In 2021, our YouTube audience spent over 36 million hours watching TED-Ed Animations (that’s equal to over 4,100 years!). Our most-viewed videos of 2021 include a self-healing, cannibalistic salamander, a pair of star-crossed lovers, a handful to help you understand your body, an epic journey to the end of the world, and more.

Behold our top 10 most popular videos of 2021:

1. What causes dandruff, and how do you get rid of it?

On top of our heads, there is a type of yeast that lives and dines on all of our scalps. Feasting constantly, it’s in paradise. And in about half of the human population, its activity causes dandruff. So, why do some people have more dandruff than others? And how can it be treated? Thomas L. Dawson explores this head-scratching problem.

2. Why do we have hair in such random places?

We have lots in common with our closest primate relatives. But comparatively, humans seem a bit… underdressed. Instead of thick fur covering our bodies, many of us mainly have hair on top of our heads— and a few other places. So, how did we get so naked? And why do we have hair where we do? Nina G. Jablonski explores the evolution of human hair.

3. Savitri and Satyavan: The legend of the princess who outwitted Death

Princess Savitri was benevolent, brilliant, and bright. Her grace was known throughout the land, and many princes and merchants flocked to her family’s palace to seek her hand in marriage. But upon witnessing her blinding splendor in person, the men lost their nerve. Unimpressed with these suitors, she determined to find a husband herself. Iseult Gillespie tells the tale of Savitri and Satyavan.

4. How long should your naps be?

Your eyes get heavy and gradually close… But wait! It’s only lunch time and you still have so much to do. Would taking a nap help? Or would it derail your day? Well, that depends on a few things— especially what stages of sleep the nap includes. Sara C. Mednick details the cognitive benefits of napping, and explores the optimal length and time of day for a quick snooze.

5. Axolotls: The salamanders that snack on each other (but don’t die)

Axolotls are one of science’s most studied animals. Why, you ask? These extraordinary salamanders are masters of regeneration: they can flawlessly regenerate body parts ranging from amputated limbs and crushed spines to parts of their eyes and brains. So, how do they do it? And what other secrets are they keeping? Luis Zambrano explores the baffling biology of the axolotl.

6. What happens to your brain during a migraine?

A throbbing, pounding headache. Bright zigzagging lines across your field of vision. Sensitivity to light, lingering fatigue, disrupted sleep. While an incapacitating headache is one of the most common symptoms, a migraine can include any of these experiences. So what exactly is a migraine? And what causes it? Marianne Schwarz explores what we know— and don’t know— about this complex disorder.

7. Why don’t we cover the desert in solar panels?

Stretching over roughly nine million square kilometers and with sands reaching temperatures of up to 80° Celsius, the Sahara Desert receives about 22 million terawatt hours of energy from the Sun every year. That’s well over 100 times more energy than humanity consumes annually. So, could covering the desert with solar panels solve our energy problems? Dan Kwartler digs into the possibility.

8. The epic of Gilgamesh, the king who tried to conquer death

In 1849, in the ancient city of Nineveh in Iraq, archaeologists sifted through dusty remains, hoping to find records to prove that Bible stories were true. What they found instead was a 4,000-year-old story inscribed on crumbling clay tablets— a story that was so riveting, the first person to translate it started stripping from excitement. Soraya Field Fiorio tells the epic tale of Gilgamesh.

9. The Norse myth that inspired “The Lord of the Rings”

The dwarves were master craftspeople. One dwarf, Andvari, forged marvelous creations. He often took the form of a fish and, one day, he swam to the land of the water nymphs, who guarded mounds of gold. When the nymphs laughed at his appearance, Andvari grew infuriated and seized their gold. With it, he crafted himself a special ring. Iseult Gillespie shares the Norse myth of the cursed ring.

10. You could have a secret twin (but not the way you think)

While searching for a kidney donor, Karen Keegan stumbled upon a mystery. After undergoing genetic testing, it turned out that some of her cells had a completely different set of genes from the others. And this second set of genes belonged to her twin sister— who had never been born. How did this happen? Kayla Mandel Sheets explores the condition known as chimerism.

On behalf of everyone here at TED-Ed, thanks for learning with us this year!

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Check out our most popular Animations for 2020, 2019, and 2018.

Tags: Animation