A groundbreaking study from the University of Arizona challenges widely held assumptions that Earth is currently undergoing a sixth mass extinction. The research, led by Kristen Saban and Professor John Wiens from the Department of Ecology and Evolutionary Biology, found that extinction rates across plants, arthropods, and land vertebrates peaked about 100 years ago and have since declined.
Published in the Proceedings of the Royal Society B, the study analyzed patterns across nearly two million species and identified 912 confirmed extinctions over the past 500 years. Contrary to popular forecasts, extinction rates are not accelerating toward catastrophe -- they're slowing down.
Many previous studies linking current biodiversity loss to a "mass extinction" are based on the assumption that past extinctions accurately forecast future risks. However, this analysis found that extinction drivers have changed dramatically over time.
"Most past extinctions were caused by invasive species on islands," said Wiens. "Today, the biggest threats are habitat loss, climate change, and human-driven environmental destruction on continents."
The researchers argue that extrapolating recent extinction data -- largely influenced by 19th and early 20th-century island events -- fails to capture the distinct threats facing modern biodiversity.
Historically, extinction patterns were dominated by species living on isolated islands, where human-introduced predators such as rats, pigs, and goats devastated local ecosystems. By contrast, today's extinctions are largely driven by deforestation, agricultural expansion, and urban development -- the widespread destruction of natural habitats rather than isolated island invasions.
The researchers found that island mollusks and small vertebrates were most impacted by invasive species in earlier centuries. Meanwhile, mainland species, especially those depending on freshwater ecosystems, are now at risk primarily from habitat loss.
"The current threats are very different," lead author Saban explained. "That's why past extinction patterns are poor and unreliable predictors of today's risks."
Using hundreds of verified extinction records, the analysis revealed a clear peak in biodiversity loss around the early 1900s, followed by a steady decline across multiple categories, including plants and terrestrial animals.
Contrary to claims of exponential extinction acceleration, extinction rates for most species groups have either stabilized or declined over the past century. Wiens noted that these findings show the value of modern conservation efforts. "One reason extinction rates have declined is that people are working hard to save species from disappearing," he said. "And we have strong evidence that conservation investments actually work."
Among the 912 identified extinctions, a majority occurred in mollusks and vertebrates, particularly those confined to small islands such as Hawaii.
For example, many snail and bird species vanished after predatory mammals were introduced by humans. However, such island-based extinction dynamics don't represent current global patterns of biodiversity loss.
Today's extinctions primarily threaten species inhabiting mainland forests, wetlands, and grasslands, where human activities have fragmented ecosystems and accelerated habitat degradation.
Surprisingly, the researchers found no direct evidence that climate change has driven widespread species extinctions over the past 200 years.
"This doesn't mean climate change isn't dangerous," Wiens clarified. "It simply means that we don't yet see large-scale extinctions caused directly by it in historical data."
Instead, the team attributes most recent biodiversity losses to invasive species and habitat destruction. Future impacts from global warming, however, remain a major concern, as rising temperatures and shifting weather patterns could dramatically reshape ecosystems in the coming decades.
The researchers also examined 163,000 species assessed by the International Union for Conservation of Nature (IUCN).
Their analysis revealed an important shift: while most historically extinct species were island dwellers affected by invasive species, the majority of currently threatened species are mainland inhabitants facing habitat loss and urbanization.
This shift highlights how extinction risk has migrated geographically, emphasizing a need for context-specific conservation strategies rather than generalized global assumptions.
"The best predictor of what comes next isn't past extinction -- it's current threat levels," said Wiens. "We must act on what species are facing right now, not what happened 200 years ago."
Despite continued environmental challenges, the study provides rare optimism: extinction rates appear to have slowed because conservation is working.
Protected areas, restoration projects, and species recovery programs have helped stabilize populations across regions previously at risk. Notably, proactive measures to curb illegal hunting, manage invasive species, and increase habitat corridors show measurable results.
According to the researchers, this demonstrates that biodiversity loss, though serious, is not an unstoppable crisis. "We're not saying everything is fine," Saban emphasized. "We're saying our conservation efforts are making a difference -- and this should motivate us to do even more."
The new findings challenge the narrative that humanity is already in the midst of a sixth mass extinction comparable to the event that ended the dinosaurs.
Mass extinctions in Earth's history were defined by the loss of over 75% of all species within a short geological timeframe. By contrast, fewer than one percent of known species have gone extinct in the past 500 years.
Biodiversity loss remains a pressing issue. However, the data suggest that predictions of imminent global collapse may be overly pessimistic. These predictions can be potentially discouraging for public engagement. Saban cautions that overemphasizing catastrophic predictions can lead to fatalism rather than action. "If people believe the situation is as hopeless as an asteroid impact, they may think there's nothing they can do. But the evidence suggests otherwise."
The authors stress that their study should not be misinterpreted as minimizing biodiversity loss. Instead, it highlights the importance of rigorous, accurate science when communicating about ecological crises.
"Biodiversity loss is still one of humanity's greatest challenges," Saban said. "But our focus should be on understanding what's truly driving current threats and building effective solutions."
Wiens agreed, adding that science must remain transparent and contextually accurate: "We want people to act on sound information, not exaggerated claims." Both researchers advocate for greater investment in data collection. They emphasize improved habitat protection. Additionally, they support global cooperation in conservation policy as realistic pathways for long-term biodiversity preservation.
Ultimately, the study offers a measured yet hopeful perspective -- biodiversity decline is real, but it is not inevitable.
Policymakers can learn from the last 500 years of species extinctions. They can apply smarter, targeted actions to address present-day threats like deforestation. Other threats include overexploitation and environmental pollution.
"If we continue investing in conservation and habitat protection," said Wiens, "we have every reason to believe extinction rates can decline. They can decline even further." Saban concluded, "The goal is not to downplay what's happening. It's to help people see that progress is possible. Progress happens when we act with precision, urgency, and hope."