[♪ INTRO].

The Medieval times are famous for being a period of darkness in the history of science. And in a lot of ways, they were—for the Western world.

But just south and east of the Mediterranean Sea, the Islamic world was in its golden age. Between around 750 and 1250 C. E., the Islamic empire made incredible advances in science, and many of these discoveries have shaped our modern world, giving us things like cataract surgery and algebra.

But there’s also another major lesson that came out of this period:. Diversity makes for better science. At this time, the Islamic empire stretched all the way from the Arabian peninsula east into China, as well as west across North Africa and the Iberian peninsula.

And there was a lot about this empire that set it up for this golden age of science. Like, in the early years of Islam, the mission to understand the world was a religious one and a scientific one— there was no difference. So, Muslim scholars translated hundreds of thousands of manuscripts from Greek,.

Roman, Persian, Indian, and Egyptian scientists into Arabic. So they had the combined knowledge of all these civilizations as a base. But it wasn’t just the knowledge that was diverse:.

It was a massive empire, and it included Persians, North Africans,. Spaniards, Portuguese, Chinese, and Arabs. And across the region, all of these people with different backgrounds were sharing, translating, and exchanging ideas.

One of the most famous scientists from this period is the Persian scholar known as the father of algebra, Muḥammad ibn Mūsā al-Khwarizmi. Al-Khwarizmi worked in a library in Baghdad called the House of Wisdom, where academics from all different backgrounds came together to work side by side. They included some of the most famous scientists of the time— and they worked on all types of science.

But while his colleagues pored over ancient texts, studied the stars, and invented medical treatments, al-Khwarizmi wrestled with math. And one of the problems he took on was the quadratic equation. People had been working on this equation for thousands of years.

The ancient Egyptians, Chinese, Babylonians, and Greeks all recognized that if you have an area enclosed by a square, the amount of stuff you can put in that area is related to the length of one side. In other words, the length squared was related to area. And any time you have an equation with a certain value and the square of that value, it’s called a quadratic equation.

These equations could be important for practical reasons:. Like, say you want to build a shed and it needs to have a certain capacity. It would be useful to know exactly how long to make the sides so you don’t overshoot or undershoot.

Various civilizations managed to solve certain specific problems like this in one way or another—so, they might have been able to figure out how long to make one particular shed. But they didn’t have expressions that would let them relate something like length with area in a general way. Al-Khwarizmi was the first to do that.

Instead of solving problems with specific numbers, he used variables as placeholders. It’s not clear where he got that idea, but it made it possible for him to grasp the universal form of the problem— and come up with a universal procedure for solving it. In doing this, al-Khwarizmi essentially founded algebra.

Because that’s what algebra is: manipulating symbols to find general solutions that work with any numbers. Al-Khwarizmi was familiar with a lot of the work that had been done before him. He seems to have integrated knowledge that Indians,.

Babylonians, and Greeks developed over centuries. But by introducing the concept of manipulating variables, he gave us a whole new power. While al-Khwarizmi worked on algebra, three of his contemporaries worked on another enormous accomplishment from the House of

Wisdom: “The Book of Ingenious Devices.” The book was written by three Persian brothers called the Banu Musa, and it documented about 100 automatic devices—things like fountains, clocks, and toys. Some of these were their own inventions, but the book also compiled a bunch of existing devices. It included a bunch of inventions documented by the Greeks, but which likely came from various places, like Iran, India, and China. Even though they leaned heavily on Greek texts, the Banu Musa approached their work differently:.

While the Greeks tended to focus on the principles of mechanics, the brothers focused more on the applications. In other words, they wanted to build something that worked— they weren’t as worried about how. Now, many of their devices weren’t actually that useful… but that wasn’t necessarily the point.

Because at the time, engineering was seen a lot like art. People may have collected these devices the way they would collect paintings. But even if the brothers didn’t intend to revolutionize modern life, they did end up building some devices that were kind of useful.

For instance, a handful of their devices used an automatic crankshaft. These were contraptions that had a jar or water trough that was designed to automatically fill back up from some reservoir any time it was emptied. They used a floater to gauge the water level, and the floater was attached to a rod.

As that rod went up and down, it turned a valve, which controlled the flow of water from a big bucket that served as a reservoir. This was the first automatic crankshaft ever documented. It didn’t make a full turn, so it didn’t look exactly like today’s crankshafts, but it did serve the same general purpose: It turned linear motion into rotational motion.

Today, your basic engine does the same thing: It has pistons going up and down, and they attach to a crankshaft that rotates a wheel. No one is sure if there’s any direct connection between the Banu Musa brothers and the crankshaft that emerged around 500 years later in Europe, which eventually went on to be used in engines. But even if not, the brothers showed that they had a grasp of some of the engineering principles that still power the world today.

Finally, although both the Banu Musa brothers and al-Khwarizi were based at the House of Wisdom in Baghdad, that wasn’t the only hub for academics. Another was at Bukhara, a Persian city in what’s now Uzbekistan. Like Baghdad, Bukhara was right along the major East-West trade route called the Silk Road, so there were always people circulating through.

And it became a hub for arts and sciences during Islamic times. That was the home and workplace of scientist. Abū-ʿAlī al-Ḥusayn ibn-ʿAbdallāh Ibn-Sīnā.

Ibn-Sīnā was Persian philosopher, physician, and physicist known for uniting ideas from the East and West. And, really, it’s hard to decide what to even focus on, because the guy had a hand in just about every kind of science. Like, he worked on principles of motion and figured out the concept of linear momentum centuries before Isaac Newton.

He also observed a supernova and wrestled with problems like consciousness and the concept of infinity. But what he’s most famous for is writing a book called “The Canon of Medicine,” which outlined principles for treating illness and injury and feels surprisingly modern. For instance, it outlined a procedure for cataract surgery.

Cataracts are clumps in the eye’s lens that form as proteins in the eye break down. They get worse over time and can cloud a person’s vision. But Ibn-Sīnā came up with a procedure to restore vision in people with cataracts:.

A surgeon would insert an instrument into the eye and just nudge the cataracts down, out of the line of sight. It didn’t look much like today’s surgeries, where cataracts are typically broken up by a laser or ultrasound and then removed, but it did the trick. The Canon also spells out a process for testing and administering new drugs that isn’t so far off from what we do today.

For instance, Ibn-Sīnā highlighted how important it is to isolate the illness to understand whether or not a drug works. In other words, you can’t reliably test a drug on someone with multiple illnesses. He also emphasized that it’s necessary to test drugs in human bodies, not just other animals.

Today, these concepts sound basic. But they don’t go without saying. And the principles that Ibn-Sīnā laid out around a millennium ago are still relevant in drug trials today.

But although he was precocious, the practices and procedures outlined in Ibn-Sīnā’s books weren’t just born out of his own brilliance. Starting as a kid, he had lots of wide-ranging influences. He learned Indian arithmetic from a local grocer, and read the texts of many scientists who’d come before him.

He also adopted certain practices from Indian and Chinese medicine, like the use of medicinal herbs. And he pulled theories and principles from Greek medicine and integrated them into his own teachings. Thanks to these influences, he created a powerful, holistic practice of medicine that he’s still known for today.

In a lot of ways, this history speaks for itself:. It shows that the science that defined this golden age grew out of connections between people with totally different social and academic backgrounds. And sure, some of that is because they were all in the right place at the right time to take advantage of centuries’ worth of knowledge from different civilizations.

But what we know about diversity today suggests that wasn’t the whole story. Even now, diversity still produces better science— even though we have the internet and don’t need cross-cultural collaborations to exchange knowledge. And that strongly suggests that diversity itself plays a role.

One major study on this came out of Harvard in 2015. The authors were curious if there was any relationship between the quality of a study and the ethnic diversity of a research team. So they examined 2.5 million scientific papers published by teams based in the U.

S. between 1985 and 2008. They used the authors’ last names as a way to gauge the amount of ethnic diversity. And they used the number of citations and place of publication as markers of success.

These are crude approximations, and of course, last names aren’t perfect or exclusive signals of diversity. But even so, a couple trends jumped out. For instance, teams with authors of four or five different ethnic backgrounds got 5 to 10% more citations than non-diverse teams.

They also published in more reputable journals. The study authors acknowledged that you could interpret these findings in a few ways. Like, maybe more diverse teams have broader professional networks, so their work has a broader reach, even if it’s not necessarily better.

But other research lends weight to the idea that diversity improves the quality of research itself. Because study after study shows that diversity is linked with creativity. Research has shown that when we’re in a diverse setting, we make fewer assumptions— because we’re less likely to take it for granted that our peers will agree with us.

We also anticipate pushback, which makes us craft better arguments in the first place. That may be why studies have found that people who work outside their home countries are more creative. Or why they’ve found that people in cross-cultural relationships make better entrepreneurs.

The authors of one such study concluded that relationships that broaden our horizons actually change the way we think and also make us better at coming up with creative ideas. Overall, the Islamic golden age with all of its intersecting cultures was the perfect place for this kind of creativity to take hold. Many of the ideas that emerged changed how things worked at the time, and some of them laid the foundation for research we're still doing today.

And along the way, these discoveries continue to remind us what happens when different minds come together. Thanks for watching this episode of SciShow! And a special thanks to this month’s President of Space, Charles Szasz, and to the amazing community that supports us on Patreon.

We couldn’t make these videos without you. And if you’re not a patron but would like to help us make science education free on the internet, you can find out more at patreon.com/SciShow. [♪ OUTRO].