A large group of yellowfin tuna swimming off the coast of Italy. Like all fish, they sleep, but it’s not like human sleep.
Giordano Cipriani/The Image Bank via Getty Images
This item is available in full to subscribers.
To continue reading, you will need to either log in to your subscriber account, or purchase a new subscription.
If you are a current print subscriber, you can set up a free website account and connect your subscription to it by clicking here.
Otherwise, click here to view your options for subscribing.
If you're a print subscriber, but do not yet have an online account, click here to create one.
Click here to see your options for becoming a subscriber.