south. A forthcoming revised study suggests that the relationship between Somali and Arabic is far deeper than usually assumed—covering lexical, phonological, morphological, and grammatical comparisons. The Somali–Egyptian cognation also appears to be at an unexpected level.
For instance, why is Somali the only Cushitic language that shares with Egyptian the word for dog (Somali ay, Egyptian ayu)? All other Lowland Eastern Cushitic languages call the animal karre, a word absent in main Somali. This is but one example among many [ref: ].
Taking the economic lexemes and the Black core lexemes together, it becomes clear that Somali does not contain a substratum. The Somali language did not lose contact with Arabic and Egyptian, nor was it exposed to any earlier or stronger culture that might have replaced such connections. Its residence in a wide peninsula, surrounded inland by related languages, helped it sustain a relative closeness to Proto-Afroasiatic.