The Islamic Republic of Iran is believed to have the highest brain drain in the world. According to this BBC report in January:

According to the IMF more than a 150,000 of the best young minds in Iran are leaving every year.

Recall that the word for algebra is a Persian word derived from a pamphlet written by a Persian mathematician in around 820 CE who was born in what is today Uzbekistan.

The photo above gives you an idea of what the Islamic world was able to build when it wasn't experiencing such a widespread brain drain. In fact this mosque, the Kok Gumbaz in Samarkand, was built by Ulugh Beg, a Timurid ruler, who in his spare time did groundbreaking work in astronomy, trigonometry, and spherical geometry.

But as Wikipedia writes:

Unfortunately Ulugh's scientific prowess was not matched by his administrative skills. He lost some battles to rival kingdoms, and in 1448 massacred the people of Herat after defeating Mirza Ala-u-dowleh, son of Bai sunqur. Within two years he was beheaded by his own eldest son, 'Abd al-Latif while on his way to Mecca.

Nevertheless his legacy lived on: In the 1800s a German astronomer even named the Ulugh Beigh crater on the Moon after him.

Arab brain drain: You don't have to be a genius to figure this out

Another news item from The Peninsular, Qatar's leading English-language daily:

Brain drain is the biggest challenge the Arab nations are facing today. From countries like Algeria and Tunisia, for instance, a large number of nurses and technical medical staff have migrated.

The irony is that despite having spent through the nose on education of these sons of the soil who have deserted their homeland for greener pastures, these countries have to spend additionally to import skilled manpower from elsewhere in the world to meet their own needs.

Now why would this be so? The Peninsula reports:

Surveys indicate that higher earnings are not a major consideration for most of the highly qualified Arabs to live in the West.

It is the social and political environment in their home countries which is keeping most of them away.