Humans have a long history of diving to forage from the seabed and today elite freedivers are reaching greater depths than ever. Some researchers argue humans belong in the sea.

Alessia Zechinni rests on the surface of the ocean, staring at the sky, thinking of nothing. Her mind is silent. "If some thoughts come," she says, "I gently push them down. I focus on my breathing. It brings me calm. The last breath is the biggest one. I put all the air I can into my lungs – so I am able to dive deeper."

At first Zechinni kicks her fins hard to propel herself down from the surface, arms outstretched above her head. "After about 25m (80ft), I start to kick more gently," she says. At around 60m (200ft), she stops moving her body entirely. "I free-fall. That part is amazing. It's like flying in the water."

Zechinni, a freediver and author, has broken 40 world records and earned more than 30 international medals for freediving, including 17 World Championship golds. In 2023, she reached the record-breaking depth of 123m (404ft) unassisted.

She is one of a handful of people known to have dived to these kind of depths with nothing but a lungful of air. Yet, there is growing evidence that humans may actually be better adapted to freediving than previously believed, and that it has played a crucial role in human evolutionary history. Some scientists think humans may even be natural divers, akin to otters. A rare few – like Zechinni – are able to compete with seals.

As Zechinni descends on her dive, the sunlight dwindles and cold envelops her. She doesn't look at the guideline that leads her down, but at the bright blue of the ocean as it fades into blackness. In the past, Zechinni would have used a torch to ward off the gloom. But nowadays she goes without, enjoying the "blue that is becoming darker and darker" and using the diminishing light to gauge her depth.

"The deeper you go, the stronger the narcosis gets," she says. "It's like you're drunk." Zechinni describes the "rapture of the deep" – or nitrogen narcosis. Nitrogen narcosis is usually only experienced by scuba divers when inhaling compressed gasses from a scuba tank. However, at extreme depths freedivers can also experience this phenomenon, as nitrogen stored in their lungs becomes compressed and enters the bloodstream.

Nitrogen under pressure acts as a narcotic and can induce feelings of anxiety, drowsiness and euphoria, and cause impaired judgment and hallucinations. "To be drunk at 100 metres (328 ft) is not the best," says Zechinni. "The key is to stay focused – don't think, just feel – and live the present."

Extreme Sport

Freediving is an extreme sport and is associated with number of health risks including shallow water blackout, which can lead to decompression sickness, injury to the lungs and brain, drowning and death. According to the Professional Association of Diving Instructors (Padi), freediving should only be undertaken by trained individuals and never alone.

At the bottom of the line, Zechinni turns "super gently" and prepares to make her return to the surface. "You are less than halfway," she says, "because the ascent is much harder than the descent."

For the first 60m (200ft) of the climb she kicks hard. At around 35m (115ft), Zechinni is relieved to meet the safety divers who are waiting for her. Now, she can kick more gently until she reaches the surface.

"It's beautiful," she says. "When you're coming up, the blue is getting lighter and brighter." And when she takes her first few breaths of fresh air, she says she can feels the oxygen surging through her body, filling "every cell".

As of 2024, 7,269 people are known to have looked down on the Earth from its highest peak, and more than 700 people have seen our planet from space. Zechinni is part of a rare group of people who have looked up from ocean depths of 100m (328ft) or more, with nothing but a single breath in their lungs to keep them alive.

Pushing the limits of human physiology, Branko Petrovic held his breath for 11 minutes 54 seconds in 2014. In 2023, Alexey Molchanov sunk to a record-breaking 133m (435ft) without use of weights or fins. And in 2021, Budimir Šobat set the world record for the longest breath-hold underwater, after inhaling pure oxygen, at a whopping

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