 For example, that Chinese speakers learning English as an L2 often omit third-person singular agreement morphology in obligatory contexts could easily be explained because these features are uninterpretable in Chinese.By the 2000s it was generally accepted that adult SLA differed from child L1 acquisition in process and typical outcomes and there was evidence for adult accessibility in at least some properties of UG.This motivated GenSLA theory to shift focus from questions just about UG accessibility and specific features to describing and explaining variation at group and individual levels.The last decade has also seen a significant increase in GenSLA studies that examine SLA in populations complementary to L2 acquisition including heritage bilingualism, child L2 acquisition, and multilingual acquisition to gain new insights into the latter.