`There appear to be confusion with Language and Grammer. For analysis of origin of laugnage, grammer is not the most important element. High end words such as academic terms  (greek or latin in English) or words describing foreign import (french in English) is the easiest to change.  Just because English contain lot of french, latin words doesn't make this Germanic language into a romanic language.   Then come the grammer. This is one hot potatoe in ``Altaic`` language controversy. Though Mongolian, Turkish, Manchurian, Korean and Japanese all have similar syntax structure which indicate shared ``proto`` Altaic origin, some argue that these syntax is not actually a structured syntax system but a syntax system which lost much of syntax rule. ``Altaic`` language is characterised by highly flexible sentence structure where writing can go on and on without full stop. This is because it utilise SOV (subject, object, verb) syntax or more importantly passive OVS syntax (or just OV) with use lot of which/what/when to connect sub sentence. You can see this from how I write. English on the other hand, is considered to have one of most rigid syntax system and is one of the main reason Japanese or Korean find English grammer hard to grasp. If you know Japanese, for example, most Japanese conversation doesn't make sence in itself. Conversation is just exchange of noun, like ``(Done) this?`` ``(Do) this``, ``(Do you want) this?`` or even worse, ``(Have you bought) Milk (I asked you to buy this morning)?`` This is one reason why Japanese is one of the easiest language to ``speak`` at elementary level. Subsequently, those oppose to proto-Altaic linguist theory argue that there are not such thing as proto Altaic laugnage(grammer), rather the similarity is a result of high degree of interaction between these normadic groups, which resulted in flexible syntax.   Relating to this Altaic controversy is the importance of pronounciation system and commonly used words (eat, take, rice, etc). In linguistic, this is more important than grammer because pronounciation and common words are more resilenent to change. And Korean and Japanese share very little verb or commonly used nouns not to mention totally different pronounciation system. Therefore, no linguist would put current Japanese and Korean language in the same linguistic group. This also apply to Korean which is derived from Sillian. Sillian/Korean pronounciation and commonly used words is distinctly different from not just Japanese but also Mongolian and Manchurian. Some argue, based on some reference in ancient Chinese text, that Sillian may have been a off shoot of Han, (though pronounciation lost much of tune aspect) through interaction with largely Tungustic tribes. Anyway, as far as Japanese goes, it is somewhat regarded as creole language between malay/polinesian pronoucniation and Tungustic syntax. Controversy is more about contextualisation of Japanese grammer in term of Altaic controversy which is not directly relevant to Yayoi.   `