Very happy to concede the Arabs did lead the world once upon a time so intelligence undisputed with the smart ones just trying to work out exactly why they fell behind under Islam.
Good question, Ive only got 2 overly-simplistic answers for this one
i) in-fighting resulted - a religion that grew by the sword, was ultimately destroyed by its own sword
ii) there came a critical point where our civilisations needed education, not brute force, for continued growth and sustenance - as the Islamic meme was inflexible and could only work on one cylinder, it faltered..
If anyone can do better I would also be interested to know..