- A new study finds extinction rates for plants, arthropods and land vertebrates peaked about a century ago and have since declined.
- The research challenges projections of an accelerating mass extinction, arguing past causes like invasive species on islands differ from current threats.
- Habitat destruction on continents is now the primary driver of species endangerment, not the island invasions that caused many past extinctions.
- The analysis of 912 extinct species over 500 years shows extinction risk is not uniform and past losses are poor predictors of current threats.
- Researchers emphasize the findings do not diminish the biodiversity crisis but aim to provide a more accurate, actionable understanding of it.
In a finding that challenges a central tenet of modern conservation biology, a new scientific analysis asserts that the rate at which plant and animal species are vanishing has actually slowed over the past century. Published in December 2025 in the Proceedings of the Royal Society of London by researchers Kristen Saban and John Wiens of the University of Arizona, the study provides a nuanced dissection of extinction patterns over the last 500 years. It concludes that while biodiversity loss remains a profound crisis, the drivers and rates of extinction are more complex—and in some aspects, less dire—than commonly projected, with habitat loss now eclipsing historical threats.
Re-examining the trajectory of loss
For decades, prominent scientific assessments have warned that Earth is entering a sixth mass extinction, with current extinction rates estimated to be 100 to 1,000 times higher than the natural "background" rate. These alarming projections often extrapolate from known extinctions since 1500. However, Saban and Wiens’s research, which analyzed data from 912 extinct species and threat levels for nearly 2 million more, suggests such extrapolations may be flawed. The study identifies a peak in extinction rates around the early 1900s, followed by a general decline in the last 100 years for groups like plants, arthropods and land vertebrates.
The core of their argument is that the causes of past extinctions are not the primary threats of today. "We discovered that the causes of those recent extinctions were very different from the threats species are currently facing," Wiens stated. This disconnect, the authors contend, makes simple forward projections misleading.
Islands vs. continents: A tale of two crises
A key finding of the research is the stark geographic divergence in extinction patterns. The analysis reveals that the majority of documented extinctions over the past five centuries occurred on islands, such as Hawaii. These losses were predominantly driven by invasive species—rats, pigs, goats and other animals introduced by humans that outcompeted or preyed upon native island fauna, which had evolved in isolation without defenses.
In contrast, on continental landmasses, most extinctions occurred in freshwater habitats. More critically, the study identifies habitat destruction, not invasive species, as the most significant cause of extinction in continental regions and, importantly, the dominant threat to species currently classified as endangered or threatened. This shift in the primary driver of biodiversity loss from island invasions to mainland habitat degradation changes the context of the crisis.
Past extinctions are poor predictors of future risk
The team’s analysis yielded a surprising statistical result: Knowing which groups suffered high extinction rates in the past is a weak indicator of which groups are most at risk today. For example, mollusks like snails and mussels suffered a high number of past extinctions, but their current threat profile does not necessarily follow the same pattern. Similarly, the study found no strong signal in the extinction record over the past 200 years specifically attributable to climate change, though the authors are careful to note this does not mean climate change is not a major future threat.
"It just means that past extinctions do not reflect current and future threats," Wiens explained. The current "threat level" of species, as cataloged by the International Union for Conservation of Nature (IUCN), presents a different pattern: a preponderance of mainland species jeopardized by habitat loss.
A call for accurate diagnosis, not complacency
The researchers are emphatic that their findings should not be interpreted as evidence that the biodiversity crisis is over or unimportant. "Biodiversity loss is a huge problem right now, and I think we have not yet seen the kinds of effects that it might have," Saban said. Instead, they frame their work as a move toward more precise scientific rigor to better direct conservation efforts. If the problem is misdiagnosed—framed as an unstoppable, accelerating juggernaut akin to an asteroid impact—it can seem insurmountable.
The noted decline in extinction rates over the past century may itself be a sign that conservation actions can work. "One of the reasons for declining extinction rates 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," Wiens noted.
Reframing the conservation imperative
This study injects a critical dose of complexity into the global conversation about extinction. It argues that the narrative of relentlessly accelerating loss may not accurately reflect the latest data and that the nature of the threat has evolved. The historical epicenter of extinction—islands ravaged by invasive species—has been joined, and arguably surpassed, by the systemic erosion of natural habitats on continents. For scientists and policymakers, the implication is clear: Effective conservation must be guided by the specific, contemporary drivers of endangerment, primarily habitat destruction, rather than projections based on past patterns. The goal remains the urgent prevention of future loss, but the path forward requires a clear-eyed view of a changing landscape of threat.
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