Humans have been shaping their environment since time immemorial. From cities to farms to highways, our impact has grown so large that we have transcended the planet’s boundaries, raising concerns about climate change and rising extinction rates among the animals and plants we share the earth with.
But accurately measuring the extent to which human activity has driven species to extinction is never easy. While headline-grabbing projects to bring back lost species, such as those promoted by companies like Colossal, offer a glimmer of hope, they may be just drops in a vast ocean of biodiversity under threat.
Earth has seen five mass extinctions caused by natural disasters, and some scientists now say a sixth may have already begun, but this time it was caused entirely by humans. Are we really on the brink of another planetary collapse? Or could the situation be more nuanced than the alarmist headlines suggest?
There is no clear definition of mass extinction
There is more to the definition of mass extinction than most people realize. Scholars widely agree that it involves the loss of at least 75% of species within less than two million yearswhich is a geologically short period. However, from the human perspective, it may not take millions of years to see that something has stopped.
And here the discussion begins. Although humans have not yet caused the roughly 75% loss, proponents of the sixth mass extinction say that in our relatively short existence on Earth, we have caused so much disruption that it is comparable on a smaller scale.
But not everyone agrees. John Wiens, a professor of ecology and evolutionary biology at the University of Arizona, questions whether these claims hold up under close scientific scrutiny.
“Some people have said, especially regarding a sixth mass extinction, anything above the background extinction rate,” Wiens says. “But because the background extinction rate is basically an average, it will always fluctuate above and below it, regardless of extreme extinction events.” “If you look at very short time periods, you can get huge fluctuations that don’t mean much in the long run.”
Wiens stresses that the time frame is key. Extinction measured over millions of years behaves differently from extinction measured over centuries. Which level of the evolutionary tree you study—species, genus, or family—can change the entire story.
“Generas will be older than species, so losing them is much worse than just losing random species,” he explains. “We’re missing all that evolutionary history. That’s part of the reason we focus on genera and not just species.”
Read more: Understanding ocean recovery after mass extinction events could help us in the future
Extinction rates have begun to decline again
Recent wins He studies This takes a comprehensive perspective, examining extinctions over the past 500 years across higher taxa. Using the IUCN Red List, a global database of threatened species, Wiens and Harvard graduate student Christine Saban found that 102 genera have become extinct, along with 10 families and two orders, which translates to nearly 900 species.
Most extinct genera were monophyletic, meaning they contained only one species, and most were restricted to islands. But here’s the amazing part: in the grand scheme of things, less than half a percent of all recorded races disappeared during this period. Even more surprising is that the loss rate peaked about a century ago and has been declining ever since.
This contrasts sharply with the claims of scholars such as Ceballos et al.Who argue that the current extinction event threatens the continuation of human civilization.
Wiens also highlights the difficulty of measuring extinction. We don’t actually know how many species there are on Earth; Estimates range from two million to three trillion. A widely cited study puts the number at around eight million, although 80% of these species remain hypothetical.
Sometimes species that were thought to have disappeared reappear, e.g Lord Howe stick insect, rediscovered in 2001 On a remote Australian island nearly a century later. It is likely that many others disappeared before scientists could document them. All of this makes extinction data inherently incomplete, forcing researchers to interpret trends through the fog of uncertainty.
These may be early stages of a mass extinction
Scientists who argue in favor of a sixth mass extinction say such doubts mask a deeper crisis. They point out that the Red List, although widely used, is Highly biased: Almost all birds and mammals have been evaluated, but only a small portion of invertebrates (animals that do not have a backbone and make up more than 90 percent of known species) have been evaluated. They say that accounting for potential losses in invertebrates would push extinction rates significantly higher.
AmphibiansIn particular, under threat. A third or more of the 6,300 known frogs, salamanders and caecilians are endangered, especially in tropical regions with narrow ranges. For many biologists, this concentration of risks suggests that we may be in the early stages of a sixth mass extinction.
Human activity is central to this interest: no other species has been able to reshape Earth’s ecosystems on this scale. Even as protection expands, many species continue to disappear unnoticed. Some researchers believe that this is a natural extension of human dominance; Others warn that it represents a biodiversity crisis unprecedented in Earth’s history.
Read more: Permian extinction: Life on Earth nearly disappeared during the ‘Great Dying’
Conservation is important no matter what
Wiens agrees that extinctions occur above background levels and that humans are responsible for them, but he stops short of calling it a mass extinction.
“We have to get the science right,” he says. “For it to be the sixth, it must be compared to the other five.”
He prefers the term “extinction crisis,” which better reflects the data and moral urgency. “It shouldn’t matter whether there are consequences for humans at all, because none of these extinctions were supposed to happen,” Wiens says. “Everyone matters. It’s the wrong thing to do, and we need to stop it.”
Accuracy is essential for conservation science to remain credible, he says. “People will not take us seriously if we claim that human life will become extinct because some birds have been lost on the islands for a hundred years,” he says. “This doesn’t help. It doesn’t mean you’re against the idea of an extinction event but you’re trying to make science healthy.”
The study also offers hope: perhaps conservation is working. “The reason we think we’re seeing this decreasing pattern is because of conservation,” he says.
The decline in extinction rates over the past century could reflect the results of global efforts to protect species and habitats. While the debate over the sixth mass extinction continues, human action remains important. Rigorous science, combined with thoughtful conservation, can make a tangible difference in the future of life on Earth.
Read more: Oasis of life plants protected during the Permian mass extinction event
condition sources
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