Was the Emergence of Intelligent Life on Earth Just a Fluke? Some Scientists Think Not

A panoramic view of Earth taken by astronauts aboard the International Space Station (ISS), showing east-central Texas on September 6, 2011 REUTERS/Nasa Earth Observatory/Handout/File Photo
A panoramic view of Earth taken by astronauts aboard the International Space Station (ISS), showing east-central Texas on September 6, 2011 REUTERS/Nasa Earth Observatory/Handout/File Photo
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Was the Emergence of Intelligent Life on Earth Just a Fluke? Some Scientists Think Not

A panoramic view of Earth taken by astronauts aboard the International Space Station (ISS), showing east-central Texas on September 6, 2011 REUTERS/Nasa Earth Observatory/Handout/File Photo
A panoramic view of Earth taken by astronauts aboard the International Space Station (ISS), showing east-central Texas on September 6, 2011 REUTERS/Nasa Earth Observatory/Handout/File Photo

Roughly 300,000 years ago, our species first appeared on the African landscape before spreading globally and coming to dominate the planet. All this happened about 4.5 billion years after Earth formed, with innumerable steps occurring in between that made our planet a cradle for intelligent life.

An influential scientific thesis - called the "hard steps" theory and first presented in 1983 - has held that this outcome was a long shot and that the emergence of technological-level intelligent life on Earth or elsewhere was highly improbable. But perhaps this result was not so unlikely after all, according to scientists who are now advancing an alternative theory, Reuters reported.

These scientists propose that Homo sapiens and analogous extraterrestrial life forms may be the probable end result of biological and planetary evolution when a planet has a certain set of attributes that make it habitable, rather than requiring countless lucky breaks.

The path toward intelligent life, they argue, may be more of a predictable process, unfolding as global conditions allow in a manner that should not be considered unique to Earth.

"In short, our framework shows how hard steps may not actually exist - past evolutionary transitions that needed to happen for us humans to be here may not have been hard or unlikely in the available time," said Dan Mills, a postdoctoral researcher in geomicrobiology at the University of Munich and lead author of the study published on Friday in the journal Science Advances, opens new tab.

Physicist Brandon Carter devised the hard steps theory. It stresses that the long road to the emergence of humankind necessitated passage through various intermediate steps, each highly unlikely.

Over the years, scientists have tried to identify some of these hard steps. These include the emergence of single-celled living organisms on primordial Earth, the initial oxygenation of the atmosphere by photosynthesis, the evolutionary transition from prokaryotic cells that lack a nucleus and other internal structures to eukaryotic cells that have them, and the appearance of complex organisms such as multicellular animals. And then, the final proposed hard step is the appearance of Homo sapiens and milestones such as language and technology.

A species with advanced technological capabilities emerged on Earth relatively late in the Earth's habitable history, with the sun expected to increase in luminosity and boil away our planet's oceans about a billion years from now. This has inspired the argument that Earth is an incredibly rare planet that managed to accomplish the needed hard steps before becoming rendered uninhabitable.

The new theory was devised by a team of two geobiologists and two astronomers.

They propose that humankind's emergence followed the sequential opening of various "windows of habitability" over Earth's history, driven by factors such as changes in nutrient availability, sea surface temperatures, ocean salinity levels and atmospheric oxygen levels. Due to these factors, Earth only relatively recently became hospitable to a species like ours, they said, and that once those conditions existed the evolutionary path was relatively rapid.

"Biological innovations proposed as hard or unlikely might actually occur quickly - geologically speaking - as soon as the environment permits," said Penn State microbiologist Jennifer Macalady, one of the researchers.

"For example, life might have originated very quickly once temperatures were appropriate for the stability of biomolecules and liquid water. The Earth has only been habitable for humans since the second rise of oxygen in the atmosphere approximately 0.5 billion years ago, meaning that humans could not have evolved on Earth prior to that relatively recent moment," Macalady added.

Astronomers are searching for evidence of life beyond Earth and have identified roughly 5,800 exoplanets - planets beyond our solar system. Some of them are uninhabitable gas giants akin to Jupiter but some of them are rocky worlds like our solar system's four terrestrial planets that include Earth.

Astrophysicist and study co-author Jason Wright, director of the Penn State Extraterrestrial Intelligence Center, said that a best estimate right now is that somewhere around half of stars have a planet about the size of Earth orbiting at about the right distance to host liquid water, a key ingredient for life.

"Understanding the probability of intelligent life emerging helps us understand our own place in the world," Mills said. "Are we humans a cosmic fluke, as the hard steps model predicts? Or are we instead the more expected and typical outcome of a living planet, as our alternative framework suggests?"



River Seine Reopens to Public Swimming for 1st Time in a Century

A view of one of the three Seine swimming pools, Thursday, July 3, 2025 which will open during the 'Paris Plages' event from July 5 to Aug. 31 in Paris. (AP Photo/Aurelien Morissard)
A view of one of the three Seine swimming pools, Thursday, July 3, 2025 which will open during the 'Paris Plages' event from July 5 to Aug. 31 in Paris. (AP Photo/Aurelien Morissard)
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River Seine Reopens to Public Swimming for 1st Time in a Century

A view of one of the three Seine swimming pools, Thursday, July 3, 2025 which will open during the 'Paris Plages' event from July 5 to Aug. 31 in Paris. (AP Photo/Aurelien Morissard)
A view of one of the three Seine swimming pools, Thursday, July 3, 2025 which will open during the 'Paris Plages' event from July 5 to Aug. 31 in Paris. (AP Photo/Aurelien Morissard)

For the first time in over a century, Parisians and tourists will be able to take a refreshing dip in the River Seine. The long-polluted waterway is finally opening up as a summertime swim spot following a 1.4 billion euro ($1.5 billion) cleanup project that made it suitable for Olympic competitions last year.

Three new swimming sites on the Paris riverbank will open on Saturday — one close to Paris’ Notre Dame Cathedral, another near the Eiffel Tower and a third in eastern Paris.

Swimming in the Seine has been illegal since 1923, with a few exceptions, due to pollution and risks posed by river navigation. Taking a dip outside bathing areas is still banned for safety reasons.

The Seine was one of the stars of the Paris Olympics in 2024, whether as the scene of the ambitious opening ceremony or the triathlon and marathon swimming competitions. That didn't go without challenging hurdles such as rainfall increasing levels of bacteria, which postponed some competitions.

This city's authorities have given the green light for the public opening, with water quality results consistently in line with European regulations.

Making splashes in Paris city center “It’s a symbolic moment when we get our river back,” said sports coach and influencer Lucile Woodward, who will participate in the first amateur open water competition in the Seine on Sunday.

Woodward, who enjoyed a dip alongside Paris Mayor Anne Hidalgo just before the start of the Olympic Games, is confident things will go well.

“We're going to enjoy swimming in it, being there and setting an example," she said. "Once people will see that in the end there are hundreds of people who have fun and enjoy it, everyone will want to go!”

“For families, going to take a dip with the kids, making little splashes in Paris, it’s extraordinary,” Woodward added.

Olympic athletes competing in the river was a spectacular reward for the cost of the cleanup effort.

In the run-up to the Games, authorities opened new disinfection units and created a huge storage basin meant to prevent as much bacteria-laden wastewater as possible from spilling directly into the Seine when it rains.

Houseboats that previously emptied their sewage directly into the river were required to hook up to municipal sewer systems. Some homes upstream from Paris also saw their wastewater connected to treatment plants instead of the rainwater system flowing directly into the river.

Green flag for swimming Paris Deputy Mayor Pierre Rabadan said water is tested daily to confirm it's safe to swim. As on French beaches, different colored flags will inform visitors whether or not they can go in.

“Green means the water quality is good. Red means that it's not good or that there's too much current,” he said.

Tests have been in line with European regulations since the beginning of June, with only two exceptions due to rain and boat-related pollution, Rabadan said.

“I can’t make a bet on the numbers of days when we’ll have to close this summer, but water quality seems better than last year,” he added. “We’re in a natural environment ... so weather condition variations necessarily have an impact."

Last year, several athletes became ill after competing in the triathlon and open water races during the Olympics, though in most cases it was not clear if the river was to blame for their sickness.

World Aquatics stressed the conditions met the sport’s accepted thresholds.

“The legacy of these efforts is already evident, with the Seine now open for public swimming — a positive example of how sports can drive long-term community benefits,” the organization said in a statement to The Associated Press.

Skepticism remains about water quality Dan Angelescu, founder and CEO of Fluidion, a Paris and Los Angeles-based water monitoring tech company, has routinely and independently tested bacterial levels in the Seine for several years. Despite being in line with current regulations, the official water testing methodology has limitations and undercounts the bacteria, he said.

“What we see is that the water quality in the Seine is highly variable,” Angelescu said. “There are only a few days in a swimming season where I would say water quality is acceptable for swimming.”

“All we can say is that we can raise a hand and say look: the science today does not support the current assessment of water safety used in the rivers around Paris, and we think that there is major risk that is not being captured at all,” he said.

Some Parisians also have shown skepticism toward the idea of swimming in the Seine. The feeling is often reinforced by the water's murky color, floating litter and multiple tourist boats in some places.

Enys Mahdjoub, a real estate agent, said he would not be afraid of swimming, but rather "a bit disgusted. It’s more the worry of getting dirty than anything else at the moment.”

A dream come true Until the end of August, swimming sites will be open for free at scheduled times to anyone with a minimum age of 10 or 14 years, depending on the location. Lifeguards will keep a watchful eye on those first dips.

“It’s an opportunity, a dream come true," said Clea Montanari, a project manager in Paris. "It’d be a dream if the Seine becomes drinkable, that would be the ultimate goal, right? But already swimming in it is really good.”