Record-breaking divers are pushing human limits and reshaping scientists' view of our species

BBC News

26-07-2025

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."
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 24 minutes and 37 seconds.
When you consider the standard depth of an Olympic swimming pool is recommended to be between 2.5-3m (8-10ft) and the average person can hold their breath for 30 to 90 seconds, these feats of athleticism may seem impossible. But freediving has likely been practised by humans for tens of thousands of years.
Around 90,000 years ago, Neanderthals – who spent so much of their time in the water they were prone to swimmer's ear – would dive into the ocean to collect clam shells from the seafloor. Around 350BC, according to Aristotle, skin-diving sponge fishermen used lead weights to reach the seabed. And the Ama freediving fisherwoman of Japan have been harvesting shellfish and seaweed for over 2,000 years.
The nomadic Bajau of Southeast Asia rarely set foot on land and have relied on breath-hold diving for thousands of years. Bajau divers can accumulate up to five hours underwater per day over hundreds of dives foraging from the seafloor with the help of a set of weights, a pair of wooden goggles – and an unusually large spleen, which acts as an oxygen reservoir, a kind of "biological scuba tank".
The Haenyeo of Jeju Island, Korea, also have a physiological advantage when it comes to freediving. Recent research revealed these "sea women" posses a genetic variant associated with lower than average blood pressure.
The Haenyeo have been collecting sea urchins, abalone and other seafood from the ocean floor for thousands of years – often diving throughout pregnancy. Diving into water triggers vasoconstriction in most humans, causing blood pressure to rise, which can be dangerous during pregnancy. Researchers think the Haenyeo's genetic trait may have evolved to keep their unborn children safe.
While the abilities of these elite and traditional freedivers might seem superhuman to most of us, some experts think humans could, in fact, be natural shallow-sea foragers akin to otters.
"Among all the diving species that we know of in mammals, most are found in the shallow diving category," says Erika Schagatay, professor of animal physiology at Mid Sweden University. "Shallow divers – like the beaver, otter and muskrat – forage underwater. And humans fit right into that shallow diving mammal category."
Humans, like other diving mammals, have a dive response which is brought on by entering water and apnoea. Their heart rate slows to conserve oxygen consumption; the blood vessels narrow particularly in the extremities, selectively redistributing blood flow to critical organs, such as the brain and heart. The spleen also contracts, injecting a supply of oxygenated red blood cells into the animal's circulatory system.
In her research, Schagatay compares the diving ability of a variety of aquatic, semiaquatic and terrestrial species – looking at the depth and duration of their diving, as well as the proportion of time spent under water during repeated dives.
She defines three distinct groups of diving mammals. "Deep divers" such as sperm whales and elephant seals regularly dive to depths of 200m (660ft) for more than 20 minutes at a time.
"Moderate divers" like sea lions, bottlenose dolphins, long-finned pilot whales, along with most other pinnipeds and cetaceans, regularly dive for 10-20 minutes, reaching depths of up to 100m (330ft).
The third group is made up of species which "are specialised to shallow diving", says Schagatay. This is where humans fit in, she says, alongside otters, beavers and hippos. A dive for a "shallow diver" would last up to two minutes, typically within the upper 50m (165ft) of water.
Humans' "maximum diving capacity is well within the typical ability performed by shallow near shore foragers", writes Schagatay in her research paper. Humans can repeatedly dive to 20m (65ft) and spend as much as 60% of the time submerged – much like other species in the shallow diving group.
The Bajau aim to be on the seafloor for as much time as possible in one day in order to collect as much as they can, says Schagatay, who has been studying this ethnic group for almost 40 years. "That is how they make a living," she says. To do this, they make many shallow dives, rather than one deep one. "The trick is to rest for as short a time as possible at the surface before the next dive."
During one hour of diving Schagatay says "the best Baja divers" spend 50-60% of their time underwater. "If you take the sea otter, [the diving pattern] is almost identical: half time under, half time on the surface. They don't go deeper than 20m [65ft], they stay in the shallows. Most people think 20m diving is quite deep, but as a diving instructor I know that, with some training, most people can learn to dive to 20m. And the dive doesn't have to be very long. It can be less than a minute. So, we [humans] are quite well equipped to repeated shallow diving for foraging."
Schagatay also places some species of seal in the group of shallow divers alongside humans. Yet seals possess a number of traits that set them apart from humans, says Chris McKnight, a research fellow St Andrew's University Sea Mammal Research Unit in Scotland.
For us, the urge to breathe is triggered when our brains detect slight changes to blood pH caused by rising carbon dioxide (CO2) levels. This elicits a feeling of panic, telling a diver they should immediately return to the surface – before they blackout and drown.
But seals are not sensitive to changes in CO2 like us, says McKnight. His research reveals that, as well as being able to store oxygen efficiently, seals have a unique ability to cognitively perceive oxygen levels in their blood. This means they can sense when their oxygen stores are low and return to the surface to breathe.
In addition, he says, seals are "incredible" in terms of the regulation of heart rate. "Their heart rate drops remarkably suddenly as soon as they start diving. A grey seal can go from 120 beats per minute to four beats per minute in just a couple of seconds. That heart rate is held throughout the dive until they get to the surface again."
Seals can also match their cardiovascular responses to how long they're expecting to dive for, he adds. "[The heart rate might change] from 120 beats a minute to 60 beats a minute, or 40 beats a minute. That change correlates very well with how long that dive is going to be." What this process is driven by though, he says, remains a mystery. And it is something far beyond the abilities of humans.
"Marine mammals are not really from our world," argues McKnight. "The majority of their life is spent underwater. So, they're really underwater animals that only occasionally come up to our world to breathe. It's like the inverse of diving."
So, are we powerless to the evolutionary state we find ourselves in? Or can humans train to dive like a seal? Today, a growing number of people are taking up recreational freediving, perhaps made all the more popular by Netflix hits The Deepest Breath and My Octopus Teacher.As a child, Zechinni – who appeared in a 2023 documentary about freediving called The Deepest Breath – says, swimming was the best training. At 13, she began to increase her lung capacity. "I started to take huge breaths and stretch [my lungs], little by little. Now, I have two litres more [capacity]." As an adult, she spends hours in the pool and in the gym everyday. "We can improve ourselves," she says.
However, Zechinni knows the dangers of freediving only too well, having witnessed the death of her long-time friend and safety diver, Stephen Keenan in 2017. Zechinni had been attempting to pass under a 25m-long (82ft) tunnel, at 55m (180ft) deep in Dahab's notorious Blue Hole, Egypt – a sinkhole nicknamed the "diver's cemetery". When she became disorientated, Keenan was quick to follow Zechinni in order to assist her. On nearing the surface, both freedivers fell unconscious and Keenan did not survive.
According to the Divers Alert Network (Dan), there were just 19 freediving-related deaths recorded in 2019, the latest data available. A further 31 deaths were reported in people who had been attempting some sort of breath-holding while snorkeling.
Ever since the dawn of competitive freediving, there has been debate about the ultimate limits of human apnoeic performance. However, "divers have thus far surpassed all former predictions by physiologists in depth and time", wrote Schagatay in 2009.
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In 2021, Schagatay and McKnight monitored five elite competitive freedivers. When the divers reached depths of up to 107m (351ft), they were found to have brain oxygen levels lower than seals during their deepest dives – levels that would usually induce unconsciousness in humans. And their heart rates dropped as low as those of diving seals, whales and dolphins. "Our studies have shown this is, at least partially, a result of training," says Schagatay.
And research does show some of the traits we see in traditional freedivers may develop in response to environmental pressures – rather than as a result of evolution.
Take the "sea-nomad" children of Thailand who developed built-in goggles – eyes that can see clearly underwater like dolphins. Researchers found this extraordinary characteristic was developed through training and was "replicable in a European cohort".
"And [the Bajau] do have a large spleen, just like high altitude populations like the Sherpa," says Schagatay. But, she points out that when Sherpa move to live at lower altitudes, their spleen volume shrinks, indicating having a larger spleen to cope with the high altitude is also a matter of exposure, and not purely a genetic trait.
The human diving response, too, has been found to be "highly variable", say experts, and can be altered. This can been seen in elite breath-hold divers who have developed adaptions through repeated training, such as greater tolerance to low levels of oxygen and high levels of CO2.
Many people feel a deep connection to the ocean and research shows blue spaces make us happy. So, are humans really just land animals – or is there a part of us all that belongs in the sea?
"My first dive was when I was seven or eight years old. I dove next to a turtle in the Mediterranean Sea," says Zechinni. This was the moment she knew she would spend a large part of her life underwater. In her book she writes: "I decided that the depth of the sea was immensely more fascinating than the surface of the Earth. I left the safety of the surface to dive deeper and explore a world that was so close and yet so profoundly different."
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