New research finds extinction rates have been declining for a century, challenging assumptions of an ongoing mass extinction. Credit: Shutterstock
A new University of Arizona study challenges the idea that Earth is undergoing a rapidly accelerating mass extinction.
By analyzing 500 years of data across plants and animals, the researchers found that extinction rates actually peaked around a century ago and have since declined.
Rethinking the Idea of a Modern Mass Extinction
For years, several scientific reports have suggested that Earth may be entering another mass extinction event. These predictions often rely on extending extinction patterns from the past 500 years into the future and on the assumption that species loss is speeding up dramatically.
A new study from Kristen Saban and John Wiens of the University of Arizona Department of Ecology and Evolutionary Biology offers a contrasting view. Their findings indicate that extinctions among plants, arthropods and land vertebrates reached their highest point roughly a century ago and have decreased since that time.
The researchers also noted that the earlier extinctions often used to justify current forecasts were primarily driven by invasive species on islands rather than today’s primary threat, which is widespread habitat destruction.
A Malabar gliding frog (Rhacophorus malabaricus) hides between foliage in the Western Ghats mountains in southern India. This family of tree frogs has had more species go extinct than any other amphibian family. Credit: John Wiens
Study Challenges Assumptions Behind Extinction Forecasts
The authors argue that many claims about a modern mass extinction rely on projections that do not account for how the drivers of extinction have shifted over time. Their work, published in the journal Proceedings of the Royal Society of London, is the first to examine recent extinction rates, causes, and patterns across both plant and animal groups.
To conduct their analysis, Saban and Wiens reviewed extinction data for 912 plant and animal species known to have disappeared over the past five centuries. In total, information from nearly 2 million species was incorporated into the study.
“We discovered that the causes of those recent extinctions were very different from the threats species are currently facing,” said Wiens, professor of ecology and evolutionary biology. “This makes it problematic to extrapolate these past extinction patterns into the future, because the drivers are rapidly changing, particularly with respect to habitat loss and climate change.”
Why Past Extinctions Do Not Predict Current Risks
Saban and Wiens noted that recent extinctions provide the most direct evidence of species loss. Despite this, many projections assume that these past patterns can be applied evenly across modern groups, regions and environments. Their findings do not support this assumption.
“To our surprise, past extinctions are weak and unreliable predictors of the current risk that any given group of animals or plants is facing,” said lead author Saban, who recently graduated from the U of A and is currently a doctoral student at Harvard University.
Extinction rates differed significantly across species groups. Mollusks such as snails and mussels, as well as vertebrates, were most affected, while plants and arthropods experienced far fewer documented losses. Many of the extinctions occurred on isolated islands, including the Hawaiian Islands. On continents, most losses took place in freshwater ecosystems.
Invasive species were the dominant cause of extinction on islands, but habitat loss emerged as the leading cause (and remains the primary threat) in continental areas. Predators and competitors introduced by humans, including rats, pigs and goats, likely drove many island species to extinction.
Climate Change Did Not Increase Extinctions in the Past Two Centuries
Another unexpected finding was that extinction rates over the last 200 years do not show evidence of an increase caused by climate change.
“That does not mean that climate change is not a threat,” Wiens said. “It just means that past extinctions do not reflect current and future threats.”
The team also evaluated threat categories such as “threatened,” “endangered” or “least concern” for 163,000 species assessed by the International Union for Conservation of Nature.
“The current threat level provides probably our best hint of what is currently happening and might happen in the near future,” Wiens said. “We found the patterns of today’s threats to be different from those of past extinctions. For example, most extinct species are mollusks and vertebrates on islands that were driven extinct by invasive species, but most threatened species today are mainland species facing habitat destruction.”
Understanding Biodiversity Loss With Greater Precision
Saban emphasized that the study should not be used to imply that human impacts are unimportant or that species are no longer at risk.
“Biodiversity loss is a huge problem right now, and I think we have not yet seen the kinds of effects that it might have,” she said. “But it’s important that we talk about it with accuracy, that our science is rigorous in how we’re able to detail these losses and prevent future ones.”
The study also contradicts widespread claims that extinction rates are accelerating.
“We show that extinction rates are not getting faster towards the present, as many people claim, but instead peaked many decades ago,” Wiens said.
For several groups, including arthropods, plants, and land vertebrates, extinction rates have steadily declined over the last century, particularly since the early 1900s. Wiens noted that one likely explanation “is many people are working hard to keep species from going extinct. And we have evidence from other studies that investing money in conservation actually works.”
Moving Beyond Doomsday Scenarios
Saban explained that the study was partly motivated by a desire to step away from overly catastrophic narratives about extinction.
“If we’re saying that what is happening right now is like an asteroid hitting Earth, then the problem becomes insurmountable,” she said. “By looking at the data in this way, we hope that our study helps inform our overall understanding of biodiversity loss and how we can come up with better ways to address it.”
Reference: “Unpacking the extinction crisis: rates, patterns and causes of recent extinctions in plants and animals” by Kristen E. Saban and John J. Wiens, 15 October 2025, Royal Society B: Biological Sciences.
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