It’s true: Muslims once led the rest of the world in various intellectual endeavors, notably mathematics and science. But there was such a decline after this “Golden Age” that of the age itself there is scarcely any trace left in the Islamic world.
Take, for example, the medical sciences. Muslims established the first pharmacies and were the first to require standards of knowledge and competence from doctors and pharmacists, enforced by an examination . At the time of the fifth Abbasid caliph, Harun al-Rashid (763-809), the first hospital was established in Baghdad, and many more followed. Yet it was not a Muslim, but a Belgian physician and researcher, Andreas Vesalius (1514-1564), who paved the way for modern medical advances by publishing the first accurate description of human internal organs, De Humani Corporis Fabrica (On the Fabric of the Human Body) in 1543. Why? Because Vesalius was able to dissect human bodies, while that practice was forbidden in Islam. What’s more, Vesalius’s book is filled with detailed anatomical drawings — but also forbidden in Islam are artistic representations of the human body.
In mathematics, it’s the same story. Abu Ja’far Muhammad ibn Musa al-Khwarizmi (780-850) was a pioneering mathematician whose treatise on algebra, once translated from Arabic, introduced generations of Europeans to the rarified joys of that branch of mathematics. But in fact, the principles upon which al-Khwarizmi worked were discovered centuries before he was born — including the zero, which is often attributed to Muslims. Even what we know today as “Arabic numerals” did not originate in Arabia, but in pre-Islamic India — and they are not used in the Arabic language today. Nonetheless, there is no denying that al-Khwarizmi was influential. The word “algebra” itself comes from the first word of the title of his treatise Al-Jabr wa-al-Muqabilah; and the word “algorithm” is derived from his name. Al-Khwarizmi’s work opened up new avenues of mathematical and scientific exploration in Europe, so why didn’t it do the same in the Islamic world? The results are palpable: European’s ultimately used algebra, in conjunction with other discoveries, to make significant technological advances; Muslims did not. Why?
One answer is that Europe had a long-standing intellectual tradition that made such innovations possible, while the Islamic world did not. This even included making use of Arabic works in ways that Muslims themselves did not: Aristotle, along with his Muslim commentators Avicenna and Averroes, were studied in European universities in the twelfth century and after, while in the Islamic world their work was largely ignored and certainly not taught in schools, which concentrated then, as now, mostly on memorization and study of the Qur’an…
Much of the responsibility for this must be laid at the feet of the Sufi Abu Hamid al-Ghazali (1058-1128). Although he was a great thinker, he nevertheless became the chief spokesman for a streak of anti-intellectualism that stifled much Islamic philosophical and scientific thought…
In his Incoherence of the Philosophers, al-Ghazali accordingly accused Muslim philosophers of “denial of revealed laws and religious confessions” and “rejection of the details of religious and sectarian teaching, believing them to be man-made laws and embellished tricks” . He accused the Muslim philosophers al-Farabi and Avienna of challenging “the very principles of religion” …
Al-Ghazali’s attack on the philosophers was a sophisticated manifestation of a tendency that has always hindered intellectual development in the Islamic world:
There is a prevailing assumption that the Qur’an is the perfect book, and no other book is needed. With the Qur’an the perfect book and Islamic society the perfect civilization, too many Muslims didn’t think they needed knowledge that came from any other source — certainly not from infidels.
 Philip Hitti, The Arabs: A Short History (Washington, DC: Regnery, 1996), 141-42.
 Abu Hamid al-Ghazali, The Incoherence of the Philosophers, translated by Michael E. Marmura. (Provo, UT: Brigham Young University Press, 200), 2.
 Ibid., 8.
Chapter 7, “How Allah Killed Science”
The Politically Incorrect Guide to Islam (and The Crusades)