Comparing some localised idiosynchrasies, particularly in media that mutate fast and allow local variation (such as re-allocation of the same set of sounds to different elements of the same set of meanings), reveal only our innate need to seem to have different identities. Underlying stuctures, even in all cultural media, are universal, as archetypal as physics, chemistry and number.
You accept the broad scientific assumption that cultural behaviour could arise only from either invention or adoption (Endicott and Welsch, in 'Taking sides, clashing views on controversial issues in anthropology', do not probe much further either, but they separate biological, migration, linguistic, and culture issues), but you do not study this question. Language and other media, for example, are not inseparable. You study migration routes, and superficial correspondences. These mutate within narrow ranges, like DNA and technology do. You pick out some isolated features, much like some linguists pick out the sound of some words to track migration. Yet a new study proves that all languages tend to use similar sound patterns for similar meanings. Language, particularly grammar, and thus meaning, and thus perception, is hard wired in us and in our environment. So are all cultural media.
As I posted in comment on your article, you adopt some of the silent assumptions of isolationism; that culture needs time to be ‘invented’ and ‘developed’; and that stylistic markers indicate transmission routes of the core content of culture. You may as well argue that technology (ensemble), intelligence and even perception depends on empire, or Head Office. As you argue that “cultures that do not interact ultimately stagnate… stunted growth in the backwaters of the world.”
There is a test case of a culture isolated in time and place by low population and weather, at Gobekli Tepe, about BC 8500. Their scouts brought flint from far and wide. Their cultural record is a full ensemble, including snakes. Their influence by conscious diffusion on the next known civilisation, Sumeria, next door but 4000 years later, is doubtful.
Compare Gobekli reliefs (particularly the two complex artworks on pillar D43 and pillar H56), with Harappan, Mohenjo Daro relief seals, some of them are on
You would need several stretches of supposed oral tradition and cultural missions to explain the overwhelming similarities.
There is a simpler explanation for culture; one DNA, one environment, one species, one consciousness. Same dreams, stories, calendar, ritual cycle, aspirations, technology, art, music, grammar. Some media allow thick layers of idiosyncrasy, of which every group makes full use to bond for the purpose of getting a corner on exploiting the environment, and rival groups, and one another. Those differences are artificial, but camouflage our overwhelming similarities.
You are practicing a kind of correspondence theory; these aprons or rituals or words or things look the same, therefore one set was the model for the other (which is often true), and therefore they were not re-invented (which is usually true); and therefore every society needs instruction, or it would devolve (which is false).