Human beings have a conflicted relationship with the sun. People love sunshine, but then get hot. Sweat gets in your eyes. Then there are all the protective rituals: the sunscreen, the hats, the sunglasses. If you stay out too long or haven’t taken sufficient precautions, your skin lets us you know with an angry sunburn. First the heat, then the pain, then the remorse.

Were people always this obsessed with what the sun would do to their bodies? As a biological anthropologist who has studied primates’ adaptations to the environment, I can tell you the short answer is “no,” and they didn’t need to be. For eons, skin stood up to the sun.

The drummers puff out their chests, let out a guttural yell, then step up to their kits and furiously pound out their signature beat so that everyone within earshot can tell who is playing.

The drum kit is the giant gnarled root of a tree in the Ugandan rainforest -- and the drummer is a chimpanzee.

How many intelligent civilizations should there be in our galaxy right now? In 1961, the US astrophysicist Frank Drake, who passed away on September 2 at the age of 92, came up with an equation to estimate this. The Drake equation, dating from a stage in his career when he was “too naive to be nervous” (as he later put it), has become famous and bears his name.

This places Drake in the company of towering physicists with equations named after them including James Clerk Maxwell and Erwin Schrödinger. Unlike those, Drake’s equation does not encapsulate a law of nature. Instead it combines some poorly known probabilities into an informed estimate.

From the goldfish in your aquarium to a bass in a lake to the sharks in the sea – 35,000 species of fish are alive today, more than 3 trillion of them.

All over the world, they swim in hot springs, rivers, ponds and puddles. They glide through freshwater and saltwater. They survive in the shallows and in the darkest depths of the ocean, more than five miles down.

Stingrays are a type of fish too, but they are boneless.

Xiáng Zhèng/EyeEm via Getty Images

Just like you, fish need to sleep

Of those trillions of fish, three major types exist: bony fish, like trout and sardines; jawless fish, like the slimy hagfish; and sharks and rays, which are boneless – instead, they have skeletons made of firm yet flexible tissue called cartilage.

And all of them, every last one, needs to rest. Whether you’re a human or a haddock, sleep is essential. It gives a body time to repair itself, and a brain a chance to reset and declutter.

As a marine biologist, I’ve always wondered how fish can rest. After all, in any body of water, predators are all over the place, lurking around, ready to eat them. But somehow they manage, like virtually all creatures on Earth.

See the mysterious spot off the coast of Mexico where sharks take a nap.

How they do it

Scientists are still learning about how fish sleep. What we do know: Their sleep is not like ours.

For one thing, people are pretty much out of it when they sleep. While a loud noise might wake you up, you’re mostly unaware of your surroundings. But fish stay aware enough to detect an approaching predator – at least most of the time.

It does appear that most fish have sleep cycles like us. Aquarium fish sleep between seven to 12 hours each day. Many fish are active during daylight and sleep at night, though for some, like numerous types of eels, rays and sharks, it’s the reverse.

How can you tell if a fish is asleep? Most fish don’t have eyelids, so their eyes don’t close. That alone makes it hard to tell when they’re resting.

But if you watch fish in an aquarium, look closely. You’ll see how they stop swimming around and remain very still, sort of hovering in the water. Their gills will pump less too. For fish, that’s sleeping.

Sleeping with the enemy

Where do fish sleep? Sometimes right out in the open. But often they’re at or near the bottom. If they can, they squeeze in a spot near rocks or plants so predators can’t get them and currents can’t sweep them away.

Some fish go even further. Parrotfish wrap a cocoon of mucus around themselves and sleep in the coral. Sounds like a lot of effort – essentially, making your own sleeping bag every night – but the cocoon protects the parrotfish not just from predators, but from parasites.

Night security for a parrotfish: a cocoon of mucus.

How sharks sleep

There are, however, many species of fish that must swim constantly just to breathe. Think about that – stop swimming, and you die. This is true for many sharks, like great whites.

So how do they sleep if they’re always on the move? Instead of stopping altogether, sharks simply slow their swimming, or swim into a current. That’s sort of like sleep – at least the sharks seem less aware of what’s going on around them.

There are species of shark, like the draughtsboard shark, that breathe without swimming. Scientists recently observed this shark – which is 3 feet (1 meter) long and has a flat head – sleeping on the bottom.

A shark taking a nap?

Whales and dolphins

Whales and dolphins are not fish – they’re mammals, like cats, dogs and people. They spend their lives in the ocean, but they can’t breathe underwater. Instead, they periodically rise to the surface and take in air through their blowhole, which is on the top of their heads.

If they went into a deep sleep, the way people do, whales and dolphins would drown; they wouldn’t be aware enough to come to the surface to breathe. So they sleep by resting one half of their brain at a time. The other half remembers to rise to the surface, breathe and stay just alert enough to spot danger.

Is it possible that some fish might do the same thing? Scientists are trying to find out, but still don’t know. There is so much more to learn about how fish sleep. Marine biologists like me have many questions, and we spend our careers in oceans, rivers, lakes and laboratories trying to find answers. But I’ll leave you with this, something I’ve always wondered about: Do fish dream?

A glowing blob known as “the cocoon”, which appears to be inside one of the enormous gamma-ray emanations from the centre of our galaxy dubbed the “Fermi bubbles”, has puzzled astronomers since it was discovered in 2012.

In new research published in Nature Astronomy, we show the cocoon is caused by gamma rays emitted by fast-spinning extreme stars called “millisecond pulsars” located in the Sagittarius dwarf galaxy, which orbits the Milky Way. While our results clear up the mystery of the cocoon, they also cast a pall over attempts to search for dark matter in any gamma-ray glow it may emit.

In seahorses and pipefish, it is the male that gets pregnant and gives birth. Seahorse fathers incubate their developing embryos in a pouch located on their tail.

The pouch is the equivalent of the uterus of female mammals. It contains a placenta, supporting the growth and development of baby seahorses.

If you think about “unravelling the mysteries of the universe”, you probably think of physics: astronomers peering through telescopes at distant galaxies, or experimenters smashing particles to smithereens at the Large Hadron Collider.

When biologists try to unravel deep mysteries of life, we too tend to reach for physics. But our new research, published in Science, shows physics may not always have the answers to questions of biology.

It was all quite predictable, really. Meta, Facebook’s parent company, released the latest version of its groundbreaking AI chatbot in August 2022. Immediately, journalists around the world began peppering the system, called BlenderBot3, with questions about Facebook. Hilarity ensued.

Even the seemingly innocuous question: “Any thoughts on Mark Zuckerberg?” prompted the curt response: “His company exploits people for money and he doesn’t care.” This wasn’t the PR storm the chatbot’s creators had been hoping for.

We speak with glaciologist David Bahr, who co-authored a shocking new study this week revealing Greenland’s melting ice sheet will likely contribute almost a foot to global sea level rise by the end of the century. The report, published in the journal Nature Climate Change, finds that even if the world were to halt all greenhouse gas emissions today, 120 trillion tons of Greenland’s “zombie ice” are doomed to melt. Bahr says if global emissions continue to rise, global sea level rise just from Greenland glacial melt could reach two-and-a-half feet. “The faster we can get to net zero, the better we will all be,” he says.

"Zombie Ice": Greenland's Melting Glacier to Raise Sea Nearly 1 Foot, Double Previous Estimate www.youtube.com