From your readings and Google searches, put in an explanation or some information about the concepts and people discussed in this topic. Try to paraphrase. Be short and simple.

Suggested keywords:

Natural order hypothesis, acquisition/learning hypothesis, monitor hypothesis, input hypothesis, affective filter hypothesis, caretaker talk/baby talk, base line talk, foreigner talk, roughly-tuned input, finely-tuned input, the critical period hypothesis ...

Stephen Krashen, Eric Lenneberg ...