I want to know the answer to the following question:
What researcher posited that the lowering of diphthongs is "natural"?
All the background I'm provided with is that "Stroop theorizes that the lowering of open-mid to open diphthongs is a phonetically "natural" and inevitable development and that Dutch, after having diphthongised the long high vowels like German and English, "should" have lowered the diphthongs like German and English as well.". Is that enough to answer the question?
Answer: yes