Did contact with Homo floresiensis simplify some Indonesian languages? That’s the intriguing hypothesis put forward by linguist John McWhorter.
The languages of Keo, Rongga, and Ngadh, spoken on the island of Flores in Indonesia, are completely analytic (meaning of a very simplex grammatical form), and yet are surrounded by hundreds of related languages that are much more complex.
Hat tip to Bjorn Ostman at Pleiotropy. Bjorn points out,
In 2008 McWhorter published an article  in which he made the argument that it is not just rare that languages evolve to become simpler overall without the language being acquired by adults, but that such simplification is indeed impossible.
McWhorter thinks that such simplification occurs only when the language is spoken imperfectly by strangers who never learn all its complexity. Then those adults must be in the community so that children of the community hear the simplified language as they are growing up.